Short-term effects of aluminium at alkaline pH on the structure and function of the photosynthetic apparatus |
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Authors: | M Moustakas EP Eleftheriou and G Ouzounidou |
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Institution: | (1) Department of Botany, School of Biology, Aristotle University of Thessaloniki, GR-540 06 Thessaloniki, Greece |
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Abstract: | A 24 h exposure of the salt-tolerant grass Thinopyrum bessarabicum (Savul. and Rayss) A. Love seedlings to 1 mM aluminium
(Al) in nutrient solution at pH of 9.0 resulted in a significant reduction of the biomass. In control samples the mesophyll
chloroplasts exhibited the usual lens shape with most grana arranged in straight or slightly curving lines, and only 6.5 %
of the grana were out of order. In Al-treated plants the mesophyll chloroplasts displayed a slightly distorted shape and distended
size with most grana arranged in bow-like lines, while in the central region of the organelle as many as 26.7 % of the grana
were independent and out of order in relation to the long axis. The morphological changes in the chloroplast shape and grana
arrangement were probably due to swelling and distension of the chloroplasts in consequence to the altered membrane permeability.
The initial in vivo chlorophyll (Chl) fluorescence FO, as well as the intermediate FI and peak fluorescence FP were increased
under the Al stress: this indicated a destruction of photosystem (PS) 2 reaction centres and increased reduction of QA. The
(FI-FO)/(FP-FO) ratio exhibited a significant increase indicating higher proportion of PS2 centres unable to reduce QB. Changes
in the chloroplast ultrastructure seemed to be the reason of photosynthetic electron transport inhibition. Yet all these changes
in the photosynthetic performance and chloroplast ultrastructure were considered as indirect effects of Al treatment since
Al concentration in the leaves was undetectable. Disturbances in the chloroplast ultrastructure could be caused by a reduced
uptake and/or transport of other nutrients.
This revised version was published online in June 2006 with corrections to the Cover Date. |
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Keywords: | chlorophyll fluorescence chloroplast ultrastructure photosynthesis photosystem 2 Thinopyrum bessarabicum |
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