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Changes in respiratory metabolism in the cut region, a region 0-2 mm below the cut surface, of the decapitated epicotyl of etiolated Stizolobium hassjoo seedling were followed under the dark and light conditions; under the former conditions the callus formed on the cut surface, under the latter not. The following results were obtained. 1) The rate of 14CO2 output from G-U-14C increased after cutting both in the dark and in the light, but more notably under the dark conditions. 2) In the dark, malonic inhibition rate of CO2 release from glucose decreased remarkably in a day after cutting, while in the light, such a drastic change was not observed. 3) Cs/C1 ratio rapidly fell in a day after cutting in the dark. In the light the change in the ratio was not so striking. From these results it is suggested that under the dark conditions, drastic changes in metabolic activity occur in the cut region in a day after cutting, when any notable morphological change can not yet be observed, and that the activity of the pentose phosphate pathway considerably increases there. As already reported'', when the epicotyl of etiolated seedling of Stizolobium hassjoo, ca. 10 cm long, is cut at the position more than 3-4 cm distant from the tip, a callus remarkably outgrows from the cut surface. It has been shown2' that in the callus, the contribution of the pentose phosphate (PP) pathway to glucose catabolism is much greater as compared with that in the part of the epicotyl, where the callus derives. For investigating the mechanism of the callus formation, it is important to know the metabolic processes through which cell division in callus development is induced. In this study, the changes in the respiratory metabolism in the cut region of the epicotyl were followed with time after cutting. Material and Methods Material : The plant material used in this study was the same as that described in previous papers1-4'. The seeds of Stizolobium hassjoo were sown in quartz sand without any nutrient and kept at 27-30 ° in the dark. When the epicotyls of etiolated seedlings grew to be 10-12 cm long (about a week after sowing), they were decapitated at the position 5 cm distant from the tip and the seedlings kept in the dark * Department of Botany , Faculty of Science, University of Tokyo, Hongo, Tokyo, Japan. July August, 1968 MOROHASHI, Y., et al. 363 or in the light (fluorescent lamp, 3,6001ux). All experiments in this work were carried out with slices. A part of the epicotyl 0-2 mm under the cut surface was named "cut region" and two successive 1 mm sections were transversely taken from this part, and each section was separately used for experiments. In addition, 1 mm slices from the part VII were also used as a control. Various parts of an epicotyl were designated as shown in Fig. 1. Nitrogen determination: Total and protein nitrogen contents were determined by the same methods as in the previous paper4'. Measurements of respiratory gas exchange : The output of 14C02 from 14C-labeled glucose supplied to slices was examined in the following manner. In a flask with a center well, about 30 sections of slices were put together with 7 ml of phosphate buffer (10_2 M, pH 6) and 3 ml of radioactive glucose solution (0.15 ,u c, about 10 mg) were added. The flask was shaken at 30 ° for 2-2.5 hours in the dark. When malonic acid was used as a respiratory inhibitor, it was dissolved in the buffer and the pH adjusted to 6 with NaOH. The final concentration of malonic acid was 5>< 10-2 M. Respiratory CO2 containing 14C02 was trapped with NaOH in the center well of the flask. The radioactivity of trapped 14CO2 was estimated as usual5'.

Physiological Studies on the Outgrowth of the Epicotyl in Stizolobium hassjoo