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 rnol m-3 NaCl, 50 rnol 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 callus, and selected callus grew optimally on the type of salt on which it was selected. Conventional (whole plant analysis) and electron probe X-ray microanalysis showed that selected callus accumulated more ions (approximately 1.5-3.0-fold) than non-selected callus on all salts, and there was a positive correlation between vacuolar ion concentration and fresh weight. Growth of NaCl-selected callus but not non-selected 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 levels of glycinebetaine, choline and proline were measured. Sucrose, glucose, fructose, sorbitol and malate concentrations significantly increased in callus grown on NaCl or mannitol, and selected callus produced 4-fold more sugars than non-selected callus. The total increases in concentrations of all measured sugars were 210 μmol gFW-1 in NaCl-selected callus grown on 50 mol m-3 NaCl, and 296 μmol gFW-1 in mannitol selected callus grown on 100 rnol m-3 mannitol. The results of this study 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 physiological mechanism of adaptation.