Induced resistance mechanisms

In the family of the Gramineae, which includes some of man s most important crops, active lignification seems to be of special importance for induced resistance mechanisms (19,20). This may be correlated with the nearly complete absence of phytoalexins in this family (21). In spite of an intensive search for such infection-induced fungitoxic substances, no phytoalexins have been found in wheat to date (22). Nevertheless, induced lignification has been shown to play an important role in disease resistance of wheat against a variety of fungal pathogens (4) ... 

ABA is another important plant hormone that participates in plant diseases and stress resistance (Mauch-Mani and Mauch 2005). The role of ABA in CTS-induced plant immunity was studied by Iriti and Faoro (2008). Chitosan application induced ABA accumulation in leaf tissues at 24 h after treatment, and elicited resistance against TNV. Besides, treatment with nordihydroguaiaretic acid (an ABA inhibitor) before chitosan application reduced tobacco resistance to the necrosis virus. It is indicated that ABA plays an important role in CTS-induced resistance mechanism. 

Acquired resistance has been observed by constitutive upregulation of mdr efflux pump expression due to a mutation inactivating a respective repressor or inducibly, caused by molecules transiently inactivating repressor molecules upon binding. Depending upon the substrate spectra of the respective subset of efflux pumps upregulated, a multiple drug resistance (mdr) phenotype is expressed, which in combination with a specific resistance mechanism can contribute to a clinically relevant level of resistance. 

Sequiera, L. (1983). Mechanisms of induced resistance in plants. Annual Review of Microbiology, 37, 51-79. 

Effect on content of polyphenolic compounds Complete protection from stress, however, appears to reduce plant synthesis of polyphenolic compounds, which are known to be produced as part of the plant s inducible resistance response to fungal and pest attack, but are also produced in response to certain abiotic stress factors such as mechanical injury (Feucht and Treutter, 1999). 

Toth et al. 2005), induced resistance was found only in the top blades of S.filipendula (Taylor et al. 2002). The authors concluded that valuable basal stipes are mechanically and constitutively defended, while the valuable meristematic tissues have inducible chemical defenses (Taylor et al. 2002). 

Induced resistance is the qualitative or quantitative enhancement of a plant s defense mechanisms against pests in response to extrinsic physical or chemical stimuli. These extrinsic stimuli are known as inducers or elicitors. 

A better understanding of the role of phytoalexins in plant defenses and of the mechanisms of induced resistance may potentially open a powerful new approach to the control of insect pests of cultivated plants. If indeed, in light of the hypothesis of optimal defense strategies (3), a post-attack response is a more efficient line of defense than the attack-independent accumulation of allelochemics, the exploitation of phytoalexin-producing mechanisms may represent a fertile field for future investigations. Several uses of induced resistance may be conceived. Four of these approaches are briefly discussed. 

Systemic acquired resistance an inducible defence mechanism in plants... 

Culture Filtrates. SchBnbeck et al. (26) applied culture filtrates from various fungi and bacteria to beans and induced resistance to bean rust. The induction of resistance occurred at a distance from the site where the inducer was applied indicating it was systemic. A period of at least two days was required for the Initiation of the resistance response. The phenomenon appeared to be nonspecific since the culture filtrates induced resistance in other plants and against various pathogens however, only against obligate parasites. The active compounds in the culture filtrates have not been identified and their mechanism of action is unknown. 

In general, microbial biocontrol mechanisms have been classified according to effect (Baker, 1968) and have included such actions as parasitism/predation, niche competition, antibiosis and systemic induced resistance - the latter three falling... 

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