ACCUMULATION OF L-ASCORBIC-ACID IN TUBERISING STOLON TIPS OF POTATO (SOLANUM-TUBEROSUM L.)

Swelling stolen tips (diameter >2 mm) and small developing tubers of u p to 7.5 mm diameter from glasshouse-grown potato plants (cv. Desiree) contained 5-7 fold more L-ascorbic acid (AsA) compared with non-swell ing stolen tips (diameter <2 mm). Similarly, when single-stem cuttings of potato (cv. Bintje) were cultured on tuber-inducing medium, a 10-f old accumulation of AsA occurred between day 6 and day 7, 1 day after the synchronous tuberisation of the shoots originated from the cutting s. No accumulation of AsA was observed in cuttings cultured under non- permissive conditions for tuberisation. The precursor L-galactono-gamm a-lactone (GL) was rapidly converted into AsA by isolated tissue from leaves, stems and tuber and by non-swelling stolen tips. Inclusion of GL in the culture medium of potato cuttings induced a large accumulati on of AsA in the tissue, proportional to the concentration of GL in th e medium, but did not affect the timing of tuberisation or tuber morph ology. It is concluded that AsA is not a tuberisation-inducing compoun d but its presence in high concentration is required for specific proc esses associated with the tuberisation event.