Interactive effects of boron and NaCl stress on water and nutrient transport in two broccoli cultivars

In arid regions, the water from aquifers usually contains high NaCl levels, and alternative water sources, such as desalination plants, produce boron accumulation and have an adverse effect on crops. We studied the water transport and membrane integrity of two broccoli (Brassica oleracea L.) cultivars (Naxos and Viola) in the response to two boric acid levels, (1.8mgL-1 and 4.3mgL-1), alone or in combination with salinity (0 or 80mM), and the involvement of plasma membrane intrinsic protein (PIP) aquaporins in this response. Nutritional status was also evaluated, as it affects the structural and functional integrity of the membranes. Since B is partly responsible for changes in the concentration and metabolism of phenolic compounds in vascular plants, these compounds were determined. In Naxos, the effect of 1.8mgL-1 B concentration on the plasma membrane influenced plant salinity tolerance through the associated changes in the root hydraulic conductivity and the recovery of biomass production with regard to the NaCl treatment. By contrast, in Viola, a different PIP abundance pattern was observed indicating that the threshold B concentration differs between Viola and Naxos, resulting in higher sensitivity. In fact, a decreased transpiration and photosynthetic rate observed in Viola after the addition of 4.3mgL-1 boric acid highlighted the highest sensitivity to boron, although this level had no adverse effect on the plasma membrane. The results suggest that B and NaCl trigger a hydric response involving aquaporins, together with changes in nutrient transport and plasma membrane stability.