Effects of low nitrogen supply on biochemical and physiological parameters related to nitrate and water, involving nitrate transporters and aquaporins in Citrus macrophylla.

The reduction of chemical N-based application has been investigated in Citrus plants. As the N and water uptake is connected, the relationship between physiological response of reductions of N have been studied in relation to nitrogen metabolism and water. We studied the response in new and mature leaves, and roots of Citrus macrophylla plants grown in controlled conditions and treated with different concentrations of nitrogen: 16 mM, 8 mM and 4 mM. The changes in growth and development, were determined in biochemical (mineral content, photosynthetic pigments, proteins and nitrate and nitrite reductase activities) physiological (photosynthesis and transpiration) and molecular parameters (relative expression of nitrate transporters and aquaporins) The data obtained showed that only plants treated with 4mM N showed a reduction of growth. Although, there were changes in parameters like NR activity, protein synthesis, and chlorophylls in 8mM N and 4mM N plants, highly related with aquaporin and nitrate transporter expression. The results revealed new findings about the relationship between aquaporins and nitrate transporters in new leaves of Citrus, suggesting a mechanism for ensuring growth under low nitrogen when new tissue is under formation.