Photoassimilate availability drives sunflower sugar storage capacity through plastic changes in organ size

Abstract

Sunflower capacity to synthesize and accumulate soluble carbohydrates that willultimately contribute to grain filling, either via actual photosynthesis or previously storedreserves, has been largely neglected despite its relevance regarding crop yield. Thepresent work is aimed at studying the effect of photoassimilate availability on thedynamics of production and distribution of soluble carbohydrates in the plant duringvegetative and reproductive phases. Plant photoassimilate availability was modifiedfrom production crop level in two hybrids during two field experiments by shading orthinning plants, which resulted in a range of intercepted radiation between 20 and 300MJ per plant, and also by removal of the main sink, the capitulum. Plants under higherlight availability developed larger leaves and accumulated much more biomass thanshaded ones. In general, plant sugar storage increased up to flowering, and washighest in the developing capitulum and upper stem internodes. Increasing lightavailability led to a strong growth promotion that was especially remarkable in thecapitulum and stem upper internodes, which precluded an increase in sugarconcentration in these parts. Capitulum removal led to sugar remobilization to the plantbase, resulting in a strong growth promotion of roots, basal stem internodes and evenin leaves from the lower strata, showing an extremely high plasticity of all sunflowerorgans in response to photoassimilates. These results also suggest that sugars per semay drive plastic changes of organ size ultimately conditioning plant capacity to storesugars and crop yield.