PHYSIOLOGICAL AND ENVIRONMENTAL REQUIREMENTS FOR POPLAR (POPULUS-DELTOIDES) BARK STORAGE PROTEIN-DEGRADATION

In poplar (Populus deltoides Bartr. ex Marsh), a 32-kD bark storage pr otein (BSP) accumulates in the bark during autumn and winter and decli nes during spring shoot growth. We investigated the physiological and environmental factors necessary for the degradation of poplar BSP. Pop lar plants were exposed to short-day (SD) photoperiods for either 28 o r 49 d. Plants exposed to short days for 28 d formed a terminal bud bu t were not dormant, whereas exposure to short days for 49 d induced bu d dormancy. BSP accumulated in bark of plants exposed to both SD treat ments. The level of BSP declined rapidly when nondormant plants were r eturned to long days. BSP levels did not decline in dormant plants tha t were exposed to long-day (LD) conditions. If dormant plants were fir st treated with either low temperatures (0-degrees-C for 28 d) or with 0.5 m H2CN2 to overcome dormancy and then returned to long days, the level of BSP declined. Removal of buds from non-dormant or dormant pla nts in which dormancy had been overcome inhibited the degradation of B SP in LD conditions. BSP mRNA levels rapidly declined in plants expose d to long days, irrespective of the dormancy status of the plants or t he presence or absence of buds. These results indicate that the buds o f poplars are somehow able to communicate with bark storage sites and regulate poplar BSP degradation. These results further support an asso ciation of BSP mRNA levels with photoperiod because short days stimula te BSP mRNA accumulation, whereas long days result in a decline of BSP mRNA abundance.