CHEMICAL AND BIOCHEMICAL RESPONSES OF THE MATURE SUGAR BEET ROOT TO DEFOLIATION BY FROST AND KNIFE

Abstract

The tops of mature field-grown sugar beets were frozen or removed by knife and the leaves allowed to regrow, or removed by knife and all regrowth continuously removed, for a period of 16 days. Sample roots were dug from the ground one, four, eight, 12, and 16 days after the original defoliation, and dry weight, sucrose, invert sugar, starch dextrin, total nitrogen, and insoluble nitrogen determined. The activity of catalase, phosphorylase, phosphatase, beta-amylase, and invertase was measured. Compared with untreated plants, all treatments affected in a similar way the substances or activities measured, with the exception of phosphatase and catalase activity. Dry weight decreased, and percentage sucrose based on fresh weight, fell steadily, and was 2.89 below that of controls on the 16th day. Ou a dry weight basis the sucrose percentage of roots of defoliated plants did not differ significantly from that of roots of untreated plants. It is suggested that the continued fall in sucrose percentage on a fresh weight basis is the result of continued absorption of soil water. Invert sugar was higher in treated plants and increased with time. Changes in starch dextrin content were small. The total N content of the various plants showed no significant differences. Insoluble N was not altered in a recognizable pattern. The activity of catalase and phosphorylase was lower in treated plants, while phosphatase and invertase showed increased activity. Beta-amylase activity was low in all roots.