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

Conditions in which seeds of beetroot (Beta vulgaris L.) willgerminate are relatively narrowly limited by a deficient oran excessive water-supply. The ovary cap, which covers eachseed situated within its locule in the seed cluster, has beenshown to be responsible, under wet conditions, for preventingaccess of oxygen to the embryo, owing to its imperviousnessto gas and to the production of mucilage around its rim in thepresence of excess water. Seeds in intact clusters germinatein the wet if the oxygen pressure is increased. Removal of theovary cap enables seeds to germinate even under water. Preliminarywashing of the clusters increases germination under dry conditions,owing to the elimination from them of an endogenous water-solublegermination inhibitor complex. Washing also improves germinationunder wet conditions; and measurements of oxygen uptake suggestthat the dilute inhibitor may further depress the respirationalready obstructed by the ovary cap. Conversely, removal ofthe ovary cap appears to have the same effect as eliminatingthe inhibitor complex. Depressed germination is usually correlatedwith depressed oxygen uptake of the imbibing seeds but an exceptionallyhigh concentration of inhibitor can uncouple respiration. The production of beetroot seeds with a low level of inhibitorin the cluster material and with loose and non-mucilaginousovary caps, or the washing and drying of clusters prior to sowingshould widen the range of moisture conditions over which beetrootseeds are able to germinate.