THE CORRELATION OF ENHANCED PROTEIN SYNTHESIS WITH EXPRESSION OF MILO DISEASE SYMPTOMS (HOST-SELECTIVE TOXIN, MERCURY, HEAT SHOCK, PC-TOXIN)
Abstract
The root rot fungus Periconia circinata produces a host-selective toxin (PC-toxin) that enhances the rate of synthesis of 16 kD proteins in sorghum genotypes that are susceptible to the fungus and sensitive to PC-toxin. This study examined the correlation in sorghum of susceptibility to the fungus, sensitivity to toxin, and enhanced synthesis of 16 kD proteins. Sorghums included near-isogenic lines of susceptible (S) and resistant (R) cv Colby, S and R shattercane, selections from China and Nigeria, spontaneous resistant mutants of cv Colby, and an F(,1) hybrid of R x S genotypes. Toxin enhanced the rate of synthesis of 16 kD proteins in all S genotypes but not in R genotypes. The F(,1) hybrid responded intermediately to toxin, suggesting a gene dosage response to toxin. Whether the enhanced synthesis of the 16 kD proteins was directly or indirectly induced by toxin was examined by comparing the response of sorghum to toxin with the response to general stress agents. Heat shock suppressed electrolyte leakage and symptom development in toxin-treated S seedlings and prevented enhanced synthesis of 16 kD proteins in toxin-treated excised root tips. Although heat shock induced or enhanced the synthesis of at least 18 heat shock proteins, it did not enhance the synthesis of the 16 kD proteins. Mercuric chloride induced characteristic milo disease symptom in seedlings of both S and R genotypes and enhanced the rate of synthesis of the 16 kD proteins in excised root tips. No other changes in protein synthesis were observed. Apparently toxin and mercury cause the same biochemical disturbance in sorghum. The site of action and the site of selectivity of the toxin apparently are different. The results of this study demonstrated that susceptibility to P. circinata, sensitivity to PC-toxin, and enhanced synthesis of the 16 kD proteins in response to toxin are strictly correlated in sorghum. The enhanced rate of synthesis of the 16 kD proteins induced by toxin is probably not a general stress response. Apparently, it is a specific response to toxin that is involved in the development of milo disease symptoms in sorghum. The similar response of sorghum to mercuric chloride and to toxin suggests that mercury can be used to identify possible mechanisms of action of toxin. Mercury has the advantage of being chemically well defined, easily detected in plant tissues, and physiologically and biochemically well studied.
Degree
Ph.D.
Subject Area
Plant pathology
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