ROOTS ARE NECESSARY FOR THE RESPONSES OF IN VITRO-CULTURED CITRUS PLANTS TO HIGH SALINITY BUT NOT TO OSMOTIC STRESS

In the field, plants are exposed simultaneously to variable biological and environmental conditions that can make physiological studies very difficult. The in vitro tissue culture techniques can overcome some of these limitations. In the present work, this methodology was applied to the study of salt and osmotic stress conditions on ‘Carrizo’ citrange. The stress conditions were generated by adding either NaCl or polyethylene glycol, to the culture medium. Micropropagated shoots, growing under salt- or osmotic-stress, shown symptoms of leaf damage very similar to those found in intact plants, which confirmed the incidence of the imposed stress on plant physiology. In whole plants, it has been reported that physiological responses to water and salt stress are essentially identical; in the opposite, in shoots cultured in vitro, levels of stress markers such as malondialdehyde (MDA) and proline increased only under water deficiency but not under elevated salt conditions. Differences were also observed in the hormonal regulation of the shoots subjected to each abiotic stress. Abscisic acid concentration increased in shoots grown under osmotic stress conditions whereas no differences with the controls were observed in salt-stressed ones. It can be concluded that, at least when culture in vitro, citrus roots are necessary for the perception and signaling of the salt stress conditions. On the contrary, the presence of this organ is not necessary to modulate the response of shoots to osmotic stress.