Browsing by Subject "chlorophyll"
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- ItemRestrictedDifferences in rehydration of three desiccation-tolerant angiosperm species.(Oxford University Press, 1996) Sherwin, H; Farrant, JThe rehydration characteristics of the desiccation-tolerant plantsCraterostigma wilmsii andMyrothamnus flabellifolia (homoiochlorophyllous) andXerophyta viscosa (poikilochlorophyllous) were studied to determine differences among them. A desiccation-sensitive plant (Pisum sativum) was used as a control. Recovery of water content, quantum efficiency (FV/FM), photosynthetic pigments and chloroplast ultrastructure as well as damage to the plasmamembrane were studied. P. sativum did not recover after desiccation and considerable damage occurred during rehydration. The desiccation-tolerant plants appeared to differ in their responses to dehydration and rehydration. The small herbaceousC. wilmsii generally showed little damage in the dry state and recovered faster than the other tolerant species.M. flabellifolia took longer to recover thanC. wilmsii probably due to the presence of a woody stem in which dehydration-induced xylem embolisms slowed the rate of recovery. The poikilochlorophyllous speciesX. viscosa took the longest to recover because it took longer to reconstitute the chloroplasts and the photosynthetic pigments. Quantum efficiency recovered in all species before water content and chlorophyll content recovered to control levels. The significance of these different responses to desiccation and recovery from desiccation is discussed.
- ItemOpen AccessIndian Ocean Dipole and El Niño/Southern Oscillation impacts on regional chlorophyll anomalies in the Indian Ocean(2013) Currie, J C; Lengaigne, M; Vialard, J; Kaplan, D M; Aumont, O; Naqvi, S W A; Maury, OThe Indian Ocean Dipole (IOD) and the El Niño/Southern Oscillation (ENSO) are independent climate modes, which frequently co-occur, driving significant interannual changes within the Indian Ocean. We use a four-decade hindcast from a coupled biophysical ocean general circulation model, to disentangle patterns of chlorophyll anomalies driven by these two climate modes. Comparisons with remotely sensed records show that the simulation competently reproduces the chlorophyll seasonal cycle, as well as open-ocean anomalies during the 1997/1998 ENSO and IOD event. Results suggest that anomalous surface and euphotic-layer chlorophyll blooms in the eastern equatorial Indian Ocean in fall, and southern Bay of Bengal in winter, are primarily related to IOD forcing. A negative influence of IOD on chlorophyll concentrations is shown in a region around the southern tip of India in fall. IOD also depresses depth-integrated chlorophyll in the 5–10° S thermocline ridge region, yet the signal is negligible in surface chlorophyll. The only investigated region where ENSO has a greater influence on chlorophyll than does IOD, is in the Somalia upwelling region, where it causes a decrease in fall and winter chlorophyll by reducing local upwelling winds. Yet unlike most other regions examined, the combined explanatory power of IOD and ENSO in predicting depth-integrated chlorophyll anomalies is relatively low in this region, suggestive that other drivers are important there. We show that the chlorophyll impact of climate indices is frequently asymmetric, with a general tendency for larger positive than negative chlorophyll anomalies. Our results suggest that ENSO and IOD cause significant and predictable regional re-organisation of chlorophyll via their influence on near-surface oceanography. Resolving the details of these effects should improve our understanding, and eventually gain predictability, of interannual changes in Indian Ocean productivity, fisheries, ecosystems and carbon budgets
- ItemRestrictedProtection mechanisms against excess light in the resurrection plants Craterostigma wilmsii and Xerophyta viscosa.(Springer, 1998) Sherwin, H; Farrant, JMechanisms of avoidance and protection against light damage were studied in the resurrection plants Craterostigma wilmsii and Xerophyta viscosa. In C. wilmsii, a combination of both physical and chemical changes appeared to afford protection against free radical damage. During dehydration leaves curled inwards, and the abaxial surface became exposed to light. The tissue became purple/brown in colour, this coinciding with a three-fold increase in anthocyanin content and a 30% decline in chlorophyll content. Thus light-chlorophyll interactions are progressively reduced as chlorophyll became masked by anthocyanins in abaxial layers and shaded in the adaxial layers. Ascorbate peroxidase (AP) activity increased during this process but declined when the leaf was desiccated (5% RWC). During rehydration leaves uncurled and the potential for normal light-chlorophyll interaction was possible before full hydration had occurred. Superoxide dismutase (SOD) and glutathione reductase (GR) activities increased markedly during this stage, possibly affording free radical protection until full hydration and metabolic recovery had occurred. In contrast, the leaves of X. viscosa did not curl, but light-chlorophyll interactions were minimised by the loss of chlorophyll and dismantling of thylakoid membranes. During dehydration, free radical protection was afforded by a four-fold increase in anthocyanin content and increased activities of AP, GR and SOD. These declined during rehydration. It is suggested that potential free radical damage may be avoided by the persistence of anthocyanins during the period of thylakoid membrane re-assembly and full chlorophyll restitution which only occurred once the leaves were fully rehydrated.