Acclimation to low temperature by microsomal membranes from tomato cell cultures

Sealed vesicles were prepared from microsomal membranes from cell suspension cultures of tomato (Lycopersicon esculentum Mill cv VF36). ATP-dependent proton transport activity by the vesicles was measured as quenching of fluorescence of acridine orange. Measurements of proton transport were correlated with the activity of a nitrate-inhibitable ATPase. The initial rate of proton influx into the vesicles was strongly temperature dependent with a Q(10) of 2 and a maximum rate near 35 degrees C. The data suggest that passive permeability did not increase at chilling temperatures but did increase rapidly with temperatures above 30 degrees C. A comparison was made between membranes from cell cultures grown at 28 degrees C and 9 degrees C. The temperature optimum for proton transport broadened and shifted to a lower temperature range in membranes from cells maintained at 9 degrees C.