The salt stress effect in root growth and antioxidative response were investigated in two cowpea cultivars which differ in salt
tolerance in terms of plant growth and leaf oxidative response. Four-day-old seedlings (establishment stage) were exposed to 100
mM NaCl for two days. The roots of the two cultivars presented distinct response in terms of salt-induced changes in elongation and
dry weight. Root dry weight was only decreased in Pérola (sensitive) cultivar while root elongation was mainly hampered in Pitiúba
(tolerant). Root relative water content remained unchanged under salinity, but root Na+ content achieved toxic levels as revealed by
the K+/Na+ ratio in both cultivars. Then, root growth inhibition might be due to ionic toxicity rather than by salt-induced water deficit.
Although electrolyte leakage markedly increased mainly in the Pérola genotype, lipid peroxidation decreased similarly in both saltstressed
cultivars. APX and SOD activities were reduced by salinity in both cultivars reaching similar values despite the decrease in
Pitiúba had been higher compared to respective controls. CAT decreased significantly in Pitiúba but did not change in Pérola, while
POX increased in both cultivars. The salt-induced decrease in the CAT activity of Pitiúba root is, at principle, incompatible to allow a
more effective oxidative protection. Our results support the idea that the activities of SOD, APX, CAT and POX and lipid peroxidation
in cowpea seedling roots were not associated with differential salt tolerance as previously characterized in terms of growth rate and
oxidative response in plant leaves.
