Metabolism and morphogenesis in a newBlastocladiella
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One phase of morphogenesis (production of resistant sporangia) in the life cycle ofBlastocladiella has been investigated experimentally in some detail, and the underlying biochemical transformations have, in part, been elucidated. Conversely, morphogenesis has been made to serve as a tool in physiological studies.
Elevated concentrations of CO2 sources induce R.S. spores to develop directly into resistant-sporangial plants instead of gametophytes. The phenomenon, furthermore, is dependent upon additional factors found in a non-standardized peptone, but not in vitamin-free casein hydrolysate. Such factors can be effectively replaced by certain Krebs-cycle intermediates (e.g.a-ketoglutarate and citrate) and oxidative-decarboxylation inhibitors or carbonyl reagents (e.g. arsenite and semicarbazide).
Biotin completely eliminates the effect ofa-ketoglutarate in inducing the formation of R.S. plants; this offers strong indirect evidence for the role of biotin in the oxidative decarboxylation ofa-ketoglutarate.
Blastocladiella is heterotrophic for thiamine. The remarkable fact that it can be replaced by a combination of bicarbonate, acetate, and pantothenate is suggestive of the substitution of a Coenzyme A-dependent acetylation reaction for the decarboxylation of pyruvate during growth.
It has been concluded that retardation of the oxidative decarboxylation ofa-ketoglutarate, and simultaneous accumulation of its precursors back to the citrate stage, is directly or indirectly related to the formation of R.S. The strong lactate production, the thiamine heterotrophy, the supposedly weak C2-forming mechanism associated with it, the probably-functional Wood-Werkman reaction, and the by-passing of the B1-deficiency with a source of CO2, acetate, and pantothenate are further discussed with relation to the biosynthetic mechanism underlying the morphogenetic pattern.
The germination of resistant sporangia, a very precise mechanism, is separable into two distinct phases; one, a period (e.g. 60 min. atca. 20° C.) terminating with cracking of the thick pitted wall, and the other, a subsequent period which leads to the final discharge of spores. Relatively low concentrations of anions, as well as different temperatures, exert a pronounced differential influence on the two processes.
KeywordsBiotin Thiamine Arsenite Lactate Production Casein Hydrolysate
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