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Growth and metabolic responses of the bush bean to potassium naphthenates Fattah, Quazi Abdul

Abstract

Recent investigations have shown that application of appropriate concentrations of naphthenate induces greater growth and yield of several crop plants. However, reports are lacking on the effect of naphthenate on plants grown under various temperature and light conditions and also on physiological and biochemical changes induced in bush bean (Phaseolus vulgaris L.Var. Top Crop) plants following naphthenate treatment. In the course of the present work the following aspects were investigated: 1) juvenile growth, as measured by fresh and dry weight of roots, stem and leaves, number and area of leaflets and plant height; 2) reproductive growth, as measured by flower number, number and fresh weight of pods, and number and weight of dry seeds; 3) chemical composition, such as moisture content of roots, stem, leaves, and pods, chlorophyll and carotenoid content of leaves, ascorbic acid content of green pods and loss of ascorbic acid by pods during storage for five days, and 4) such physiological and metabolic changes as rates of apparent photosynthesis and dark respiration, activities of the enzymes nitrate reductase, glutamic-pyruvic transaminase, phosphorylase and phosphoglyceryl kinase. Subsequent to KNap treatment, plants in some experiments were grown in growth rooms provided with 26°/26°, 26°/21° and 15°/15°C, day/night temperature. At 26°/26° and 15°/15° plants were grown under three different light intensities, 1500, 1000 and 500 ft-c. The results revealed that: (1) treatment with KNap resulted in increases in plant height, number and area of leaflets, fresh and dry weight of roots, stem and leaves, and total chlorophyll content in leaves; (2) measurements made with intact plants using an infrared CO₂ analyzer revealed increases in rates of apparent photosynthesis and dark respiration in treated plants; (3) the activity of the four enzymes mentioned was stimulated in plants treated with KNap; (4) increases in number and fresh weight of green pods, number and weight of seed were observed in treated plants; (5) treatment resulted in higher ascorbic acid content in green pods at harvest and the treatment had a protective action on ascorbic acid loss during storage. Different plant organs were found to respond differently to treatment depending on temperature and light intensity in which the plants were grown. The maximum relative stimulatory effect of KNap treatment was found mostly at 26°/21° and it was followed by 26°/26° and 15°/15°, in plants grown under a light intensity of 1500 ft-c. Plants grown at 26°/26° showed maximum relative stimulation in most instances in high light. The maximum relative stimulation for plants grown at 15°/15° was in medium light generally speaking. In proposing a physiological and biochemical basis for the stimulation of growth and yield following KNap treatment, the following points may be emphasized: (a) the stimulated rate of photosynthesis produced a larger amount of photosynthate which could be utilized in the biosynthesis of all cell constituents and serve as substrate for respiration and other chemical processes; (b) the stimulated rate of respiration and activity of phosphoglyceryl kinase resulted in an increased supply of available energy, as ATP and reduced nucleotides, for biosynthesis; (c) the augmented supply of amino acids resulting from the greater activity of nitrate reductase and transaminase would be favorable for enhanced synthesis of protein, evident in stimulated growth.

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