THE DESMOSTEROL REDUCTASE ACTIVITY OF RAT BRAIN DURING DEVELOPMENT1

Abstract— The reduction of desmosterol by cell-free preparations from developing rat brain was established and the age-dependent alterations in reductase activity were correlated with levels of desmosterol in brain. An increase in enzymic activity followed closely the sharp increase in levels of desmosterol that was observed at about 5 days of age and that reached a maximum at 8-11 days of postnatal age. Furthermore, the abrupt decrease in the desmosterol content of brain at 13-15 days of age was associated with a decrease in enzymic activity. We suggest that the enzyme may be substrate-induced and that this attribute may be of significance with respect to the ontogenesis of myelin. Cerebral desmosterol reductase exhibited a specific requirement for NADPH and was primarily a particulate enzyme.     

Role of auxin and gibberellin in the synthesis of Ascorbic Acid and growth of tissue explants

Coleoptile and root tips ofTriticum aestivum cv. Arnej 624 and those ofAvena sativa cv. Victory (Svalöf) as well as dry excised embryos ofTriticum aestivum cv. Rival (Svalöf) and those ofArachis hypogaea cv. 34 3A. H. were cultivated in media containing various concentrations of sucrose and growth regulators, like ascorbic acid, indole-3-acetic acid and gibberellin. Growth, differentiation and water uptake of the various explants were determined at regular time intervals. Further, the concentration of the endogenous ascorbic acid in mg./g. fresh weight, as well as the amount of this growth regulator utilized as per cent of the total were determined. Although all the three growth regulators promote growth in the explants, their effect is best felt when sucrose of a higher concentration (1.0 per cent) is added to the medium. In fact, the response to 1.0 per cent sucrose is sometimes as good as a combination of a growth regulator with sucrose, especially in the case of root explants. The results clearly indicate that the biosynthesis of ascorbic acid in the explants is catalyzed by the addition of indole-3-acetic acid as well as gibberellin. Simultaneously, the utilization of ascorbic acid is also appreciably increased by the presence of these growth regulators. Addition of 1.0 per cent sucrose to the medium containing the above mentioned growth regulators augments to a considerable extent not only the concentration of ascorbic acid, but also steps up its utilization. Enhancement of ascorbic acid as well as its increased utilization are correlated with rapid imbibition of water, growth and differentiation. The role of ascorbic acid in growth is discussed; and on the basis of the data presented here it is postulated that: (1) auxin and gibberellin function in the growth process by catalyzing the biosynthesis of ascorbic acid; and (2) that ascorbic acid not only participates in activation of various enzyme systems, but also stimulates the production of adenosine triphosphate by acting as an electron donor in photosynthetic phosphorylation as well as oxidative phosphorylation; (3) that the above action of ascorbic acid creates a favourable redox balance for synthesis of nucleic acids, proteins, enzymeproteins, and cell-wall constituents, thus enabling the processes of cell division and enlargement to proceed at a fast rate; and (4) that the relative rates of cell division and cell enlargement as well as “ageing” will determine the pattern of plant development.     

Inositol Metabolism in Plants. IV. Biosynthesis of Apiose in Lemna and Petroselinum

The biosynthesis of apiose was investigated in cell wall polysaccharide of Lemna gibba G3 (duckweed) and in detached leaves of Petroselinum crispum (parsley). Lemna grown either in short days or in continuous light incorporated ¹⁴C from a medium containing myo-inositol-2-¹⁴C into d-apiosyl and d-xylosyl units of cell wall polysaccharides. Labeled d-apiose was characterized by paper chromatography, by formation of labeled crystalline di-O-isopropylidene d-apiose, and by gas chromatography of trimethylsilyl derivatives of apiose and of its sodium borohydride reduction product, apiitol. Periodate oxidation of labeled apiose revealed 86 to 94% of the ¹⁴C was located in formaldehyde fragments corresponding to C3′ and C4. Comparison of this result with work reported by Grisebach and Doebereiner and by Beck and Kandler supports the conclusion that myo-inositol-2-¹⁴C was converted to d-apiose labeled specifically at C4.