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Destructive hydrogen peroxide production in Eucheuma denticulatum (Rhodophyta) during stress caused by elevated pH,high light intensities and competition with other species
Authors:Matern SP Mtolera  Jonas Collén  Marianne Pedersén  Adelaida K Semesi
Institution:1. Institute of Marine Sciences , University of Dar es Salaam , PO Box 668, Zanzibar, Tanzania;2. Department of Physiological Botany , Uppsala University , Villav?gen 6, S-752 36, Uppsala, Sweden;3. Department of Physiological Botany , Uppsala University , Villav?gan 6, S-752 36, Uppsala;4. Department of Botany , University of Dar es Salaam , PO Box 35060, Dar es Salaam, Tanzania
Abstract:Growth of Eucheuma denticulatum was studied in the field and in laboratory experiments. Field co-cultivation of E. denticulatum with the green alga Ulva reticulata or the seagrass Thalassia sp. reduced daily growth rate (DGR) of a Tanzanian and a Philippine strain of E. denticulatum by 10–100% and 10–55%, respectively, depending upon the type of water current: a unidirectional water current produced the best growth. Laboratory co-cultivation of a Tanzanian strain of E. denticulatum with U. reticulata also reduced DGR (to 8% of the control) and nitrate-nitrogen uptake rate (to <30% of the control) of E. denticulatum and, moreover, it increased epiphytism of a red filamentous alga on E. denticulatum. E. denticulatum monoculture at pH 8·6 ± 0·5 or at photosynthetic photon flux densities (PPFDs) higher than its growth optimum (350 ± 50 μmol photons m-2 s-1) also increased epiphytism. The lack of a competitive mechanism for inorganic carbon uptake in Eucheuma may have contributed to its reduced growth during co-cultivation. During co-cultivation, elevated pH regimes (pH > 8·5) were created around the Eucheuma thalli as a result of photosynthesis, thus decreasing the concentration of CO2 in the seawater to values around 1 μmM. As Eucheuma depends mainly on the CO2 in the seawater for its growth, a higher pH can cause CO2 limitation by decreasing CO2 concentration. Hydrogen peroxide (H2O2) production from the Tanzanian strain was also determined by luminol-dependent chemiluminescence. H2O2 production was found to increase with increased pH and PPFD (probably as a result of oxidative stress). Preincubation of plants with catalase for 5 min before addition of luminol prevented chemiluminescence, confirming H2O2 as the substrate of the luminol reaction. We suggest that the inefficiency of E. denticulatum in HCO- 3 utilisation contributes to its poor growth during field coexistence with seagrasses or Ulva sp. and that carbon deficiency induces H2O2 production in E. denticulatum.
Keywords:Carbon limitation  ecological competition  Eucheuma sp    hydrogen peroxide production  Thalassia sp    Ulva sp  
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