The phi thickening in roots of broccoli plants:: An acclimation mechanism to salinity?

Although broccoli is moderately tolerant to salt stress, the tolerance mechanism is still unknown. Therefore, in this article, the uptake and transport of nutrients and water in relation to the changes in root anatomy (phi thickening appearance) caused by salinity stress have been studied. The effect of phi thickening in the response of these plants to salinity was studied by comparing two methods of measuring root hydraulic conductance, pressurizing roots and natural exudation, and analyzing the nutrient concentrations in the xylem. The permeability properties of phi thickening were tested by a tracer that moves only via the apoplastic pathway. Brassica oleracea L. var. Italica plants, grown under different levels of NaCl ( 0, 40, and 80 mM), showed modifications in the cell wall of the cortical layer bordering the endodermis, such as phi thickenings. The results also showed a decrease of the L-0 and G(S) of plants under salinity stress and an ionic imbalance in the xylem sap. Na+, Mg2+, SO42-, and Cl- concentrations increased, while Ca2+ decreased. The fact that the proportion of apoplastic movement, which was higher when plants were measured with the Scholander chamber than with natural exudation, was lower for NaCl-treated plants whereas the alteration of nutrient uptake was similar suggests that the phi thickenings could be a physical barrier only to apoplastic water transport.