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Sugar-enzyme relationships were evaluated among 12 Puerto Rico sugarcane varieties. There were two objectives: 1, To discover enzyme-activity trends which would help account for characteristic variety properties; and 2, to seek enzyme-activity trends which indicate at an early age the sugar-producing capacity of new or test varieties. All plants were grown in sand culture with controlled nutrient supply. Leaf and meristem samples were frozen at 10 weeks for sugar and enzyme assay. Sugar and enzyme values varied greatly among the 12 varieties, although at harvest all varieties appeared quite similar as to size and vigor. Fructose and sucrose content differed by as much as tenfold among variety extremes. Amylase, invertase, tyrosinase, and peroxidase all exhibited broad differences. Three variety characteristics were correlated with enzyme action, including cane tonnage, percent-sugar in cane, and sugar per acre. Leaf amylase appeared to affect both cane tonnage and percent-sugar in cane. Leaf phosphatase was particularly active in varieties rated as "low" sugar producers. In meristem, both invertase and peroxidase showed direct correlations with cane tonnage, with activity increasing from low to high as tonnage potential increased. High invertase also correlated with "low" percent-sucrose, and with "low" sugar per acre. Both meristem tyrosinase and peroxidase were excessively active among varieties rated as "low" sugar producers. Since meristematic enzymes can be assayed at a very early age, it was suggested that invertase be employed as an early indicator of sugar-producing potential with test varieties. Peroxidase and amylase also show promise in this respect.

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.

In vitro studies of invertase action patterns were conducted in the presence of silicon (Si). This element is known to inhibit the enzyme both in living tissues and cell-free preparations. Substrates included sucrose, raffinose, stachyose, and turanose. Sugarcane acid invertase was prepared from lyophilized immature storage tissue and was partially purified by salt fractionation, dialysis, and gel filtration. Enzyme products were studied by paper chromatography. Two products, fructose and glucose, were quickly obtained in large quantity from sucrose. Against raffinose the reaction proceeded more slowly but yielded a total of four products. This suggests a powerful work potential of cane invertase since complete acid hydrolysis of raffinose gives only three products. It is proposed that both 1 —> 6 and 1 —> 2 linkages are broken. Fructose appears by direct hydrolysis of raffinose and by secondary attacks upon the intermediate product sucrose. Use of stachyose as substrate gave additional evidence for hydrolysis of the 1 —> 6 linkage. Three products were obtained in the presence of only one 1 —> 2 fructosidic linkage. Incorporation of Si into invertase digests abruptly terminated the reactions against sucrose, raffinose and stachyose. The effective Si concentration was slightly more than 3 µmoles of Si per milliliter of digest. Significance of the invertase inhibition is mentioned both from the standpoint of increasing sucrose yield and as an analytical indicator of silicic acid content of plant tissues. When the disaccharide turanose was employed as substrate, increasing Si levels gave additional products rather than suspended enyme action. Four products appeared in the presence of 9 µmoles of Si. The substrates sucrose and raffinose yielded masses of variably-staining products at Si levels above 27 µmoles per milliliter. The latter products were of low chromatographic mobility and resembled fragments of hydrolyzed starch. To account for Si action on invertase it is proposed that a silicic acid gel forms around the enzyme in direct proportion to Si concentration. Inhibition of sucrose hydrolysis does not stem from severe protein structural changes. Rather, the hypothetical, gel-encased enzyme might cease to function against one substrate while retaining or increasing its capacity to attack others.