Phytotoxic Glycopeptide Produced by Corynebacterium sepedonicuml

A purified toxic glycopeptide from Corynebacterium sepedonicum (Speick.) Dows., possesses the capacity to wilt plant cuttings. The toxin induces a rapid g:neral flaccidity in stem tissues followed by a leaf wilt making its effects significantly different from that induced by high molecular weight substances (dextrans). In the latter case, the initial effect of -a dextran induced wilt is a leaf wilt presumably caused iby the plugging of xylem elements. However, physiological experiments including dve transport studies, plasmolytic studies, measurements on electrolytes, studies on the movement of 3H,,O through tomato cuttings, and toxin binding studies all strongly suggest that the primary effect of the toxin is to destroy the integrity of cellular membranes resulting in the net loss of water from the cell. Membrane damage in toxin treated plants was confirmed by electron microscopic observations. Evidence of damage were seen in chloroplasts, m,itochondria, the plasma membrane, and the structural integrity of the cell wall. These effects appeared to be a direct cause ard rot a secondary restult of the toxin as shown by autoradiographic studies using 3H.toxin. Phytotoxic polysaccharides from some plant pathogenic bacteria exert their effect on plants by causing wilting. In the case of Pseudomonas solanacearum Husain and Kelman (4) have postulated a causal relationship between toxic polysacsharide production and pathogenicity of the organism. Some of the same pathological relationiships that these authors presented for P. solanacearum have also been reported by Spencer and Gorin (9) for Corynebacteriurn insidiostum and C. sepedonicunt. In most instances, the mode of action of toxic polysaccharides in wilt induction has been attributed to a blockage of water flow in the vascular system of the plant (4,6). This theory has been supported by the following facts: 1) Plant cuttings wilted by polysaccharides regain turgor upon reimmersion in distilled water, and 2) It is extremely difficult to get water to move through a wilted stem when negative pressure is applied at one end of a wilted stem. However, Strobel (11) suggested that some mechanism other than plugging seemed to be necessary to explain the wilting caused by the toxic glycopeptide of C. sepedonicurn. This suggestion was based on the fact that only 50 j,ug of the toxin was necessary to wilt an 8 cm tomato leaf. Thus, this report is a series of experiments done with the ' Supported in part by NSF grants GB-5557 to G. A. Strobel and GE-7002 to W. M. Hess. Montana Agricultural Experiment Station Paper No. 908, Journal Series. purified toxic glycopeptide of C. sepedonicint to elucidate its effects on plant tissues. *The hypothesis of this report is that the glycopeptide of C. sepedonicum acts to induce the flaccidity of plant tissues as a result of interference with cellular membrane systems. Materials and Methods The purified phytotoxic glycopeptide used in this study was prepared from cultures of C. sepedonticunt as described by Strobel (11). The glycopeptide has a molecular weight of 21,450, and empirical formula of C48H96048N, is antigenic and yields glucose, mannose, 3 unidentified compounds and 6 amino acids upon acid hydrolysis. Both '-C-labeled purified toxin (141,400 d'pm/mg) and 3H-labeled toxin (432,000 dpm/mg) were prepared, by feeding 25 ml cultures of C. sepedonicumn, 25 ,uc of mannose-'4C and 0.5 mc of mannose-3H, respectively. In all studies radioactivity was determined by liquid scintillation countinig on a Nuclear Chicago Model 6804 counter. The solvent and fluor svstem used was the same as that previously described (11). All counts were converted to dpm by the quench correction method. Tomato plants used were from the variety Earliana and were either young plants (5-8 cm tall) cut off at the soil line or were young intact plants. Tritiated Water Tranisport. A tomato cutting was placed in tritiated water with a specific radioactivity of 1.0 mc/4.0 ml. Tlle upper portion of 1673 www.plantphysiol.org on July 15, 2017 Published by Downloaded from Copyright © 1968 American Society of Plant Biologists. All rights reserved.