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      Arbuscular mycorrhizal fungi (AMF) increase growth and secondary metabolism in cucumber subjected to low temperature stress

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      Scientia Horticulturae
      Elsevier BV

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          Functional analysis of the Arabidopsis PAL gene family in plant growth, development, and response to environmental stress.

          Phenylalanine ammonia-lyase (PAL) catalyzes the first step of the phenylpropanoid pathway, which produces precursors to a variety of important secondary metabolites. Arabidopsis (Arabidopsis thaliana) contains four PAL genes (PAL1-PAL4), but there has been no genetic analysis to assess the biological functions of the entire gene family. Here, we report the generation and analysis of combined mutations for the four Arabidopsis PAL genes. Contrary to a previous report, we found that three independent pal1 pal2 double mutants were fertile and generated yellow seeds due to the lack of condensed tannin pigments in the seed coat. The pal1 pal2 double mutants were also deficient in anthocyanin pigments in various plant tissues, which accumulate in wild-type plants under stress conditions. Thus, PAL1 and PAL2 have a redundant role in flavonoid biosynthesis. Furthermore, the pal1 pal2 double mutants were more sensitive to ultraviolet-B light but more tolerant to drought than wild-type plants. We have also generated two independent pal1 pal2 pal3 pal4 quadruple knockout mutants, which are stunted and sterile. The quadruple knockout mutants still contained about 10% of the wild-type PAL activity, which might result from one or more leaky pal mutant genes or from other unknown PAL genes. The quadruple mutants also accumulated substantially reduced levels of salicylic acid and displayed increased susceptibility to a virulent strain of the bacterial pathogen Pseudomonas syringae. These results provide further evidence for both distinct and overlapping roles of the Arabidopsis PAL genes in plant growth, development, and responses to environmental stresses.
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            Flavonoid oxidation in plants: from biochemical properties to physiological functions.

            Flavonoids protect plants against various biotic and abiotic stresses, and their occurrence in human diet participates in preventing degenerative diseases. Many of the biological roles of flavonoids are attributed to their potential cytotoxicity and antioxidant abilities. Flavonoid oxidation contributes to these chemical and biological properties and can lead to the formation of brown pigments in plant tissues as well as plant-derived foods and beverages. Flavonoid oxidation in planta is mainly catalyzed by polyphenol oxidases (catechol oxidases and laccases) and peroxidases. These activities are induced during seed and plant development, and by environmental stresses such as pathogen attacks. Their complex mode of action is regulated at several levels, involving transcriptional to post-translational mechanisms together with the differential subcellular compartmentalization of enzymes and substrates.
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              Polyphenol oxidases in plants and fungi: going places? A review.

              The more recent reports on polyphenol oxidase in plants and fungi are reviewed. The main aspects considered are the structure, distribution, location and properties of polyphenol oxidase (PPO) as well as newly discovered inhibitors of the enzyme. Particular stress is given to the possible function of the enzyme. The cloning and characterization of a large number of PPOs is surveyed. Although the active site of the enzyme is conserved, the amino acid sequence shows very considerable variability among species. Most plants and fungi PPO have multiple forms of PPO. Expression of the genes coding for the enzyme is tissue specific and also developmentally controlled. Many inhibitors of PPO have been described, which belong to very diverse chemical structures; however, their usefulness for controlling PPO activity remains in doubt. The function of PPO still remains enigmatic. In plants the positive correlation between levels of PPO and the resistance to pathogens and herbivores is frequently observed, but convincing proof of a causal relationship, in most cases, still has not been published. Evidence for the induction of PPO in plants, particularly under conditions of stress and pathogen attack is considered, including the role of jasmonate in the induction process. A clear role of PPO in a least two biosynthetic processes has been clearly demonstrated. In both cases a very high degree of substrate specificity has been found. In fungi, the function of PPO is probably different from that in plants, but there is some evidence indicating that here too PPO has a role in defense against pathogens. PPO also may be a pathogenic factor during the attack of fungi on other organisms. Although many details about structure and probably function of PPO have been revealed in the period reviewed, some of the basic questions raised over the years remain to be answered.
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                Author and article information

                Journal
                Scientia Horticulturae
                Scientia Horticulturae
                Elsevier BV
                03044238
                August 2013
                August 2013
                : 160
                :
                : 222-229
                Article
                10.1016/j.scienta.2013.05.039
                80cebfb6-c730-4eb2-b7b2-097a19e832b7
                © 2013
                History

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