Production of mycosporine-alanine, acetic acid and uridine by cultures of Colletotrichum graminicola: Their role in conidial maturation and development
Abstract
Bioassays demonstrated the existence of two mechanisms of self-inhibition in Colletotrichum graminicola cultures. The first was caused by a low-molecular-weight compound in the mucilage that surrounds conidia. The second was the result of the production of a volatile component. The low molecular weight self-inhibitor was isolated and analyzed by mass spectrometry. The molecular mass obtained was consistent with the structure of mycosporine-alanine. Mycosporine-alanine, the production of which was shown to be light dependent, was easily detected as part of the mucilage due to its specific peak of absorption at 310 nm. The presence of high concentrations (4 mM) of this inhibitory component in the mucilage of acervuli was consistent with the necessity of a self-inhibitor where conidium concentration is the greatest. It is surprising that the self-inhibition caused by mycosporine-alanine is dependent on conidium age. Conidia from 14-day-old cultures were consistently inhibited under the proper conditions. However, it was observed that, as conidia age, the effect of the self-inhibitor was progressively decreased. HPLC analysis also demonstrated the presence of uridine in the mucilage but its significance was not determined. The volatile inhibitor was demonstrated to be acetic acid which was detected by gas chromatography-mass spectrometry (GC/MS). Acetic acid is known to be a strong sporostatic factor. The volatile acetic acid from a parent culture was shown to prevent conidium germination but not to kill conidia. This effect was reproduced in experiments that showed that the volatile material prevented conidia from causing disease on sorghum seedlings. However, long-term inhibition without conidial death could not be completely reproduced "in vitro" in experiments with a commercial source of acetic acid at various concentrations. I assume that there are many components in the phenomenon of inhibition by the volatile acetic acid that are not understood. Both types of inhibitory activity could be reversed by addition of exogenous nutrients. In addition, conidium viability remains unchanged throughout the inhibition period. Therefore, both inhibitors represent natural mechanisms which prevent conidia from germinating under unfavorable conditions.
Degree
Ph.D.
Advisors
Nicholson, Purdue University.
Subject Area
Plant pathology
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