Browsing by Subject "Craterostigma wilmsii"

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    Cell wall characteristics and structure of hydrated and dry leaves of the resurrection plant Craterostigma wilmsii, a microscopical study.
    (Elsevier, 1999) Vicré, M; Sherwin, H W; Driouich, A; Jaffer, M A; Farrant, J M
    The cell wall architecture of leaf tissues of the resurrection plant Craterostigma wilmsii at various stages of dehydration and rehydration was studied using electron microscopy and immunocytochemistry with antibodies to a hemicellulose (xyloglucan) and pectins. Upon dehydration, the cell walls were shown to fold extensively. It is thought that this folding may prevent excessive mechanical stress developing between the cell wall and the plasmalemma. Our immunocytochemical results show a significant increase in labelling of xyloglucan and unesterified pectins in the cell wall during drying, with levels declining again during rehydration. These components are known to play an important structural role within the cell wall, giving it more tensile strength. It is hypothesised that this increase in tensile strength allows the cell wall to contract and then fold as the plant dries and ultimately prevents the total inward collapse of the cell walls in dry tissue. The increased tensile strength may also be necessary to prevent the cell wall from unfolding and expanding too rapidly upon rehydration, thus allowing plasmalemma-cell wall connections to be reestablished.
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    The effect of drying rate on the survival of three desiccation-tolerant angiosperm species.
    (Oxford University Press, 1999) Farrant, J; Cooper, K; Kruger, L; Sherwin, H
    The effect of drying rate on the survival of three angiosperm resurrection plants, Craterostigma wilmsii (homoiochlorophyllous), Xerophyta humilis (poikilochlorophyllous) and Myrothamnus flabellifolius (homoiochlorophyllous) was examined. All species survived slow drying, but only C. wilmsii was able to survive rapid drying. C. wilmsii was rapidly able to induce protection mechanisms such as folding of cell walls to prevent mechanical stress and curling of leaves to minimize light stress, and thus survived fast drying. Rapid drying of X. humilis andM. flabellifolius appeared to allow insufficient time for complete induction of protection mechanisms. In X. humilis, there was incomplete replacement of water in vacuoles, the photosynthetic apparatus was not dismantled, plasma membrane disruption occurred and quantum efficiency of photosystem II (FV/FM) did not recover on rehydration. Rapidly dried leaves of M. flabellifolius did not fold tightly against the stem and FV/FMdid not recover. Ultrastructural studies showed that subcellular damage incurred during drying was exacerbated on rehydration. The three species co-occur in environments in which they experience high desiccation pressures. C. wilmsii has few features to retard water loss and thus the ability for rapid induction of subcellular protection is vital to survival. X. humilis and M. flabellifolius are able to retard water loss and protection is acquired relatively slowly. Copyright 1999 Annals of Botany Company.
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    Isolation and characterisation of chloroplasts from Myrothamnus flabellifolius Welw.
    (Elsevier, 2000) Koonjul, P; Brandt, W; Lindsey, G; Farrant, J
    Chloroplasts isolated from the resurrection plant Myrothamnus flabellifolius using trehalose gradients had a higher buoyant density than chloroplasts isolated from another resurrection plant Craterostigma wilmsii. The latter had the same buoyant density as those isolated from the desiccation-sensitive (DS) plant Pisum sativum. The increased buoyant density in M. flabellifolius was ascribed to the unusual ultrastructure of the thylakoid membranes. Standard chloroplast isolation protocols resulted in membrane damage in both resurrection plants. Trehalose rather than sucrose gradients were required for isolation of intact chloroplasts. Immunological studies showed that epitopes related to the desiccation stress protein dsp 21 from Craterostigma plantagineum were present in M. flabellifolius. Several small (10–15 kDa) unique stromal proteins were also present. Polyphenolics, including anthocyanins, accumulated in leaves and chloroplasts of M. flabellifolius during drying. Envisaged functions for these are maintenance of membrane integrity, chlorophyll masking and antioxidant protection. Metal (Ca2+, Cu2+, Fe2+, Mg2+ and Mn2+) concentrations declined and thylakoid membranes separated upon drying. We propose that this might be a mechanism to put a stasis on photosynthesis and minimise photo-oxidation damage under water stress conditions.
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    Leaf tensile properties of resurrection plants differ among species in their response to drying
    (2009) Hedderson, N.; Balsamo, R. A.; Cooper, K.; Farrant, J. M.
    Previous studies report that leaf tensile strength (TS) of the desiccation tolerant (resurrection) grass Eragrostis nindensis does not change on drying, but increases in dried desiccation sensitive Eragrostis species. In this paper we tested whether unchanging TS on dehydration is a common feature among 4 resurrection species, Craterostigma wilmsii, Sporobolus stapfianus, Xerophyta humilis and Xerophyta schlecteri, and how this might relate to leaf structure and mechanisms of protection against mechanical stress of drying. Desiccation sensitive controls were Zea mays and Arabidopsis thaliana. Light and transmission electron microscopy of leaves was performed to determine lignification and the nature of subcellular mechanical stabilization. There was a positive correlation between % lignin/unit cross-sectional area and TS of hydrated leaves. Only the grass, S. stapfianus, did not change TS when naturally dried. All others increased in TS when naturally dried, but there was variation among them when flash dried. In S. stapfianus, mechanical stabilization was by both wall folding (mesophyll) and vacuole packaging (bundle sheath) as reported for E. nindensis. This combination may account, in part, for unchanging TS during drying and may be a feature of resurrection grasses. We conclude that leaf tensile properties differ among resurrection plants and are not necessarily affected by protection mechanisms associated with mechanical stress.
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    Leaf tensile properties of resurrection plants differ among species in their response to drying.
    (Elsevier, 2009) Hedderson, N; Balsamo, R; Farrant, J; Cooper, K
    Previous studies report that leaf tensile strength (TS) of the desiccation tolerant (resurrection) grass Eragrostis nindensis does not change on drying, but increases in dried desiccation sensitive Eragrostis species. In this paper we tested whether unchanging TS on dehydration is a common feature among 4 resurrection species, Craterostigma wilmsii, Sporobolus stapfianus, Xerophyta humilis and Xerophyta schlecteri, and how this might relate to leaf structure and mechanisms of protection against mechanical stress of drying. Desiccation sensitive controls were Zea mays and Arabidopsis thaliana. Light and transmission electron microscopy of leaves was performed to determine lignification and the nature of subcellular mechanical stabilization. There was a positive correlation between % lignin/unit cross-sectional area and TS of hydrated leaves. Only the grass, S. stapfianus, did not change TS when naturally dried. All others increased in TS when naturally dried, but there was variation among them when flash dried. In S. stapfianus, mechanical stabilization was by both wall folding (mesophyll) and vacuole packaging (bundle sheath) as reported for E. nindensis. This combination may account, in part, for unchanging TS during drying and may be a feature of resurrection grasses. We conclude that leaf tensile properties differ among resurrection plants and are not necessarily affected by protection mechanisms associated with mechanical stress.
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    Recovery of the resurrection plant Craterostigma wilmsii from desiccation: protection versus repair
    (Oxford University Press, 2002) Cooper, Keren; Farrant, Jill M
    Craterostigma wilmsii Engl. (homoiochlorophyllous) is a resurrection species that is thought to rely primarily on the protection of cellular components during drying to survive desiccation. The time taken for this protection to be instituted is thought to preclude recovery after rapid drying. Thus the response of C. wilmsii plants to rapid dehydration was investigated. The effect of rapid drying on sucrose accumulation was determined and the cellular ultrastructure was investigated during natural (slow) and rapid dehydration and on subsequent rehydration. The dependence of naturally and rapidly dried C. wilmsii on de novotranscription and translation during and after rehydration was determined by examining quantum efficiency, changes in photosynthetic pigments and subcellular organization of excised leaves with rehydration in water and using the metabolic inhibitors, distamycin A and cycloheximide. Slowly dried C. wilmsii required no new transcription or translation during rehydration in order to recover. With rapid dehydration, cells showed ultrastructural damage, which indicated that at least some protective mechanisms were affected (as evidenced by a reduced accumulation of sucrose). C. wilmsii was able to limit the damage and recover upon rehydration in water, but rapidly dried plants did not survive if mRNA or protein synthesis was inhibited by distamycin A or cycloheximide, respectively. This demonstrates an induction of repair mechanisms during rehydration, which enables recovery from rapid drying. Thus, although C. wilmsii does rely almost entirely on protection during natural drying, it apparently has the ability to repair if protection is inadequate and damage is incurred.