Food Storage Strategies in Plants and Animals
Introduction
How do people store food? Dry seeds like wheat, barley and pulses are kept free of moisture, they can be stored for long time. Even some animals do this. Honey bees store nectar, squirrels stock up nuts in autumn.
One particular method of storing food is the only means available to most animals. Eat the food whenever it is available, and store it as fat inside the body, which is safe in the adipose tissues. For many animals finding continuous food supply is very difficult, so storing enough nutrients and energy inside their won body is essential. And for the animals that hibernate in long winter when no food is available, eating fat in autumn is the only way to survive from year to year.
In green plants food is only supplied through photosynthesis that requires only light water and carbon dioxide for preparation of their food. Storing food reserves is not a problem in the plants growing in temperature, water, etc are always available. But deciduous plant growing in temperate and hot regions drop which drop their leaves and become dormant in adverse conditions are similar to animals in that need to have stored food to maintain their life cycle while leafless. If a plant had no nutrient reserve inside his body when it dropped its leaves, it would not even be able to make new leaves on the onset if spring. It will die.
We and animals store our reserve energy as fats. Our adipose tissues are located in different part of our body as stomach, arms legs, etc. A little bit of energy is stored as glycogen, present in our muscle cells and liver, but that is only enough to keep us going for a few hours as any runner or cyclist knows. The long-term energy storage compound is fat. The plants on the other hand, virtually never store fats as reserve energy but store as a starch instead. Why do plants and animals differ on such a simple feature?
An energy storing molecule must store energy of course, but it should not be too heavy and it must be stable enough that it does not go bad within the plant or animal's body. Fat is the most light weight molecule storing energy. One gram of fat stores more energy than one gram of starch or protein. For an organism that needs to move, weight will be less if it stores fat instead of starch. Thanks to god, we don't store starch.
But pant don't move around so weight saving is not a real necessity. The heavy starch molecule is more stable than the lighter fat molecule which is comparatively more important for plants for long-term stability. Many plants starch is a better option. For example, many plants bloom only alternate year, and their stored energy must last at least two years. Some plants bloom only once after growing 2-15 years, and fishtail palms may not bloom until they are more than 70 years old. Such plants store up some starch every year, and then use it all at once during flowering. Fat would not last that long because it becomes moldy if exposed to oxygen and the whole plant is well exposed to air.
Seeds and pollen grains of plants are exceptional in which oil is present. In many plants, flowers produce pollen grain with a drop of oil instead of starch grain, which makes it lighter easier for wind or insect to carry it to another flower for pollination. In case of sesame, peanuts and cashews, seeds store oil and thus become lighter and smaller, so that they can easily be moved by animals. Seeds of avocados are very rich in oil, but rather than being an energy storage mechanism, it is a reward that attracts animals to eat the fruit and then dispersing the seeds far and wide. This type of dispersal of seeds in important for moving seeds to new sites, otherwise seeds would fall only near the parent plant, germinate, and compete with the parent for sunlight, minerals, water and space. Dispersal reduces this competition, thus it is important for seeds to be light enough and delicious that animals don't mind to carry them.
The site of energy storage is also very important in the body so that the energy-storage tissues are vascularized and the circulatory system can deposit or withdraw fats as and when needed. Plants also store a little starch throughout their body, some in cortex, some in path cells, and even in wood. But when plants store a lot of starch, it is almost always in its roots. The thick enlarged roots of radish, beet root, carrot, etc are filled with starch. The plants are putting their food reserves underground, out of sight of hungry animals. The soil a more stable environment, being neither as hot during summer nor does a cold in winter, and similarly it maintains a uniform humidity, all of which contribute to the stability of starch. Root storage foods are well vascularized.
Thick storage roots are not confined just to food plants, but many different plants store starch in roots too. Many cacti store their water in above ground succulent shoots and their starch below the ground in enlarged roots. The nutrient rich roots are not well protected by plants as they never have spines, rarely poisonous, so if ever an animal finds the storage root, here is nothing to stop it from eating.
Even though animals and plants store their energy differently, the reasons are understandable when we consider the consequences of each alternative. Animals need mobility and plants favour stability.
By making en elaborate and deep study of these food storage techniques in nature we can develop safer and efficient food storage techniques in future, particularly for special applications like high mountain expeditions and space travels.
Source
Invention Intelligence, July - August 2007
