Contrasting Responses of Plastid Terminal Oxidase Activity Under Salt Stress in Two C Species With Different Salt Tolerance.

The present study reveals contrasting responses of photosynthesis to salt stress in two C species: a glycophyte () and a halophyte (). Specifically, the effect of short-term salt stress treatment on the photosynthetic CO uptake and electron transport were investigated in and its salt-tolerant close relative . In this experiment, at the beginning, plants were grown in soil then were exposed to salt stress under hydroponic conditions for two weeks. demonstrated a much higher susceptibility to salt stress than ; while, was incapable to survive subjected to about 100 mM, can tolerate salt concentrations up to 550 mM with slight effect on photosynthetic CO uptake rates and electrons transport chain conductance ( ). Regardless the oxygen concentration used, our results show an enhancement in the P oxidation with increasing O concentration for SV following NaCl treatment and almost no change for SA. We also observed an activation of the cyclic NDH-dependent pathway in by about 2.36 times upon exposure to 50 mM NaCl for 12 days (d); however, its activity in drops by about 25% compared to the control without salt treatment. Using PTOX inhibitor () and that of the Q-binding site of Cytb/f (DBMIB), at two O levels (2 and 21%), to restrict electrons flow towards PSI, we successfully revealed the presence of a possible PTOX activity under salt stress for but not for . However, by q-PCR and western-blot analysis, we showed an increase in PTOX amount by about 3-4 times for under salt stress but not or very less for . Overall, this study provides strong proof for the existence of PTOX as an alternative electron pathway in C species (), which might play more than a photoprotective role under salt stress.