AUTHOR=Essemine Jemaa , Lyu Ming-Ju Amy , Qu Mingnan , Perveen Shahnaz , Khan Naveed , Song Qingfeng , Chen Genyun , Zhu Xin-Guang 

TITLE=Contrasting Responses of Plastid Terminal Oxidase Activity Under Salt Stress in Two C4 Species With Different Salt Tolerance

JOURNAL=Frontiers in Plant Science

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.01009

DOI=10.3389/fpls.2020.01009

ISSN=1664-462X

ABSTRACT=<p>The present study reveals contrasting responses of photosynthesis to salt stress in two C<sub>4</sub> species: a glycophyte <italic>Setaria viridis</italic> (<italic>SV</italic>) and a halophyte <italic>Spartina alterniflora</italic> (<italic>SA</italic>). Specifically, the effect of short-term salt stress treatment on the photosynthetic CO<sub>2</sub> uptake and electron transport were investigated in <italic>SV</italic> and its salt-tolerant close relative <italic>SA</italic>. In this experiment, at the beginning, plants were grown in soil then were exposed to salt stress under hydroponic conditions for two weeks. <italic>SV</italic> demonstrated a much higher susceptibility to salt stress than <italic>SA</italic>; while, <italic>SV</italic> was incapable to survive subjected to about 100 mM, <italic>SA</italic> can tolerate salt concentrations up to 550 mM with slight effect on photosynthetic CO<sub>2</sub> uptake rates and electrons transport chain conductance (<italic>g<sub>ETC</sub></italic>). Regardless the oxygen concentration used, our results show an enhancement in the P<sub>700</sub> oxidation with increasing O<sub>2</sub> concentration for SV following NaCl treatment and almost no change for SA. We also observed an activation of the cyclic NDH-dependent pathway in <italic>SV</italic> by about 2.36 times upon exposure to 50 mM NaCl for 12 days (d); however, its activity in <italic>SA</italic> drops by about 25% compared to the control without salt treatment. Using PTOX inhibitor (<italic>n-PG</italic>) and that of the Q<sub>o</sub>-binding site of Cytb<sub>6</sub>/f (DBMIB), at two O<sub>2</sub> levels (2 and 21%), to restrict electrons flow towards PSI, we successfully revealed the presence of a possible PTOX activity under salt stress for <italic>SA</italic> but not for <italic>SV</italic>. However, by q-PCR and western-blot analysis, we showed an increase in PTOX amount by about 3–4 times for <italic>SA</italic> under salt stress but not or very less for <italic>SV</italic>. Overall, this study provides strong proof for the existence of PTOX as an alternative electron pathway in C<sub>4</sub> species (<italic>SA</italic>), which might play more than a photoprotective role under salt stress.</p>