| It is well known that PI 4169347 is an Al-tolerant soybean genotype. In our experiment results, it is further estimated that Al-induced citrate secretion is one of the most important Al-tolerant mechanisms in soybean. During the 12 hour Al treatment period, the amount of citrate secretion increases with increasing concentration of Al (0-50 uM). When citrate is inhibited by A9C, PI 416937 has obvious Al toxic phenomena.The usual anion channel blockers, A9C, PG and DIDS are used to investigate the mechanism of citrate efflux in soybean. The different concentration of one inhibitor may have different effects on Al-induced citrate secretion, so we design several concentration gradients in experiment. Among them, A9C (10, 20, 30 μ M ) strongly inhibits Al-induced citrate secretion, both PG (5, 10, 20, 30) and DIDS (5, 10, 20, 30) have no obvious effect on the citrate efflux under Al stress. In the 12h treatment period, we can not detect any citrate in the treatments of -AH-10 μ M A9C -Al+10 μ M PG and -Al+10 μ M DIDS. So, we speculate that Al-induce citrate secretion via the opening of citrate-permeable anion channels of Al-tolerant soybean roots. Three blockers have different effect on the citrate-permeable anion channel studied in our experiment.ABA is the known signal substance in the adversity and can modulate the S-type anion channel situated in the guard cells. In our experiment, we can not detect any citrate secretion in the treatment of external 5,10, and 15 μ M ABA. However, the amount of citrate secretion in the treatment of+A1+5 μ M ABA almost double that of the treatment of +A1. ABA obviously stimulates the Al-induced citrate secretion. So, we speculate that ABA is the possible signal substance between Al stress and citrate secretion. This conclusion need to be further studied and estimated.Citrate is synthased in mitochondria, so how it is transported out of mitochondria is very important for its efflux. Mersal, PP and PITC are known citrate carrierinhibitors. Mersal is specific to the -SH of Cys and, PP and PITC to Lys. In the 12h treatment period, Mersal (5, 10 # M) can strongly inhibit Al-induced citrate secretion, however, higher cone. Mersal increase the citrate efflux compared with the above treatments, which may be caused by the toxic effect of Mersal on membrane structure. PP (1, 5, 10 u M) has no obvious effects on Al-induced citrate secretion. In the 12h, we can not detect citrate in the treatments of-Al+10 u M Mersal and -Al+10 # M PP. It is doubtful that the soybean seedlings above ground express very obvious stress phenomena when treated soybean roots with PITC contained or not Al. So PITC has so much toxic effect on soybean that it loses its significant meaning as a citrate carrier inhibitor in our experiment. So, we can conclude that citrate carrier functions in transporting citrate synthased in mitochondria to protoplast, which facilities its efflux to rhizospere. Moreover, Cys is possiblely included in the citrate carrier. We can not determine if Lys is contained in the carrier.In our experiment, we detect the amount of citrate by RP-HPLC. |
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