Protein synthesis during fungal spore germination. V. Evidence that the ungerminated conidiospores of Botryodiplodia theobromae contain messenger ribonucleic acid

Ungerminated conidiospores of Botryodiplodia theobromae were examined for the presence of mRNA. A comparison of the incorporation kinetics of ¹⁴C-leucine and ¹⁴C-uracil into pulse-labeled germinating spores indicated that a cycloheximide-sensitive protein synthesis began immediately upon germination in the apparent absence of RNA synthesis; the rate of incorporation of ¹⁴C-leucine increased sharply later in the germination sequence when an actinomycin D-sensitive ¹⁴C-uracil incorporation began. Polyribosomes characteristic of eukaryotic cells were detected in spores at all stages of germination, including the ungerminated spores. The mRNA in polyribosomes of ungerminated spores was probably functional because the ribosomal aggregates became associated in vivo with ¹⁴C-labeled amino acids during the first 30 min of germination. Ribosome fractions enriched with polyribosomes were isolated from both ungerminated and germinated spores, and these fractions, when tested with a supernatant enzyme fraction from germinated spores, stimulated appreciably more amino acid incorporation than did purified monoribosomes from the same spores. It is concluded that ungerminated spores of this fungus contain mRNA which is translated immediately upon the onset of germination.