| Abstrakt: |
Depending on the species coppicing (decapitaiton) may promote vigorous growth (Eucalyptus camaldulensis Dehn), or cause rapid senescence and death (Eucalyptus obliqua L' Herit). In seedling of the latter species, the presence of a small upwardly directed shoot on the decapitated stump prevents or delays decline. Coppiced seedlings of E. camaldulensis and E. obliqua, with and without a remaining shoot, were analyzed for starch and soluble sugars (with the anthrone method), gibberellin-like substances (GAs) and cytokinin-like substances (by bioassay), and ethylene (by gas-liquid chromotography) before and after decapitation. Levels of soluble sugars declined similarly in both varieties of eucalypts, and starch reserves appeared adequate for sprouting, and did not diminish following decapitation of the susceptible species. Decapitation did not markedly alter the relatively high amounts of GAs in roots and shoots of E. obliqua, the susceptible species, although increased levels of GAs were observed in the stumps of seedlings left with 1 shoot after decapitation. The overall levels of GAs were relatively low in the roots and stems of the resistant E. camaldulensis but higher in the shoots. Marked qualitative changes in GAs with decapitation were apparent in the shoots of E. camaldulensis. A single major GA peak occurred prior to decapitation but after decapitation several additional peaks of GA-like activity appeared. Cytokinin-like activity was initially low in all tissues, but increased dramatically in stump and shoot tissue following decapitation. Increase ranged from approximately 5-fold (stump tisue of either species, minus-shoot treatment) to approximately 40-fold (shoot tissue of the resistant E. camaldulensis seedlings left with 1 shoot). In both E. Camaldulensis and E. obliqua ethylene production increased to a peak 7 days after decapitation provided a shoot had been retained. This ethylene peak precedes a marked upturning of the retained shoot, and was present in the stumps of totally decapitated seedlings. For totally decapitated seedlings ethylene evolution in E. obliqua (the susceptible species), but not E. camaldulensis (the resistant species), had ceased by 15 days. [ABSTRACT FROM AUTHOR] |
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