Primary Metabolic Pathways In Plants

To make some sense out of the various "highways and by-ways" of plant metabolism, we have put together the scheme shown in Figure 2.1. It depicts the interrelationships between the major metabolic pathways that occur in plants. Similar schemes have been produced for the major pathways for mammalian and microbial metabolism. Some pathways are unique to plants, such as the carbon reduction cycle in photosynthesis and the shikimic acid pathway which produces, among other things, essential amino acids (like tryptophan) that animals cannot live without. These aromatic amino acids are also required for the production of many plant-specific, nitrogen-containing, and phenolic compounds. Microbes and mammals also have their own unique pathways such as those involved in steroid hormone production, but common to plants, microbes, and mammals are the pentose phosphate pathway, glycolysis, and the tricar-boxylic acid (TCA) cycle that are concerned with aerobic respiration and adenosine triphosphate (ATP) biosynthesis — the key energy molecule of the cell.

The scheme shown in Figure 2.1 for plant metabolic pathways will be an essential reference when we discuss individual metabolic pathways and sites where they are known to occur in plant cells. This scheme does not indicate where these pathways occur in plant cells; that will be covered in the next section. It also does not show the individual enzymatic steps that occur in each of the pathways shown. What it does show, however, is (1) the major kinds of metabolites produced by plants (most of these are indicated around the right and bottom fringes of this scheme); (2) the interrelationships between each of the major metabolic pathways; and (3) the molecule, carbon dioxide, which when fixed in photosynthesis leads to the formation of all the other kinds of molecules shown in the diagram. We have tried to show that the larger categories of all plant products are few in number. The majority of all essential products are made from sugars, acetyl CoA, (coenzyme A) or amino acids (which make up all the proteins in the plant including the all-important enzymes involved in each biochemical pathway). The same holds for products having somewhat less of an impact on the growth and development of the plant. These are generally considered to fall into three categories — terpenoids, nitrogen-containing compounds, and phenolic compounds. Some of these compounds require the addition of some soil nutrients such as nitrogen or sulfur, and many are the building blocks for higher organisms and thus are absolutely necessary for life on this planet. Therefore, the fact that plants can utilize the energy of the sun to convert carbon dioxide into more complex compounds is the primary factor that makes plants so essential and so interesting.

FIGURE 2.1 Illustration of the primary metabolic pathways in plants.

FIGURE 2.1 Illustration of the primary metabolic pathways in plants.

Copyright © 1999 CRC Press, LLC.

Was this article helpful?

0 0
Healthy Chemistry For Optimal Health

Healthy Chemistry For Optimal Health

Thousands Have Used Chemicals To Improve Their Medical Condition. This Book Is one Of The Most Valuable Resources In The World When It Comes To Chemicals. Not All Chemicals Are Harmful For Your Body – Find Out Those That Helps To Maintain Your Health.

Get My Free Ebook


Post a comment