Photosynthetic electron flow during leaf senescenc

Authors: C Kotakis A Kyzeridou Y Manetas

Publish Date: 2015/10/16

Volume: 52, Issue: 3, Pages: 413-420

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Abstract

Limitations in photosystem function and photosynthetic electron flow were investigated during leaf senescence in two fieldgrown plants ie Euphorbia dendroides L and Morus alba L a summer and winterdeciduous shrub and tree respectively Analysis of fast chlorophyll Chl a fluorescence transients and postillumination fluorescence yield increase were used to assess photosynthetic properties at various stages of senescence the latter judged from the extent of Chl loss In both plants the yield of primary photochemistry of PSII and the content of PSI remained quite stable up to the last stages of senescence when leaves were almost yellow However the potential for linear electron flow along PSII was limited much earlier especially in E dendroides by an apparent inactivation of the oxygenevolving complex and a lower efficiency of electron transfer to intermediate carriers On the contrary the corresponding efficiency of electron transfer from intermediate carriers to final acceptors of PSI was increased In addition cyclic electron flow around PSI was accelerated with the progress of senescence in E dendroides while a corresponding trend in M alba was not statistically significant However there was no decrease in PSI activity even at the last stages of senescence We argue that a switch to cyclic electron flow around PSI during leaf senescence may have the dual role of replenishing the ATP and maintaining a satisfactory nonphotochemical energy quenching since both are limited by hindered linear electron transfer

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