[Identification of gravity-related esterases (grEST1 and grEST2) in carrot callus cells]

A horizontal clinostat which mimics the microgravity in space was used to study its effects on carrot cells. After using boric acid buffer (pH 8.8) as extraction medium, PAGE pattern of esterase isozymes of carrot callus cells displayed 8 bands of which the activities of only 2 were affected by microgravity. They were named grEST1 and grEST2, where grEST stands for gravity-related esterase. The rates of increase in activity of them in carrot cells when cultured on a rotating horizontal clinostat were lower than that cultured in normal gravitational environments, and the difference increased with the culture time. The activities of grEST1 and grEST2 in carrot callus cells subjected to horizontal rotation were found to return to their original levels after being placed under normal gravity (1 x g) for 7 days. We suggest that the effect of simulated microgravity conditions on grEST1 and grEST2 activities in carrot callus cells is through affecting their synthesis. In addition, the activities of grEST1 and grEST2 were not inhibited by eserine, acetylcholine iodide, diisopropyl fluorophosphate and p-chloromercuribenzoate, which indicates that they are acetylesterases.