Plastic Responses to Light Availability in Sunflower: A Trade-Off between Growth and Sugar Storage Capacity

Abstract

Changes in plant structure may define plant capacity to synthesize and accumulate soluble carbohydrates that will ultimately contribute to grain filling in sunflower, via actual photosynthesis or previously stored reserves. The present work is aimed at studying the relationship between light-driven changes in organ size and sugar accumulation in this species. We performed two field experiments with two sunflower hybrids each under contrasting irradiance or capitulum removal treatments. We analyzed growth parameters and the dynamics of production and distribution of soluble carbohydrates in plant organs during vegetative and reproductive phases. When light availability increased from shaded to control treatment a moderate enhancement of the volume of storing organs and an increase in soluble carbohydrates concentration were observed. In contrast, when light availability increased from control to high irradiances (thinned treatment) a strong growth promotion was observed, but no increase in sugar concentration was found. Increased C investment in growth, and higher volume, of storing organs, would preclude achieving very high sucrose concentration in tissues. This fact would prevent the induction of fructan metabolism, and also the inhibition of photosynthesis by end product. Both light and carbohydrates per se affected this plastic growth response of organs, which was independent from genetic background and may directly impact on plant capacity to store sucrose, ultimately conditioning crop yield under stress.

Keywords: capitulum, carbohydrate reserves, Helianthus annuus, high irradiance, organ plasticity, sucrose