Selective Effects of Purine and Pyrimidine Analogues and of Respiratory Inhibitors on Perithecial Development and Branching in Sordaria

Abstract

Sumimtary. The initiation of perithecia in the homothallic ascomycete Sordaria fimiiicola was completely suppressed, without seriously inhibiting vegetative growth, by growing the fungus on an agar medium containing one of the following additions: 1) 1 uM 5-fluorouracil, 2) 10 to 100 jum 6-azauracil, 8-azaguanine or 8-azaadenine, 3) 50 to 500 uM cyanide or azide, 4) 5 % (w/,v) casein 'hydrolysate. In contrast to the selective activity of the analogues of 3 RNA bases, whose inhibition could be reversed by the appropriate normal bases only, none of the analogues of thymine were active, neither were the thio-derivatives of RNA bases. Other inhibitors of RNA and protein synthesis, like actinomycin D, puromycin and cycloheximide, were also without selective activity, although the last of these inhibited perithecial maturation at 0.1 um concentration but not initiation. Amino acid analogues were inactive, as were the metabolic inhibitors thiourea, 2,4-dinitrophenol and fluoride. The compounds which inhibited the formation of perithecia also lowered the branching frequencv of leading hyphae, but not their linear growth rates. Consequently, the branch (lensities wvere diminished in their presence. Hypotheses to account for these findings are discussed in terms of inhibition of growth in general, of the synthesis of some specific messenger RNAs, and of RNA-mediated transport across membranes, the last of which seeming the most fruitful for further work.Purine and pyrimidine analogues have been found to intervene at crucial developmental stages in both plants and animals. One of the most direct of these effects on p'aants was the suppression by some of the RNA base analogues of the normal sheet-like (cordate) growth of fern gametophytes while permitting their continued filamentous growth (3,20,21,22,29,30). None of the strictly DNA base analogues had such effect (29). Actinomycin D was effective (30), and so were 2 amino acid analogues, 5-methyltryptophane and ethionine (20-22), but not any of the common respiratory and glycolytic inhibitors (20). The leaf morphology of a water fern could be affected by application of 5-fluorouracil and 2-thiouracil, in the sense that normal lobation was suppressed and the characteristic sunken stomata of the land-form were favored (39). Similarly, 2-thiouracil affected leaf morphogenesis in flowering plants (17), and 5-fluorouracil has been demonstrated as an inhibitor of flower induction (8).

Promotion of Perithecial Initials in Monacrosporium doedycoides by 6-Methyl Purine

“…Lindenmayer and Schoen (1967) found no effect with protein synthesis inhibitors on their systems and were also unsure as to an explanation. Lindenmayer and Schoen (1967) found no effect with protein synthesis inhibitors on their systems and were also unsure as to an explanation.…”

Thioguanine-dependent Light Sensitivity of Perithecial Initiation in Sordaria fimicola

“…Whether there is any connexion between the shutting off of carotenoid production and the start of melanin production in the absence of blue light, is an interesting problem. The black pigment of the vegetative mycelium as well as of the perithecia turns yellow when placed in sodium dithionite solution, a strong reducing agent, and turns black again when reoxidized by H202, indicating the presence of quinone groups and conforming to the reactions of allomelanins as described by Nicolaus (1968).…”

“…The culture techniques and the medium, aside from the addition of I ~~-6 -t h i oguanine before autoclaving, were the same as in the previous work (Lindenmayer & Schoen, 1967). The medium was a sucrose nitrate medium, containing biotin and thiamine (pH 5-5 to 6.0), and is known to stimulate the production of perithecia (Bretzloff, 1954).…”

“…Alternating light and darkness affect the spore discharge from mature perithecia of this organism (Ingold & Dring, 1957;Walkey & Harvey, 1967) but not their initiation, although the perithecia may attain a larger size under alternating conditions than under continuous light or continuous darkness. In the course of previous work (Lindenmayer & Schoen, 1967) it was found that certain purine and pyrimidine analogues, and particularly 5-fluorouracil, could specifically inhibit perithecial initiation in this organism at concentrations at which only slight inhibition of vegetative growth was observed. We also noticed a marked sensitivity of perithecial production to light-dark conditions when the organism was grown in the presence of I to 1 o p~-6 -thioguanine or 8-azaguanine.…”

“…Since our experiments showed an in vivo photodynamic effect of these compounds, involving presumably a native cellular pigment as the photosensitizing dye, and since the effect consists of the specific suppression of an important morphogenetic process, we decided to investigate this system. But only 6-thioguanine was used in our experiments because 8-azaguanine gave rise to irregular vegetative growth, while 6-thioguanine did not inhibit vegetative growth at all, in fact it stimulated growth somewhat (Lindenmayer & Schoen, 1967).…”