Enzyme-Sugar Relationships in Immature Sugarcane Treated With Ascorbic Acid, Cysteine, Hydroxylamine, Cyanide, Silicon, and Iron

Abstract

Immature sugarcane was treated with chemical additives to determine whether significant and predictable changes could be induced in enzyme behavior. All plants were grown in sand culture with controlled nutrient supply. One group received foliar application of ascorbic acid, cysteine, hydroxylamine and cyanide; the other group received silicon, iron, and cyanide as nutrient-solution supplements. Enzymes assayed included acid phosphatases, invertase, amylase, peroxidase, and tyrosinase (polyphenoloxidase). Each of the chemicals tested was known to affect one or more enzymes in vitro. Plants receiving 1,000 p.p.m. of cyanide as a foliar spray increased sucrose in leaves and meristem within 3 days. All enzymes measured were suppressed by CN. Amylase was markedly stimulated by 50 and 1,000 p.p.m. of cysteine. All the enzymes assayed were moderately stimulated by 50 p.p.m. of cysteine, whereas 1,000 p.p.m. caused general suppression. Plants receiving 200 p.p.m. of cyanide as a nutrient-solution supplement were greatly stunted and revealed low sugar content of leaf and meristem tissues. Tyrosinase was about 3 times more active in high-cyanide plants than in controls. Silicon added to nutrient solutions at rates of 20 and 200 p.p.m. greatly retarded invertase and tyrosinase. This confirms similar observations recorded earlier, and it is suggested that enzyme inhibition is a physiological function of silicon in sugarcane. Iron added to nutrient solutions at the rate of 10 p.p.m. caused general enzyme suppression, particularly with regard to meristem peroxidase and invertase. Significance of enzyme regulation in living cane is briefly discussed.