GERMINATION, GROWTH, AND RESPIRATION OF RICE AND BARLEY SEEDLINGS AT LOW OXYGEN PRESSURES

Abstract

On the other hand, it is a common agricultural practice to germinate rice seeds in standing water 1 to several centimeters in depth. This behavior of rice has been observed on several occasions but with one recent exception, no attempt has been made to establish the oxygen relations of germinating rice on a quantitative basis. In an exhaustive review of the literature on oxygen relations of plants (6), the general effects on the respiration of a wide variety of plants show an independence of oxygen until a partial pressure of 2 per cent, oxygen is reached. Below this point a very sharp decline follows in respiration, measured in most experiments by carbon dioxide production. Mack (?) germinated wheat seeds aerobically and after 42 hours transferred the seedlings to 12 different oxygen tensions ranging from 0.6 per cent, to 98.3 per cent, and covering five temperatures from 10? C. to 30? C. at 5 degree intervals. The carbon dioxide evolved was measured at several intervals within a 46-hour period and the shoot lengths determined at the end of this time. The anticipated inter-dependence of temperature and oxygen was found. The respiration curves for each of the 3 highest temperatures, oxygen taken as the variable, assume parallel shapes differing only as to absolute values. The effect on shoot growth is greater than that on respiration in response to temperature change, and to oxygen at the lowest pressures. The maximum in respiration occurs uniformly at 30? C, and the shoot growth attains a maximum between 20? and 25? C. Takahashi (11) germinated rice in oxygen-free water but growth was limited to a small amount of plumule development which ceased after reaching a length of 3 cm. Yokoi (14) likewise obtained only shoot growth of rice under water, and in sand cultures the relative growth of the radicle increased at the expense of the shoot as the water content of the sand declined. These observations have been repeated by Nag ai (10). The germination of rice on the surface of submerged soil has been found to be superior to that of seeds placed below the soil (5). The catalase activity in barley, wheat, and rice has been compared in aerobic and anaerobic atmospheres (7). The catalase activity was shown to