Irradiance affects sugar distribution and storage in the sunflower plant

GARCIA L; MARTÍNEZ NOËL G; GIORGI ME; TOGNETTI J; DOSIO G

Santa Fe

Congreso; RAFV2021; 2021

SAFV

In sunflower, photoassimilates accumulated at flowering contribute up to 15% of grain final weight. It is assumed that these reserves are located in the stem and promoted by increase radiation, but little information about their distribution in plants under different light levels is available. To analyze this, sunflower plants (Advanta 5304) were field grown in Balcarce, Argentina in 2018/9 and 2019/20, under three irradiances: 50% shading, control (both at density = 5.5 plants m-2) and thinned (to 25%). Treatments were set at apex induction into reproductive stage (approximately 10 leaves > 4 cm in length). We measured the concentration and amount of soluble carbohydrates in leaf, stem (upper, middle, basal), receptacle, and roots at flowering.In both years, the increase in irradiance between shaded and controls led to higher sugar concentration in all plant organs. However, irradiance rise between controls and thinned plants did not significantly promote sugar concentration in middle and upper stem parts, in which most of these reserves were stored, while carbohydrate concentration increased about 100% in roots. Intermediate promotion values were found for receptacle and basal internodes. On the other hand, higher radiation determined large increases in the weight of all plant organs, and this was particularly remarkable between control and thinned plants, leading to a strong increase in sugar total amount per plant.Our results suggest that sunflower has a high morphological plasticity to changes in radiation, which may strongly affect plant capacity to deliver reserves to grains, while maintaining relatively constant stem sugar concentrations.