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Dormancy in Cereal Seeds: II. THE NATURE OF THE GASEOUS EXCHANGE IN IMBIBED BARLEY AND RICE SEEDS
Authors:MAJOR  WENDY; ROBERTS  E H
Abstract:When barley seeds imbibe water, the O2 uptake of non-dormantseeds is considerably less than that of dormant seeds for atleast the first 6 h, irrespective of the rate at which the seedshad previously lost dormancy. During the initial 6 h of imbibition, the CO2 output of dormantbarley seeds is usually only slightly greater than and sometimesno different from that of nondormant seeds. The CO2 output ofdormant seeds is reduced by about 66 percent by millimolar KCN,whereas that of non-dormant seeds is decreased by about 12–13per cent only. The CO2 output of dormant barley in nitrogenis considerably less than the CO2 output of non-dormant seedsunder the same conditions. Dormant rice seeds also show a higher initial O2 uptake thannon-dormant seeds, though this is not generally as marked asin barley. Similarly, the initial CO2 output of dormant seedsis distinctly greater than that of non-dormant seeds, but inmillimolar KCN it is depressed to a greater extent than in non-dormantseeds. In nitrogen, the CO2 outputs of dormant and non-dormantseeds were found to be the same. Consequently, unlike barley,dormant rice seeds appear to be as capable of carrying out alcoholicfermentation under anaerobic conditions as nondormant seeds. In barley, increasing the O2 tension from 21 per cent to 100per cent increased the oxygen uptake of dormant seeds more thanthat of non-dormant seeds (an increase of 53 per cent as against20–23 Per cent). In dormant seeds there was a concomitantincrease in CO2 output (about 50 per cent), but the CO2 outputof non-dormant seeds was hardly affected. High concentrations of CO2 are inhibitory to the germinationof both dormant and non-dormant barley seeds. At a concentrationof 10 per cent, however, CO2 is inhibitory only to dormant seeds,although at 2.5–5 per cent it is sometimes stimulatoryto the germination of dormant seeds. A 24–h treatmentwith appropriate concentrations of ethanol, lactic acid, oracetaldehyde is also stimulatory to the germination of dormantbarley seeds. Histochemical investigations in barley indicated the presenceof peroxidase, cytochrome oxidase, and {alpha}-glycero-phosphate dehydrogenasein the embryo, aleurone layer, and in a layer associated withthe testa. A number of other redox enzymes were detected inthe embryo and aleurone layer only. No differences in distributionor intensity of activity were detected between dormant and nondormantseeds.
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