Arrested Leaf Abscission in the Non-Abscising Variety of Pubescent Birch: Developmental,Morphological and Hormonal Aspects

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Abstract
A novel type of abscission development, arrested abscission, is described for a rare variety of pubescent birch (Betula pubescens Ehrh. f. hibernifolia Ulvinen), the leaves of which dehydrate and remain attached to the plant. Anatomical examination of the abscission zone revealed that its development is temporally and spatially similar to that of normal leaves of Betula pubescens.Flooding and exogenous ethylene were effective in inducing shedding of the leaves at the beginning of the growing season, butthis effect was lost in senescing leaves. Leaf hydration and abscission were retained in the presence of external abscisic acid (ABA)in the non-abscising variety, which also had a lower level of endogenous ABA. The observed responses together with the alteredhormonal level in this variety suggest that apart from ethylene, ABA is involved in autumnal abscission indirectly by regulatingthe leaf water status.

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