Translocation and distribution of photosynthetically assimilated <SUP>13</SUP>C to ‘Tsugaru’ apple fruits

Abstract

Photosynthetically assimilated carbon C is transported from source leaves to fruits depending on their development stage. To examine the translocation of the assimilated C in a shoot with a fruit throughout the development process, we constructed an in-situ 13 CO 2 exposure chamber system for a fruit-bearing apple shoot and measured the assimilation of 13 C in leaves and its translocation to the fruit in an early maturing apple Malus domestica cultivar 'Tsugaru'. Fruitbearing shoots were exposed three times during the development period early development, fruit development, and mature stages to 13 CO 2 for 1 h in the chamber and collected 72 h after exposure, followed by analysis of 13 C inventory in each organ leaves, branch, and fruit . We evaluated the translocation of 13 C using two indices:13 C remaining ratio 13 C inventory in each plant organ / net assimilated 13 C during exposure , and 13 C distribution ratio 13 C inventory in each plant organ / total 13 C inventory in the shoot . Although the 13 C remaining ratio in the fruit during the early development stage was slightly lower than that at the fruit development and mature stages, the ratio at the mature stage was similar to that at the fruit development stage, indicating that the ability of source leaves to allocate photoassimilates to fruit was maintained until fruit maturation. The 13 C distribution ratio of the fruit was similar regardless of its development stage, although biomass proportion of fruit increased with the development stages. This suggests that the sink strength of the fruit-bearing shoots of 'Tsugaru' may not be altered by fruit development.