1. Temperature-induced Transitions in Photosynthetic Apparatus of Bean Plants Probed by JIP-test

The reaction of the photosynthetic apparatus in higher plants to high- and low-temperature stress could be analyzed using a JIP-test. Segments of primary leaves of decapitated bean plants were placed on a metal surface at temperatures 0°, 5° and 10°C (low-temperature jump) or 30°, 35°, 37.5°, 40°, 42.5°, 45°, 47.5° and 50°C (high-temperature jump). Onesecond OJIP-transients of chlorophyll fluorescence and the simultaneous signal of modulated light scattering at ë = 820 nm with 30 s dark interval were recorded for 20 min. Each induction curve was subjected to the JIP-test analysis to calculate the parameters characterizing: the quantum efficiencies of the electronic flow in PS II, PS I and the electron transport chain between the two Photosystems; the concentration of the active reaction centers of PS II; the electron capacity of the electron transport chain and a total parameter characterizing the effects of the primary productivity in the photosynthetic apparatus. It was shown that the low-temperature stress temporary lowered the photosynthetic efficiency of the electron transport, while the high-temperature stress at temperatures above 42.5°C induced inactivation processes of the photosynthetic reactions. The sensitivity of the different sites of the electron transport chain to the heat stress decreased in the following order: (RC of PS II) > (QA-PQ-pool) > (PQ.H2-PC-PS I-acceptors of PS I). A conclusion was made that the JIPtest is an informative means of evaluating the dynamics of the stress response and the plant state after stress.