Retardation of soybean leaf senescence and associated effects on seed composition

Soybean leaf senescence, leaf abscission, and pod yellowing were markedly delayed by sprays of 10^–4 M 6-benzylamino-9-(tetrahydropyran-2-yl)purine plus 5×10^–5 M -naphthalene acetic acid. The pods on the sprayed plants turned yellow 5–7 days later than those on the control plants, and the treated leaves remained dark green even when the pods had already desiccated. The antisenescence spray did not change pod numbers, seed numbers, seed size, or the yield. By retarding senescence, seed nitrogen content was increased in both TCA-soluble and TCA-insoluble fractions. Seed total protein, buffer-extractable total protein, and globulin were increased by 26, 28, and 33 mg/g of seed flour, respectively, and albumin was decreased by 6 mg/g. The overall increase in seed protein caused by spray treatment is confined to the globulin portion.