Role in plant disease resistance

Like other micronutrients. Mo has been found to influence the incidence of plant diseases. Molybdenum application has been reported to decrease leaf-spot infection caused by Septoria sojina in soybeans (Girenko, 1975) and to decrease Verticillium wilt in tomatoes (Dutta and Bremner, 1981) and cotton (Gossypium spp.) (Miller and Becker, 1983). It also reduces the production of roridin E toxin by Myrothecium roridum (Fernando, Jarvis, and Bean, 1986) and zoosporangia formation by Phytophthora spp. (Halsall, 1977). Haque and Mukhopadhyay (1983) observed that soil application of Mo caused some reduction in the population of parasitic nematodes. Whether these effects are due to some specific role of Mo in plant disease resistance or are indirect effects of Mo through plant metabolism is not certain. 

Plant phytoalexins [natural plant antibiotics] [1] have the potential of becoming a new class of useful compounds in the control of insect pests. Some phytoalexins have been demonstrated as deterrents to insect feeding. Considerable progress has been made to characterize them chemically and to extend the study of their function in plant disease resistance, but exploration of their role in the control of insect pests is just beginning. 

Phytoalexins are low molecular weight, antimicrobial compounds that are both synthesized by and accumulated in plants after exposure to microorganisms [1.]. Several lines of evidence suggest that these compounds have an important role in plant disease and pest resistance [12.]. ... 

Sohn, K.H., S.C. Lee, H.W. Jung, J.K. Hong, and B.K. Hwang. 2006. Expression and functional roles of the pepper pathogen-induced transcription factor RAV1 in bacterial disease resistance and drought and salt tolerance. Plant Mol. Biol. 61 897-915. 

The bioactive compounds isolated from plants and responsible for the medicinal properties mentioned here and different health -improving effects are named secondary metabolites [9]. It is generally believe that they do not play an essential role in plant growth and development. However, they participate in plant adaptation responses and defense functions. It is well known that these compounds play an important role in their survival in the ecosystem because they are involved in the resistance against pests, diseases and other functions such as attraction of pollinators and interactions with organisms of their enviromnent [1, 6, 9]. 

ABA is another important plant hormone that participates in plant diseases and stress resistance (Mauch-Mani and Mauch 2005). The role of ABA in CTS-induced plant immunity was studied by Iriti and Faoro (2008). Chitosan application induced ABA accumulation in leaf tissues at 24 h after treatment, and elicited resistance against TNV. Besides, treatment with nordihydroguaiaretic acid (an ABA inhibitor) before chitosan application reduced tobacco resistance to the necrosis virus. It is indicated that ABA plays an important role in CTS-induced resistance mechanism. 

Copper is an essential micronutrient required in the growth of both plants and animals. In humans, it helps in the production of blood haemoglobin. In plants, copper is an important component of proteins found in the enzymes that regulate the rate of many biochemical reactions in plants. Plants would not grow without the presence of these specific enzymes. Research projects show that copper promotes seed production and formation, plays an essential role in chlorophyll formation and is essential for proper enzyme activity, disease resistance and regulation of water in plants (Rehm and Schmitt, 2002). 

Polyphenol oxidase occurs within certain mammalian tissues as well as both lower (46,47) and higher (48-55) plants. In mammalian systems, the enzyme as tyrosinase (56) plays a significant role in melanin synthesis. The PPO complex of higher plants consists of a cresolase, a cate-cholase and a laccase. These copper metalloproteins catalyze the one and two electron oxidations of phenols to quinones at the expense of 02. Polyphenol oxidase also occurs in certain fungi where it is involved in the metabolism of certain tree-synthesized phenolic compounds that have been implicated in disease resistance, wound healing, and anti-nutrative modification of plant proteins to discourage herbivory (53,55). This protocol presents the Triton X-114-mediated solubilization of Vida faba chloroplast polyphenol oxidase as performed by Hutcheson and Buchanan (57). 

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