Temperature sensitivity of photosystem II in isolated thylakoid membranes from fluridone-treated pea leaves

Authors: KOLYO DANKOV, GEORGI RASHKOV, AMARENDRA MISRA, EMILIA L. APOSTOLOVA

Abstract: High temperature-induced changes in the photosystem II (PSII) activity of thylakoid membranes isolated from pea (Pisum sativum L. 'Ran') plants treated with low (10^-8 M) and high (10^-7 M) concentrations of fluridone were investigated. Pulse amplitude modulated (PAM) chlorophyll fluorescence and photosynthetic oxygen evolution (measured by polarographic oxygen rate electrode) were used to estimate the effect of high temperature on the functional activity of PSII. Higher temperature treatments lead to stronger inhibition of the flash oxygen evolution than the primary photochemistry of PSII (F_v/F_m). The inhibitory effect of higher temperature on the PSII? centers is stronger than on the PSIIß centers. The heat-induced damage in the PSII$\alpha$ centers as well as in the donor side of all PSII centers (PSII$\alpha$ and PSIIß) is accentuated by fluridone.

Keywords: Fluridone, PAM chlorophyll fluorescence, photosynthetic oxygen evolution, PSII? centers, PSIIß centers, carotenoids

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