AbstractEnzyme-sucrose relationships were studied in immature sugarcane 9 weeks after foliar treatment with gibberellic acid (GA). Silicon (Si) was used to induce sucrose and enzyme behavior patterns which then were compared between GA-treated and non-GA treated plants. The ultimate purpose is exploration of the enzyme basis for the growth and sugar decline which supersedes GA growth stimulation. During the present study three objectives were attempted: 1, To induce definite sucrose accumulations by daily use of Si; 2, to induce enzyme trends which could be correlated with changing sucrose level; and 3, to demonstrate that enzymes of cane no longer experiencing growth stimulation behave essentially the same as their counterparts in non-GA treated plants. The following results were obtained: 1. Plants given foliar GA (0.01 percent) experienced initial internode elongation and increased fresh weight. The growth effects outwardly ceased by 9 weeks. Si at the 250 and 500 p.p.m. levels caused moderate growth stunting. This effect was markedly less severe in GA-treated plants. 2. Sucrose levels increased in leaf, immature storage, and stalk tissues in response to progressively higher Si supply. Optimum Si for growth and sucrose production lay between 100 and 250 p.p.m. 3. Evidence was found of a Si-moderating mechanism against relatively extreme shifts in leaf enzyme behavior. 4. Peroxidase, polyphenol oxidase, phosphatase, and ATP-ase were strongly suppressed in leaves as Si supply was raised. In each instance the enzyme sensitivity to Si was vastly altered in plants treated with foliar GA. Amylase sensitivity to Si was similarly changed by GA. 100 p.p.m. Si now caused amylase stimulation rather than retardation, and higher Si concentrations generally failed to cause major enzyme suppression. 5. Enzyme and sugar data were interpreted as follows: GA-induced growth and sucrose increases, while still easily detectable, were no longer in progress at 9 weeks. The necessary enzymatic basis for the growth and sucrose increases was no longer present. An enzyme status different both from non-treated and actively-stimulated plants was now operative. 6. It was concluded that additional GA treatments aimed at furthering growth and sugar production would be received by plants biochemically distinct from those given the initial treatment. Practical implications of the growth, sugar and enzyme data are discussed.
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