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Growth and development of winter rye at cold‐hardening temperatures results in thylakoid membranes with increased sensitivity to low concentrations of osmoticum
Author(s) -
Huner N. P. A.,
Hopkins W. G.
Publication year - 1985
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1985.tb08524.x
Subject(s) - thylakoid , photophosphorylation , chloroplast , photosystem i , photosystem ii , biophysics , electron transport chain , photosynthesis , chemistry , electrochemical gradient , membrane , biochemistry , biology , gene
Chloroplasts developed at cold‐hardening (5°C) and non‐hardening temperatures (20°C) were compared with respect to the stability of photosynthetic electron transport activities, the capacity to produce and maintain a H + gradient and the capacity fat photophosphorylation as a function of resuspension in the presence or absence of osmoticum. The results for electron transport indicate that whole chain, photosystem I and pfaotosystem II activities in non‐hardened chloroplast thyalkoids were unaffected by resuspension in the presence of high or low osmoticum. In contrast, the same electron transport activities in cold‐hardened chloroplast thylakoids exhibited a 3‐ to 4‐fold decrease in activity when resuspended in the presence of low osmoticum. Impairment of electron transport through photosystem II of cold‐hardened thylakoids resuspended in the presence of low osmoticum was supported by room temperature fluorescence induction kinetics. Since the presence of Mn 2+ partially overcame this inhibition, it is concluded that this osmotically‐induced inhibition of PSII activity in cold‐hardened chloroplast thylakoids may, in part, be due to damage to the H 2 O‐splitting side of photosystem II. Both the initial rate and the maximum capacity for cyclic photophosphorylation were significantly inhibited in cold‐hardened as compared to non‐hardened thylakoids upon resuspension in the presence of low concentrations of osmoticum. This was correlated with an inability of the cold‐hardened chloroplast thylakoids to maintain a significant transrnembrane H + gradient. The results indicate that cold‐hardened thylakoid membranes required an osmotic concentration (0.8 M ) twice as high as non‐hardened thylakoids (0.4 M ) to produce the same initial rate of H + uptake. In addition, the capacity to produce a proton gradient in cold‐hardened thylakoids was less stable than that in non‐hardened thylakoids regardless of the osmotic concentration tested. It is concluded that development of rye thylakoid membranes at low temperature results in a differential sensitivity to low osmoticum and thus extreme caution should be exercised when comparing the structure and function of isolated thylakoids developed under contrasting thermal regimes.