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Plant and Cell Physiology, 1995, Vol. 36, No. 7 1221-1227
© 1995

Temperature Dependent Alterations in the Pattern of Photochemical and Non-Photochemical Quenching and Associated Changes in the Photosystem II Conditions of the Leaves

Manoj K. Joshi1, T.S. Desai2 and Prasanna Mohanty1

1 School of Life Sciences, Jawaharlal Nehru University New Delhi, 110067, India
2 Molecular Biology and Agriculture Division, Bhabha Atomic Research Centre Trombay, Bombay, 400085, India

The alterations in the PSII activity of leaves, subsequent to a mild or severe heat stress were characterized by monitoring the Chl a fluorescence and thermoluminescence emission from intact leaves. The Chl a fluorescence measurements were carried out in leaves adapted to either ‘state I’ or ‘state II’ since under these two conditions the photosynthetic apparatus is known to have distinctly different structure-function relationships. The pattern of Chl a fluorescence induction in state II-adapted leaves was different from that of state I-adapted leaves due to the alterations in the extent of photochemical (qQ) and non-photochemical (qE) quenching during the time course of induction. The pattern of changes in qQ and qE values was also altered by heat treatment depending on the severity of heat stress; severe heat stress (47°C) suppressing these parameters drastically. Mild heat treatment (42°C) did not affect the ability of leaves to undergo state I to state II transition whereas the severe heat stress totally abolished such transition. The fluorescence and thermoluminescence characteristics of the leaves that have been exposed to the severe heat stress suggest that a large number of affected PSII units retain a functional water-oxidizing complex at the donor side.

(Received June 14, 1994; Accepted July 19, 1995)
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