Nitrogen assimilation pathways and ionic homeostasis are crucial for photosynthetic apparatus efficiency in salt-tolerant sunflower genotypes

Sunflower (Helianthus annuus L.) is an important oilseed crop that is sensitive to salt stress. We performed an investigation to elucidate the mechanisms of salinity tolerance in two commercial sunflower genotypes of contrasting salt tolerance. The BRS 321 genotype exhibited greater plant growth than the Catissol genotype upon exposure to 100mM NaCl-stress, indicating that BRS 321 is more tolerant to salt stress than Catissol. The superior performance of BRS 321 plants was attributed to the decreased accumulation of toxic ions (Na+) in roots and improved photosynthetic machinery efficacy. In NaCl-stress conditions, BRS 321 plants displayed greater CO2 assimilation which was associated with an increase in the effective quantum yield of PSII, electron transport rate, and photochemical quenching (qP), as well as improved chlorophyll and carotenoid contents. Significantly, nitrogen metabolism in the salt-tolerant genotype was altered to act as an alternative electron sink, dissipating excess energy and increasing the plant's capacity to withstand the deleterious salt effects. In conclusion, salt tolerance in BRS 321 compared to the Catissol genotype could be attributed to improved photosynthetic performance and decreased Na+ uptake.