Abstract
Aluminium is a potent toxicant in acidic soils. The present study was taken up to analyze the effects of Al on enzymes of nitrogen assimilation in excised bean (Phaseolus vulgaris) leaf segments so as to gain an insight of the mechanism involved. Supply of 0.001 to 0.1 mM AlCl3 to excised bean leaf segments affected the in vivo nitrate reductase activity differently in the presence of various inorganic nitrogenous compounds, being inhibited with 5 mM ammonium nitrate and 10 mM ammonium chloride but enhanced with 10 mM potassium nitrate. Al effect with 50 mM KNO3 varied with time, showing an increased activity at shorter duration, but decreased at longer duration. Al effect on in vivo NRA was dependent upon the nitrate concentration, thus, inhibiting it at 0, 1 and 50 mM KNO3, while increasing at 2 and 10 mM. Further, saturating and non-saturating effects were observed in the absence and presence of Al. Al supply influenced the in vitro NRA also, being increased at 10 mM, but decreased at 50 mM KNO3. Supply of Al to excised leaf segments substantially inhibited the glutamate dehydrogenase activity in the absence as well as presence of 5 mM NH4NO3 but increased the glutamate synthase activity. Inhibition of specific glutamate dehydrogenase activity by Al supply was also observed. However, specific glutamate synthase activity was increased in the presence of NH4NO3 only. The experiments demonstrated that effect of supply of aluminium on in vivo nitrate reductase activity depended upon nitrogenous source as well as nitrate concentration and it exerted reciprocal regulation of glutamate dehydrogenase and glutamate synthase activities, which depended upon N supply too.
Highlights
Aluminium (Al), one of the most abundant metals, is not regarded as an essential nutrient for plants, but low concentrations can sometimes increase plant growth or induce other desirable effects [1]
Of 0.001 to 0.1 mM AlCl3 to excised bean leaf segments in the presence of 10 mM KNO3 gradually increased in vivo nitrate reductase activity (NRA) (Table 1)
Of 0.1 mM Al in the presence of 50 mM KNO3 for short interval up to 4 h maintained a higher level of in vivo NRA over control ranging from 15% to 36% (Figure 1)
Summary
Aluminium (Al), one of the most abundant metals, is not regarded as an essential nutrient for plants, but low concentrations can sometimes increase plant growth or induce other desirable effects [1]. When applied along with ammonia, it has been reported to promote growth in tropical plants adapted to acid soils [2]. Beneficial effects of Al on plant growth have been reported in Camellia sinensis [3], Miconia albican Steud [4] and Pinus radiata D. Aluminium is one of the most toxic metals for plant growth in acidic soil. Several phytotoxic effects of aluminium have been reported including the inhibition of root growth and nutrient uptake; the mechanism is not well understood [7]-[9]. Aluminium causes significant decline in the leaf area, fresh weight and dry weight [10]
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