RHYTHMIC GROWTH AND CARBON ALLOCATION IN QUERCUS-ROBUR .1. STARCH ANDSUCROSE

Changes in the concentrations of sucrose and starch during endogenous rhythmic growth, under controlled conditions, have been studied in the aerial and underground parts of young common oak (Quercus robur L.). A given flush contributes to the development of the following flush by partial and temporary mobilization of stem carbohydrate reserves. Dur ing a flushing event, the starch deposition in storage tissues of stem s and leaves occurs simultaneously with stem elongation and leaf expan sion. Otherwise both sink storage tissues and sink demand for flush de velopment are equally important. The young leaves accumulate simultane ously starch and sucrose until the fourteenth day of the flush of grow th. Then sucrose concentration decreases. These changes correspond to the development stage transition from importing leaves to autotrophic leaves and to exporting leaves. Only the photosynthates provided by fl ush mature leaves are translocated for a new flush development, while the starch content in these leaves is not hydrolysed. The changes in t he sucrose content of stems are strongly linked to the periodic growth of the aerial parts. The roots are not an important storage tissue. T heir continuous growth and the low levels of starch and sucrose may in dicate that roots are a permanent sink with constant requirements in t he course of the flushing episodes of the aerial parts.