Differential response of carbon and nitrogen metabolism to fluoride application in fruiting structures of chickpea (Cicer arietinum)

The effect of sodium fluoride (10 and 50 mol.m(-3)) on the activities of su crose metabolizing enzymes, transaminases and glutamine synthetase in relat ion to the transformation of free sugars to starch and protein in the fruit ing structures (pod wall, seed coal, cotyledons) of chickpea was studied by culturing detached reproductive shoots in a liquid medium. Addition of flu oride to the culture medium drastically reduced starch content of the cotyl edons and caused a marked build-up of total free sugars comprised mainly of reducing sugars in the pod wall and seed coat, and sucrose in the cotyledo ns. Concomitantly, the activity of soluble invertase was stimulated in the pod wall but reduced in the cotyledons. However, soluble protein content of both the pod wall and the cotyledons increased in conjunction with an incr ease in the activities of glutamate-oxaloacetate transaminase, glutamate-py ruvate transaminase and glutamine synthetase. Disruption of starch biosynth esis under the influence of fluoride and the resulting accumulation of free sugars possibly resulted in their favoured utilization in nitrogen metabol ism. Labelling studies with [U-C-14]-sucrose showed that the (14)Cincorpora tion into total free sugars was enhanced by fluoride in the pod wall but re duced in the seed coat and cotyledons, possibly due to an inhibitory effect on their translocation to the developing seeds.