DIFFERENTIAL ADAPTATION OF ROOTS AND SHOOTS TO SALT STRESS CORRELATES WITH THE ANTIOXIDANT CAPACITY IN MUSTARD (BRASSICA JUNCEA L.)

Salt adaptive mechanisms of the shoots and roots in mustard (Brassica juncea L.) were studied by examination of their growth parameters, biomass, photosynthesis, malondialdehyde (MDA) content and some key antioxidants. Mustard seedlings were treated at four levels of salt (0, 50, 100 and 200 mM NaCl) at various times of exposure. Severe salt stress significantly inhibited the growth of shoots by causing a reduction in the leaf area and dry and fresh weights. The inhibitory effect of salt on the shoots positively correlated with the decrease in chlorophyll content and performance index and negatively correlated with the content of MDA in leaves. Higher salinity for the roots under stress proved to positively affect growth. The root-shoot ratio, number of first-order lateral roots and the lateral root density were higher than those of the control group by 26.1%, 28.7% and 58.5%, respectively. The levels of MDA remained the same. Coordination of the antioxidant enzymes ensures the plants are highly effective at scavenging reactive oxygen species (ROS). These results strongly suggest that the antioxidant system is involved in the adaptive regulation of root growth to avoid the harmful effects of high soil salinity.