Using Pressure-Volume Analysis to Characterize NaCl-induced Osmotic and Turgor Adjustment in in vitro Cultures

Abstract

The applicability of pressure-volume (PV) analysis for characterizing osmotic and turgor adjustments in in vitro cultures was tested using salinized orchardgrass callus. Thermocouple psychrometry was used to derive PV curves in three experiments: (a) adjustment to varying concentrations of NaCl, (b) recovery from NaCl stress and (c) influence of NaCl acclimation to an additional, increased NaCl challenge. Callus growth and water relations were unaffected by 50 mM NaCl. Harvest and zero turgor osmotic potentials were decreased about 0.7 and 0.9 MPa, respectively, in callus grown for three weeks on 100 and 150 mM NaCl. Turgor was 0.2 to 0.4 MPa higher in 100 and 150 mM treatments across a range of callus water potential, compared to 0 or 50 mM NaCl. Salinization resulted in decreased estimates of callus elasticity and increased values of relative water and osmotic water content at zero turgor. The effects of NaCl stress on elasticity and osmotic potential were still evident three weeks after transfer to fresh medium containing 0 mM NaCl. A three-week acclimation of callus to 50 mM NaCl increased turgor and decreased osmotic potential and elasticity compared with unacclimated callus when cultures were subsequently grown on 100 mM NaCl. Apoplastic water percentages ranged from 21 to 35 % and showed no response to salinization. Psychrometric PV analysis appears to offer a promising alternative for the assay of component water potentials and water contents, elasticity and apoplastic/symplastic water partitioning in callus tissue.