Photosystem photochemistry, prompt and delayed fluorescence, photosynthetic responses and electron flow in tobacco under drought and salt stress

The present study aimed to understand the photosynthetic responses and chlorophyll fluorescence transient in tobacco under drought and salt stress. Net CO2 assimilation rate, stomatal conductance, intercellular CO2 concentration and transpiration rate decreased significantly under drought and salt stress. The maximum quantum efficiency of PSII and electron transport rate were lower in tobacco under drought and salt stress. The maximum carboxylation rate, maximum electron transport rate, triosephosphate utilization efficiency, and mesophyll conductance decreased under drought and salt stress, while dark respiration increased. A pool size of the electron acceptors on reducing side of PSII and activity of water-splitting complex on the donor side of the PSII decreased during drought and salt stress. Present results suggested upregulation of the photorespiratory pathway as a strategy to maintain the ribulose-1,5-bisphosphate regeneration for maintenance of photosynthesis under drought and salt stress. Chlorophyll fluorescence indicated the impaired electron transfer and changes in the architecture of light-harvesting complex in tobacco leaves under drought and salt stress.