Volume 6, Number 1, p.p. 19-24
Malic and tartaric acid formation in grapevines
L. Beriashvili1 and T. Beriashvili2
1
Tbilisi Javakhishvili State University, Department of Bioorganic Chemistry, 1 Chavchavadze Ave, 0128 Tbilisi, Georgia.
2
Durmishidze Institute of Biochemistry and Biotechnology, Georgian Academy of Sciences, David Agmashenebeli Allée, 10km,
0159 Tbilisi, Georgia.
Highly radioactive malic acid is quickly formed from 14CO2, assimilated with light in the clusters and leaves of the Rkatsiteli grapevine (Vitis vinifera L.) during the first period of berry growth. More than 90% of the radioactivity in malic acid was found to be evenly incorporated into its carboxylic groups, while tartaric acid was incorporated only after a comparatively long exposure time. It seems that in grape berries, tartaric acid is not formed by direct carboxylation of three-carbon compounds. It was shown in the dark that malic acid is formed from 14CO2 by β−carboxylation of phosphoenolpyruvate produced through glycolysis. Incorporation of 14C into tartaric acid in the dark was not observed. The first carbon atom of glucose participated more actively in the formation of tartaric acid than the sixth carbon atom, but both the first and the sixth carbon atoms participated about equally in the formation of malic acid. The metabolism of malic acid occurs via the Krebs cycle as well as via the glyoxylate cycle. During the first periods of berry growth, organic acids were synthesized mainly in the berries. Organic acid synthesis in berries decreased from the beginning of ripening and the rôle of the leaves in supplying the berries with organic acids increased.
Keywords: berries, CO2, glucose, grapevine, leaves, malic acid, photosynthesis, tartaric acid