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Many plants (e.g. roses, palms) can be protected from frost during the winter if shielded with an appropriate coat that can be bought in garden shops. Do plants produce any heat that can be kept inside with these "clothes"?
Cellular respiration in plants is slightly different than in other eukaryotes because the electron transport chain contains an additional enzyme called Alternative Oxidase (AOX). AOX takes some electrons out of the pathway prematurely - basically the energy is used to generate heat instead of ATP.
The exact purpose of AOX in plants is still unclear. Plants will make more AOX in response to cold, wounding, and oxidative stress. We know of at least one plant (skunk cabbage) that exploits this pathway to generate enough heat to melt snow. This link gives a pretty good overview.
(AOX is dear to my heart, since my first 3 years working in a laboratory were spent studying this gene <3)
Plants will be respiring continuously, which is an exothermic process. Therefore the plants will be producing a small amount of heat. The protection from frost may be more a result of the vastly smaller convection current of the coat compared to the atmosphere rather than by reducing any conduction away of heat produced by the plant, however.
Keeping the plant out of the wind by 'dressing it' will reduce the rate of transpiration when the stomata are open. I would very tentatively suggest that, as water has a very high specific heat capacity, having a greater volume of water within the plant would help to retain any heat that was produced by respiration. However this is entirely speculation on my part.
Some plants have mitochondrial pathways that produce heat. That's why skunk cabbage can be seen poking outing of the snow in late winter/early spring. Here's a review: http://onlinelibrary.wiley.com/doi/10.1111/j.1744-7909.2010.01004.x/pdf
Yes, respiration is exothermic and plants (like all living things) respire.
I think the effect of covering the plant has to more to do with reducing sensible heat loss , e.g. direct transfer of heat from plant to air) rather than latent heat loss (through evaporation).
The cover is effectively reducing the mixing of the air near the plant (and closer to the temperature of the surface of the earth) with the free atmosphere (closer to the temperature reported by the weatherman)
Do plants produce any heat? - Biology
In the weird and wonderful world of cannabis plants, hermaphroditism isn’t as rare as you might expect. While it’s not the kind of thing we often see affecting humans or the animal kingdom, it’s surprisingly common with plants. In fact, it is a perfectly natural feature of many plants and trees – some of which rely on the presence of both male and female flowers to reproduce and thrive. Nevertheless, this doesn’t mean that it’s a particularly good thing when you find yourself dealing with hermaphrodite cannabis plants.
When a cannabis plant develops both male and female flowers, you have yourself a hermaphrodite. Once again, this is a completely natural occurrence and so doesn’t suggest that there is anything fundamentally wrong with your crop. Nevertheless, it is a highly undesirable trait for anyone cultivating cannabis for the purposes of consumption. The reason being that what you intended to be a haul of premium-quality cannabis can in fact turn into plants chock-full of seeds.
Which is, suffice to say, never a particularly positive outcome unless you are breeding and wanting to create a stash of seeds.
Hibernation is a mechanism used by many mammals to reduce energy expenditure and survive food shortages over the winter. Hibernation may be predictive or consequential. An animal prepares for hibernation by building up a thick layer of body fat during late summer and autumn that will provide it with energy during the dormant period. During hibernation, the animal undergoes many physiological changes, including decreased heart rate (by as much as 95%) and decreased body temperature.  In addition to shivering, some hibernating animals also produce body heat by non-shivering thermogenesis to avoid freezing. Non-shivering thermogenesis is a regulated process in which the proton gradient generated by electron transport in mitochondria is used to produce heat instead of ATP in brown adipose tissue.  Animals that hibernate include bats, ground squirrels and other rodents, mouse lemurs, the European hedgehog and other insectivores, monotremes and marsupials. Although hibernation is almost exclusively seen in mammals, some birds, such as the common poorwill, may hibernate.
Diapause is a predictive strategy that is predetermined by an animal's genotype. Diapause is common in insects, allowing them to suspend development between autumn and spring, and in mammals such as the roe deer (Capreolus capreolus, the only ungulate with embryonic diapause [ citation needed ] ), in which a delay in attachment of the embryo to the uterine lining ensures that offspring are born in spring, when conditions are most favorable.
Aestivation, also spelled estivation, is an example of consequential dormancy in response to very hot or dry conditions. It is common in invertebrates such as the garden snail and worm but also occurs in other animals such as lungfish, salamanders, desert tortoises, and crocodiles.
While endotherms and other heterotherms are described scientifically as hibernating, the way ectotherms such as lizards become dormant in cold is very different, and a separate name was invented for it in the 1920s: brumation.  It differs from hibernation in the metabolic processes involved. 
Reptiles generally begin brumation in late autumn (more specific times depend on the species). They often wake up to drink water and return to "sleep". They can go for months without food. Reptiles may eat more than usual before the brumation time but eat less or refuse food as the temperature drops.  [ unreliable source? ] However, they do need to drink water. The brumation period is anywhere from one to eight months depending on the air temperature and the size, age, and health of the reptile. During the first year of life, many small reptiles do not fully brumate, but rather slow down and eat less often. Brumation is triggered by a lack of heat and a decrease in the hours of daylight in winter, similar to hibernation.
In plant physiology, dormancy is a period of arrested plant growth. It is a survival strategy exhibited by many plant species, which enables them to survive in climates where part of the year is unsuitable for growth, such as winter or dry seasons.
Many plant species that exhibit dormancy have a biological clock that tells them when to slow activity and to prepare soft tissues for a period of freezing temperatures or water shortage. On the other hand, dormancy can be triggered after a normal growing season by decreasing temperatures, shortened day length, and/or a reduction in rainfall. Chemical treatment on dormant plants has been proven to be an effective method to break dormancy, particularly in woody plants such as grapes, berries, apples, peaches, and kiwis. Specifically, hydrogen cyanamide stimulates cell division and growth in dormant plants, causing buds to break when the plant is on the edge of breaking dormancy. [ citation needed ] Slight injury of cells may play a role in the mechanism of action. The injury is thought to result in increased permeability of cellular membranes. [ citation needed ] The injury is associated with the inhibition of catalase, which in turn stimulates the pentose phosphate cycle. Hydrogen cyanamide interacts with the cytokinin metabolic cycle, which results in triggering a new growth cycle. [ citation needed ] The images below show two particularly widespread dormancy patterns amongst sympodially growing orchids:
When a mature and viable seed under a favorable condition fails to germinate, it is said to be dormant. Seed dormancy is referred to as embryo dormancy or internal dormancy and is caused by endogenous characteristics of the embryo that prevent germination (Black M, Butler J, Hughes M. 1987). Dormancy should not be confused with seed coat dormancy, external dormancy, or hardheadedness, which is caused by the presence of a hard seed covering or seed coat that prevents water and oxygen from reaching and activating the embryo. It is a physical barrier to germination, not a true form of dormancy (Quinliven, 1971 Quinliven and Nichol, 1971).
Seed dormancy is desired in nature, but the opposite in the agriculture field. This is due to agricultural practice desires rapid germination and growth for food while as in nature, most plants are only capable of germinating once every year, making it favorable for plants to pick a specific time to reproduce. For many plants, it is preferable to reproduce in spring as opposed to falling even when there are similar conditions in terms of light and temperature due to the ensuing winter that follows fall. Many plants and seeds do recognize this and enter a dormant period in the fall to stop growing. The grain is a popular example in this aspect, where they would die above ground during the winter, so dormancy is favorable to its seedlings but extensive domestication and crossbreeding has removed most dormancy mechanisms that their ancestors had. 
While seed dormancy is linked to many genes, Abscisic Acid (ABA), a plant hormone, has been linked as a major influencer to seed dormancy. In a study on rice and tobacco plants, plants defective in zeaxanthin epoxidase gene, which are linked to ABA-synthesis pathway. Seeds with higher ABA content, from over-expressing zeaxanthin epoxidase, led to an increased dormancy period while plants with lower numbers of zeaxanthin epoxidase were shown to have a shorter period of dormancy. A simple diagram can be drawn of ABA inhibits seed germination, while Gibberellin (GA, also plant hormone), inhibits ABA production and promotes seed germination.  
Typically, temperate woody perennial plants require chilling temperatures to overcome winter dormancy (rest). The effect of chilling temperatures depends on species and growth stage (Fuchigami et al. 1987).  In some species, rest can be broken within hours at any stage of dormancy, with either chemicals, heat, or freezing temperatures, effective dosages of which would seem to be a function of sublethal stress, which results in stimulation of ethylene production and increased cell membrane permeability.
Dormancy is a general term applicable to any instance in which a tissue predisposed to elongate or grow in some other manner does not do so (Nienstaedt 1966).  Quiescence is dormancy imposed by the external environment. Correlated inhibition is a kind of physiological dormancy maintained by agents or conditions originating within the plant, but not within the dormant tissue itself. Rest (winter dormancy) is a kind of physiological dormancy maintained by agents or conditions within the organ itself. However, physiological subdivisions of dormancy do not coincide with the morphological dormancy found in white spruce (Picea glauca) and other conifers (Owens et al. 1977).  Physiological dormancy often includes early stages of bud-scale initiation before measurable shoot elongation or before flushing. It may also include late leaf initiation after shoot elongation has been completed. In either of those cases, buds that appear to be dormant are nevertheless very active morphologically and physiologically.
Dormancy of various kinds is expressed in white spruce (Romberger 1963).  White spruce, like many woody plants in temperate and cooler regions, requires exposure to low temperature for a period of weeks before it can resume normal growth and development. This “chilling requirement” for white spruce is satisfied by uninterrupted exposure to temperatures below 7 °C for 4 to 8 weeks, depending on physiological condition (Nienstaedt 1966, 1967).  
Tree species that have well-developed dormancy needs may be tricked to some degree, but not completely. For instance, if a Japanese Maple (Acer palmatum) is given an "eternal summer" through exposure to additional daylight, it grows continuously for as long as two years. Eventually, however, a temperate-climate plant automatically goes dormant, no matter what environmental conditions it experiences. Deciduous plants lose their leaves evergreens curtail all new growth. Going through an "eternal summer" and the resultant automatic dormancy is stressful to the plant and usually fatal. The fatality rate increases to 100% if the plant does not receive the necessary period of cold temperatures required to break the dormancy. Most plants require a certain number of hours of "chilling" at temperatures between about 0 °C and 10 °C to be able to break dormancy (Bewley, Black, K.D 1994).
Short photoperiods induce dormancy and permit the formation of needle primordia. Primordia formation requires 8 to 10 weeks and must be followed by 6 weeks of chilling at 2 °C. Bud break occurs promptly if seedlings are then exposed to 16-hour photoperiods at the 25 °C/20 °C temperature regime. The free growth mode, a juvenile characteristic that is lost after 5 years or so, ceases in seedlings experiencing environmental stress (Logan and Pollard 1976, Logan 1977).  
Many bacteria can survive adverse conditions such as temperature, desiccation, and antibiotics by forming endospores, cysts, or states of reduced metabolic activity lacking specialized cellular structures.  Up to 80% of the bacteria in samples from the wild appear to be metabolically inactive  —many of which can be resuscitated.  Such dormancy is responsible for the high diversity levels of most natural ecosystems. 
Recent research  has characterized the bacterial cytoplasm as a glass forming fluid approaching the liquid-glass transition, such that large cytoplasmic components require the aid of metabolic activity to fluidize the surrounding cytoplasm, allowing them to move through a viscous, glass-like cytoplasm. During dormancy, when such metabolic activities are put on hold, the cytoplasm behaves like a solid glass, 'freezing' subcellular structures in place and perhaps protecting them, while allowing small molecules like metabolites to move freely through the cell, which may be helpful in cells transitioning out of dormancy. 
Dormancy in its rigid definition doesn't apply to viruses, as they are not metabolically active. However, some viruses such as poxviruses and picornaviruses after entering the host can become latent for long periods of time, or even indefinitely until they are externally activated. Herpesviruses for example can become latent after infecting the host and after years activate again if the host is under stress or exposed to ultraviolet radiation. 
Pyrethrins are pesticides found naturally in some chrysanthemum flowers. They are a mixture of six chemicals that are toxic to insects. Pyrethrins are commonly used to control mosquitoes, fleas, flies, moths, ants, and many other pests.
Pyrethrins are generally separated from the flowers. However, they typically contain impurities from the flower. Whole, crushed flowers are known as pyrethrum powder.
Pyrethrins have been registered for use in pesticides since the 1950’s. They have since been used as models to produce longer lasting chemicals called pyrethroids, which are man-made.
What are some products that contain pyrethrins?
Currently, pyrethrins are found in over 2,000 registered pesticide products. Many of these are used in and around buildings and on crops and ornamental plants. Others are used on certain pets and livestock. Pyrethrins are commonly found in foggers (bug bombs), sprays, dusts and pet shampoos. Some of these products can be used in organic agriculture. Pyrethrins are also found in some head lice products regulated by the Food and Drug Administration.
Always follow label instructions and take steps to avoid exposure. If any exposures occur, be sure to follow the First Aid instructions on the product label carefully. For additional treatment advice, contact the Poison Control Center at 1-800-222-1222. If you wish to discuss a pesticide problem, please call 1-800-858-7378.
How do pyrethrins work?
Pyrethrins excite the nervous system of insects that touch or eat it. This quickly leads to paralysis and ultimately their death. Pyrethrins are often mixed with another chemical to increase their effect. This second chemical is known as a synergist.
How might I be exposed to pyrethrins?
Exposure can occur if you breathe it in, get it on your skin or eyes, or eat it. For example, exposure can occur while applying sprays or dusts during windy conditions. This can also happen if you apply a product in a room that is not well ventilated. People using foggers may be exposed, especially if they come back too early or fail to ventilate properly. Exposure can also occur if you use a pet shampoo without wearing gloves. You can limit your exposure and reduce the risk by carefully following the label instructions.
What are some signs and symptoms from a brief exposure to pyrethrins?
In general, pyrethrins are low in toxicity to people and other mammals. However, if it gets on your skin, it can be irritating. It can also cause tingling or numbness at the site of contact.
Children who have gotten lice shampoo containing pyrethrins in their eyes have experienced irritation, tearing, burns, scratches to the eye, and blurred vision. When inhaled, irritation of the respiratory passages, runny nose, coughing, difficulty breathing, vomiting and diarrhea have been reported.
Dogs fed extremely large doses of pyrethrins have experienced drooling, tremors, uncoordinated movement, and difficulty breathing. Increased activity, exhaustion, convulsions, and seizures have also been reported with high doses.
When exposed to pyrethrins, people have reported some of the same symptoms that are associated with asthma. These include wheeze, cough, difficulty breathing, and irritation of the airways. However, research has not found a link between exposure to pyrethrins and the development of asthma or allergies.
What happens to pyrethrins when it enters the body?
When eaten or inhaled, pyrethrins are absorbed into the body. However, they are absorbed poorly by skin contact. Once inside, they are rapidly broken down into inactive products and are removed from the body. In a study with mice, more than 85 percent left the body in feces or urine within two days. Removal of pyrethrin 1, a major component of pyrethrins, from goats and hens was also very rapid. However, studies have found very small amounts in the milk and eggs of exposed animals.
Are pyrethrins likely to contribute to the development of cancer?
In two studies, mice and rats were fed low to high doses daily for 1.5 to 2 years. At the highest dose, some rats had an increased number of liver tumors. However, the changes in the liver leading to tumors only occurred above a certain threshold. Based on these studies, the EPA has classified pyrethrins as not likely to cause cancer. However, this rating is limited to doses below this threshold.
Has anyone studied non-cancer effects from long-term exposure to pyrethrins?
In separate studies, rats and dogs were fed low to moderate daily doses of pyrethrins for one to two years. At moderate doses, there were effects to the thyroid in rats and the liver in dogs. In another study, rats breathed in low to moderate doses daily for several months. At low doses, damage to tissue along the nasal and respiratory passages was observed. At moderate doses, lower body weights, difficulty breathing, and tremors were observed.
Scientists have also tested whether pyrethrins cause developmental or reproductive effects in rats and rabbits. In these studies, animals were fed low to moderate doses daily throughout their lives or during their pregnancies. Effects were only observed at moderate doses. These included lower body weights in some adult rats and their young. Drooling, unusual postures, and difficulty breathing were observed in one adult rabbit. Also, two rabbits lost their pregnancies. However, it is unclear if the lost pregnancies were related to pyrethrins. No effects were observed in rats or their young when fed solely during their pregnancies.
Are children more sensitive to pyrethrins than adults?
Children may be especially sensitive to pesticides compared to adults. However, there are currently no conclusive data showing that children have increased sensitivity specifically to pyrethrins.
What happens to pyrethrins in the environment?
In the presence of sunlight, pyrethrin 1, a component of pyrethrins, breaks down rapidly in water and on soil and plant surfaces. Half-lives are 11.8 hours in water and 12.9 hours on soil surfaces. On potato and tomato leaves, less than 3% remained after 5 days. Pyrethrins do not readily spread within plants.
In the absence of light, pyrethrin 1 breaks down more slowly in water. Halflives of 14 to 17 days have been reported. When water was more acidic, pyrethrin 1 did not readily break down. Pyrethrins that enter the water do not dissolve well but tend to bind to sediment. Half-lives of pyrethrin 1 in sediment are 10.5 to 86 days.
Pyrethrins also stick to soil and have a very low potential to move through soil towards ground water. In field studies, pyrethrins were not found below a soil depth of 15 centimeters. However, pyrethrins can enter water through soil erosion or drift. In the top layers of soil, pyrethrins are rapidly broken down by microbes. Soil half-lives of 2.2 to 9.5 days have been reported. Pyrethrins have a low potential to become vapor in the air.
Can pyrethrins affect birds, fish, or other wildlife?
Pyrethrins are practically non-toxic to birds but highly toxic to honey bees. However, some of the risk to pollinators is limited by their slight repellent activity and rapid breakdown.
Pyrethrins are highly to very highly toxic to fish. They are also very highly toxic to lobster, shrimp, oysters, and aquatic insects. This may be partly due to their higher toxicity at lower temperatures. There is evidence that long term exposure to pyrethrins can cause reproductive effects in fish and aquatic insects. In separate studies, minnows and water fleas were exposed to very small amounts of pyrethrins for one month. Fewer minnow eggs hatched and fewer water flea young were produced.
Do Plants Grow Better in Sunlight or Artificial Light?
In this experiment, we will discover if an artificial light source will yield the same plant health and growth rates as light from the sun.
Plants grow through a process called photosynthesis. This requires sunlight to take place. The chlorophyll located in the chloroplast of the plant cells grabs sunlight and starts the reactions (such as sugar) that are needed to make the plant grow. Water is also needed in the growth equation, because like humans and animals, plants need moisture to quench their thirst.
While it is somewhat debatable as to who invented the light bulb, it has become common knowledge that we associate the light bulb with Thomas Edison. He created an incadescent light bulb that outsmarted his fellow inventors because it was fully integrated with an effective incadescent material, a higher vacuum than others, and a high resistance which made powering up the lightbulb with electricity economical.
- An incadescent light bulb
- Light timer (if you don't have this. there is an alternative: keep reading)
- 2 beans (i.e. lima beans, lentils, pinto beans)
- 2 pots with soil
- Water (same amount for each pot, we are only changing the light source)
- Pen and paper
- First we will pot the beans. Use your finger and make a small hole about 2 inches deep into the soil of each of the 2 pots. Put a bean into each hole and cover it up with soil. Give it a pat.
- Label each pot with the type of light it will receive- sunlight or light bulb light.
- Take one pot and put it under a light bulb and turn it on. Set it on timer so that it can mimic the time the sun rises and sets daily. If you don't have a timer, you'll have to wake up in the morning and turn the light on and close it at night when the sun sets.
- Take the other pot and put it in a place with lots of bright sunlight. Perhaps a windowsill.
- Give the plants their first taste of water. Just give them a little water. Just a sprinkle, spritz, or &ldquorain&rdquo would do. Do not overwater them with too much! You will water them the same amount at least daily or when they are dry. You can test if they are getting too much water by just sticking your finger to the side of the bean and into the soil. If your finger comes out muddy, they have too much water and you shouldn't water them. The soil should be a nice dampness or dry.
- The beans should germinate in 2-5 days, depending on location and conditions. After this, you should start monitoring their daily growth for 2 weeks and measure how tall the sprout is for each sample. Which one is growing at a faster rate? Is there any difference? Any other things you see like a difference in plant healthiness?
- After 2 weeks, analyze your results.
Terms/Concepts: Incadescent light bulb filament plant growth heat sunlight photosynthesis
Hyne, Norman J. (1991). Dictionary of petroleum exploration, drilling & production. pg. 190: PennWell Books. pp. 625. ISBN 0878143521 .
Disclaimer and Safety Precautions
Warning is hereby given that not all Project Ideas are appropriate for all individuals or in all circumstances. Implementation of any Science Project Idea should be undertaken only in appropriate settings and with appropriate parental or other supervision. Reading and following the safety precautions of all materials used in a project is the sole responsibility of each individual. For further information, consult your state's handbook of Science Safety.
Plants can grow well in an optimum temperature range. Weather that is colder than plants can handle slows down life processes in those plants and causes them to eventually wither away. Plants adapt their physiology and morphology according to their habitat by developing adaptations. For example, coniferous trees have adapted themselves to grow in cold climates. Similarly, desert plants such as cactus have adapted themselves to thrive thrive at high temperatures.
Appropriate temperatures help plants maintain their growth processes at an optimum level. The right range of temperatures affects transpiration and helps plants to maintain their water content.
Understanding Osmosis in General
By definition, osmosis is the spontaneous movement of a solvent (water) through a cellular membrane. This is a special kind of diffusion that moves water molecules from a place of higher concentration to a place of lower concentration to create a stable and equal cellular environment. The process of osmosis is kind of like squeezing the middle of a water balloon. When you squeeze right in the middle the water displaces to either side equally. If you squeeze on one end all of the water (and weight) goes to one side or the other. Osmosis seeks to create a balance between the two sides of the water balloon like if you were to squeeze it in the center. Osmosis continues until there is an equal pressure of fluid on either side of the membrane.
The water creates a pressure that makes the balloon expand, right? In plants this pressure is called turgor pressure, or the pressure that pushes the cell membrane against the plasma wall to maintain the cell’s shape. Turgor pressure is effected by osmotic pressure, or the pressure differentials that cause osmosis to occur. If one side of the membrane has a higher pressure, it will cause the other side of the cell to have low pressure which equals a not-well-supported plant structure. This difference in concentration is an osmotic pressure differential. The fuller the vacuoles, cellular sacs that hold fluid like water, the healthier the plant is and the more alive the plant looks. This also indicates successful and ongoing osmosis to make sure all of the cells have equal volume and pressure. Studying for the GCSE? Prep for the test with the course GCSE Biology.
Falko P. Drijfhout , E. David Morgan , in Comprehensive Natural Products II , 2010
α- Solanine ( 306 ) from the potato, Solanum tuberosum, and the tomato Lycopersicon esculentum (both Solanaceae) and α-chaconine ( 307 ), also from the potato and other Solanum species, are known antifeedants toward snails, but recent tests showed that these two glycoalkaloids act synergistically. Tested alone, both compounds deterred feeding of the test snail, Helix aspersa, with chaconine ( 307 ) being more effective than solanine ( 306 ). But when they were tested as a mixture, the inhibition increased significantly more than that of each compound on its own. 134 At 0.2 mmol l –1 , chaconine inhibited feeding by 30% whereas 0.2 mmol l −1 of solanine did not affect feeding at all. Yet a mixture of solanine and chaconine, both at 0.2 m mol l −1 inhibited feeding by 60%. It is worth noticing that when the mixture was diluted and tested against the extract of the peel of the potato variety Home Guard, the 10 times diluted peel extract was still active as antifeedant, while the authentic glycoalkaloid mixture was not active at this dilution. This gives rise to the question whether other glycoalkaloids maybe present and also working synergistically.
Fruit Ripening: Meaning, Factors and Controls | Plant Physiology
There are several developmental phases through which the fruit passes and fruit ripening is one of them. In fact, ripening begins moment the growth of the fruit is completed. Fruit maturity is a stage of fruit harvesting while fruit ripening is a stage of fruit consumption.
The fruit ripening is associated with many visible changes in the colour, the flavour and the aroma. Thus, the fruit is ready for eating purposes. Fruit ripening is a type of ageing and many people prefer to call it “fruit ageing” than fruit ripening. In many fruits the ripening occurs after picking or the process is hastened after picking. Ripening processes are of degradative nature.
Studies in recent years have shown that several biochemical processes must occur sequentially. However, these processes may not be linked with each other.
Factors Affecting Fruit Ripening:
In the following some of the important factors affecting fruit ripening are described:
The visible changes in the fruit leading to ripening are accompanied by a rapid increase in respiration. This process is called climacteric and is distinctly visible in many fleshy fruits like apple, banana, apricots, papaya, tomato etc. However, fruits like figs or cherries do not show climacteric.
This does not mean that the non-climacteric fruits always have low rate of respiration. Some of the compound fruits in fact have high activity of respiration. In general climacteric fruits are rich in carotenoids whereas non-climacteric fruits contain anthocyanins. In apple once the climateric begins the free fructose disappears from the cytoplasm due to phosphorylation.
Simultaneously there is a change in tonoplast permeability which presumably permits movement of fructose from the vacuole to the cytoplasm. Thus, there is an increased respiration. The alternative explanation is that the rate of respiration is regulated by ADP. Thus respiration rate in low if ATP/ADP ratio is high.
The climacteric rise in respiration results from a high energy requirement in the initial stages of fruit ripening. The respiration is enhanced when ATP is split and level of ADP rises. Tomato fruits when sprayed with 2, 4- DNP are prevented from ripening.
One of the factors inducing increased respiration is natural un-couplers of oxidative phosphorylation. Climacteric fruit extracts did act as un-couplers of oxidative phosphorylation. The present thinking is that increased respiration may be attributed to high energy requirements in ripening.
Tracer studies have shown that in several fruits increased RNA synthesis accompanies fruit ripening. Most of the evidence is based on assays of the rate of incorporation of RNA precursors and indicates that RNA synthesis includes mRNA and is enhances during early part of climacteric rise.
In picked up apples about 50% RNA increased at the initiation of the climacteric increase. When the climacteric is high the increase in its synthesis does not occur.
In general, new synthesis of RNA seems to be essential for the ripening process. Pears sprayed with Act.D did not ripe. The rise in the RNA concentration is followed by an increase in the protein content because of new synthesis. Indeed the synthesis of new proteins is essential for the ripening of many fruits.
When the mature, unripe banana and pears were sprayed with cycloheximide, ripening was inhibited. This was especially so when it was administered during early stages. It is assumed that enzymes involved in ripening were synthesized during the early stages.
Changes in the pattern and activities of several enzymes are reported during fruit ripening. In general, several hydrolytic enzymes increase. These include polygalacturonase, cellulase, pectin methyl esterase, etc. Some of the enzymes soften the fruits and bring about changes in taste as well. The sweetness in several fruits is caused by breakdown of starch into sugar. Sometimes fruits abound in free fatty acids.
However, the importance of several enzymes in ripening of fruit is not clear. This category includes lipidase and peroxidase. It is believed that these enzymes may be involved in the biosynthesis of ethylene. Sometimes different isozymes are associated with fruit ripening.
Increase in chlorophyllase, lipase causes breakdown of chlorophyll and free fatty acids, respectively. Similarly increased lipoxidase is also reported. Large increase in acid phosphatase activity parallels the climacteric in mangoes. In several fruits enzymes of glycolysis, oxidative processes—HMP shunt and citric acid cycle also increase.
Fruit ripening is also accompanied by dramatic changes in its colour e.g., in tomato following sequence of colour changes are observed:
The red colour is due to lycopene. Carotenoid formation occurs when chloroplast is converted into chromoplast. However, not in all the cases the change in fruit colour is associated with the formation of carotenoids.
On the contrary in many fruits anthocyanin is synthesized during ripening as in apple. The present thinking is that synthesis of carotenoids and anthocyanin in ripening fruits is regulated by phytochrome system.
v. Effect of Potassium Nutrition on Fruit Ripening:
In tomato fruit increased potassium (K + ) nutrition causes an increase in the concentration of organic acids, in particular citric and malic acids. It may be recalled that tomato is a climacteric fruit so that the pre-climacteric respiration minimum is followed by a peak during which the rate rises by 110—250%.
When the plants are supplied with high concentrations of K they have reduced rate of respiration especially during the climacteric phase. There is great accumulation of oxaloacetic acid (OAA) which is also increased by K application.
This increase is due to the oxidation of malate by malate dehydrogenase and can be inhibited by malate and succinate oxidation by tomato fruit mitochondria. The rate of endogenous concentration of OAA could be controlled by the rate of transamination with L-glutamate through the action of GOT.
Fruit ripening is also retarded by osmotic water intake and by washing out of some unidentified substances. Besides the climacteric respiration, other characteristic metabolic pathways can be seen. For instance, in ripening mango fruits aspartate and glutamate decrease, while α-aminobutyrate increases.
Together with changes in enzyme activities, the following metabolism of aspartate and glutamate must occur:
This metabolism indicates that the most significant amino acids are decomposed. This may partly explain why protein synthesis ceases during ripening.
Hormonal Regulation of Fruit Ripening:
As many as five types of plant hormones are known to regulate fruit ripening. In recent years occurrence of IAA in fruits has been demonstrated beyond doubt. While young seeds are the main site of IAA synthesis, in the mature fruit it is synthesised in the fruit flesh. In fact auxins slow down fruit ripening except in some cases where they may quicken.
Perhaps auxins prevent ethylene formation in fruits. Obviously auxins must be degraded endogenously through series of enzymes like IAA—oxidase, etc. to control fruit ripening. Moment the auxins are degraded the fruit tissue becomes sensitive to ethylene.
Very little is known about the endogenous cytokinin content and its metabolism in fruits. On the basis of their function in the leaves, they possibly contribute in keeping the protein and chlorophyll content constant.
The effect of gibberellins in a way is comparable to auxins and cytokinins. Most studies have been done on oranges where GA inhibits degradation of chlorophyll/and delay carotenoids accumulation. Thus pigment formation is delayed. Similarly banana fruits sprayed with GA do not undergo yellowing even though other processes occur normally.
In large number of fruits, before the ripening is ultimately achieved there is accumulation of ABA (Fig. 25-2). Perhaps this phytohormone regulates fruit ripening. In apples after a week of harvesting ABA content increases many times. ABA concentration is very high in the inner part of the green fruit flesh of tomatoes.
It may be mentioned that tomatoes ripen in a centrifugal direction and as the process progresses the relationship is reversed. Thus in ripened part ABA level falls down. In the following diagram (Fig. 25-3) a relationship between phytochrome, ABA and lycopene content of ripening tomatoes is given.
It will be observed that with the red light illumination of tomatoes, ABA content rises several-fold in first few days and then declines. The present thinking is that ABA triggers lycopene synthesis.
Ethylene is an important hormone concerned with ripening. Fruits fail to ripen in the absence of ethylene. It is shown that ethylene probably brings about the climacteric. Similarly, non-climacteric fruits once treated with ethylene also show increased respiration. Perhaps difference between climacteric and non-climacteric fruits may be due to ethylene production. Ripening can be induced only when auxin is degraded by IAA oxidase, etc.
In view of the reported effect of ethylene in altering the proportion of individual tRNA species, ethylene may be regulating translation of mRNA and thus initiate ripening. In tomatoes, exogenous application by ABA enhances ethylene production.
Whether ABA induces ethylene synthesis in vivo is not clear. Light is also shown to induce ethylene formation. For instance, red light induces ethylene formation while FR slows it. Obviously the phenomena of fruit ripening appear to by a set of highly complex physiological events.
It may be stated that ethylene formation in plants is not exclusively induced by light. It is also produced when a tissue is injured, or diseased or due to physical and chemical stresses. Even action of some metal ions e.g. Cu ++ and Ca ++ causes ethylene formation. Most studies are available in tomato.
In the following scheme a possible relationship between phytochrome and some hormones in fruit ripening has been elucidated:
The above scheme provides tentative relationships between various components though precise relationships between various components though precise relationship of ABA and ethylene is not well understood. There are reports that ethylene causes increase in ABA level and the latter hormone might initiate fruit ripening by stimulating ethylene production.
During ripening there is breakdown of insoluble protopectin into soluble pectic compounds. The process is enzymes mediated. No detailed mechanism of softening is known. During ripening there is shortening of the polymer chain length, demethylation of carboxyl groups and deacetylation of hydroxyl groups.
All these affect cell wall consistency through change in the bonding with associated cell wall constituents e.g., cellulose, hemicellulose.
Most climacteric fruits possess starch as a storage reserve. This is broken down into soluble sugars due to enzymes. Thus fruit attains sweetness.
Loss of Astringency:
In some fruits which are unripe, there is abundance of tannins of low molecular weight (polyphenols) which react with proteins e.g. banana or sapota. When eaten they give astringent taste. With ripening, tannins polymerise into large molecules and lose their capacity to react with protein. Instead they get trapped in the cell.
Sourness of fruits is due to organic acids. The taste is determined by the ratio of sugars and acids. With increased ripening, the total activity decreases. However, in banana, the acids increase on ripening.
Aroma and Flavour:
Ripe fruits have intense aroma and flavour. Aroma is due to the volatile chemical compounds which are enzymatically synthesised and emitted. These volatile compounds are esters and lactones, alcohols, acids, aldehydes, ketones, acetals, phenols, ethers, etc.
Harvesting does not indicate the end of a fruit life. Several of the fruits can be successfully stored up to several weeks by controlling mechanical injury, transpiration, respiration, decay and physiological breakdown. Several physiological and chemical agents are employed to slow down metabolic rates in fruits.
By refrigeration of fruits, storage period is enhanced. It helps in two ways: slowing down respiration due to low temperature and checking microorganisms development. Temperature also influences endogenous ethylene production.
Recently controlled atmosphere (CA) storage is used in collaboration with refrigeration. These processes maintain high quality of fruits. The technique is affectively used in storing apples, citrus, etc. The CA is affected by increasing CO2 in the atmosphere or reducing O2 levels.
Similarly, some fruits are stored under low pressure. It is a new approach in the long-term storage of fruits. In this method, ethylene evolved is removed, and the partial presence of oxygen is lowered. This slows down the ripening.
Studies at the Bhabha Atomic Research Centre, Mumbai have demonstrated the potential of low- dose gamma irradiation for retarding ripening in mango, papaya and banana. Irradiation also increases pigmentation.
Sometimes fruits are dipped in wax emulsions or plastic films. Even treatment with GA retards ripening.
Artificial Fruit Ripening:
Ethylene is currently used commercially to induce ripening in mangoes, tomatoes, banana, and even degreasing citrus fruits. Temperature affects the process of artificial ripening with ethylene. This gas merely removes chlorophyll and unmasks yellow and orange pigments.
In some fruits, there is synthesis of these pigments also. In fruits with pronounced climacteric, 0.1-100 ppm ethylene is effective when applied in the pre-climacteric stage. There are several sources of ethylene (ethrel, CPTA). Sometimes acetylene and carbon monoxide are also used for artificial ripening of bananas and mangoes.
Hot water dip treatment of mangoes enhances ripening and colour development. This also lessens microbial growth. The ripening is independent of maturity of fruit. In order to have characteristic taste, only optimal mature fruits should be artificially ripened.
How Do Plants and Animals Obtain Energy?
Plants absorb energy from the sun and use photosynthesis to make sugars. Animals have mitochondria that use the sugars provided by plants to produce their own cellular energy. Plants that produce their own food, and food for other plants and animals using photosynthesis, are called autotrophs.
The sun provides energy for plants that absorb it into their chloroplasts. Chloroplasts use this energy to create sugar molecules that help the plants grow and reproduce. Then, animals come along and eat the plants and absorb their energy. They use the energy obtained from the plants to produce their own energy and convert it into water and carbon dioxide. Plants use the carbon dioxide and water, and the cycle begins again. In order to obtain energy, animals do not always have to eat plants. They can also get energy from eating other animals that eat plants.
There are many different processes that go on in plants and animals that require energy. Synthetic work involves things like the production of DNA, and it requires energy to occur. The mechanical work involved in moving muscles requires energy, as do the electrical impulses that travel from the brain to the rest of the body. Without enough energy, these processes become difficult or impossible.