Analytic studies in plant respiration VII—Aerobic respiration in barley seedlings and its relation to growth and carbohydrate supply

Abstract

Preliminary to a study of seedling respiration as affected by varying concentrations of oxygen, some sets of experiments were carried out in air as a standard oxygen medium. In these experiments growth was also measured and the relation between the rates of these two processes was determined. The major features of the carbon metabolism in the young seedling are, (1) hydrolysis of starch in the endosperm, (2) formation of new dry matter in the embryo by growth, (3) respiration of carbohydrates to carbon dioxide and water in both endosperm and embryo. By relating (1) with (2) and (3) we arrive at (4) the rate of translocation of carbohydrates from endosperm to embryo. All these activities may be expressed, for numerical comparison, in terms of hexose units per unit of time, so that it is possible to survey, on this common basis, the balance and relative rates of these processes. The rates of the component parts of the system are to be labelled as follows: H , production rate of liexoses by hydrolysis of carbohydrate reserves in the endosperm; R 1 ,respiration rate of hexoses in the endosperm; T , translocation rate of hexoses from the endosperm to the embryo; R 2 , the respiration rate of the embryo; G , the rate of growth of dry weight of the embryo material. We may add to this series P (as a subsection of G ) the rate of transitory deposition in the embryo of mobile reversible carbohydrate reserves such as starch, which are later available for respiration. G less P would stand for the irreversible growth of new tissue substance, in a restrictive sense, while G stands for the whole dry-weight increase.