Effect of meta-topolin and bohemine derived from benzylaminopurine on PSII function in artificially senescing wheat leaves

Abstract

Cytokinin 6-benzylaminopurine (BA) is known to slow down chlorophyll and protein degradation and decrease of photosynthetic function induced by leaf senescence. An effect of BA and its two derivatives - meta-topolin (mT; 6-(3-hydroxybenzylamino)purine, a natural derivative with cytokinin activity) and bohemine (boh; 6-benzylamino-2-(3-hydroxypropyl-amino)-9-isopropylpurine, a synthetic derivative acting as a cyclin-dependent kinase inhibitor) on photosynthetic pigment content and photosystem II (PSII) function was studied in wheat (Triticum aestivum L. cv. Hereward) leaves during artificial senescence. PSII function was evaluated using of parameters of fast chlorophyll fluorescence induction (an O-J-I-P transient). In control leaf segments (stored in distilled water), a very pronounced decrease in chlorophyll and carotenoid content was observed. An increase of the relative height of a J step (VJ) in the O-J-I-P transient and a decrease in the FV/FP ratio were observed indicating an increase in a relative content of QB-nonreducing reaction centres of PSII and an inhibition of PSII photochemistry, respectively. BA and mT slowed down the decrease in chlorophyll and carotenoid content and suppressed the changes in VJ and FV/FP which indicated their positive effect on maintenance of PSII structure and function. This effect was more pronounced in case of mT. Bohemine did not affect the decrease in photosynthetic pigment content and rather accelerated the decrease in PSII function in comparison with control.