Salinity modulates negatively nitrate uptake and assimilation in cowpea plants

Abstract

This present work aims to perform a study on the NO₃^- uptake and assimilation in cowpea plants, analyzing how the two processes are related front to salinity conditions and clarify possible mechanisms of plant modulations under salt stress. Plants with 14 days old grown in nutrient solution (Absence NH₄⁺) were subjected to KNO₃ 10 mM and NaCl 100 mM for ten days. Was evaluated NO₃^- net uptake and content, nitrate reductase activity (RN), transpiration, soluble proteins and total free amino acids (ALT). Application of NaCl resulted in reduced net uptake and the content of NO₃^-, mainly in roots. The reduction of NR activity was positively correlated with the reduction of transpiration, but no relation was established with the reduction in the soluble proteins levels, which was more conspicuous on roots. ALT levels were higher in roots of control plants and treated with NaCl. The results indicate a possible mechanism of modulation due to lower protein levels and higher ALT levels in roots under saline conditions. In summary, salinity modulates the uptake and assimilation of NO₃^- in cowpea plants, in principle, by the reduction in the soluble proteins and amino acids accumulation in roots and the non-competitively inhibition by NaCl indicates that competition between NO₃^- and Cl^- by the sites is not the most limiting factor to modulate the NO₃^- uptake.