MICRONUTRIENTS - THEIR FUNCTION IN METABOLISM - INTRODUCTION

 

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Micronutrients have many functions, but our study will be restricted to how they activate a few enzymes of the many that function in plant growth. These enzymes and their metal keys have been identified and their chemical functions partially traced. Not all of the processes are clearly understood, but from what is known and what is theorized, we can introduce the following enzymes systems and their micronutrient keys:

Enzyme	Element
Nitrate reductase	Molybdenum
Glutamic dehydrogenase	Copper
Phospoholiopase	Manganese
Cytochrome	Iron
Starch phosphorylase	Boron
Auxin enzyme	Zinc

As we trace the roles of these enzymes systems in plant metabolism we will get involved with the major processes of plant growth – photosynthesis, respiration, protein formation, vitamin and hormone development, and others.

 

The Cell, A Unique Factory

To simplify things we will look inside a leaf cell to see what happens. As in a factory, specialized functions take place – in this case, the basic functions of metabolism, photosynthesis and respiration. In photosynthesis, water and carbon dioxide are put together and activated by light from the sun to form sugar. Respiration is the oxidizing or "burning" of that sugar to give energy for the growth process. In this way the sun's energy is converted to growth energy in the plant. Here also we find the enzyme system at work.

 

A Factory Organized and Managed by Enzymes

Joined with respective micronutrients, the compact and configured protein masses become activated enzymes. As new cells separate from the parent cell, each of these enzymes is patterned into the new plant cell and turns it into a productive, useful organism.

Let's look at just a few of the busy enzymes in a plant – an efficient cell factory!

Mo

+

Nitrate Reductase

+

NO3-

---->

NH4+

Perhaps the least familiar of the micronutrients, due to the very small amount found in plants, is molybdenum. So let's begin our journey in that part of the factory where this element is utilized.

Molybdenum turns on the nitrate reductase enzyme system. Deficiency causes a marked decrease in the plant content of two vitamins, ascorbic acid and niacin. In general, plants are unable to utilize nitrogen without molybdenum.

In the presence of molybdenum-activated nitrate reductase, nitrate nitrogen is converted to ammonia, which is added to carbon compounds by a copper-linked enzyme system to synthesize amino acids. If, however, molybdenum is lacking in the plant, very little ammonia is produced, and sugar content will build up. In very unusual cases, this increase in sugar content may give red and purple color to leaves and can be mistaken for a phosphorus deficiency. Generally, molybdenum deficiency closely resembles nitrogen deficiency. Molybdenum is also particularly important to the nodule bacteria of legumes. In that relationship it functions a bit differently but is still involved with the nitrogen status of the plant.

Now, let's trace the work of nitrate reductase, an enzyme that helps get your liquid fertilizer working for growth.

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