Seed size is associated with sucrose synthase activity in developing cotyledons of chickpea

Seed size, a key quality determinant in the marketing of the cool-season food legume chickpea (Cicer arietinum L.), can be reduced under terminal drought. Sucrose synthase and invertase, important enzymes in sugar metabolism, play an important role in seed filling. This study aimed to determine whether these enzymes in the developing cotyledons are associated with the final seed size of chickpea by following their level of activity during seed filling in large- and small-seeded chickpea genotypes. The level of invertase in the cotyledons was unchanged during seed filling, but sucrose synthase reached a maximum about 500 to 600 growing degree days (GDD) after flowering when cell numbers were no longer increasing, but the cotyledons were increasing rapidly in dry weight. In a range of genotypes differing in seed size, the level of sucrose synthase activity in the developing cotyledons at 500 to 600 GDD was correlated with the final seed size at maturity when measured at a rainfed site in two different years. The level of activity of sucrose synthase at the same stage of development in F₂, F₃, and F₇ populations of crosses between a large-seeded cultivar and two small-seeded genotypes was also correlated with final seed size. It is concluded that sucrose synthase, but not invertase, in developing cotyledons is the key enzyme influencing seed size in chickpea.