rowth stimulation and inhibition by salt in relation to na+ manipulating genes in xero-halophyte atriplex halimus l.

In the present study, Na+ manipulating genes could contribute not only to ion homeostasis

but also to growth stimulation with exposing the halophyte Atriplex halimus L. to moderate NaCl

concentration. The stimulation of growth was attributed to Na+ accumulation inside the vacuole

leading to increase leaf cell size as well as accelerate leaf cell division. Increasing the assimilatory

surface could result in enhancing the photosynthetic rate. The reduction of A. halimus growth

compared to optimum growth at 50 and 200 mM NaCl could be attributed to osmotic effect rather than

the ionic one of salt stress. The inhibition of photosynthesis seemed to be resulted from limitation of

CO2 due to the osmotic effect on stomatal conductance rather than the activity loss of photosynthetic

machinery. The depletion of starch content along with the increase in sucrose content could imply that

photosynthesis may be a limiting for A. halimus growth. The fast coordinate induction of Na+

manipulating genes could reveal that the tolerance of A. halimus to high concentrations evolved from

its ability to regulate and control Na+ influx and efflux. V-H+-PPase may play a vital role in A. halimus

tolerance to osmotic and/or ionic stress due to its kinetics of induction. It seemed that H+-ATPase play

a pivotal role in A. halimus tolerance to stress due to the increase in its protein level was detected with

all NaCl concentrations as well as with PEG treatments. Both of these genes might be useful in

improving stress tolerance in transgenic crops.