| Discussion The results of the present study corraborate the classical finding of VAN OVERBEEK (1935). Thus the tall variety C-306 possessed more IAA-like promotors than the three dwarfs. BHARDWAJ & DUA (1974) also reported similar results. The overall changes in IAA-like promoting or inhibiting substances did not commensurate with growth pattern. A similar report was published by MURAKAMI (1961). It is not necessary also that growth changes should correlate with hormonal changes, since altered tissue response might have resulted in the presence of other growth substances, inhibitors, physiological age of tissue etc. (MCCOMB & MCCOMB 1970). That may probably be how, the varieties exhibited different GA responsiveness. Effect of gibberellic acid on IAA-like promotors indicated a considerable enhancement in C-306 and Kalyansona, a mild increase in Sonalika and an adverse effect in Moti the triple dwarf variety. The present study thus confirms the earlier report of KEFFORD & GOLDACRE (1961), if the former three varieties are considered. In certain instances gibberellic acid has been reported not to affect endogenous IAA content (CLELAND 1969) but the results of Moti do not fall in line with this either. It became amply clear from this investigation that GA induced growth in wheat is auxin mediated, contrary to earlier conviction (RIZVI & SIROHI 1974). However, the way the gibberellin control auxin level is a controversial one. The most accepted view is that gibberellin influence oxidative or proxidative enzyme activity resulting a decrease in IAA degradation or an increase in IAA synthesis (PALEG 1965). The authors have reported GA3 induced decrease in polyphenol oxidase activity in the varieties presently undertaken (KUMAR et al. 1981) which probably could account for the increase in IAA level in C-306, Sonalika and Kalyansona but not in Moti. It may further be noted that IAA content increased in those varieties which showed GA induced protease activity (KUMAR et al.1982) and catalase activity (KUMAR et al. 1981). This could reflect a relationship of IAA synthesis from tryptophane. The later being made available as a result of proteolysis and the catalase indicating the interconversions in amino acids (BALDWIN 1963) either of which was not observed in Moti. KUMAR & BAIJAL (1984) opined that some proteinaceous inhibitor/antagonist might be involved in triple dwarf Moti which checks the expression of GA induced activity of several enzymes and consequent metabolic pathways including probably that of IAA too. Thus the complex interaction between exogenously applied GA, abnormal protein metabolism and IAA-like substances suggests that they are associated with GA insensitivity and dwarfism in wheat, albeit indirectly. |
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