Photoinhibition in Codium fragile

Sealey, R.V., 1991. Photoinhibition in Codium fragile. PhD, Nottingham Trent University.

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Initial polarographic studies with intact fronds and isolated chloroplasts revealed an essentially stable photosynthetic response throughout the yearly life cycle. A light - induced increase in the rate of dark oxygen uptake that was unrelated to photosynthetic photon flux density (PPFD) was observed, a possible explanation being increased rates of photorespiration/ glycolate production, Mehler reaction and/ or chlororespiration, processes which may aid in the prevention of photoinhibition. Photosynthesis saturated rapidly and at low PPFD indicating efficient light harvesting and photoinhibition was not observed in intact fronds even at supraoptimal PPFD. In contrast, photoinhibition of isolated chloroplasts rapidly occurred at supraoptimal PPFD. The higher the chlorophyll concentration of the chloroplast suspension the higher the PPFD required for maximum photosynthesis (i.e. saturation) and the less dramatic the reduction in photosynthesis (j.e. photoinhibition) once the optimum irradiance was surpassed. The differences in the photosynthetic response of the intact frond and isolated chloroplasts must be due to properties of the former not shared by the latter, which enable the prevention of photoinhibition. The 'mimicking' of the frond response at high chlorophyll concentration in the chloroplast study suggests that the number and arrangement of chloroplasts within the frond may confer a vital 'self - shading' mechanism in the avoidance of photoinhibition by this alga.

Photoinhibited thylakoids exhibited an initial loss of Qb - dependent activity (DMBQ assay) followed by a loss of Qb - independent activity (SiMo assay) whilst photoinhibition of isolated chloroplasts caused an initial rise in F" and a preferential quenching of Fv. Fluorography provided preliminary evidence for a loss of - Met from D1 during 15 - 240 min photoinhibition of chloroplasts pre - radiolabelled in organello. These results may suggest that under the conditions of this study, photoinhibition of isolated C. fragile chloroplasts initially (0-10 min) results in damage to Qa and that only after this primary lesion has occurred does increased D1 turnover ensue.

The adaptations of C. fragile that enable the apparent paradox of efficient photosynthesis at the low PPFD experienced at high tide without accompanying photoinhibition at the supraoptimal PPFD experienced at low tide, in conjunction with other features of the growth strategy of this alga, may contribute to successful colonisation, despite the extreme environment, of the intertidal zone.

Item Type: Thesis
Creators: Sealey, R.V.
Date: 1991
ISBN: 9781369324211
Rights: This copy of the thesis has been supplied on condition that anyone who consults it is understood to recognise that its copyright rests with the author and that no quotation from the thesis and no information derived from it may be published without the author’s prior written consent.
Divisions: Schools > School of Science and Technology
Record created by: Linda Sullivan
Date Added: 11 Nov 2020 12:21
Last Modified: 11 Oct 2023 09:24

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