Defense, inducible systems phytoalexins

Inducible systems of defense (phytoalexins) are widespread in plants and are effective against many types of fungi and bacteria (37,38). Similar systems have been demonstrated in a few cases with insects and are probably common in nature (see for example reference 39). Although Inducible systems of insect resistance would seem to be efficient and effective, no system is foolproof. The larvae of Epilachna tredecimnotata cut a circular trench in Cucurbita leaves and prevent mobilization of the deterrent substances to the area which is then consumed (40). 

Secondly, the deacetylated form of chitin, chitosan, does not induce phytoalexin formation in the rice system but is active in other plant culture systems [99]. Glucan elicitors induce phytoalexins in legumes (soybean, chickpea, bean, alfalfa, pea) and solanaceous sp. (potato, sweet pepper) [100]. However, anthraquinone biosynthesis was stimulated in Morinda citrifolia by both chitin and chitosan. The degree of acetylation was found to be important in inducing defense responses. During the first few days of incubation after adding elicitor,... 

Immunization of cucumbers by (L lagenarium, C. cucumerinum, P. 1achrymans or TNV generates a systemic increase in peroxidase activities (. TJ, ] 9, 8U) > Like 1 i gni f ic a t ion and phytoalexin induction, peroxidase activities also rise more quickly in response to infection in leaves of immunized plants, even though total activity eventually may be highest in infected susceptible leaves (77). Several other stimuli can induce local (mechanical and chemical injury) or systemic (senescence, ethylene) peroxidase increases that are not accompanied by increased disease resistance. Thus, enhanced peroxidase activity per se may not be a defense mechanism, but may be a necessary adjunct with appropriate chemical substrates for processes important in disease resistance, e.g., lignification, suberization, and me 1anization. 

In this section, based on the methodology presented in the previous section, we describe multidimensional fluorescence imaging and its application to tracking cell responses. We developed the time- and spectrally-resolved fluorescence imaging system based on line illumination, which is capable of rapid acquisition of fluorescence intensities as a function of Em, x, and xy-positions. We applied it to the analysis of an induced plant defense response, that is, the accumulation of antimicrobial compounds or phytoalexins, in oat (Avena sativa). 

In addition, the methodology was applied to fluorescence imaging based on the autofluorescence signals of native molecules in cells or tissues. The imaging system is capable of the rapid acquisition of fluorescence intensities as a function of Em, t, and xy-positions, which is achieved by line illumination of the excitation laser beam. We applied this system to the analysis of a plant defense response, accumulation of phytoalexin in oat leaves, induced by elicitor treatment. In oat leaves treated with an elicitor, we successfully observed weakly fluorescent components, one of which possibly originated from avenanthramide A as a phytoalexin, in addition to the strong fluorescence from chlorophyll molecules. 

It is envisioned that the defensive systems of plants include preformed physical and chemical barriers as well as inducible defenses that also can be either physical or chemical. An example of an inducible defense is the synthesis of specific antimicrobial compounds such as phytoalexins or phytoanticipins. However, in other instances plants react to pests by developing long-lasting, broad-spectrum systemic resistance to later attacks by pathogens. This type of resistance is referred to as systemic acquired resistance, and was discovered in tobacco by Ross (1961). This form of resistance is almost universally... 

C12H18O3, Mr 210.27, viscous oil, bp. (0.13 Pa) 125 °C, [oId-83.5° (CHCI3) np 1.4885. In higher concentrations a phytotoxic compound, structurally similar to the prostaglandins of animals, isolated from Jasmi-num spp. Low concentrations of J. stimulate the defensive system of plants ( phytoalexin) by inducing the formation of hydrocarbons that attract parasitic wasps which feed on plant-destroying caterpillars. 

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