High salt stress in coupled and uncoupled thylakoid membranes: a comparative study.
The effect of high salt concentration on photosystem II (PS II) electron transport rates and chlorophyll a fluorescence induction kinetics was investigated in coupled and uncoupled spinach thylakoid membranes. With increase in salt concentration, the rates of electron transport mediated by PS II and the F(v)/F(m) ratio were affected more in uncoupled thylakoids as compared to coupled thylakoid membranes. The uncoupled thylakoid membranes seemed to behave like coupled thylakoid membranes at high NaCl concentration (approximately 1 M). On increasing the salt concentration, the uncoupler was found to be less effective and Na+ probably worked as a coupling enhancer or uncoupling suppressor. We suggest that positive charge of Na+ mimics the function of positive charge of H+ in the thylakoid lumen in causing coupled state. The function of NaCl (monovalent cation) could be carried out by even lower concentration of Ca2+ (divalent cation) or Al3+ (trivalent cation). We conclude that this function of NaCl as coupling enhancer is not specific, and in general a positive charge is required for causing coupling in uncoupled thylakoid membranes.
Mehta
P
P
School of Life Sciences, Devi Ahilya University, Indore, 452017, India.
Jajoo
A
A
Mathur
S
S
Allakhverdiev
S I
SI
Bharti
S
S
D002412:Cations / Q000378:metabolism; D002734:Chlorophyll / Q000737:chemistry; D004579:Electron Transport / Q000502:physiology*; D005453:Fluorescence; D007700:Kinetics; D009994:Osmolar Concentration; D009997:Osmotic Pressure / Q000502:physiology*; D045332:Photosystem II Protein Complex / Q000378:metabolism; D012965:Sodium Chloride / Q000378:metabolism; D018724:Spinacia oleracea / Q000378:metabolism*; D013312:Stress, Physiological; D020524:Thylakoids / Q000378:metabolism*; D014475:Uncoupling Agents / Q000378:metabolism*
D002412:Cations; D045332:Photosystem II Protein Complex; D014475:Uncoupling Agents; D002734:Chlorophyll; D012965:Sodium Chloride