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UBC Theses and Dissertations

Chemical control of growth in sugar beet (Beta saccharifera L.) Singh, Bharat

Abstract

Metabolic inhibitors and growth regulators were used in an attempt to control the growth of sugar beet plants at the time of "ripening" of the roots. Maleic hydrazide (MH), pyrocatechol (PC), and vanadium sulphate (VS) were found to be most effective in controlling growth regardless of the age of the plants. The solutions containing MH, PC, or VS were applied to the foliage of 4.5-month-old plants and the effects on leaf expansion and content of sucrose, reducing sugars, nitrite, nitrate, ammonia, amino acid, protein and total nitrogen were determined 7, 14, and 21 days after treatment. The rate of photosynthesis and respiration and the activity of nitrate reductase, transaminase, invertase, adenosine triphosphatase (ATP-ase), glucose-1-, glucose-6-, fructose-6-phosphatase, uridine diphosphate glucose pyrophosphorylase (UDPG-pyrophosphorylase), sucrose synthetase and sucrose phosphate synthetase was measured. Compared with untreated plants, with few exceptions, all treatments affected the growth; the chemical compositions the rate of photosynthesis and respiration, and the activities of enzymes measured, in a similar manner. Growth of the plants was determined by measuring the leaf area. MH, PC, and VS significantly inhibited growth of leaves under both "summer" and "fall" conditions. In the treated plants, the percentage reducing sugars, based on fresh weight of the root, decreased and percentage sucrose increased steadily. Application of MH, PC, and VS resulted in a significant decrease in nitrite and an increase in nitrate content of roots. Ammonium nitrogen of the plants treated with MH was more than that of the untreated plants on the 7th, 14th, and 21st day after treatment. Plants reacted with PC and VS had a lower ammonium content on the 7th and the 14th day but more on the 21st day. The soluble amino acid content of the roots of MH-treated plants was higher than that of the controls. PC-treated plants had a lower amino acid content on the 7th day but a higher content on the 14th and 21st day. VS caused a reduction in amino acid content of the roots on all dates of harvest. The rate of photosynthesis was measured by infrared technique. MH and VS caused a stimulation in the rate of net C0₂ assimilation, however, PC inhibited the rate of net C0₂ assimilation on the 7th day after treatment. The rate of respiration of the storage roots, measured by the Warburg technique, was lower than that of the control plants in the case of MH-and VS-treated plants and it was higher in the PC-treated plants. The results indicated that the application of MH, PC, and VS caused significant reduction in the activity of nitrate reductase, transaminase, inver-tase, ATP-ase, glucose-1-, glucose-6-, and fructose-6-phosphatase. These treatments also resulted in the stimulation of the activity of UDPG-pyrophos-phorylase, sucrose synthetase and sucrose phosphate synthetase. The inhibition of growth by MH, PC, and VS is discussed on the bases of the reductions in the activities of invertase, nitrate reductase, and transaminase. The increase in sucrose content of the roots is explained on the bases of low invertase and high sucrose synthetase and sucrose phosphate synthetase activities in the treated plants. The possible participation of the phosphatases in the regulation of sucrose biosynthesis is indicated by the negative correlations between the activities of phosphatases and sucrose phosphate synthetase.

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