Abstract:
The germination of wheat kernels, Triticum aestivum cv. Betta, occurred optimally at a temperature of 28°C, while germination was inhibited at the supra-optimal temperature of 40°c. The rate of water uptake increased with temperature, and it was concluded that the effect which temperature had on germination could not be attributed to an insufficient rate of water uptake. The respiratory metabolism, one of the most frequently used criteria for the determination of the metabolic state of seeds, was then investigated. The rate of oxygen uptake and carbon dioxide emission by intact kernels increased with temperature. Closer examination of gas exchange by embryonic axes, indicated that the rate of oxygen uptake was slightly lower at 40°C, in relation to that at 25 °C. The rate of oxygen uptake by the endosperm and associated tissues, increased with temperature over the 25-40°C range. Gas exchange could have emanated from systems other than respiratory metabolism. The rate of residual oxygen uptake was found to increase slightly with temperature, but was only a minor contributor to the total rate of oxygen uptake of wheat kernels. Mitochondrial oxygen uptake of isolated embryonic axes, endosperm tissues and whole kernels, were not restricted to such an extent that it could be suspected to be the cause of reduced germination at supra-optimal temperatures. As the rate of mitochondrial oxidation was found to increase with temperature, a greater amount of energy was probably required for germination than would be the case under normal conditions. A linear increase in ATP content and total adeny late content was found by subjecting seeds to temperatures ranging from 25 to 40 ° C. It would therefore seem that the energy supply was adequate at 40°C, and failure of wheat to germinate at this temperature was probably not due to the disruption of the energy metabolism. In conclusion, 40°C inhibited wheat kernel germination, but not respiration. The high rate of oxygen uptake observed at 40°C, is probably related to a higher ATP production in order to satisfy a higher energy demand for germination processes at 40 ° C compared to that at 25 °C.
