Abstract. The origin of the ethylene carbon skeleton in Penicilliumr digitatum appears to be intimately associated with the Krebs cycle acids, particularly the middle carbon atoms of dicarboxylic acids. Among the other compounds studied, certain carbon atoms of /-alanine, propionic acid, and methionine can be incorporated into the ethylene carbon skeleton presumablv by way of an indirect route via the Krebs cycle acids. Carbon atoms of acrylic acid, particularly C-2, were also found to be incorporated into the ethylene skeleton. Inhibition of ethylene but not respiratory CO., formation in the mold by cis-3-chloroacrylic acid at 1 X 10-3 M pointed to the possibility that acrylic acid may be related to the precursor for ethylene.
The time course study of the utilization of specifically labeled glucose by yeast has been carried out under proliferating conditions. The rate of change of specific activity in the respiratory COs from the respectively labeled substrate agrees with the known breakdown pathways of glucose in this organism. Calculations were made on the basis of cumulative radiochemical recoveries of metabolic CO, from each labeled glucose which revealed that approximately 87% of the administered glucose was metabolized by way of the Embden-Meyerhof pathway in combination with the tricarboxylic acid cycle, and 13% was consumed through phosphogluconate decarboxylation. The efficiency of the utilization of each glucose carbon atom in biosynthesis also was estimated.
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 be1Received revised manuscript March 16, 1960.
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