Chemical and biochemical responses of sugar beet root to foliar freezing and defoliation

Sugar beet seed, S.K.E.-R-11, was obtained from the B.C. Sugar Co. Ltd., Vancouver, B.C. and germinated in flats in a greenhouse on January 29, 1954. The beet plants were transplanted to a fertilized field on May 2, 1954. A randomized lot design was chosen in order to reduce error caused by soil differences, moisture variations, and pH etc. Thirty groups of 10 beets per group were selected from the randomized lot. The leaves of 6 groups were frozen with dry ice and the other groups were defoliated, decrowned continuously defoliated, or used as controls. The regrowth on the continuously defoliated beets was removed every two days following initial defoliation. Defoliation was effected by slicing off the leaves one-quarter inch above the crown. Decrowning was done by cutting the beet root transversely just beneath the outer ring of meristematic buds. The: defoliated beets were used to serve as a parallel to the destruction of leaves by freezing. The continuously defoliated beets were a check on the defoliated beets, where it was considered that photosynthesis in the new regrowth leaves would partially offset a large sugar loss in the root. Two experiments were completed. The first experiment and treatment began on August 16, 1954; the second on October 13, 1954. Harvest times were at the 1, 4, 8, 11, 16 and 20 day intervals following Aug. 16, and at the 1, 4, 8, 12 and 15 day intervals following October 13. Enzyme activity only was determined in the second experiment. 'The fresh leaf weights of the defoliated and control beets were recorded and later compared with leaf regrowth weights and sugar content. The beets were harvested in groups of 10 beets all treated in one specific manner. Ten beets of each group were removed from the soil and each beet sliced diagonally across the centre region. The sections were washed in water and pulped in a meat grinder giving approximately 2000 grams of pulp from 10 sections. Three hundred grams of pulp was used in dry weight -determination. Forty grams of fresh pulp from each group was blended for 2 minutes with 100 ml. of distilled ice water in a Waring blendor. The solution was filtered through broadcloth and used in enzyme activity measurements. In the second experiment, 47 grams of pulp was blended with 100 ml. of distilled ice water for 2 minutes. The crown portion of the root was used in the estimation of invertase activity. A check on the sampling method showed that the 40-gram aliquot of pulp used for enzyme determination represented the sample. Sucrose percent and phosphatase activity were used as the basis of this test. The fresh pulp was analyzed for sucrose, invert sugars, dry weight, catalase, phosphorylase, beta-amylase and invertase enzyme activities. The dried pulp was ground to 40-mesh and analyzed for total nitrogen, sucrose and invert sugars. Insoluble nitrogen and starch-dextrins were determined in ethanol extracted pulp. Duplicate determinations were made on each sample. Percentages are based on both dry and fresh weights and given as T/C values. Phosphorylase, phosphatase, catalase, beta-amylase, invertase were measured. Sucrose, invert sugars, starch-dextrin3, and total and insoluble nitrogen were also determined. The.highest amount of leaf regrowth occurred 4-17 days after freezing. The results indicated no relation between leaf weights and sucrose content nor between root weight and sugar content in mature beets. The percent dry weight decreased in all treated beets from the 1st to the 20th days after treatment. This decrease is likely a result of sucrose loss and an increased hydration in the beet root. Sucrose percent based on dry and fresh weight generally decreased following all- treatments. A positive correlation between percent sugar loss and leaf regrowth is suggested. There was an increase in the amount of reducing sugars after foliar loss. The suggestion has been made that the monosaccharide sugars are utilized almost immediately in leaf regrowth or in (increased respiration in the beet crown. The percent, of starch-dextrins tended to decrease in the treated beets but this is most likely not significant. The decrease in percent of total carbohydrates found follows the fact that sucrose disappears. Total carbohydrate estimations seem to provide a reasonable basis for determining the amount of sucrose loss. Total and soluble nitrogen values decreased to the 8th day after treatment and increased after this time. Insoluble nitrogen results were generally inconclusive. The results suggested a translocation of soluble nitrogenous compounds to the beet crown where active growth was occurring. The apparent activity of phosphorylase decreased with time in all treatments. Starch phosphorylase in sugar beet root likely has a minor role in total carbohydrate metabolism of the tissue. Phosphatase activity decreased to -the 11th day in every treatment except decrowned. The reason for a lower apparent phosphatase activity in treated beets in this experiment is not known. It may be associated with an increase respiratory rate. There were no significant changes in beta-amylase activity and no correlation could be found between starch-dextrin content and amylase activity. Catalase activity based on monomolecular values, decreased with time after treatment. A decrease in catalase activity might be expected in the mature, cells of the root as the respiration rate decreases with age. A correlation between invertase activity and sucrose loss was indicated in the frozen and decrowned beets but not in the defoliated beets. From the results of this experiment it seems unlikely that invertase is alone responsible for a sucrose decrease. The results found in this experiment were largely negative.

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