investigation of physiological responses of tow citrus rootstocks to in vitro salt stress

in this experiment, physiological responses of two citrus rootstocks [sour orange (citrus aurantium l.) and trifoliate orange (poncirus trifoliata raf.)] were investigated under in vitro salt stress conditions. this study was conducted on a completely randomized factorial design. explants (nucellar seedling obtained from seeds) of both rootstocks were transferred to murashige and skoog (ms) solid proliferation medium containing 8.9 µm ba and 0.5 µm naa with different concentrations 0, 50, 100, 150, 200 mm of sodium chloride (nacl) whit six replicates. results show that leaf chlorophyll index, photosynthesis rate, stomatal conductance, internal co2 concentration (ci), total protein content decreased in both rootstocks by increasing salinity levels, although there was no significant difference for above-mentioned characteristics in the interaction of salinity and rootstock. the amounts of reduction in total protein content, chlorophyll loss and internal co2 concentration (ci), in trifoliate orange genotype were greater than the sour orange. also, peroxidase enzyme activity increased by increasing salinity level in both rootstocks, but, the rate of increase in the trifoliate orange was higher than the sour orange. by increasing salinity levels in the cultural medium, the uptake of sodium (na+) and chlorine (cl-) significantly increased in both rootstocks over 6 weeks culture period. comparison in to trifoliate orange, sour orange less sodium and chlorine were taken up. based obtained results, can be declared, salt tolerance has a negative correlation with na+ and cl- content in plant tissues, and the plant have a less na+ and cl- in tissues are more resistant. thus, sour orange was more tolerant than trifoliate orange to salt stress and could be has more resistant to high concentration salinity.