ISSN:
1573-5079
Keywords:
desiccation
;
oxygen evolving complex
;
relative water content
;
thermoluminescence
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract An effect of desiccation (a decrease of relative water content from 97% to 10% within 35 h) on Photosystem II was studied in barley leaf segments (Hordeum vulgare L. cv. Akcent) using chlorophyll a fluorescence and thermoluminescence (TL). The O-J-I-P fluorescence induction curve revealed a decrease of FP and a slight shift of the J step to a shorter time with no change in its height. The analysis of the fluorescence decline after a saturating light flash revealed an increased portion of slow exponential components with increasing desiccation. The TL bands obtained after excitation by continuous light were situated at about –27°C (Zv band – recombination of P680+QA −), –14 °C (A band – S3QA −), +12 °C (B band – S2/3QB −) and +45 °C (C band – TyrD+QA −). The bands related to the S-states of oxygen evolving complex (A and B) were reduced by desiccation and shifted to higher and lower temperatures, respectively. In accordance with this, the band observed at about +27 °C (S2QB −) after excitation by 1 flash fired at –10 °C and band at about +20 °C (S2/3QB −) after 2 flashes decreased with increasing water deficit and shifted to lower temperatures. A new band around 5 °C appeared in both regimes of TL excitation for a relative water content of under 42% and was attributed to the Q band (S2QA −). It is suggested that under desiccation, an inhibition of the formation of S2- and S3-states in OEC occurred simultaneously with a lowering of electron transport on the acceptor side of PS II. The temperature down-shift of the TL bands obtained after the flash excitation was induced at the initial phases of water stress, indicating a decrease of the activation energy for the S2/3QB −recombination.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1006472129684
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