osmotic adjustment in sugar beet plant under salinity stress

this study was carried out in the general commission for scientific agricultural research (gcsar) at der ez zour agricultural research center, during 2009- 2010 growing seasons. the role of na+, k+, na+/k+, carbohydrates accumulation of leaves, and sugar content of roots on the osmotic adjustment was studied in 10 sugar beet genotypes (five were monogerms and five were multigerms), under salinity stress. sugar beet plants were irrigated with saline water, with the electrical conductivity (ec) ranging from 8.6-10 ds.m-1 in the first year and 8.4-10.4 ds.m-1 in the second year. a randomized complete block design (rcbd) with three replicates was used. the results showed that na+ content in leaves and roots of all genotypes was increased in salinity stress, but the increment in leaves was higher than in roots. k+ contents in leaves and roots were decreased in all genotypes, but this reduction was lower in roots as compared with leaves. this may be due to the substitution of na+ with k+ in such condition. however, under salinity stress concentrations of inorganic solutes (na+, and k+) in leaves was higher than those in roots. kawimera (multigerm) was considered the most tolerant genotype because of high na+ content in its leaves and roots, whereas the most sensitive genotype was tigris (multigerm), which had the lowest content of na+ in leaves and roots. generally, the accumulation of soluble sugars in leaves was higher in tolerant genotypes as compared with non-tolerant ones. the results exhibited no correlation between sugar content in roots and salinity stress. correlation analysis showed na+ content followed by soluble sugars as the main solutes for osmotic adjustment in sugar beet leaves under salinity conditions. moreover, both sucrose and na+ contents in beet root could be considered the main solutes for osmotic adjustment.