Physiological and biochemical studies on germinating seeds

Abstract

Tritiated water has been used as the aqueous medium for the germination of irradiated Sinapis alba seeds (white mustard). The results show that heavily irradiated seeds can carry out active metabolism, leading to the formation of tritiated γ-aminobutyric acid (GABA), alanine, malic acid and citric acid. This metabolism does not lead to the formation of a seedling in those seeds which received a dose of 2.98 Mrep and above. The compounds which are not labelled in heavily irradiated seeds but which are labelled in non-irradiated seeds are the following: lactic acid, glutamine sucrose, glutamic acid, aspartic acid, and sugar phosphates. Recovery has been shown to occur by both physiological and biochemical tests, after storage under moist conditions but not after storage under conditions of low relative humidity. These results have been attributed to the inactivation of a cofactor necessary for the many biochemical reactions which have been shown absent in the irradiated seeds. A possible explanation in terms of the "poison theory" has also been discussed. This radiation-induced secondary dormancy could be a useful method for the storage of seeds which would normally lose their viability after a short period of storage. A metabolite tentatively identified by earlier workers as fructose has been shown to be sucrose. The reaction of the labelled compounds, tentatively identified as sugar phosphates, with alkaline phosphatase has been examined. Mustard seeds have bean shown to possess the ability to germinate in the dark. Unlike lettuce (Lactuca sativa L., Grand Rapids) seeds the absence of red light does not prevent germination although previous workers had classified Sinapis alba seeds as being light-requiring. Germination of seeds at low temperatures has been examined and has been correlated to the rate of formation of water in the Electron-Transport System. An increased partial pressure of oxygen increases the rate of this reaction and hence the rate of germination. For wheat, oat and cress seeds at 2°C, the higher the oxygen concentration the more rapid was the rate of germination and the higher the total percentage germination after 100 days. Yates ornamental corn will germinate at 0°C under pure oxygen but will not germinate in air at the same temperature. Literature reviews on the dormancy of seeds, germination, the effects of γ-radiation and germination at low temperatures are included.