Retardation of Bean Leaf Senescence by Benzyladenine and Its Influence on Phosphate Metabolism

Abstract

The levels of glucose, sugar phosphates, and adenosine phosphates were determined in primary leaves of intact bean plants during normal senescence and compared to leaves in which senescence was delayed by application of benzyladenine (BA). In both cases there was a rise with time in the levels of glucose 1-phosphate, glucose 6-phosphate, and fructose 6-phosphate, and a decline in 2-phosphoglyceric acid, inorganic phosphate, and the adenosine phosphates (AMP, ADP, ATP). The levels of fructose 1,6-diphosphate remained fairly constant. Although the levels of hexose phosphates, adenosine phosphates, and inorganic phosphate were lower in the BA-treated leaves, the incorporation of 32P into these compounds by 3-and 6-week-old plants was higher than in the controls. These results suggest that the retardation of leaf senescence by BA in intact bean plants is associated with increased utilization of metabolites, indicating a more rapid turnover of the adenosine phosphates. It is concluded that this effect is brought about by a regulatory coordination of metabolic processes in relation to energy production and utilization.During leaf senescence there is a decline in the levels of chlorophyll, protein, and RNA (10, 12), associated with the loss of mitochondrial function and phosphorylative activity (13,25). In 1957 Richmond and Lang (21) reported that kinetin retarded senescence of detached Xanthium leaves. It has since been demonstrated that various growth substances, particularly the cytokinins, are capable of delaying senescence of detached leaves (16) and intact plants (10).It has been suggested that increased longevity due to N6-benzyladenine treatment may be a consequence of enhanced nucleic acid and protein metabolism (10, 12) and a decrease in respiration (9) via the inhibition of respiratory kinases (24). However, the retardation of lettuce leaf senescence by BA8 was not always associated with a reduction in respiration (14). MacLean and Dedolph (19) using 2,4-dinitrophenol for studies of respiration in broccoli concluded that retardation of leaf senescence was due to conservation of ATP rather than inhibition of respiration per se.I This study was supported by grants from the National Research Council of Canada. Extraction of Metabolites. Starting from the 3rd week at weekly intervals, each leaf was excised from the petiole and weighed. A set of leaves from another plant was dried in a forced air oven at 65 C for 24 hr, and the percentage of dry matter was determined. The fresh leaves were extracted in methanolchloroform-formic acid-water (12:5:1:2, v/v) (MCF) by a procedure similar to that described by Bieleski and Young (7). The leaves were homogenized in 25 ml of MCF for 10 min, and the Blendor was rinsed twice with 25 ml of MCF. The homogenate was centrifuged (8000g) for 15 min at 0C. The supernatant was decanted, the residue was re-extracted twice, and the supernatant fractions were pooled and concentrated in vacuo at 40 C. Chlorophyll and phospholipids were removed with hexane, and the extracts wer...

Role of Cytokinins in Senescence, Antioxidant Defence and Photosynthesis

“…The diverse effects of particular CKs regarding physiological responses to exogenous application have also been documented. Whereas BAP is widely known for its antisenescence effect on leaves of, e.g., broccoli, bean, barley, maize and wheat [85,87,137,152,153], after application to lettuce, no or only a weak effect was found [152,154]. Similarly, kin has repeatedly been reported as very active in senescence deceleration (e.g., [155,156,157]), however it showed an ambiguous effect on Anthurium [82].…”

The effect of hormones and chemical growth regulators on ear development and grain yield of nonprolific corn (Zea mays L.)

“…Dostal et al (1965) supported the evidence for the hypothesis that BA is functional by means of affecting an increase in the amount of organ ic phosphate, particularly in the adenosine triphosphate fraction. Adedipe and Fletcher (1970) found that the retardation of the leaf senescence by BA in intact bean plants is associated with increased utilization of me tabolites, indicating a more rapid turnover of the adenosine phosphates.…”