Factors Concerned in Leaf Senescence. I. Effects of Age, Chemicals, Petiole, and Photoperiod on Senescence in Detached Leaves of Hibiscus rosa-sinensis L.

The effects of age, the chemicals benzimidazole (BZI), gibberellic acid (GA3), 2-chloroethyl-trimethylammonium chloride (CCC) and indole-3-butyric acid (IBA), the presence of the petiole, and photoperiod on the senescence of detached leaves of Hibiscus rosa-sinensis L were studied. Age determined the time of complete senescence to a great extent. Removal of the petiole brought about a marked delay in senescence. Benzimidazole and GA3 were strong senescence inhibitors; CCC was a milder type, and IBA was the mildest inhibitor. Senescence was delayed longest in a 16-hr photoperiod and least in an 8-hr photoperiod with intermediate results in a 12-hr photoperiod and under natural photoperiod (11 hr 20 min). A 16-hr photoperiod combined with BZI at 50 ppm was slightly more effective in delaying senescence than the photoperiod alone. The delay in senescence caused by BZI application at 50 ppm is accompanied by an initial rise in sugar content, titratable acidity, and respiratory rate for a number of days, as well as by the maintenance of chlorophyll, potassium, phosphorus, and nitrogen at almost the same levels for the first few days before their decline, a condition quite in contrast to that in water controls.