Leaf water balance mediated by aquaporins under salt stress and associated glucosinolate synthesis in broccoli

Broccoli (Brassica oleracea L. var. Itálica) plants are known to be moderately tolerant to salinity, although scarce information exists about the mechanisms of their tolerance. Therefore, in this work, we have explored more thoroughly the response of these plants to salinity, focusing the studies on the leaf cellular water transport mediated by aquaporins, sulphur assimilation in relation to the osmotic adjustment and glucosinolates accumulation under salt-stress conditions (40 and 80 mM NaCl). At 1 day and 15 days, the osmotic water permeability coefficient (Pf) was determined in protoplasts of broccoli leaves together with the leaf cell hydraulic conductivity (Lpc). Decreases in Pf and Lpc were observed with salinity and the reductions were stronger earlier in the treatments than with long-term salt treatments. The water channel-blocking effect of HgCl2 showed the involvement of the aquaporins in the process of adaptation to salinity. In order to determine the involvement of sulphur assimilation in the osmotic adjustment under salt stress, we determined the content of glucosinolates, total sulphur (S) and sulphate (SO42−) ions. Although there were no significant differences in the S content between the salt treatments, 15 days after 80 mM NaCl addition, a decrease in SO42− and an increase in glucosinolates were observed, indicating the involvement of these compounds in the water-relations response of broccoli to salt stress.