Starch serves as an overflow product in the regulation of carbon allocation in strawberry leaves in response to photosynthetic activity

Abstract

The carbon allocation in source leaves between sucrose and starch is an important mechanism that affects plant productivity. We previously found that strawberry plants accumulate starch in response to excess carbon supply from photosynthesis compared with translocation and sucrose storage capacity in source leaves. However, because these data were acquired from three separate cultivation seasons in field conditions, seasonal impacts could not be ruled out. Therefore, herein, we aimed to investigate the role of starch in carbon allocation in strawberry leaves and to explore whether the relationship between sucrose and starch reported in our previous study is an inherent characteristic that is independent of seasonal variations. To prevent seasonal influences, carbohydrate dynamics in strawberry leaves were studied under controlled environmental conditions with high (High) and low (Low) photosynthetic activity. During the day, both sucrose and starch concentrations increased in the High treatment, but starch concentration increased only marginally in the Low treatment. Furthermore, starch production was enhanced in the High treatment when sucrose concentration exceeded 150 mmol C m− 2. Consistent with previous findings, the current findings indicated that photosynthetically fixed carbon is initially allocated to sucrose; however, when photosynthetic activity increases and leaf sucrose concentration exceeds its storage capacity, the excess carbon is then allocated to starch. This study provides strong evidence that, regardless of season, starch serves as an overflow product with sucrose storage capacity as a threshold during carbon allocation in strawberry leaves.