The effects of NaCl stress and K⁺ nutrition on photosynthetic parameters of isolated chloroplasts were investigated using PAM fluorescence. Intact mesophyll cells were able to maintain optimal photosynthetic performance when exposed to salinity for more than 24 h whereas isolated chloroplasts showed declines in both the relative electron transport rate (rETR) and the maximal photochemical efficiency of PSII (F_v/F_m) within the first hour of treatment. The rETR was much more sensitive to salt stress compared with F_v/F_m, with 40% inhibition of rETR observed at apoplastic NaCl concentration as low as 20 mM. In isolated chloroplasts, absolute K⁺ concentrations were more essential for the maintenance of the optimal photochemical performance (F_v/F_m values) rather than sodium concentrations per se. Chloroplasts from halophyte species of quinoa (Chenopodium quinoa Willd.) and pigface (Carpobrotus rosii (Haw.) Schwantes) showed less than 18% decline in F_v/F_m under salinity, whereas the F_v/F_m decline in chloroplasts from glycophyte pea (Pisum sativum L.) and bean (Vicia faba L.) species was much stronger (31 and 47% respectively). Vanadate (a P-type ATPase inhibitor) significantly reduced F_v/F_m in both control and salinity treated chloroplasts (by 7 and 25% respectively), whereas no significant effects of gadolinium (blocker of non-selective cation channels) were observed in salt-treated chloroplasts. Tetraethyl ammonium (TEA) (K⁺ channel inhibitor) and amiloride (inhibitor of the Na⁺/H⁺ antiporter) increased the F_v/F_m of salinity treated chloroplasts by 16 and 17% respectively. These results suggest that chloroplasts’ ability to regulate ion transport across the envelope and thylakoid membranes play a critical role in leaf photosynthetic performance under salinity.

Item Type:	Refereed Article
Keywords:	photosynthesis, potassium, sodium, ROS, membrane transport, non-stomatal limitation
Research Division:	Biological Sciences
Research Group:	Plant Biology
Research Field:	Plant Physiology
Objective Division:	Environment
Objective Group:	Control of Pests, Diseases and Exotic Species
Objective Field:	Control of Animal Pests, Diseases and Exotic Species in Farmland, Arable Cropland and Permanent Cropland Environments
Author:	Percey, WJ (Mr William Percey)
Author:	McMinn, A (Professor Andrew McMinn)
Author:	Bose, J (Dr Jayakumar Bose)
Author:	Breadmore, MC (Professor Michael Breadmore)
Author:	Guijt, RM (Dr Rosanne Guijt)
Author:	Shabala, S (Professor Sergey Shabala)
ID Code:	113147
Year Published:	2016
Web of Science® Times Cited:	5
Deposited By:	Ecology and Biodiversity
Deposited On:	2016-12-14
Last Modified:	2018-04-19
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