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Growth and biochemical responses of the tomato (Lycopersicum esculentum var. Bonny Best) to K naphthenates Chu, Soong-ming

Abstract

Recent reports, especially those of Russian scientists, have emphasized that application of stimulatory concentrations of naphthenates (Naps) induced greater and better growth and productivity of a number of species of plants. This stimulatory action of Naps has been found to result from seed soaking and spraying seeds or developing plants once or repeatedly. However, no systematic attempt has so far been made to investigate physiological and biochemical changes induced in a relative short period following immediately these treatments. A correlation of such changes with final improvements in growth and yield may provide a better understanding of the mechanism of action of Naps It was therefore essential and significant to investigate these aspects. Seeds of tomato (Lycopersicum esculentum var. Bonny Best) were germinated in wooden flats containing sterilized soil and were transplanted when 10 days old to plastic pots of 6 inche diameter containing sterilized soil. The plants were grown in a growth room. In separate experiments, potassium naphthenate (KNap) aqueous solutions, 2,500 ppm and 5,000 ppm, were sprayed onto tomato leaves when plants were 2, 3, and 4 weeks old. Measurements of vegetative growth, based on fresh and dry weights of plant tops, indicated that maximum stimulation was induced by the 5,000 ppm KNap solution applied to plants when 3 weeks old. It was then decided to investigate the biochemical and physiological responses of the tomato plants to 5,000 ppm KNap when treated at the age of 3 weeks. Determinations of pigment content, intensities of photosynthesis and respiration, activity of enzymes involved in nitrogen metabolism, such as nitrate reductase (NRase) and glutamic-pyruvic transaminase (transaminase), and of enzymes involved in carbohydrate metabolism, such as succinic dehydrogenase, phosphorylase, and phosphoglyceryl kinase were made three times at 2-week intervals, beginning 2 weeks after the spraying. Number and fresh weight of tomato fruits, quality of tomato fruits in terms of sugars, titratable acidity and ascorbic acid were also investigated at scheduled intervals. Results indicated the following: (1) In the treated plants, the content of the pigments chlorophyll a and b, and especially carotenoid, in the leaf blades was higher than in control plants, (2) Measurements made with intact plants using an infrared CO₂ analyzer revealed increases in intensities of photosynthesis and respiration of the aerial portions 4 weeks after treatment but the opposite was true 2 weeks after treatment, (3) Under the influence of KNap, of the 5 enzymes examined only phosphorylase activity was found to be stimulated at all three observation times. Transaminase activity was greater 6 weeks after treatment. Activities of succinic dehydrogenase, NRase, and phosphoglyceryl kinase were all reduced by treatments, (4) In a subsequent experiment, leaf blades of plants treated when 2 weeks old were analyzed for succinic dehydrogenase activity 4, 8, 12, 16, 20, and 24 days after spraying. The effect on succinic dehydrogenase activity fluctuated with the age of the plant. Parallel changes in the protein content of the enzyme extract could not be detected, (5) Tomato fruit yield, based on number and fresh weight, was decreased by 2,500 ppm KNap treatment but increased by 5,000 ppm KNap. In addition, 5,000 ppm KNap-treated plants were more resistant to blossom-end rot and showed better and quicker recovery when the deficiency disease was treated with CaCl₂. Earlier maturity was found in 5,000 ppm KNap-treated plants, (6) The mature tomato fruits from 5,000 ppm KNap-treated plants contained larger amounts of sugars (reducing sugar and sucrose) than the controls, and the sugars in mature tomato fruits were lost at a lower rate during the storage period. The treatment resulted in decreased titratable acid and ascorbic acid content. It afforded no protection against loss of titratable acid and ascorbic acid during storage.

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