Response of photosynthetic apparatus in some sunflower cultivars, i.e., S.28111, Hysun-33, Hysun-39, and SF0049, to salt, drought, and combined stresses were studied. The combined stress caused severe damage to photosynthetic apparatus as compared to single stress. The maximum quantum yield of PSII, phenomenological fluxes, plastoquinone pool size, performance indexes, and driving force of absorption were greatly affected by the combined stress. Among the cultivars, the combined stress produced synergistic effect (greater damage) in Hysun-33 and cross-tolerance (lesser damage) in S.28111. Similarly, concerning the ion imbalance, S.28111 and SF0049 showed lower Na + and Clconcentrations with lesser electrolyte leakage as compared to Hysun-33 and Hysun-39 under salt and combined stress. Results revealed that the disturbance in photosynthetic performance could be easily determined using JIP test by measuring chlorophyll a fluorescence. This information can be useful for the screening of oil-seed crop plants having better photosynthetic performance under salinized and desertified conditions.Additional key words: electron transport rate; malondialdehyde; nonphotochemical quenching; OJIP transient. Abbreviations: ABS/RC -apparent antenna size of active PSII RC; Area -area over the fluorescence curve between F0 and Fm; DFABSdriving force on absorption basis; DI0/RC -effective dissipation of energy in active RC; ET0/RC -electron transport per active reaction center; F0 -minimum fluorescence; F0/Fv -efficiency of water-splitting complex; F0/Fm -quantum yield baseline; Fm -maximum fluorescence; Fm/F0 -electron transport rate through PSII; Fv/F0 -size and number of active reaction centers of photosynthetic apparatus; Fv/Fm -maximum quantum yield of PSII; J -linear electron transport rate; MDA -malondialdehyde; NPQ -nonphotochemical quenching; PIABS -performance index on absorption basis; PICS -performance index on cross-section basis; PItot -total performance index; qN -nonphotochemical quenching coefficient; qP -photochemical quenching; RC/ABS -density of reaction centers on chlorophyll basis; RC/CSm -amount of active reaction centers per excited cross section; TR0/DI0 -ratio of trapping and dissipation fluxes; TR0/RC -maximal trapping rate of absorbed photons in RC; δR0 or RE0/ET0 -probability that an electron is transported from reduced PQ to electron acceptor side of PSI; ΔVIP -amplitude of the relative variable fluorescence of the I-to-P-rise; ΦPSII -efficiency of PSII or quantum yield of PSII; ϕR0 -quantum yield for reduction of the end electron acceptors at the PSI acceptor side (RE); ψ0yield of electron transport per trapped excitation or probability with which a PSII trapped electron is transferred from reduced QA to QB.

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