Source‐Sink Alterations Affect the Number of Cells in Soybean Cotyledons

Abstract

The ability of an individual soybean [Glycine max (L.) Merr.] seed to utilize assimilate is an important part of the yield production process. Cotyledon cell number is a major determinant of genetic differences in seed growth rate. Experiments were conducted in the field and greenhouse with ‘McCall’, ‘Williams’, and ‘York’ cultivars to determine if source‐sink alterations would affect cotyledon cell number. Source‐sink alteration treatments (66% defoliation, 80% depodding, and 63% insolation reduction) were applied when tagged fruits were 20 to 25 mm long. Seeds from the tagged fruits were harvested at maturity and cotyledon cells were counted. Defoliation or shading reduced cotyledon cell number by 21 to 55% for McCall and York in the greenhouse and Williams in the field. Depodding increased cotyledon cell number by 26 to 102%. Cotyledon growth rates in an in vitro culture system increased with increasing sucrose concentrations and reached a maximum at 100 to 200 mM. Cotyledon growth rates in vitro with saturating levels of sucrose and asparagine were closely correlated with cotyledon cell number across treatments and genotypes. The data indicate that cotyledon cell number in soybean is influenced by the physiological environment during the cell division phase of seed development and that both cotyledon cell number and assimilate supply are important in determining seed growth rate.