The Effect of Boron and Gibberellic Acid on the Senescence of Leaf Discs from Lycopersicon esculentum cv. Rutgers

When leaf discs of Lycopersicon esculentum Mill. cv. Rutgers were floated on solutions containing 4.33 × 10^–6 M gibberellic acid (GA₃), 1.0 ×x 10^–6M boron (B), separately and together, senescence was retarded with respect to controls. Degradation of chlorophyll, total protein, RNA, and DNA was delayed, and decreases in fresh weight and leaf disc diameter checked. The loss of chlorophyll, protein, RNA, DNA, fresh weight, and diameter were 10, 20, 30, 8, 28, and 0 per cent with GA₃ alone; 15, 25, 35, 8, 31, and 0 per cent with B alone; 8, 14, 25, 7, 25, and 0 per cent with GA₃ plus B; contrasted with 50, 40, 50, 9, 42, and 3 per cent for the controls. An analysis of variance was performed on all data except for disc diameter. All sources of variance were significantly or highly significant at the 1 per cent level except for the effect of boron on DNA level, which was significant only at the 2.5 per cent level. Retardation of senescence by GA₃ may be associated with the known ability of GA₃ to stimulate m-RNA and protein synthesis. The effect of boron may be due to an effect on sugar and starch balance, translocation of sugar, or on water balance, but more likely boron plays a role in nucleotide and protein metabolism in plants. Boron may be involved in the synthesis of DNA, a role perhaps mediated by GA₃.