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FUNGAL PATHOGENICITY AND QUANTITATIVE CHARACTERISTICS OF PRIMARY PROCESSES OF PHOTOSYNTHESIS
AK KUKUSHKIN, FAP EKOBENA

Faculty of Physics, MV Lomonosov Moscow State University, Vorobjevy Gory, Moscow, 119899 Russia


Background and objectives
The claryfying of background of pathogen - cell interactions on the molecular level is the main aim of modern plant pathology. Thegoal of this work was to study the effects of plant deseases (grey mould, stem rust, powdery mildew) on the elementary rate constants of photosynthetic processes in photosystem 2.


Materials and methods
We studied the healthy and infected cucumber (Cucumis sativus L. cv. lzyachnyi), bean (Vicia faba cv. Russian black) and wheat (Triticum aestivum L. cv. Markiz) plants. We used the following pathogens: grey mould ( Botrytis cinerea ), mildew (Sphaerotheca fuiiginea), powdery mildew (Erysiphe graminis f. sp. tritici). For investigation of primary photosynthetic processes we used the optical methods of thermoluminescence and luminescence and computer simulation.


Results and conclusions
By given methods for leaves of plants infected by grey mould (cucumber, beans) we have earlier discovered by methods of thermoluminescence the changes in the reactions of electron transport near the reaction center of photosystem 2 and by the use of slow fluorescence induction - the changes in the electron transport rate between the photosystems. The similar qualitative changes were found in wheat after stem rust and powdery mildew infection [1]. These changes correlated with several biochemical parameters such as the intensity of photosynthesis, chlorophyll concentration, peroxidase and polyphenoloxidase activity. However, the previous papers contained only qualitative characteristics of photosynthetic reactions. Earlier we have developed a quantitative theory of primary processes and reductive pentose phosphate cycle that explained such phenomena as induction processes and Caivin cycle as well as the main regulation links. By this theory we received the analytical formulae for TL and fluorescence intensity, that contain the elementary rate constants and external parameters (light intensity, carbon dioxide concentration and so on) [2]. Using this theory we determined the changes of elementary characteristics (some rates of electron transport, the component concentrations) under the infection by pathogens. For example, after the computer analysis of experimental data we have shown that during the Botrytis cinerea infection the thermoluminescence A maximum moved to higher temperatures, the exact value of the shift being dependent on the age of the leaf. It means that in this case the population of (S3)+P(QA)-(QB)2- state of RC of photosystem 2 increases [2].


Refere,nces
1. Sointsev MK, Ekobena FHP, Tashish, Yurina EV, Yurina TP, 1996. Modern Fungicides and Untifungal Compounds, ed. by Lyr H et al, pp. 257-262, 2. Kukushkin AK, Ekobena FHP, 1997. Developements in Plant Pathology. Diagnosis and ldentifiction of Plant Pathogens. Proceedings 4-th ]nt Symp Eur Foundation for Plant Pathology, pp. 519-521.