Volume 37, Issue 2
February 1953, pages 33-81
pp 33-53 February 1953
Further observations on the effects of certain cultural and environmental factors on biosynthesis of ascorbic acid in germinating seeds ofmüng (Phaseolus radiatus) are reported. Seed embryos separated from the reserve food store in cotyledons and grown on a semi-solid nutrient medium have been employed in some of these studies. Concomitant changes in nicotinic acid have been also followed.
In confirmation of earlier work, hexoses, particularly, glucose and mannose, have a pronounced enhancing effect on ascorbic acid formation.
Certain intermediates of carbohydrate metabolism such as citrate, succinate, fumarate and malate, induce increased synthesis of vitamin C; the effects of succinate and fumarate are noteworthy.
Thiamine, riboflavin, nicotinic acid and biotin stimulate ascorbic acid elaboration.
Accelerating effects are also noted with tryptophane, tyrosine, serine and glycine.
A parallelism between the biogeneses of ascorbic and nicotinic acids, under various cultural treatments is observed.
The possible implications of these observations have been discussed indicating probable involvement of hexose intermediates in ascorbic acid synthesis.
pp 54-71 February 1953
Further studies on the changes in ascorbic acid elaboration by germinatingmüng with various cultural additions have been carried out with a view to elucidate the postulated role of intermediaries of glucose metabolism.
Selective inhibitors of certain enzymes concerned in glucose breakdown and in phosphorylation, such as azide, fluoride and 2:4 dinitrophenol adversely affect ascorbic acid formation.
Malonate, a competitive inhibitor of succinic dehydrogenase, depresses ascorbic acid elaboration. Involvement of fumarate in reactions leading to synthesis of ascorbic acid is thus inferable.
In proper concentrations, certain mitotoxic agents like chloretone, urethane and coumarin favour synthesis of ascorbic acid.
Phosphorylation inhibitors such as atabrine and 2:4 dinitrophenol adversely affect phosphatase and, more particularly, pyrophosphatase activities which are stimulated by fumarate or succinate and by mitotoxic agents like chloretone in suitable concentrations. Phosphorylation of intermediates seems therefore a necessary step in ascorbic acid elaboration.
In general, changes in nicotinic acid are parallel to those in ascorbic acid.
The related observations have been discussed and it is concluded that metabolic breakdown of glucose is a probable prerequisite to its transformation into ascorbic acid.
pp 72-81 February 1953
Much of the confusion in the interpretation of the cytological pictures observed in yeasts could be traced to the wrong assumption that cells from cultures under entirely different physiological conditions should exhibit uniform cytological behaviour.
The only rational method of approach will be to investigate the nuclear behaviour under each specific cultural condition. A critical evaluation of some recent publications is presented.
Photomicrographs showing the cytological pictures during the aerobic and anaerobic phases are presented to illustrate the confusion that would result if attention is confined to either of the above cultural methods, for evaluation.
The cytological pictures observed in cells taken from a 24-hour agar slant are entirely different from that observed in actively proliferating cells in well aerated media. Photomicrographs and camera lucida drawings are presented as evidence that the varying number of bodies seen represent an ascending grade of endopolyploidy.
It is emphasized that the behaviour of the yeast nucleus under aerobic proliferation alone should be taken as the standard for the evaluation of the changes under different cultural conditions.
Endopolyploidy appears to be a specific modification to meet particular conditions of existence.