Water Relations of Beetroot Seed Germination II. Effects of the Ovary Cap and of the Endogenous Inhibitors

Abstract

Conditions in which seeds of beetroot (Beta vulgaris L.) will germinate are relatively narrowly limited by a deficient or an excessive water-supply. The ovary cap, which covers each seed situated within its locule in the seed cluster, has been shown to be responsible, under wet conditions, for preventing access of oxygen to the embryo, owing to its imperviousness to gas and to the production of mucilage around its rim in the presence of excess water. Seeds in intact clusters germinate in the wet if the oxygen pressure is increased. Removal of the ovary cap enables seeds to germinate even under water. Preliminary washing of the clusters increases germination under dry conditions, owing to the elimination from them of an endogenous water-soluble germination inhibitor complex. Washing also improves germination under wet conditions ; and measurements of oxygen uptake suggest that the dilute inhibitor may further depress the respiration already obstructed by the ovary cap. Conversely, removal of the ovary cap appears to have the same effect as eliminating the inhibitor complex. Depressed germination is usually correlated with depressed oxygen uptake of the imbibing seeds but an exceptionally high concentration of inhibitor can uncouple respiration. The production of beetroot seeds with a low level of inhibitor in the cluster material and with loose and non-mucilaginous ovary caps, or the washing and drying of clusters prior to sowing should widen the range of moisture conditions over which beetroot seeds are able to germinate.