Journal Article

Reduction to below Threshold Levels of Glycolate Oxidase Activities in Transgenic Tobacco Enhances Photoinhibition during Irradiation

Katsushi Yamaguchi and Mikio Nishimura

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 41, issue 12, pages 1397-1406
Published in print December 2000 | ISSN: 0032-0781
Published online December 2000 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcd074
Reduction to below Threshold Levels of Glycolate Oxidase Activities in Transgenic Tobacco Enhances Photoinhibition during Irradiation

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The effects of decreased flux in the glycolate pathway on photoinhibition was investigated in transgenic tobacco (Nicotiana tabacum L. cv. SR1) plants. These plants harbored a pumpkin cDNA for glycolate oxidase (GO), an enzyme in the glycolate pathway, under the control of the cauliflower mosaic virus 35S promoter. Some transformants showed both reduced amounts and reduced activities of GO. The decrease of GO was enhanced at a later growth stage of these transformants, whereas no changes were observed in the amounts of other enzymes in the glycolate pathway, such as hydroxypyruvate reductase and serine glyoxylate aminotransferase. The phenotype grown under a low light condition (30 µE s–1 m–2) resembled that of the wild type. Transformants with about 35% lower GO activity than wild type, had a lower Fv/Fm under 500 µE s–1 m–2 irradiation for 8 h. After 60 µE s–1 m–2 irradiation for 8 h, Fv/Fm was lowered in some transformants with less than 20% of the GO activity of the wild type. These results suggest that photosynthesis was susceptible to photoinhibition with reduction to below threshold levels of GO activities and that higher activities of GO are required under a higher irradiation. The increase in the electron transport rate (ETR) with increased irradiation was suppressed only in transformants that had GO activity one-third less than the wild type, suggesting that the regeneration of the substrate for the Calvin cycle was decreased only when there was an extreme reduction of GO. These results also suggest that the photosystem was disturbed when the concentration of the substrate for the Calvin cycle decreased until it became insufficient to receive the excess photon energy generated in each light environment.

Keywords: Key words: Calvin cycle — Glycolate oxidase — Glycolate pathway — Hydroxypyruvate reductase — Photoinhibition — Photorespiration.; Abbreviations: ETR, electron transport rate; Fd, ferredoxin; GO, glycolate oxidase; HPR, hydroxypyruvate reductase; RuBP, ribulose-1,5-bisphosphate; SGAT, serine glyoxylate aminotransferase.

Journal Article.  5869 words.  Illustrated.

Subjects: Plant Sciences and Forestry ; Biochemistry ; Molecular and Cell Biology

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