Studies on the Regeneration of Apple Cultivars from Root Cuttings. II. Carbohydrate and Auxin Relations

Abstract

The effects of endogenous carbohydrate and auxin levels on shoot regeneration from apple root cuttings were studied in relation to season. Storage polysaccharides were estimated by periodate oxidation following organic acid hydrolysis. Maximum accumulation occurred in autumn (November) coinciding with the highest regeneration potential and survival rate of cuttings. Cold storage of cuttings (5°C) increased soluble sugars and subsequently accelerated callusing and shoot production. During regeneration polysaccharides were gradually depleted, whereas soluble sugars remained constant at their initial level (1–2 g/10 g residual dry weight). Cuttings started rotting at a polysaccharide level of approximately 3 g/10 g RDW. Fluorimetrie assay of endogenous IAA confirmed that auxin was directly involved in correlative inhibition of bud initiation and outgrowth. IAA moved rapidly and acropetally within detached root cuttings causing depletion and allowing preferential bud initiation to occur at the proximal end. IAA levels were lower in roots during autumn/winter than in midsummer (150 and 750 ng/50 g fresh wt respectively for Lambourne). In summer the IAA content of scion roots (Lambourne) was 3–4 times as high as in rootstock roots (M.26); however, storage carbohydrate in Lambourne in the autumn was only one-third as much as in M.26 which correlates with the greater survival and regenerative capacity of the latter.