CHANGES IN NONSTRUCTURAL CARBOHYDRATES IN OLIVE (OLEA-EUROPAEA) LEAVES DURING ROOT-ZONE SALINITY STRESS

Self-rooted olive (Olea europaea L.) plants were grown in hydroponics at various NaCl concentrations (from 0 to 200 mM) for 28 to 32 days fo llowed by 28 to 30 days of relief from salinity over two growing seaso ns. Olive leaves accumulated both glucose and mannitol during the peri od of salinity stress. The concentrations of fructose, myo-inositol, g alactose, galactinol, sucrose, raffinose, and stachyose were not signi ficantly affected by salinity. Starch content was decreased by salinit y. The mannitol/glucose and mannitol/soluble carbohydrates ratios incr eased as the external NaCl concentration was increased, but returned t o the control levels during the relief period. The increase in mannito l or glucose molar concentrations, expressed on a leaf tissue water ba sis, was partially due to a reduction in leaf tissue water content und er salinity stress. However, an increase in mannitol concentration was also observed when expressed on a dry weight basis. The accumulation of mannitol in leaf tissue preceded any reduction in leaf area rate or net assimilation rate. The increase in leaf mannitol or glucose conce ntration was positively correlated with the increasing level of salini ty at the root zone, but not with the accumulation of Na+ in the shoot . The role of mannitol, a potential osmoregulator in leaf mesophyll du ring salinity stress, is discussed in relation to the complex carbohyd rate composition of olive leaves.