PHYSIOLOGICAL ADAPTATION TO HIGH ION CONCENTRATIONS OR WATER DEFICIT BY CALLUS-CULTURES OF HIGHBUSH BLUEBERRY, VACCINIUM-CORYMBOSUM

Callus cultures of highbush blueberry were selected for 10 passages on medium supplemented with 50 mol m-3 NaCl, 50 mol m-3 KCl, 25 mol m-3 Na2SO4, 25 mol m-3 K2SO4 or 100 mol m-3 mannitol. On all salts, growth of selected callus was greater (200-250%) than that of non-selected c allus, and selected callus grew optimally on the type of salt on which it was selected. Conventional (whole plant analysis) and electron pro be X-ray microanalysis showed that selected callus accumulated more io ns (approximately 1.5-3.0-fold) than non-selected callus on all salts, and there was a positive correlation between vacuolar ion concentrati on and fresh weight. Growth of NaCl-selected callus but not non-select ed callus was greatly enhanced (2.25-fold) in the presence of 100 mol m-3 mannitol, while growth of a mannitol-selected callus line was also enhanced. In callus grown on NaCl or mannitol, slight increases in le vels of glycinebetaine, choline and proline were measured. Sucrose, gl ucose, fructose, sorbitol and malate concentrations significantly incr eased in callus grown on NaCl or mannitol, and selected callus produce d 4-fold more sugars than non-selected callus. The total increases in concentrations of all measured sugars were 210 mumol gFW-1 in NaCl-sel ected callus grown on 50 mol m-3 NaCl, and 296 mumol gFW-1 in mannitol selected callus grown on 100 mol m-3 mannitol. The results of this st udy indicate that adaptation of blueberry callus cultures for optimal growth on salt-containing media is probably due to adaptation to water stress, not tolerance to specific ions. Osmotic adjustment, achieved by ion uptake and production of sugars, appears to be the physiologica l mechanism of adaptation.