Radiorespirometric Studies of Glucose Catabolism in Tomato Fruit.

The occurrence of various catabolic pathways of glucose in plant materials has attracted considerable interest in recent years (1, 3, 6). In an earlier report (2), studies on the catabolism of glucose in fruit by a radiorespirometric method were described. The radiorespirometric method previously has been successfully applied to other intact biological systems such as microorganisms and insects (11, 13). Essentially, the catabolic pathways for glucose utilization in fruit were detected and estimated by comparing the rates of C140. formation from fruit administered vith C14 specifically labeled glucose samples. In applying this method to study tomato catabolism, it is important that the labeled substrate is introduced into an intact fruit by a reliable technique so that it wvill mix rapidly and evenly with a defined amount of endogeneous substrate. Fullfillment of these conditions will then make it possible to compare the rate of C140, production from a set of fruit metabolizing concurrently C14 specifically labeled substrates. The vacuum infiltration technique described in an earlier paper was found to be satisfactory by examining the reproducibility of a large number of radiorespirometric data in a series of test experiments. In order to understand better the nature of the vacuum infiltration process and to estimate the amount of fruit glucose located at the infiltrated area, isotopic dilution technique has been applied in the present work to further examine the validity of the technique described earlier for substrate administration. Results of several series of radiorespirometric experiments are also presented to provide experimental evidence in substantiating the assumptions given in the earlier paper (2) for estimating pathway participation in the glucose catabolism of tomato fruit. These assumptions, concerned with the catabolic be-