Molecular and Physiological Responses of Naturally Grown Atriplex halimus L. to Drought-Stress Recovery in the Absence or Presence of Na+ Ions Under Natural Conditions

It was suggested that Na+ ions could play a vital role in the growth of xero-halophyte Atriplex halimus. This study aims at investigating the impact of Na+ ions on the response of droughted A. halimus seedlings to the recovery in the natural habitat. The time-course regulation of recovery-responsive genes and the changes in physiological attributes during the recovery were examined in the absence (RW) or presence of 300 mM NaCl (RS). After 30 min and up to the end of the experiment, photosynthetic rate (A), stomatal conductance (gs) and leaf fresh and dry weights (FW) were enhanced by RW. Meanwhile, there was a sudden decline in (A) and (gs) rates after 30 min followed by a recovery in both rates after 3 h of RS. In response to RS, the change in carbon and nitrogen balance may act as a signal to regulate (A) and (gs) rates, in an attempt to control the upload of Na+ ions via transpiration. After 30 min or 3 h of the RW or RS onset, respectively, 1) the increase in 9-cis epoxycarotenoid dioxygenase (NCEDs) and abscisic acid (ABA) levels could stimulate the recovery-responsive genes rather than controlling (gs) and 2) the induction of ABA-dependent/independent transcription factors and recovery/salt-inducible genes could suggest their effective contributions to the recovery adaptation. After 5 d of the recovery onset, RS lowered FW by 82% whereas RW increased FW by 110%. Na+ ions could not enhance the performance of A. halimus seedlings during the recovery, perhaps, due to the non-constitutive expression of salt-responsive genes.