Cotton terpenoid aldehydes

The toxicity of the cotton terpenoid aldehydes to different larvae has been reported by several groups (227, 259, 270-275). These results are summarized in Table 2. Although there is variation in the test results among the different laboratories, it is obvious that gossypol and probably the other terpenoid aldehydes have a wide range of toxicity to many moth larvae. 

Phillip, V. A. and Hedin, P. A. (1990). Spectral techniques for the structural analysis of the cotton terpenoid aldehydes gossypol and gossypolone. J. Agric. Food Chem. 38, 525-528. 

Stipanovic, R. D., Altman, D. W., Begin, D. L., Greenblatt, G. A., and Benedict, J. H. (1986). Effects of cotton terpenoid aldehydes on resistance to Heliothis. International Union of Pure and Applied Chemistry, Sixth Int. Congr. Pest. Chem. Ottawa, Canada, Abstract No. 2D/E-05. 

Table I. Inhibition of H. virescens larval growth by cotton terpenoid aldehydes, as percent of diet.

Concentrations of constitutive terpenoids in the root epidermis of cotton are unrelated to differences in resistance. But concentrations of terpenoid aldehydes formed in the vicinity of the pericycle, near the head of the animal, act as phytoalexins and are closely correlated with levels of resistance (11, 48). Little or no phytoalexin is formed in the pericycle of susceptible cultivars. Mixtures of terpenoid phytoalexins are more toxic to the nematode than gossypol alone, and mixtures containing methylated terpenoid phytoalexins (from 6. hirsutum) are more toxic than those that contain only nonmethyTated phytoalexins (from 6. arboreum) (49). Thus, the structure of terpenoid phytoalexins also is importan for resistance to root knot nematode. 

We have examined these lethal reactions biochemically (93, unpublished). In all cases spontaneous defense reactions (phytoalexin synthesis, tannin synthesis and tannin oxidation) occur concurrent with the onset of symptoms. The quantities of terpenoid aldehydes and tannins found in tissues of severely affected plants are usually very similar to those found in severely diseased plants dying from microbial infections. Thus, it is possible that many of the disease symptoms seen in cotton are due to the toxic terpenoids and tannins formed in response to infections. 

Figure 1. Proposed biosynthetic pathway of terpenoid aldehydes in cotton.

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