| Discussion Reports on the tannin effecting plant growth and development are often inconsistant. Root growth (EVANARI, 1949 ; HAPPICH et al. 1954) and germination (CORCORAN, 1970) may be inhibited or enhanced, seedling growth may also be affected (POPOFF, 1931). The plumule growth in the four wheat varieties, undertaken in the present study, was diversely affected by applied tannins. HARADA & NAKAYAMA (1974) observed this phenomenon in certain rice cultivars and ascribed it to endogenous tannin's level. The gibberellin induced growth was also affected due to tannins application. The finding corraborates that of CORCORAN et al. (1972) and GREEN & CORCORAN (1975). They established the tannins as inhibitory to GA induced growth and stressed their role as antagonist to GA action and by increasing the concentration of GA, they could restore the tannin depressed growth. In the present course also, the GA tends to restor (in certain cases it has actually done so) tannin depressed growth. However, the two cases may be different, since this investigation proved tannins to be inhibitory and/or promotory to endogenous growth too, besides GA3 induced growth. Thus it lent credence to the idea that tannins are involved in the normal control of the plant growth and that both GA and tannins are involved in the same physiological system. The exact mechanism of inhibition by tannins is still an enigma. PALEG (1965) suggested possible pathways in which GA antagonist could act. GREEN & CORCORAN (1975) pointed out that tannins could act as GA inhibitors by acting as protein inhibitors. But they can not be considered general protein inhibitors, firstly because of protein specificity and secondly, if the inhibition would be there, the GA application would not restore the depressed growth. It was further emphasised that antagonistic action of tannins probably does not involve GA synthesis (GREEN & CORCORAN 1975) which holds true here also, otherwise GA induced growth should not have been affected. Possibility of tannins as competitive inhibitors of GA can also be ruled out because of the dissimilarity in the chemical structure of the two group of substances. There is one possible mechanism 'that is' the tannins could act as an inhibitor of a protein which specifically recognises gibberellins to rander it incapable of promoting growth. But in any case, the exact mechanism of inhibition by tannins is by no means completely understood. An interesting point emerged out the study was that the triple dwarf Moti which is an insensitive variety to applied GA responded well to tannins and exhibited further enhancement in growth when GA was supplimented with tannins. It appears that tannins application made this variety sensitive to applied GA. Thus response of the Moti to GA in the presence of tannins seems abstruse. It has been pointed out by the authors (KUMAR 1977 ; KUMAR & BAIJAL, 1983) that non-responsiveness of this dwarf variety with respect to growth and protease activity involves some natural inhibitor which is probably produced due to altered gene action. GALE & LAW (1976) opined that in certain insensitive dwarf wheat, genes could act via the production of a GA-antagonist which must operate at the active site of GA action and not on the GA molecule itself. STODDART et al. (1974) and KOMOTO et al. (1973) reported some protein fraction from dwarf peas that selectively binds with biologically active GA's making it inactive. In the light of foregone discussion, it would appear that the two phenomenon have an unexpected corrollary and it might be possible that tannins action also involves the same fraction of protein which renders GA incapable of its activity. It is likely that in the presence of exogenous tannins, the GA is somehow released free and then both the substances act in their own way. That is probably how proteins are associated with GA and tannins which is turn determine the physiology of dwarfism. |
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