Photosynthetic responses of a wheat (Asakaze)–barley (Manas) 7H addition line to salt stress
D. Szopkó, É. Darkó, I. Molnár, K. Kruppa, B. Háló, A. Vojtkó, M. Molnár-Láng, S. Dulai
The photosynthetic responses to salt stress were examined in a wheat (Triticum aestivum L. cv. Asakaze) -barley (Hordeum vulgare L. cv. Manas) 7H addition line having elevated salt tolerance as compared to the parental wheat genotype. For this purpose, increasing NaCl concentrations up to 300 mM were applied and followed by a 7-day recovery period. Up to moderate salt stress (200 mM NaCl), forcible stomatal closure, parallel with a reduction in the net assimilation rate (P N ), was only
... in wheat, but not in the addition line or barley. Since the photosynthetic electron transport processes of wheat were not affected by NaCl, the impairment in P N could largely be accounted for the saltinduced decline in stomatal conductance (g s ), accompanied by depressed intercellular CO 2 concentration and carboxylation efficiency. Both, P N and nonstomatal limitation factors (L ns ) were practically unaffected by moderate salt stress in barley and in the addition line due to the sustained g s , which might be an efficient strategy to maintain the efficient photosynthetic activity and biomass production. At 300mM NaCl, both P N and g s decreased significantly in all the genotypes, but the changes in P N and L ns in the 7H addition line were more favourable similar to those in wheat. The downregulation of photosynthetic electron transport processes around PSII, accompanied by increases in the quantum yield of regulated energy dissipation and of the donor side limitation of PSI without damage to PSII, was observed in the addition line and barley during severe stress. Incomplete recovery of P N was observed in the addition line as a result of declined PSII activity probably caused by enhanced cyclic electron flow around PSI. These results suggest that the better photosynthetic tolerance to moderate salt stress of barley can be manifested in the 7H addition line which may be a suitable candidate for improving salt tolerance of wheat. Additional key words: chlorophyll fluorescence induction; improved salt tolerance; leaf gas exchange; recovery; wheat-barley addition. --electron flow around PSI; Ci -intercellular CO2 concentration; F -steady-state fluorescence; F0, Fm -minimum and maximum Chl fluorescence determined in the dark-adapted state; Fm' -maximal fluorescence in the light-adapted state; Fv -variable fluorescence; Fv/Fm -maximum quantum yield of PSII photochemistry; gs -stomatal conductance; Lns -nonstomatal limitation; Ls -stomatal limitation; NPQ -nonphotochemical quenching; P0 -minimal P700 signal; Pm -maximal P700 level; Pm' -maximal P700 signal in a given light state; PN -net assimilation rate; PNmax -maximal assimilation rate; RuBP -ribulose-1,5-bisphosphate; RWC -relative water content; ε -carboxylation efficiency; ɸCEF -quantum yield of cyclic electron flow around PSI; ɸNA -quantum yield of the acceptor side limitation of PSI; ɸND -quantum yield of the donor side limitation of PSI; ɸNO -quantum yield of nonregulated energy dissipation; ɸNPQ -quantum yield of regulated energy dissipation; ɸPSI -effective quantum yield of photochemical energy conversion in PSI; ɸPSII -effective quantum yield of photochemical energy conversion in PSII.