High Sucrose Levels and Abnormal Enzyme Activity as a Function of Nutritional Stress in Sugarcane

Abstract

Deficiencies of nitrogen, phosphorus, potassium, and calcium were gradually induced in sugarcane grown by sand culture. There were three objectives: 1, To determine whether nutritional stress in general is a means of inducing higher sucrose production; 2, to determine whether sucrose increases can be triggered without reaching nutrient-deficiency levels which would reduce tonnage; and 3, to ascertain whether increased sucrose production can be traced to common behavior patterns of hydrolytic and oxidative enzymes. All plants received a moderately high level of all nutrients until 14 weeks of age. Thereafter, individual nutrients were gradually lowered at intervals of 2 weeks, while control plants continued to receive the original levels. All plants subjected to nutritional stress accumulated higher leaf sucrose than control plants, regardless of the nutrient withheld. In each instance sucrose increases were recorded before nutrient supply had reached deficiency proportions. General nutritional stress thus appears to trigger variations in sugar level, with nutritional imbalance rather than actual deficiency being a critical factor. All plants under nutritional stress revealed a concurrent suppression of amylase as sucrose increased. Peroxidase was greatly stimulated by all nutritional treatments. Phosphatase was suppressed by decreasing nitrate and phosphorus, but was generally unaffected by the potassium and calcium treatments. Several distinct mechanisms of increased sucrose formation are indicated by the enzyme data. Sensitivity of amylase to changing nutrient supply is discussed from the standpoint of a possible indicator of approaching deficiency.