Trichothecenes phytotoxicity

The pigments of the Fusaria have been described in Chapter 7. Many of the characteristic phytotoxic metabolites are the sesquiterpenoid trichothecenes (8.38) (see Chapter 5). The more highly hydroxylated members have considerable mammalian toxicity as well as phytotoxicity. Trichothecenes have been identified as metabolites of species from ten of the twelve sections of the genus Fusarium as classified by Booth. The trichothecenes occur with various combinations of oxygen substituents at positions 3, 4, 7, 8 and 15. Several trichothecenes contain macrocyclic esters linking C-4 and C-15. These are known as the roridins and verrucarins. 

A detailed study of the effects of exogenously applied macrocylic trichothecenes on intact bean, corn, and tobacco plants recalls that they may induce a variety of responses that are tissue dependent and range from no effect to complete phytotoxicity (H). Initial experiments have conclusively shown that in the etiolated wheat coleoptile bioassay verrucarin A, verrucarin J, and trichoverrin B are exception-... 

Muhitch Ml, McCormick SP, Alexander NJ, Hohn TM (2000) Transgenic Expression of the TrilOl or PDR5 Gene Increases Resistance of Tobacco to the Phytotoxic Effects of the Trichothecene 4,15-Diacetoxyscirpenol. Plant Sci 157 201... 

Kuti, j. O., B. B. Jarvis, N. Mokhtari-Rejali, and G. A. Bean, Allelochemical regulation of reproduction and seed germination of two Brazilian Baccharis species by phytotoxic trichothecenes, J. Chem. Ecol, 16, 3441-3453 (1990). 

When tomato seedlings exposed to myrotoxins for 2 hr were examined, both myrotoxins A and B were detected. In an earlier paper describing trichothecene absorption by muskmelOn seedlings, we could detect trichothecenes after seedlings were exposed for 24 hr which suggests that plants are capable of absorbing compounds such as trichothecenes very rapidly. Macroscopic evidence, e.g. phytotoxicity, that tomato seedlings had been exposed to myrotoxins A and B is presented in Table 1. 

PHYTOTOXIC EFFECTS OF TRICHOTHECENE METABOLITES FROM PATHOGENIC STRAINS OF MYROTHECIUM RORIDOM ON CUCUMIS MELO L. 

The present study was conducted to determine phytotoxic effects of exogenously applied roridin E to muskmelon plant tissue and to compare these effects with those of the macrocyclic trichothecenes roridin A and myrotoxin A+B produced by other strains of Myrothecium (Jarvis et al., 1985b). 

To assess trichothecene effects on intact muskmelon seedlings, six week old seedlings at the 3-4 true leaf stage for each of the five genotypes were carefully removed from the soil medium. The roots were carefully washed in tap water to remove soil particles, then immersed in either solvent or 5y g ml of roridin E for 2 hr only root systems were immersed. After exposure, seedlings were washed and incubated with roots immersed in tap water for 24 hr under continuous light, then examined macroscopically for phytotoxic symptoms. Symptom severity was ranked on a scale of 0 to 5 0 = no visible symptoms and 5 = severe discoloration... 

Busam and Habermahl, 1982) in relatively high concentrations suggests that some plant species may be naturally resistant to the effects of macrocyclic trichothecenes. Mechanisms for such resistance have been speculated to be a rapid detoxification process within the plant cells (Jarvis et al., 1981). However baccharinoid, the macrocyclic trichothecene from Baccharis species, exhibits essentially the same degree of phytotoxicity as roridin A and E when applied to tissues of other plant species. Therefore, the vivo conversion of roridins to the baccharanoids by B, megapotomica should not be interpreted as a detoxification process (Cutler and Jarvis, 1985). 

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