Changes in inorganic and organic solutes in citrus growing under saline stresses

Salinity is a key factor limiting cirrus production in many world areas. The two citrus genotypes sour orange (Citrus aurantium L) and macrophylla (Citrus macrophylla Wester), that differ in their ability to restrict sodium (Na) and chloride (Cl) transport to the shoot under salt stress, were studied to compare the contribution of both inorganic and organic solutes in osmotic adjustment. Plants of both citrus genotypes were grown in isosmotic (0.23 MPa) solutions of different ionic composition (Na, NaCl, Cl, and concentrated macronutrients), and leaf and root solutes were measured to determine their relative contribution to osmotic adjustment. Both leaf water and osmotic potentials decreased in response to imposed stress in the nutrient media, regardless of the isosmotic treatment. Growth reduction was more severe in macrophylla than in sour orange, except for macronutrient treatment. The major components associated with the osmotic adjustment were inorganic solutes (ranging from 65 to 85% of total solutes) and organic solutes (ranging from 15 to 35%, depending on the genotype and the isosmotic treatment). Among these, carbohydrates were the major organic components (6–24%), with glucose the main osmoregulating sugar in Cl‐containing treatments. The contribution of the organic acids and amino acids to the osmotic adjustment of plant under saline stress seemed to be less important in these citrus species.