Role of plant enzymes

Because the role of plant enzymes in host-plant resistance to insects is poorly understood at both an ecological and mechanistic level, the enhancement and/or transfer of genes for crop improvement should proceed with caution. The combined input of molecular biologists, agronomists, food scientists, plant pathologists, weed scientists, and entomologists is needed to achieve optimal success in crop improvements. 

Explain the role of plant enzymes and microbes in the process of ensilage. 

Collmer A, Keen NT (1986) The role of pectic enzymes in plant pathogenesis. Ann Rev Phytopathol 24 883-409... 

Although LOX from soybean seed is the best characterized of plant LOXs, this enzyme is present in a wide variety of plant and animal tissues (Liavonchanka and Feussner, 2006). The enzyme occurs in a variety of isoenzymes, which often vary in their optimum pH and in product and substrate specificity. Given the occurrence of multiple LOX isoenzymes in soybean leaves and the proposed roles of these enzymes in the plant metabolism, it is possible that individual isoenzymes play specific functions (Feussner and Wasternack 2002). The molecular structure of soybean LOX is the most reported, and four isoenzymes have been isolated (Baysal and Demirdoven 2007). Soy isoenzyme 1 produces 9- and 13-hydroperoxides (1 9) when the enzyme acts on free PUFA at pH 9.0, its optimum pH (Lopez-Nicolas and others 1999). Soy isoenzyme 2 acts on triglycerides as well as free PUFA leading to 9- and 13-hydroperoxide... 

Much attention has been devoted to study of the role of pectic enzymes in plant pathology. Two comprehensive reviews have appeared during the past ten years.9,10 Hence, only some of the fundamental aspects and some subsequent observations will be discussed here. 

No nickel-requiring enzymes or proteins are known in vertebrates, although biological roles of nickel enzymes and cofactors have been found in plants and bacteria. Although the role of nickel in human physiology has not been confirmed directly, the evidence strongly suggests that nickel is required by humans [263],... 

It may be concluded that neither pH nor isozyme-specificity is likely to direct the exclusive formation of isodityrosine in the plant cell wall in vivo. Indeed, it might be argued that isozyme-specificity is intrinsically unlikely to direct the orientation of coupling (dityrosine vs. isodityrosine) since the role of the enzyme is thought to be merely the production of tyrosine free radicals (44) which then non-enzymically pair off. 

The purpose of this article is to outline the role of these enzyme systems in the soil/plant ecosystem and discuss how their useful characters might be elevated and exploited further. 

All plants contain a PEPCase enzyme which, among other likely roles (Vidal et al., 1986), serves to replenish tricarboxylic acid cycle intermediates that are consumed during ammonium assimilation (Latzko Kelly, 1983). The role of this enzyme, other than its presumed housekeeping function, has not been studied in any detail and its activity is probably not controlled by environmental factors. Isoforms of PEPCase have been observed in many plants (C3, C4 and CAM) for example, in rice five isoforms have been detected immunologically and in most plants two to four bands that react with anti-PEPCase antibodies are found (Matsuoka Hata, 1987). It is not clear how these isoforms arise, e.g. by post-translational modification of one form, or whether all of these forms are products of different genes. The housekeeping-type PEPCase enzyme, concerned with anaplerotic functions, is distinct from other PEPCase enzymes that function in plants with C4 and CAM metabolism (see below). 

Studies have been conducted on the amount and functionality of plasma membrane H+ATPase. The central role of this enzyme in plant growth and mineral... 

Nitrate Reductase. Nitrate reductase is found widely distributed among plants and microorganisms and catalyzes the reduction of N03 to N02" (16,17,18,19). The physiological role of this enzyme depends... 

APS reductase is found in dissimilatory sulfate reducing bacteria, such as Desulfovibrio and Desuljotomaculum, in certain Thiobadlli, in Thiocapsa roseopersicina, and in the alga Chlorella pyrenoidosa. Table XIX, compiled by Schiff (378), gives the properties of various APS reductases from plants and microorganisms. In Thiobadlli and Desvljovi-brio, APS reductase constitutes as much as 1-5% of the cell protein, which suggests the important role of this enzyme in the metabolism of these organisms 375). 

Oxynitrilases or hydroxynitrile lyases (HNL) constitute a group of enzymes that catalyze the reversible addition of HCN to ketones and aldehydes. The natural role of these enzymes is a defence mechanism of higher plants against herbivores, whereby HCN is liberated from cyanoglucosides such as prunasin (almond, cherry, apple) by the action of a glycosidase and a hydroxynitrile lyase. 

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