Behavior of Enzymes Governing Starch- and Sucrose-Forming Pathways in Two Sugarcane Varieties Supplied with Variable Nitrate and Phosphate in Sand Culture

Abstract

In order to test the hypothesis that starch formation and metabolism is of importance to the sucrose-forming potential of cane, a series of 4-week-old plants was subjected to treatments designed to cause wide fluctuations in the enzyme starch phosphorylase. Treatments included high and low nitrate to vary acidity, high and low phosphate to vary the ratio of H₃PO₄ to glucose-1-phosphate, and two varieties (Uba and M.336) with distinct reputations for producing starch and sucrose, respectively. Treatments were supplied in 2 X 2 X 2 factorial combination. Sugar and enzyme assays were conducted with leaf and meristem samples harvested after 8 weeks of treatment. Sugars included total ketose, total reducing sugars, sucrose, fructose, and glucose. Enzymes included sucrose phosphorylase, starch phosphorylase, invertase, amylase, hexokinase, peroxidase, polyphenol oxidase, and a series of acid phosphatases hydrolyzing ß-glycerophosphate, glucose-1-phosphate, glucose-6-phosphate, fructoses- phosphate, 3-phosphoglyceric acid, ATP, and ADP.