Plant Predatory Defence

May 1, 2001

By Peter J Lester

In 1963 a Dr Melvin Calvin received the Noble prize for chemistry. In his thesis he revealed that the process of photosynthesis in the plant (the conversion of solar energy into chemical energy) required the assistance of chemical activator ion's and specific enzymes. For example, his work proved that the processes of amino acid production, the building blocks from which all proteins are derived, could not proceed into full proteins unless the element calcium was present in the fluid. Calcium is not present in proteins, but it is essential for the amalgamation of the prerequisites of proteins, amino acids, and Dr. Calvin established that full proteins could not be formed in the absence of this essential element. 

The fundamental nature of photosynthesis as pointed out, is the conversion of radiant energy of sunlight into chemical energy, via plant tissue. It is the chemical energy of the plant in the form of ATP ( adenosine triphosphate) and reduced to (TPNH) triphosphopyridine nucleotide. 

The first studies date back to 1630, where van Helmont, a Flemish botanist, revealed that plants make their own organic materials and do not simply absorb them form the air. Joseph Priestly revealed in 1772 that a sprig of mint would "restore" air that had been "injured" by the burning of a candle. Seven years later in 1779 Jan Ingenhousz discovered that vegetation could restore "bad air" only if the sun was shining, and that this ability of the plant to restore "bad air" was proportional to the clearness of the day and to the exposure of the plant to the sun. In the dark, he claimed, plants gave off air "harmful to animals."

The next major step in the understanding of the processes of photosynthesis came in 1804, when de Saussure weighed both the air and the plant before and after photosynthesis and thus revealed that the increase in the dry weight of the plant was greater when carbon dioxide was removed from the air. He thus concluded that the other substance that contributed to the gain in weight was water. 

Ingenhousz suggested that light functions in photosynthesis to split carbon dioxide and thus liberate oxygen and yield "carbon," which was used to form plant substances. On this basis, living organisms were divided into green plants, which could use radiant energy for the "assimilation" of carbon dioxide, and other organisms, ones without chlorophyll, that could not use radiant energy and could not assimilate CO2. 

The logic was upset when Winogradsky discovered in 1887 chemosynthetic bacteria, organisms without chlorophyll that were also able to assimilate carbon dioxide.

Via the pathways of these many and varied chemical and biological processes, the plant produces the enzymes and proteins required for its reproduction, growth and protection. 

As in any system, when the factory, (the plant in this case) is provided with insufficient materials to perform these many and varied tasks, many of the processes are left uncompleted. Incomplete proteins are those substances that the predator requires to complete its life cycle. Predators, as the term suggests, predate, or date before the due time. As the process of nature dictate, stressed organisms are more vulnerable to predation than healthy ones. The predator is an opportunist and only attacks when the opportunity is right.

When the plant is unable to complete the processes necessary for the formation of their life sustaining biological systems, incomplete substances accumulate, and incomplete substances decay more readily than complete ones obviously. Most predators require the presence of a weakened host, as the weakened host will provide them with their food. 

As mentioned above, Dr. Calvin revealed that the base element calcium was essential in the formation of amino acids, and thus the completion of proteins. Other activator ions are still being discovered. An activator ion is an element which makes a substance active or that renders an active enzyme capable of exerting its proper effect. These may include calcium, iron, manganese, copper, zinc etc.

Enzymes are protein catalysts, and as proteins are constructed by the complex formation of amino acids, and as has been revealed by Calvin, the element calcium has to be present for the formation of amino acids. No proteins can be formed in the absence of this essential element. Each enzyme has specific activator ions as well, and each one requires these in amounts sufficient to complete its various functions. The pH of the substrate must be right, as must be temperature and the presence of the activator ions, and these must be in balance with all other prerequisites. 

For plants to protect themselves from predatory attack, they require the function of these protein catalysts, or enzymes. Most chemical reactions of biological interest require fairly high activation energies – so high, in fact, that most living processes should in theory, require temperatures far higher that that found at room temperatures. Obviously, this is not the case; if living matter were heated substantially above room temperature it would be quickly killed. The answer lies in the action of these enzymes or catalysts: it is the acceleration of reactions by means of catalysts rather than heat.

If, for any reason, the plant cannot complete the necessary steps to complete the production of full proteins it results in the formation of un-combined amino acid compounds, or amide nitrogen complexes. Such compounds are very volatile and decay sets in soon after exposure to the elements. Decomposing plant tissue invites in the decomposing organisms such as grass grubs, aphids etc. 

In a normal sequence of events, the plant takes up carbon dioxide (CO2) from which the O2 is defused and transpires from the leaf, retaining the carbon (C) This in turn then combines with water to form a weak organic acid CH2O. These compounds are quite unstable and consequently form complex bonds or form C3H6O3 to more complex C6H12O6, or D-glucose and D-fructose bonds. The transformation of the C3H6O3 compounds to the more complex glucose and fructose compounds requires the action of a catalyst. This catalyst requires the action of an activator ion, or metal. 

In the event that the plant is unable to meet the need of the chemistry reactions, much of the work is left incomplete resulting in the formation of compounds that invite predation. The organisms that live off decomposing or decaying matter are termed heterotrophs and are those organisms that cannot synthesise their own food from inorganic compounds, and therefore must live either at the expense of the autotrophs (self nourishing plant life) or upon decaying matter. The mode of their nutrition is called heterotrophic. All animals, all fungi and most bacteria are heterotrophs.

Obviously not all species have the same attraction to the same food source, this is fortunate or else the whole biotic pyramid would collapse. Nature has provided all species with differing digestive preferences. These preferences are well evident in the herds of animals in Africa. The eco system supports a grand variety of herbivore each living in seeming harmony. Each has its unique digestive microflora and each lives off a different plant or portions of the same plant. The predator was never intended to wipe out a species, but just to act as a check and balance. When the predator becomes a problem, look to the host, it is the host that has been weakened and the predator as an opportunist is taking advantage of the situation.