RESPONSES OF HEVEA-BRASILIENSIS MUELL ARG PLANTS TO LOW-TEMPERATURES UNDER CONTROLLED CONDITIONS

In this study we have examined the responses of Hevea plants to low te mperatures in growth chambers simulating winter conditions in the trop ics. The low temperatures increased the leaf diffusive resistance even with a rise in the leaf temperatures toward the end of day. The total chlorophyll levels were reduced by chilling, with no changes in the c hlorophyll a/b ratio. Neither organic solute nor electrolyte leakage w ere observed at low temperatures. These results explain the low growth rate of plants and the lack of serious chilling symptoms (necrosis) i n mature leaves during winter conditions near latitude 22 degrees S in Brazil.