Conversion of glucose-1-C14 to pectin in the boysenberry.

نویسندگان

C G SEEGMILLER

B AXELROD

R M MCCREADY

چکیده

Many authorities believe that pectins play a dominant r&e in the changes in texture of fruits during the ripening process, although the origin and fate of pectic substances in plant tissues are unknown ((1) p. 273). There is no evidence that in nature pectic substances are formed directly from galactose or galactan ((1) p. 277). To obtain some insight into the mechanism of pectin formation, glucose labeled by the incorporation of radioactive Cl4 in the carbon 1 position (aldehyde carbon) has been introduced into slightly immature boysenberries through their stems. Subsequently the “pectin” fraction of the boysenberries was isolated and hydrolyzed. This is the fraction which is insoluble in aqueous alcohol and digestible by fungal pectinase. Analyses of the hydrolysate showed that both of the main constituents of pectin, galacturonic acid and arabinose, were radioactive. Specific degradation of the galacturonic acid revealed significantly more radioactivity in the C-l position than in any other, which indicates that glucose can be converted to the galacturonic acid moiety without cleavage of the carbon chain. Essentially all of the radioactivity of the arabinose was also found in the C-l position, which suggests that the arabinose was formed from glucose in a fairly direct manner. Materials-Boysenberry twigs were cut from actively growing berry plants, and their stems were placed in radioactive glucose within 3 hours after cutting. One experiment was carried out on a twig containing several small leaves and one green but practically full grown berry. Another experiment was carried out the following year on a single green berry attached to a stem about 1 inch long, but with no leaves. Determination of Radioactivity-All samples were converted to BaC03 and mounted on small disks of Whatman No. 50 filter paper’ by filtration,

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