Plant resistance multiple factor

Hedin, P.A. et al.. Multiple factors in cotton contributing to resistance to the tobacco budworm Heliothis virescens F., in Plant Resistance to Insects, Heden, P.A., Ed., American Chemical Society, Washington, 1983, 347. 

The feasibility of using these antinutritive plant systems as multiple-factor/multiple-mechanism resistance against noctuid larvae remains to be determined. It is possible that such a multiple onslaught against nutrient acquisition is redundant. In other words, perhaps merely the use of PPO and chlorogenic acid is sufficient. It also remains to be determined whether this proposed multiple-factor/multiple-mechanism of resistance renders the insects detoxicative systems more susceptible to traditional control tactics, and whether the evolution of resistance to such multiple antinutritive factors is more difficult than to insecticides. 

Aluminium toxicity is a major stress factor in many acidic soils. At soil pH levels below 5.0, intense solubilization of mononuclear A1 species strongly limits root growth by multiple cytotoxic effects mainly on root meristems (240,241). There is increasing evidence that A1 complexation with carboxylates released in apical root zones in response to elevated external Al concentration is a widespread mechanism for Al exclusion in many plant species (Fig. 10). Formation of stable Al complexes occurs with citrate, oxalate, tartarate, and—to a lesser extent— also with malate (86,242,243). The Al carboxylate complexes are less toxic than free ionic Al species (244) and are not taken up by plant roots (240). This explains the well-documented alleviatory effects on root growth in many plant species by carboxylate applications (citric, oxalic, and tartaric acids) to the culture media in presence of toxic Al concentrations (8,244,245) Citrate, malate and oxalate are the carboxylate anions reported so far to be released from Al-stressed plant roots (Fig. 10), and Al resistance of species and cultivars seems to be related to the amount of exuded carboxylates (246,247) but also to the ability to maintain the release of carboxylates over extended periods (248). In contrast to P deficiency-induced carboxylate exudation, which usually increases after several days or weeks of the stress treatment (72,113), exudation of carboxylates in response to Al toxicity is a fast reaction occurring within minutes to several hours... 

Adapted species may have developed, however, strategies which enable them to survive allelopathic attacks. One of those strategies certainly includes detoxification of absorbed allelochemicals by constitutive or inducible pathways. Metabolization and detoxification are known reactions in a number of crops upon application of diverse synthetic herbicides.38 Enhanced herbicide detoxification is an important factor in the development of nontarget-site cross-resistance and multiple resistance. It is reasonable to expect comparable strategies in plants that are relatively resistant to allelochemicals such as DIBOA, DIMBOA, and their derivatives. Especially in ecosystems where co-existing species have to be adapted to each other, detoxification of absorbed allelochemicals may play a crucial role under defined circumstances. 

Extrapolation of these results to the real world suggests that the simultaneous use of PPO/phenolics and proteinase inhibitors as bases of resistance against certain insects may be mutually incompatible. If one were to rely on proteinase inhibitors as a basis, the elimination of high levels of polyphenol oxidase in the plant would not guarantee antibiotic activity because high levels of dietary protein can abolish PI toxicity (89) Hence, the activity of PI, PPO and phenolics in situ may require the manipulation of multiple plant factors. 

---