Photosynthesis and photoprotection in mangroves under field conditions

ABSTRACT Net CO2 exchange and in vivo chlorophyll fluorescence were studied in mangrove (Rhizophora stylosa) leaves at a field site in Western Australia, and leaf samples were collected for the analysis of enzymes and substrates potentially involved in anti‐oxidant photoprotection. Photosynthesis sa...

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Published in:	Plant, cell and environment Vol. 20; no. 5; pp. 579 - 588
Main Authors:	CHEESEMAN3, J. M., HERENDEEN, L. B., CHEESEMAN, A. T., CLOUGH, B. F.
Format:	Journal Article
Language:	English
Published:	Oxford, UK Blackwell Publishing Ltd 01-05-1997 Blackwell
Subjects:	Animal and plant ecology Animal, plant and microbial ecology ascorbate peroxidase Autoecology Biological and medical sciences Fundamental and applied biological sciences. Psychology Mehler reaction oxidative stress photoinhibition Plants and fungi Rhizophora Rhizophoraceae superoxide dismutase Australia Western Australia Oceania Light effect Oxidative stress Tropical zone Electron transfer Detoxication Plant leaf Antioxidant Study under natural conditions Hyperoxides Mangrove Photoinhibition Photosynthesis Photoprotection
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Summary:	ABSTRACT Net CO2 exchange and in vivo chlorophyll fluorescence were studied in mangrove (Rhizophora stylosa) leaves at a field site in Western Australia, and leaf samples were collected for the analysis of enzymes and substrates potentially involved in anti‐oxidant photoprotection. Photosynthesis saturated at 900 μmol quanta m−2 s−1 and at no more than 7.5 μmol CO2 m−2 s−1. However, fluorescence analysis indicated no chronic photoinhibition: Fv:Fm was 0.8 shortly after sunset, and quantum efficiencies of PSII were high up to 500 μmol quanta m−2 s−1. Electron flow through PSII was more than 3 times higher than electron consumption through Calvin cycle activity, however, even with photorespiration and temperature‐dependent Rubisco specificities taken into account. Acknowledging the growing body of literature attributing a role to antioxidant systems in photoprotection, we also assayed the activities of superoxide dismutase (SOD) and several enzymes potentially involved in H2O2 metabolism. Their levels of maximal potential activity were compared with those in greenhouse‐grown mangroves (R. mangle), and growth chamber‐grown peas. Monodehydroascorbate reductase activities were similar in all species, and glutathione reductase was lower, and ascorbate peroxidase ∼40% higher, in the mangroves. SOD activities in field‐grown mangroves were more than 40 times those in peas. Our results support the hypothesis that O2 may be a significant sink for photochemically derived electrons under field conditions, and suggest an important role for O2− scavenging in photoprotection. However, when relative patterns are compared between species, imbalances between SOD and the other enzymes in the mangroves suggest that more components of the system (e.g. phenolics or peroxidases) are yet to be identified.
ISSN:	0140-7791 1365-3040
DOI:	10.1111/j.1365-3040.1997.00096.x