An evaluation of methods for measuring cell osmolarity with invitroand invivogrownLycopersiconplants

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Abstract
Three standard techniques (thermocouple psychrometry, cell sap extraction, and plasmolysis) and two novel methods (osmometer solution, and image analysis) were comparatively evaluated for estimation of leaf cell water and osmotic potentials in vitro and in vivo. The test plants, tomato (Lycopersicon) assessionsL. esculentum ‘Chico III’,L. pennellii, L. peruvianum, and L. cheesmanii, were grown as whole plants under microculture and growth chamber cultural environments. Each of the methods for measuring total water potential (thermocouple psychrometry, osmometer solution, and image analysis) and osmotic potential (thermocouple psychrometry, cell sap extraction) yielded consistent results when applied to microculture test plants (from a highly controlled, uniform environment), but results from growth chamber grown plants were too variable (between methods) to be conclusive. Plasmolysis gave unrealistically high estimates of osmolarity in all cases. Tissue water potential and osmolarity estimates were higher for plants grown in microculture than their growth chamber counterparts. The osmometer solution and image analysis methods were practical methods for total water potential estimation, required only a fraction of the time needed for psychrometry, and could be used reliably for microcultured tissues