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Response of Plant to Diseases,Pests,and Stressful Environments
This is a research about the plant pests protection mechanism of resistance physiological ecology.
Induced resistance (IR) has emerged as a potential alternative strategy for crop protection. IR signifies the control of pathogens and pests by prior activation of plant defense pathways.
Plants activate an array of coordinated defense responses to restrict microbial attack. Timely perception of foreign molecules appears to be critical for the success of these defenses. Recent isolation of disease resistance (R) genes has revealed that R gene products have several features in common. This finding suggests that plants have evolved several common or similar signal transduction pathways to activate resistance to a range of unrelated microbes.* Three key signal molecules, namely salicylic acid (SA), jasmonate (JA), and ethylene (ET) mediate expression of both specific (R gene-mediated) as well as basal defense responses.*
Activation of inducible plant defense responses is probably brought about by the recognition of invariant pathogen-associated molecular patterns (PAMP) that are characteristic of whole classes of microbial organisms. PAMP perception systems and PAMP-induced signaling cascades partially resemble those known to mediate activation of innate immune responses in animals.*
Many progresses have been made in studies investigating roles played by some substances in plant disease resistance, such as H2O2, peroxidase (POD), -Aminobutyric acid (BABA), and benzothiadiazole.
Shetty (2007) has studied the role of hydrogen peroxide during the interaction between the hemibiotrophic fungal pathogen Septoria tritici and wheat. He found that the hemibiotroph infecting wheat (Triticum aestivum) was inhibited by H2O2 during the biotrophic phase. H2O2 removal by catalase at both early and late stages made plants more susceptible.*
Jacek Patykowski (2003) found that resistance of tomato plants to infection by the necrotrophic fungus Botrytis cinerea may result from early stimulation of hydrogen peroxide and superoxide radical generations by NADH peroxidase and SOD in apoplastic space.*
In-Chang Jang (2004) investigated changes in POD specific activity and expression of ten POD genes in four cultivars of sweet potato (Ipomoea batatas) after infection with Pectobacterium chrysanthemi. Native gel analysis revealed that one POD isoenzyme with a high electrophoretic mobility significantly increased in response to pathogen infection in all cultivars. These results indicate that some specific POD isoenzymes are involved in defense in relation to pathogenesis of P. chrysanthemi in sweet potato plants.*
BABA (-Aminobutyric acid) has proved to be a potent inducer of acquired resistance. BABA has a broad spectrum of activity against many disease-causing organisms such as virus, bacteria, oomycetes, fungi, and nematodes. This wide range of activity supports the notion of BABA as an inducer of resistance and not simply a biocidal substance.* BABA pretreatment of Brassica plants protected them against the necrotrophic pathogen Alternaria brassicae. The achieved resistance level was much higher than that seen after salicylic acid (SA) and jasmonic acid (JA) pretreatments, indicating that BABA-induced resistance is mediated through an enhanced expression of pathogenesis-related protein genes, independent of SA and JA accumulation.*
Jasmonic acid and its methyl ester are signaling molecules involved in regulating development and stress responses in plants. 12-Oxo-phytodienoic acid, a precursor in jasmonic acid biosynthesis, is also biologically active. Both oxylipins accumulate after pathogen infection.*
Benzothiadiazole (BTH) is a novel chemical activator of disease resistance in tobacco, wheat, and other important agricultural plants. It is shown that BTH works by activating systemic acquired resistance (SAR) in Arabidopsis thaliana.*
Numerous studies have shown that systemic acquired resistance (SAR) induced by the plant elicitor BTH can protect against plant pathogens. Ruth C. Plymale found that activation of SAR did not protect the plant against a chewing herbivore, and also did not reduce the effect of a natural enemy on an herbivore.*
Bacterial pathogens deliver type III effector proteins into plant cells during infection. On susceptible host plants, type III effectors contribute to virulence, but on resistant hosts they betray the pathogen to the plant's immune system and are functionally termed avirulence (Avr) proteins. Recognition induces a complex suite of cellular and molecular events comprising the plant's inducible defense response.*
M. Sedlřov (2001) has studied the role of phenolic compounds in the defense response of Lactuca spp. to lettuce downy mildew (Bremia lactucae). His results showed that the major role of phenolic compounds in studied Lactuca spp. is connected with their over expression and localized accumulation during a hypersensitive response (HR). In incompatible interactions a slight accumulation of phenols near the cell wall of infected cells was detected.*
According to B. Y. Zhao (2004), infiltration of different maize lines with a variety of bacterial pathogens of maize, rice, and sorghum identified qualitative differences in resistant reactions. Results indicate the same type of genes may contribute to both nonhost resistance and resistance to pathogens. There is, however, growing evidence that single loci can contribute significant effects toward nonhost resistance.*
Experimental evidence has shown that the response mechanism of an individual plant in its life history may vary with the changes in diseases, pests, and stressful conditions. This is a plant's intraspecific adaptive variation in defense strategy. This is an important part of the intraspecific comparative experimental system.
* For further details, please refer to Deep Structure Studies 7: Experimental Reviews and References I.


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