Photosynthetic responses of a wheat (Asakaze)-barley (Manas) 7H addition line to salt stress

Abstract

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 observed 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. ---Received 25 January 2016, accepted 5 May 2016. + Corresponding author; e-mail: ds@ektf.hu Abbreviations: 7H add -wheat-barley 7H addition line; CEF -cyclic 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 o...

Exogenous application of humic acid mitigates salinity stress in maize (Zea mays L.) plants by improving some key physico-biochemical attributes

“…Reduction in chlorophyll pigments and quantum yield was observed in the salt-stressed maize plants in the present study. Parallel findings were observed in eggplant (Hanachi et al 2014), wheat (Szopko et al 2017), cowpea (Taffouo et al 2009), bean (Turan et al 2007;Qados 2011;Aydin et al 2012), and Centaurium erythraea (Siler et al 2007) under different environmental conditions. Humic acid application was found to be effective in improving chlorophyll content in the maize plants in the present investigation.…”

Effects of water deficit and salt stress on some photosynthesis parameters in wheat and Aegilops comosa lines

“…Under water deficit and/or salt stress, the stomata closure is a wellknown phenomenon (Molnár et al 2004, Dulai et al 2014, Szopkó et al 2017b. The decrease in stomatal conductance (gs) affects not only the regulation of water loss through the transpiration, but also inhibits the photosynthetic CO2 fixation by limiting CO2 diffusion into the leaves (Chaves 1991, Cornic 2000.…”

“…comosa lines are not particularly good candidates for improving drought tolerance of wheat. Similar to drought, photosynthetic processes are also modified during salt stress (Szopkó et al 2017b). Prior to the accumulation of toxic ions, salt treatment also causes osmotic stress, influencing the water status, stomatal conductance and net carbon fixation capacity of plants Tester 2008).…”

“…Under stress conditions the limitation of photosynthetic capacity takes place in two stages: (i) limitation associated with decreased stomatal conductance, known as stomatal limitation (Ls, Centritto et al 2003, Dulai et al 2014; (ii) limitation due to nonstomatal processes (Lns) mainly at severe drought and higher salt concentrations or longer salt stress (James et al 2002, Szopkó et al 2017b. Under moderate water deficit or in the first stage of salt stress, which also has osmotic effect, the reduction in net photosynthesis (PN) mainly due to the stomatal closure (Chaves 1991;Medrano et al 2002).…”

“…At the same time, the reduced stomatal conductance (gs) may contribute to maintaining water content through a decreased transpiration rate, which could be favourable for minimizing Na + transport towards the shoots (Tester and Davenport 2003). Thus, closed stomata have both positive and negative effects on photosynthesis (Szopkó et al 2017b).…”