Investigation into the Function of Pyridoxin as a Growth Factor for Excised Tomato Roots.

Abstract

Thiamin, pyridoxin, niacin, and glycine have all been reported to act as growth factors for excised tomato roots grown in sterile culture. White (9) showed that, in basal medium plus thiamin, partial replacement of pyridoxin by glycine could be effected using any one of three different clones of excised roots. The degree to which glycine replaced pyridoxin varied with the different clones. Furthermore, it appears from photographs of the roots that basal medium plus pyridoxin and glycine gave a greater level of growth than was obtained in basal medium plus pyridoxin only. It was shown by the present author (1) that, after the requirement for thiamin was met, glycine plus niacin replaced pyridoxin using root cultures derived from either one of two inbred lines of tomato and their reciprocal crosses. The addition of glycine to basal medium plus thiamin and pyridoxin exerted an inhibitory effect with one of the parent strains and the hybrids but was, if anything, beneficial to growth of the other parent strain. In view of the many functions exerted by components of vitamin Be in co-enzymes (7) it is unlikely that all processes requiring vitamin Be in excised tomato roots are eliminated when glycine (or glycine plus niacin) is used to replace pyridoxin. It is more probable that when this replacement of pyridoxin is effected, growth occurs either 1) because glycine plus niacin exerts a sparing action upon the amount of vitamin Be synthesized by the roots or 2) because glycine and niacin are involved in the biosynthesis of Vitamin Be. This latter possibility is of particular interest as no suggestions as to the pathway of this biosynthesis have been established (11). Thus a detailed study of the replacement may be expected to yield information upon either the function, or the pathway of biosynthesis, of vitamin Be in higher plant material. Glycine, at least in part, replaced pyridoxin in the nutrition of the clone of excised tomato roots studied here. This paper describes other nutritive requirements and interrelationships of the clone. The object of the work was to obtain detailed information on the requirement of the clone for pyridoxin (or other components of vitamin Be), niacin or niacinamide and glycine.