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      Polyphenol oxidase in leaves: is there any significance to the chloroplastic localization?

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          Abstract

          Polyphenol oxidase (PPO) catalyses the oxidation of monophenols and/or o-diphenols to o-quinones with the concomitant reduction of oxygen to water which results in protein complexing and the formation of brown melanin pigments. The most frequently suggested role for PPO in plants has been in defence against herbivores and pathogens, based on the physical separation of the chloroplast-localized enzyme from the vacuole-localized substrates. The o-quinone-protein complexes, formed as a consequence of cell damage, may reduce the nutritional value of the tissue and thereby reduce predation but can also participate in the formation of structural barriers against invading pathogens. However, since a sufficient level of compartmentation-based regulation could be accomplished if PPO was targeted to the cytosol, the benefit derived by some plant species in having PPO present in the chloroplast lumen remains an intriguing question. So is there more to the chloroplastic location of PPO? An interaction between PPO activity and photosynthesis has been proposed on more than one occasion but, to date, evidence either for or against direct involvement has been equivocal, and the lack of identified chloroplastic substrates remains an issue. Similarly, PPO has been suggested to have both pro- and anti-oxidant functions. Nevertheless, several independent lines of evidence suggest that PPO responds to environmental conditions and could be involved in the response of plants to abiotic stress. This review highlights our current understanding of the in vivo functions of PPO and considers the potential opportunities it presents for exploitation to increase stress tolerance in food crops.

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          Author and article information

          Journal
          J. Exp. Bot.
          Journal of experimental botany
          1460-2431
          0022-0957
          Jun 2015
          : 66
          : 12
          Affiliations
          [1 ] Institute of Biological, Environmental and Rural Sciences (IBERS), Penglais Campus, Aberystwyth University, Aberystwyth SY23 3FG, UK.
          [2 ] Institute of Biological, Environmental and Rural Sciences (IBERS), Penglais Campus, Aberystwyth University, Aberystwyth SY23 3FG, UK ahk@aber.ac.uk.
          Article
          erv141
          10.1093/jxb/erv141
          25873687
          25951172-de25-4145-a4d9-751732c60fc5
          © The Author 2015. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.
          History

          Abiotic stress,photosynthesis,polyphenol oxidase,secondary metabolism.

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