STUDIES ON COLCHICINE-INDUCED AUTOTETRAPLOID BARLEY.: III. PHYSIOLOGICAL STUDIES

THE MORPHOLOGICAL and cytological characteristics of some colchicine-induced autotetraploid barley plants have been given in the previous paper of this series. The present account reports some physiological characteristics of these tetraploid plants. RESPIRATION. -Oxygen consumption and carbon dioxide production by the germinating seeds of 2n and 4n barley were measured by means of the microrespirometers of Warburg as used by one of us in previous measurements of respiration in germinating seeds (Tang, 1931). Seven dehulled seeds which had been germinating at 240C. for 36 hours were placed in the main portion of the respirometer vessel. The inset contained 0.2 ml. 10 per cent NaOH when oxygen consumption was to be measured, and water when cazrbon dioxide production was to be measured. Two respirometers were run at a time beside the thermobarometer, one for the 2n seeds and the other for the 4n seeds. The experiments were performed at 180, 240 and 280C. At the end of the experiments the seeds were ground and dried to constant weight and their nitrogen contents were estimated by micro-Kjeldahl. Table 1 gives the rates of 02-consumption and C02-production of the germinating seeds of the 2n and 4n barley plants used. It is seen from this table that both the rates of 02-consumption and C02-production of the 4n seeds were lower than those of the 2n seeds, whether expressed in terms of dry-weight or of nitrogen content. Taken as a whole, the respiratory quotients of the 4n seeds were found to be lower than those of the 2n seeds. 1 Received for publication September 14, 1944. Manuscript received through the Department of State, Washington, D. C. , and published under a special ruling of the Editorial Board. The R.Q. values for both kinds of seeds, however, changed with temperature, agreeing with a previous observation to this effect in Lupinus albus(Tang, 1932). The values of the temperature quotients for 02-consumption were different in the two cases, being 3.4 for the 2n seeds and 2.8 for the 4n seeds. That the lower rate of respiration in the 4n seeds is an inherent characteristic of the cells, and not due to the fact that they may contain less living matter in proportion to the reserve materials is shown by the following experiment. The embryo and endosperm were separated from each other in one hundred 2n and one hundred 4n seeds. The two portions were dried and weighed separately. No difference was found in the ratio of weight of embryo to weight of endosperm in the two types of seeds. TRANSPIRATION. -The rates of transpiration of 55-day-old 2n and 4n barley plants were measured by means of simple potometers. Seven 2n and an equal number of 4n plants, all at the 4-leaf stage, were used, each placed in a separate potometer. The experiment lasted from noon to 10 P.M. , at the end of which the leaf area and dry weight of the seedlings were ascertained. The average amount of water transpired by the seven 2n seedlings during the 10 hours of exposure was 0.38 ml. per square centimeter of leaf area. That for the seven 4n seedlings was 0.26 ml. per square centimeter. This difference becomes more apparent when the rate is expressed in terms of ml. transpired per unit dry-weight. In that case, the respective values become 78.3 ml. per gm. and 38.8 ml. per gm. OSMOTIC, CONCENTRATION AND SUCTION PRESSURE.