FAT SYNTHESIS AND ITS REGULATION IN PLANTSⅢ.THE CH...
C.N.Shih，Y.S.Zhu AND C.Tan
（Institute of Plant Physiology，Academia Sinica）
In the previous article，we showed that in the siliques of B.napus glucose can be oxidized via both EMP and HMP pathways.A series of work was then initiated to investigate the relative activities of these two pathways in relation to fat accumulation during silique development and maturation.The following results are presented in this paper：
（1）Activities of the isolated enzymes of EMP and HMP pathways vary with the stages of development of the siliques.From budding to flowering，the activities of both pathways increase，but the activities of enzymes of EMP pathway increase relatively more.From flowering to fruiting and to silique maturation，the activities of EMP enzymes decline rapidly，whereas the activities of HMP enzymes increase sharply，and maintain at a higher level or only show a slight decrease till the approach of full maturation.
（2）Experiments with inhibitors showed that the fraction of respiration sensitive to iodoacetamide and NaF，decreases with the age of the seeds，but shows a small increase again when maturation approaches.
（3）The metabolic transition from the predominance of EMP pathway to the predominance of HMP pathway in the siliques takes place between 10 to 20 or more days after flowering.From data of other authors，this period corresponds to the time of rapid fat accumulation.(https://www.daowen.com)
（4）A natural inhibitor of G-6-P dehydrogenase and 6-PG dehydrogenase was found in the reproductive organs.It is present mainly in the buds，flowers and young siliques，and is nearly absent in the old siliques.There appears to be a correlation between the presence of the inhibitor，the activities of glucose degradation pathways and fat formation.When the inhibitor eventually disappears，enzymes of the HMP pathway become activated and fat is actively synthesized.It seems that the inhibitor plays an important role in the regulation of carbohydrate breakdown and fat synthesis.
（5）The exact nature of this inhibitor has not yet been ascertained.It is soluble in water，n-butanol，ethyl ether and hot alcohol；and is insoluble in benzene and chloroform.It is non-dialyzable，not precipitated by saturated（NH4）2 SO4 solution and stable to heat.These properties indicate that it is a substance with higher molecular weight and is nonproteinous in nature.
（6）On paper chromatogram，the inhibitor is yellow in color，and shows a blue fluorescence under ultra-violet light.When exposed to the fumes of concentrated ammonia or treated with AlCl3 solution，its color become more intense and the flurescence changes.
（7）Infra-red spectrophotometric analysis indicates that it contains a carbonyl and a phenyl group.Spectral determinations show that it has an absorption maximum in the region around 260 mμm.Exposure to ultra-violet light abolishes the absorption peak and the inhibitory activity.
（8）From the evidences stated above，the inhibitor is presumed to be a flavanoid or its derivative.
