Browsing by Subject "poikilochlorophyllous"

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    Differences in rehydration of three desiccation-tolerant angiosperm species.
    (Oxford University Press, 1996) Sherwin, H; Farrant, J
    The 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.
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    Use of metabolic inhibitors to elucidate mechanisms of recovery from desiccation stress in the resurrection plant Xerophyta humilis.
    (Springer, 1998) Dace, H; Sherwin, H; Illing, N; Farrant, J
    Xerophyta humilis (Bak.) Dur. and Schinz is a poikilochlorophyllous resurrection plant in that it is tolerant of considerable water loss (< 5% relative water content [RWC]) and thylakoid membranes are dismantled and chlorophyll is lost during dehydration. In this paper we examined the processes associated with recovery from desiccation upon rehydration. Dried leaf explants were rehydrated in water (control) or in solutions of actinomycin-D or cyclohexamide in order to determine to what extent initial recovery was dependant on de novo transcription and translation respectively. Our results suggest that considerable protection of subcellular organisation and components of metabolism occurs during drying such that the initial recovery of metabolism on rehydration is virtually independent of de novo transcription of nuclear genes. However recovery does require the synthesis of new proteins. The plasmalemma remains intact and macromolecular synthesis is not required for maintenance of its integrity. Messenger RNA's for chlorophyll biosynthesis appear to be stored in a stable form in the dried leaves and are translated on rehydration. Similarly most of the mRNA's necessary for recovery of electron transport in the chloroplast (as determined by measuring the quantum efficiency of photosystem II [FV/FM] using chlorophyll fluorescence) appear to be stabily present in the dried leaves. However, for total recovery of FV/FM new genomic transcription is necessary.