SUCROSE METABOLISM IN BEAN-PLANTS UNDER WATER DEFICIT

The effects of water stress on sucrose metabolism were evaluated in bean plants of Tacarigua variety grown for 25 d. Decreasing water potential and relative water content were observed. Water stress effects resulted in a decrease of sucrose phosphate synthase (SPS) in both total (substrate saturating conditions) and Pi-insensitive (substrate limiting conditions plus inorganic phosphate) activities. The SPS Pi-insensitive activity was lower than the total SPS activity, but the decrease in activity induced by water deficit was relatively lower in the Pi-insensitive; however the activation state increased during the water deficit period. An increase in sucrose synthase activity increased the activities of both neutral and acid invertases at moderate water stress (-0.8 MPa) and decreased activities at severe water stress (-1.45 MPa). The activity values of neutral invertase were lower than those for the acid invertase. The starch/sucrose ratio decreased and the ratio of total glucose/total fructose increased. These results indicate a relevant physiological role of SPS in bean plants under water stress.