STUDIES ON THE EFFECT OF CHEMICAL AND ENVIRONMENTAL FACTORS ON GREENING AND SOLANINE ACCUMULATION IN POTATO TUBERS

Chlorophyll and solanine production was followed in light-exposed tubers of Solanum tuberosum c. v. King Edward. A significant correlation was found for the two events in this and sixteen other varieties. An ultrastructural survey demonstrated the green tubers to contain two types of chloroplast, although a TLC analysis showed the photosynthetic pigment complement to be comparable to that found in leaves. The effects of chemicals known to interact with chloroplast development and function were observed in changes in greening and solanine production. Chloramphenicol, a known inhibitor of chloroplast development in leaf systems, was found to block both greening and solanine synthesis in tuber discs whilst inhibitors of photosynthesis, Monuron and Simazine only blocked solanine production. Gibberellic acid and Nicotinic acid, which are thought to affect sterol metabolism directly, were also found to interfer with solanine production. The effect of potassium status of the soil on the greening potential of the tubers was assessed. Although large differences in edaphic potassium produced only small endogenous differences, those with higher potassium levels produced greater amounts of both chlorophyll and solanine. However, no positive correlation could be proved between endogenous potassium levels and greening in 17 potato varieties. The relevance of these results to the control of greening potential via cultural practices is discussed. The possible ways in which chlorophyll synthesis and solanine production are linked are assessed with particular emphasis on the ways in which developing chloroplast in light exposed tubers could support increased levels of solanine production.The John Innes Institute, Norwic