Researches on plant respiration IV— The relation between the respiration in air and in nitrogen of certain seeds during germination, (b) seeds in which carbohydrates constitute the chief food reserve

Abstract

The katharometer method of Stiles and Leach was used to measure the respiration at 25[degree] C of the germinating seeds of Fagopyrum escu-lentum, Zea mais and Lathyrus odoratus. Transference of germinating seeds of Lathyrus from air to N resulted in an initial lowering of CO2-output to 1/4-1/2 its normal value. Extrapolation of the curves to cover the moment of transference gave ratios of CO2 in nitrogen (NR)/CO2 in oxygen (OR) between 0.31 and 0.37. During anaerobiosis, CO2 output rose to a maximum, subsequently fell. Subsequent aerobiosis produced a sharp rise, with a falling R.Q., a temporary fall in CO2-output, and finally a rise to about the normal value, with an R.Q. approaching unity. Similar results were obtained for Zea and Fagopyrum seeds, except for the absence of the fall in CO2-output during the post-anaerobic period. The NR/OR values at the moment of change from air to N were lower, varying from 0.17 to 0.29. The value of 0.33 for NR/OR, to which Fagopyrum approximates, is the expected value for the change from complete oxidation of hexose to water and CO2 in air to anaerobic breakdown to CO2 and alcohol. So that the aerobic respiration is equivalent to the glycolysis and no oxidative anabolism occurs. It is suggested that the departure of NR/OR from 0.33 in Lathyrus and Zea is due to the difficulty of correctly extrapolating the curves, and that for all 3 seeds the following sequence of events occurs: the change to N changes the course of oxidation of hexose, with a consequent reduction in CO2 output. With oxygen excluded, some process which results in the freeing of CO2 comes gradually into action. Since its activity declines after reaching a maximum, it is probably acting on some substrate for whose formation oxygen is necessary, and which gradually is used up during anaerobiosis. The sudden increase in CO2 output on subsequent aerobiosis is attributed to the accumulation during anaerobiosis of some easily oxidizable substance. In the fat-storing seeds of Cucurbita, Helianthus and Ricinus, NR/OR has values greater than 0.33, so that in these some oxidative anabolism may occur.