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Cytoplasmic and salt-extracted peroxidase and IAA oxidase activities were studied in Phaseolus vulgaris hypocotyls treated with gibberellic acid (GA, 200 µM), naphthyl acetic acid (NAA, 100 µM) and distilled water control (DW). Peroxidase activity was assayed with four hydrogen donors during the initial phase of hypocotyl elongation. Though peroxidase activity showed a decreasing trend with time in all the hydrogen donors studied; considerable variation with different hydrogen donors was observed. NAA had maximum peroxidase activity as compared to DW or GA treatment. The activity showed a clear inverse correlation with hypocotyl growth. IAA oxidase activity showed a similar trend with growth as peroxidase activity. A highly significant correlation was observed between peroxidase and IAA oxidase activities and high molecular weight xyloglucan content (P<0.001). Finally, the possible role of peroxidase and IAA oxidase activities in hypocotyl elongation growth is discussed.
Changes in α-galactosidase, β-galactosidase, β-glucosidase and acid invertase activities were examined in Phaseolus vulgaris hypocotyls treated with gibberellic acid (GA), naphthyl acetic acid (NAA) and distilled water (DW) (control) in light condition. The activities were estimated both in cytoplasmic and ionically wall-bound fraction. The upper segment showed considerable elongation growth while there was hardly any growth in lower segment. GA and NAA showed distinct promotion and inhibition respectively in hypocotyl growth in upper segment. The glycosidase activities were detected in both the fractions but the activity was more pronounced in cytoplasmic than in wall fraction. Acid invertase activity was present only in cytoplasmic fraction. In lower segment, in both cytoplasmic and wall fraction, the glycosidase activity, in general, showed a decreasing trend and no effect of treatment could be envisaged. In upper segment, though the trend was similar to the lower one, in α- and β-galactosidase NAA treated segment had more activity. Invertase activity also did not show a clear trend to implicate its function in hypocotyl elongation growth. The results are discussed in relation to establishing a correlation between an activity (glycosidase and invertase) and a physiological process (hypocotyl elongation). It is concluded that these wall-loosening enzymes have no role in elongation growth of Phaseolus vulgaris hypocotyls.
The effect of gibberellic acid (GA) and naphthylacetic acid (NAA) on hypocotyl elongation and cell wall polysaccharides was studied using Phaseolus vulgaris seedlings grown in light condition. The hypocotyl was demarcated into two segments — one near the root was called lower and the one near the cotyledon was called upper. The upper segment showed a typical sigmoidal growth curve while lower segment did not show any growth at all. GA promoted the growth of upper segment while NAA showed clear inhibition in both the segments. Xyloglucan content showed a clear inverse correlation with growth. Pectic polysaccharides did not show a clear trend, though showed an initial inverse correlation with growth. It is concluded that degradation of low and high molecular weight xyloglucans are involved in cell wall loosening which in turn may be responsible for the elongation growth of Phaseolus hypocotyls in light.
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