OpenUCT :: Browsing by Author "Farrant, Jill M"

Browsing by Author "Farrant, Jill M"

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Open Access
A comparison of some potential indicators of desiccation-tolerance in 2 Poikilochlorophyllous Xerophyta species and Homiochlorophyllous Craterostigma wilmsii
(2002) Brown, Carly; Farrant, Jill M
Three possible indicators of desiccation-tolerance in ang10sperms: sucrose accumulation and hexose sugar flux, an increase in hexokinase activity, and accumulation of LEA-like proteins, were investigated and compared during dehydration between two moncotyledonous poikilochlorophyllous resurrection angiosperm species; Xerophyta schlecterii and Xerophyta humilis, and a dicotyledonous homiochlorophyllous resurrection species, Craterostigma wilmsii. Comparisons were also made with Xerophyta viscosa, using data from Whittaker et al, (2001). Soluble sugar concentrations and hexokinase activities were also examined during rehydration of the three species. Sucrose was accumulated during dehydration in all species examined. However, C. wilmsii had completed sucrose accumulation by the intermediate stages of drying, whereas Xhumilis exhibited a late accumulation. It was not clear if Xschlecterii exhibited late sucrose accumulation due to high standard deviations in the results. C. wilmsii accumulated higher sucrose levels than the two poikilochlorophyllous species. During rehydration the sucrose concentrations dropped in all three species, and was probably being used as an energy source for the resumption of metabolism. Glucose and fructose concentrations were relatively constant during dehydration in all three species, and did not appear to be contributing greatly to sucrose accumulation. This was further confirmed by the low levels of activity of hexokinase found in all three species during dehydration and rehydration, which suggests that the channelling of glucose and fructose into sucrose biosynthesis is not being upregulated during dehydration. C. wilmsii had an increased level of hexokinase late in dehydration, that may have been in preparation for the rapid rehydration experienced by this homiochlorophyllous species, where hexokinase would need to rapidly channel glucose and fructose into metabolism. There was not an increase in activity at the period of highest sucrose accumulation in this species. The activity of hexokinase was relatively constant throughout dehydration and rehydration for Xschlecterii, as it was for Xhumilis. Glucose and fructose levels dropped slightly in C. wilmsii during rehydration but remained relatively constant in the two poikilochlorophyllous species. The presence of LEA-like proteins was found in all three species, although the bands were very faint for X viscosa and Xhumilis. In Xschlecterii the bands were clear in the dehydrated leaf sample, but were faint or absent in the hydrated sample. It is possible that the proteins in this species were upregulated or induced by drying. A protein common to all three species in dehydrated and hydrated samples was observed between the 22.5 kDa and the 15.3 kDa molecular markers.
Open Access
Activation of seed-specific genes in leaves and roots of the desiccation tolerant plant, Xerophyta humilis
(2008) Walford, Sally-Ann; Illing, Nicola; Farrant, Jill M; Denby, Katherine J
The ability of tissues to survive almost complete loss of cellular water is a trait found throughout the plant kingdom. While this desiccation tolerance is common in seeds of most angiosperms it is rare in their vegetative tissues. Xerophyta humilis (Bak.) Dur and Schintz belongs to a small group of resurrection angiosperms and it possesses the ability to withstand extreme desiccation of greater than 90% in both its seeds and vegetative tissues and return to active metabolism upon rehydration. We have tested the hypothesis that vegetative desiccation tolerance in angiosperms has evolved as an adaptation of seed desiccation tolerance.
Open Access
ASP 53, a 53 kDa cupin-containing protein from Acacia erioloba seeds that protects proteins against thermal denaturation
(2004) Mtwisha, Linda; Lindsey, George G; Brandt, Wolf F; Farrant, Jill M
Includes bibliographical references (leaves 103-111).
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ASP53, a thermostable protein from Acacia erioloba seeds that protects target proteins against thermal denaturation.
(CSIRO Publishing, 2007) Mtwisha, Linda; Farrant, Jill M; Brandt, Wolf; Hlongwane, Caswell; Lindsey, George G
ASP53, a 53 kDa heat soluble protein, was identified as the most abundant protein in the mature seeds of Acacia erioloba E.Mey. Immunocytochemistry showed that ASP53 was present in the vacuoles and cell walls of the axes and cotyledons of mature seeds and disappeared coincident with loss of desiccation tolerance. The sequence of the ASP53 transcript was determined and found to be homologous to the double cupin domain-containing vicilin class of seed storage proteins. Mature seeds survived heating to 60◦C and this may be facilitated by the presence of ASP53. Circular dichroism spectroscopy demonstrated that the protein displayed defined secondary structure, which was maintained even at high temperature. ASP53 was found to inhibit all three stages of protein thermal denaturation. ASP53 decreased the rate of loss of alcohol dehydrogenase activity at 55◦C, decreased the rate of temperature-dependent loss of secondary structure of haemoglobin and completely inhibited the temperature-dependent aggregation of egg white protein.
Open Access
Aspects of the physiology of the resurrection plant Xerophyta Humilis under different environmental conditions
(2002) Loffell, D. A.; Farrant, Jill M; Van der Willigen, Clare
Xerophyta humilis is a resurrection monocot that is able to survive drying of its tissues to an air-dry state. in order to assess the alidity of laboratory-based experimentation, and the results obtained from such studies, a comparison of aspects of X. humilis physiology under different environmental conditions was undertaken. Analyses of chlorophyll ﬂuorescence, gas exchange parameters, pigment concentrations and electrolyte leakage were performed on plants dehydrated under laboratory conditions differing with respect to light intensity ("high light" (ca. 1400 ųmol.m-². s-¹) and "low light" (ca. 400 ųmol. m-². s-¹)). Physiological parameters were also examined during rehydration under high and low light laboratory conditions, and natural ﬁeld conditions. Plants maintained fully hydrated for some time were also examined under laboratory conditions for the occurrence of rhythmic patterns in their daily physiology, and for any evidence of acclimatisation to the different environments.
Open Access
Aspects of the prevention of light damage during drying and rehydration of the desiccation-tolerant grass Eragrostis nindensis
(1998) Bergh, Nicola G; Farrant, Jill M
There are two main mechanisms of desiccation-tolerance in angiosperms. Both of these (poikilochlorophylly and homoiochlorophylly) involve adaptations to prevent light-induced damage as the plants dry and rehydrate. The poikiolchlorophyllous grass E. nindensis was investigated to determine physiological responses to light during drying, and mechanisms of tolerance of dehydration. The desiccation-sensitive E. curvula was investigated simultaneously as a control in order to compare responses of tolerant and sensitive relatives. Quantum efficiency of photosystem II was determined using chlorophyll fluorescence parameters and levels of photosynthetic pigments (chlorophylls and carotenoids) and of anthocyanins were measured. Electrolyte leakage of drying and rehydrating leaves was monitored to determine the extent of damage to membranes. Quantum efficiency and photosynthetic pigment contents were reduced in both plant§ dehydrated to <2% RWC; only E. nindensis recovered to initial levels. Both plants accumulated anthocyanins but these reached greater levels in E. nindensis and were found on the entire length of the leaf. On rehydration, E. nindensis lost the anthocyanins as it reconstituted chlorophylls. Neither species showed marked increases in electrolyte leakage but E. curvula did not recover on rewatering.
Open Access
Biolistic-mediated transformation of Eragrostis Curvula with the HSP 12 gene
(2003) Ncanana, Sandile Welcome; Farrant, Jill M; Lindsey, George G; Brandt, Wolf F
Eragrostis curvula is a desiccation sensitive monocotyledonous plant and an economically important forage grass in southern Africa. This species has a potential to be improved for drought and salt resistance among other important agronomic traits. In this study, E. curvula was used as a model system to explore the feasibility of producing pasture grasses with increased tolerance to water deficit. To date, no reports have been published on transformation of this species. This study reports the transformation of E. curvula with Saccharomyces cerevisiae Hsp 12 gene using biolistic-mediated transformation. Firstly, a tissue culture protocol was established for E. curvula that was suitable for transformation studies. Although this species has been previously regenerated in vitro using inflorescence tissues, this study established new protocols that utilize leaf and seed as source of material. The aim of which was to find the best regenerable tissue that could be used for transformation studies. Plant regeneration was achieved from shoot explants cultured on MS medium supplemented with either 0.5 mg/I thidiazuron (TDZ) or 0.5 mg/I 6-benzylaminopurine (BAP) through the process of direct organogenesis. It was found that TDZ was the most effective cytokinin. Plant regeneration was also achieved from callus induced from immature leaves on MS medium supplemented with 2 mg/I 2,4- 0,0.01 mg/I BAP and 6 % (w/v) sucrose. Histological experiments performed gave clear evidence that plant regeneration from callus was through a process of indirect organogenesis. The regeneration protocol was combined with an optimized biolistic mediated transformation protocol using the PDS-I00/He apparatus of which both shoot explants and callus were used as target tissues. In the molecular aspect of the study, the Hsp 12 gene was ligated in the Sac I restriction site of pCAMBIAUbeeQ vector. The successful cloning of the Hsp 12 gene was confirmed by PCR and restriction endonuclease digestion. The resultant vector pCAMBIAUbeeQ Hsp 12 was purified and subsequently used for biolistic transformation of E. curvula. The regenerable shoot explants and callus tissue were bombarded with DNA (pCAMBIAUBeeQHsp12) coated on gold particles. As a comparative study, Agrobacterium tumefaciens was transformed with pCAMBIAUBeeQHsp12 vector for subsequent transformation of Nicotiana tabacum. Transient expression of GUS gene in transformed E. curvula shoot explants was visualized 72 h after bombardment. Optimized conditions for expression of GUS gene were gold micro projectiles, 7 cm travel distance and helium pressure of 9100 kPa. Transformed tissues were cultured on the regeneration medium without antibiotic selection. Putative transformants were generated and the presence of Hsp 12 gene was verified by PCR and its expression at RNA level was confirmed by RT-PCR. The presence of Hsp 12 protein in the transformed plants was analyzed using SDS-PAGE and MALDI-TOF peptide mass spectrometry.
Open Access
Cell wall involvement in desiccation tolerance in the resurrection plant Craterostigma wilmsii
(2001) Vicre, Maїté; Farrant, Jill M; Driouich, Azeddine
Resurrection plants have the unique capacity to revive from an air-dried state. In order to cope with desiccation, resurrection plants have to overcome a number of stresses, mechanical stress being one. This occurs when the cytoplasm shrinks creating tension between the plasma membrane and the cell wall. In leaves of the Craterostigma species, an extensive shrinkage occurs during drying as well as a considerable wall folding. It is thought that this folding is a well controlled process rather than a simple collapse and that the ability of the wall to fold is important for the viability of the tissues upon drying. The aim of this study was to characterize the cell wall architecture and composition in hydrated and dry leaves of C. wilmsii using microscopical and biochemical techniques. Calcium and hormone contents were also determined during drying. The development of anhydrous fixation for microscopy confirmed the important folding of the wall previously observed with chemical fixation. Using immunocytochemical techniques and a variety of well characterized antibodies, the nature and composition of wall polymers was investigated. There was nothing unusual in the wall composition of C. wilmsii leaves as compared with other dicotyledonous plants. The results show a significant increase of the hemicellulosic polysaccharide xyloglucan and of the unesterified pectins during drying with levels declining again during rehydration. In contrast no increase was observed in others polysaccharides such as ß (1-4) galactans and methylesterified pectins. Biochemical analysis allowed further characterization of cell wall composition of C. wilmsii. The data demonstrate marked changes in the pectic and hemicellulosic wall fraction from dry plants compared to hydrated ones. The most conspicuous change was a decrease in glucose content in the hemicellulose fraction of the dry plant. Together these findings show that dehydration causes important alteration of polysaccharides content in the cell wall of C. wilmsii. Such modifications might be involved in the modulation of the mechanical properties of the wall during dehydration. Furthermore calcium ions content was shown to increase in the cell wall of dry plants, this could also have a role in stabilizing the wall architecture. All these alterations might be under the control of auxin, an hormone whose content was shown to increase during dehydration.
Open Access
Characterisation of galactinol synthase II (XvGolSII) from the resurrection plant Xerophyta viscosa (Baker)
(2013) Neumann, Alexis Joy; Rafudeen, Suhail; Farrant, Jill M
The monocotyledonous Xerophyta viscosa belongs to a unique group of angiosperms known as resurrection plants. These plants possess a number of unique characteristics which allow them to survive and cope for extended periods with extreme abiotic stresses such as dehydration and cold stress. It is therefore of great interest to understand and elucidate the various molecular mechanisms which are specifically regulated in response to abiotic stress by identifying genes and proteins which may contribute to abiotic stress tolerance. These genes could potentially be utilized in the development of crops with improved tolerance to abiotic stresses. The aim of this study was to preliminarily characterize XvGolSII, a galactinol synthase, which had been isolated from a X. viscosa cold stress cDNA library. In this study, the XvGolSII cDNA was sequenced and both the nucleic and amino acid sequence analysed through in silico analysis. The XvGolSII cDNA sequence was shown to be 1434 bp in length, with an open reading frame (ORF) of 1018 bp. This ORF encodes a 339 amino acid protein with a molecular weight of 38.7 kDa, containing a characteristic hydrophobic carboxyterminal pentapeptide, APSAA. Recombinant XvGolSII protein was successfully expressed in E. coli BL21 cells using the pET29b expression vector. The recombinant XvGolSII protein showed in vitro galactinol synthase activity via an activity assay using HPAEC-PAD, where it produced galactinol from the substrates myo-inositol and UDPgalactose. Subcellular localisation examination, using an XvGolSII-YFP fusion protein, indicated localisation to the cell membrane of onion epidermal cells. Quantitative real time PCR analysis showed XvGolSII to be significantly down-regulated during dehydration stress while mildly up-regulated during the early stages of cold stress, though the latter increase was not significant. Western blot analyses did not detect XvGolSII in total protein extracted from X. viscosa leaf tissue during dehydration and rehydration treatments, using polyclonal antibodies generated from the XvGolSII recombinant protein. This study successfully characterized XvGolSII at the molecular level and provides a basis for further investigation of the role of XvGolSII in abiotic stress tolerance.
Open Access
Characterisation of two desiccation-linked dehydrins from Xerophyta humilis
(2016) Fan, Cynthia; Farrant, Jill M; Rafudeen, Suhail
In response to abiotic stresses, organisms throughout the plant kingdom, as well as microorganisms and micro-animals such as nematodes or tardigrades, have been observed to express Late Embryogenesis Abundant (LEA) proteins as protective mechanisms. However, despite two decades of research, little is understood about their physiological functions and this has led to extensive nomenclature, with a large amount of redundancy. The primary reason for this lack of insight into LEA protein functions is their highly hydrophilic and intrinsically disordered nature. Intrinsically disordered proteins (IDPs) cannot be studied using conventional methods of structural analyses such as X-ray crystallography and, therefore, alternative techniques are required. A combination of transgenic and in vitro studies have also shown that LEA proteins are most likely to behave as molecular chaperones by binding water and ions, preventing macromolecular aggregation and protecting enzymatic activity during dehydration. This study characterized two dehydrins that were expressed during dehydration in the desiccation tolerant plant, Xerophyta humilis. From a transcriptome analyses on X. humilis, cDNA for the two dehydrins were obtained. These sequences were first analysed using various in silico tools in order to identify putative dehydrin-specific characteristics. Subsequently, these two dehydrins were cloned and expressed for production of recombinant dehydrin protein. These proteins were then analysed in terms of structural and functional characteristics. Structurally, through the use of circular dichroism in an in vitro system, both dehydrins demonstrated the shift towards being increasingly alpha-helical when placed in environments of decreasing water content. The role of these two dehydrins in stabilizing enzymes during dehydration was subsequently investigated using citrate synthase (CS) and lactate dehydrogenase (LDH). The preservation of enzyme activity was observed in both CS and LDH. This preservation of enzyme activity was further maintained by the presence of trehalose. Anti-aggregation roles were also investigated, however, neither dehydrin demonstrated significant ability to minimize the aggregation of LDH. This study hopes to establish a pipeline for characterizing LEA proteins using structural and functional assays in order to provide alternative means of LEA protein classification.
Open Access
Characterization of membrane lipids and, Changes therein during desiccation and rehydration of the resurrection plant Xerophyta humilis (Bak) Dur and Schinz
(2018) Tshabuse, Freedom; Farrant, Jill M; Ruelland, Eric
Drought is the primary challenge facing agricultural productivity and food sustainability productivity in Africa and many parts of the world. Very few higher plants, including crop plants, can survive periods of extended water loss. However, a small group of angiosperms, termed resurrection plants are able to lose up to 95% of their cellular water content in vegetative tissue upon extended periods of water, remain in an air-dry for months to years and regain full metabolic activity in the same tissue upon re-watering. The aim of this study was to investigate the changes in acyl chain composition within the major glycerophospholipids (in total and chloroplast suspension) and galactolipids (chloroplast suspension) at different stages of dehydration and rehydration treatments in the resurrection plant Xerophyta humilis (Bak) Dur and Schniz. This was done in order to ascertain their roles during acquisition of desiccation tolerance in X. humilis. The galactolipids and glycerophospholipids acyl chain compositions were determined by multiple reaction monitoring (MRM) mass spectrometry. The glycerophospholipids profiles from total leaves and roots lipid extracts showed an increased representation of unsaturated molecular species such as 18:3/18:3 (in leaves) and 18:3/18:2 (in leaves and roots) during dehydration, with a decrease in saturated and mono-saturated molecular species such as 16:0/16:0. Rehydration was associated with the opposite trend. Furthermore, increased representation of molecular species with unusual fatty acids were observed during dehydration, with the odd-numbered fatty acids such as 15:0, 17:0 and 19:0 increasing during dehydration and decreasing during re-watering. On the other hand, the 23:0 and 25:0 fatty acids decreased during dehydration and increased upon rehydration. Within the chloroplast profiles, the galactolipids (i.e. monogalactosyldiacylglycerolipids and digalactosyldiacylglycerolipids) showed maintenance of 18:3/18:3 and 18:3/18:2 molecular species during dehydration and rehydration. The phosphatidylglycerolipids profiles in the chloroplast, together with the uncommon chloroplastic glycerophospholipids such as phosphatidylethanolamine, phosphatidylcholine and phosphatidylinositol also showed an increase in the unsaturated molecular species during dehydration and decrease upon rehydration. Taken together, our data suggest that water deficit in X. humilis roots and leaves induce fatty acid unsaturation, as well as production of uncommon fatty acids. These unsaturated fatty acids may aid in maintaining membrane integrity during dehydration. This study shows that changes in lipid composition are part of the desiccation tolerance strategies used by X. humilis.
Open Access
Characterization of polyphenols in leaves of four desiccation tolerant plant families
(2005) Dzobo, Kevin; Lindsey, George G; Farrant, Jill M; De Wet, Jacques
Polyphenols in plants are known to act as antioxidants, antimicrobials, antifungal, photoreceptors, visual attractors and as light screens. In this study polyphenols in angiosperms found in southern Africa and called resurrection (desiccation tolerant) plants were studied. These plants are Myrothamnus flabellifolius, Xerophyta viscosa, Xerophyta humilis, Xerophyta schlecterii, Xerophyta villosa. Craterostigma wilmsii, Craterostigma plantagineum, Craterostigma pumilum and Eragrostis nindensis. These plants are able to tolerate water stress without undergoing permanent damage. During drying these plants are subjected to different stresses and one such stress is oxidative stress. It has been suggested that polyphenols function as stress protectants in plant cells by scavenging reactive oxygen species (ROS) produced during a period of oxidative stress. In this study the total phenolic content and the related antioxidant capacity of the plants leaf extracts were analysed.
Open Access
Characterization of the Xerophyta humilis desiccation induced-1 (Xhdsi-1voc) gene : a member of the Vicinal Oxygen Chelate (VOC) metalloenzyme superfamily upregulated in X. humilis (BAK) DUR and SCHINZ during desiccation
(2008) Mulako, Inonge; Illing, Nicola; Farrant, Jill M
The resurrection plant, Xerophyta humilis is used as a model system to identify and characterise genes which play an important role in conferring desiccation tolerance in plants. In this study, the expression of a novel gene named desiccation induced-1 (dsi-1VOC) during desiccation in X. humilis and desiccationsensitive plants is characterised.
Open Access
Characterization of two, desiccation linked, Group 1 LEA proteins from the resurrection plant Xerophyta humilis
(2011) Ginbot, Zekarias Gebremedhin; Farrant, Jill M; Illing, Nicola
Studies on resurrection plants and other anhydrobiotic organisms show expression of Late Embryogenesis Abundant (LEA) proteins associated with desiccation tolerance. However, the precise role of these proteins has not been described. This study was undertaken to investigate expression, structure and function of XhLEA1-4S1 and XhLEA1-1S2, Group 1 LEA proteins from Xerophyta humilis, in order to shed light on their role in desiccation tolerance. Complementary DNA (cDNA) of these XhLEAs were cloned into bacterial expression vectors and the recombinant proteins expressed in E. coli. Antibodies were generated and used in determination of expression conditions and immunolocalization studies.
Open Access
Cloning and characterisation of a bZIP transcription factor from a resurrection grass, Eragrostis nindensis
(2004) Brocklehurst, David; Farrant, Jill M; Mundree, Sagadevan G; Thomson, Jennifer Ann
The G-box is a plant DNA cis-acting element involved in the regulation of gene expression in response to a range of environmental signals including anaerobiosis, dehydration and light as well as by abscisic acid (ABA). Basic leucine zipper (bZIP) transcription factors have been shown to specifically bind and activate transcription from G-boxes in a dimerized form. A 1.5 kb cDNA for a bZIP class transcription factor, designated EnGBF1, was cloned from a desiccation-tolerant grass, Eragrostis nindensis by degenerate RT-PCR.
Open Access
Cloning and characterisation of LEA1-EM genes in the resurrection plant, Xerophyta humilis
(2008) Ngubane, Nqobile A C; Farrant, Jill M; Illing, Nicola
The presence and expressIon patterns of orthologues of LEA group 1 genes has been characterised in the resurrection plant, Xerophyta humilis. The group I LEAs (Em I and Em6) were first identified as proteins that were abundantly and specifically expressed during the desiccation and germination phase of angiosperm seed development. The group I LEA genes are characterised by the presence of one or more tandemly repeated 20-amino acid motifs that are particularly rich in Gly residues.
Open Access
A comparison of leaf sucrose accumulation and regulation between plants of C.Plantagineum dried in the light and dark
(2002) Rojoa, N Z; Farrant, Jill M
The resurrection plant C. plantagineum is able to survive almost complete water loss in their vegetative tissues and can then rehydrate rapidly on rewatering. The ability to recover completely from dehydration has been attributed in part to the ability of the plant to accumulate large quantities of sucrose. The accumulation of sucrose stabilises membranes, protects proteins and contributes to cellular osmoregulation during water stress. However, it has been observed in C. wilmsii by research group of Farrant (unpublished) that sucrose accumulations differ significantly when dehydration is carried out in the light and the dark. Farrant (unpublished) observed a significant increase in sucrose accumulation when dehydration was carried in light while dehydration in the dark resulted in very low amount of sucrose. Based on these findings, using the plant C. plantagineum, metabolic factors, which could contribute to differences, observed in C. wilmsii for sucrose accumulation in both light and dark was examined in this project. To achieve this, three enzymes in relation to sucrose accumulation from leaves dried in both light and dark treatments were examined, namely: hexokinase, acid invertase and aldolase. The amount of glucose, fructose and sucrose during the dehydration process in both light and dark treatments were also examined. Results obtained show a significant decrease in sucrose (9.8-fold decrease) when tissues of C. plantagineum where dried in the dark as opposed to the light. Furthermore, the amount of hexose sugars was also significantly lower in dark dehydrated tissues. Moreover, the enzyme data for dark dehydrated samples showed that both aldolase and hexokinase activity levels were significantly low. In contrast, enzyme data for the light dehydrated tissues showed that aldolase and hexokinase activities were maintained, although a higher level of aldolase activity was recorded, until approximately 10% RWC where a drop-in activity was recorded for both enzyme. However, acid invertase activity was comparable for both light and dark dehydrated tissues. Thus, it seems that the down regulation of aldolase during dehydration in the dark might be responsible for the low sucrose content obtained in the dark for C. plantagineum.
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Desiccation tolerance in the vegetative tissues of the fern Mohria caffrorum is seasonally regulated
(Blackwell Publishing, 2009) Farrant, Jill M; Lehner, Arnaud; Cooper, Keren; Wiswedel, Stefan
As there is limited information on the mechanisms of vegetative desiccation tolerance in pteridophytes, we undertook a comprehensive anatomical, ultrastructural, physiological and biochemical study on the fern Mohria caffrorum. Our data show that this species is desiccation-tolerant during the dry season, and desiccation-sensitive in the rainy season. This system allows the verification of protection mechanisms by comparison of tolerant and sensitive tissues of the same species at the same developmental age. Tolerant fronds acquire protection mechanisms during drying that are mostly similar to those reported for angiosperms. These include: (i) chlorophyll masking by abaxial scales and frond curling; (ii) increased antioxidant capacity that is maintained in dry tissues; (iii) mechanical stabilization of vacuoles in the dry state; (iv) de novo production of heat stable proteins (at least one identified as a putative chaperonin); (v) accummulation of protective carbohydrates (sucrose, raffinose family oligosaccharides and cyclitols). This study has implications for the biotechnological production of drought-tolerant crops, and allows speculation on the evolution of vegetative desiccation tolerance.
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Desiccation-induced ultrastructural and biochemical changes in the leaves of the resurrection plant Myrothamnus flabellifolia
(CSIRO Publishing, 2007) Moore, John P; Hearshaw, Meredith; Ravenscroft, Neil; Lindsey, George G; Farrant, Jill M; Brandt, Wolf F
Light microscopy and low-temperature scanning electron microscopy were used to systematically compare the surface and internal ultrastructures of hydrated and desiccated leaves of the resurrection plant Myrothamnus flabellifolia (Welw.). This revealed that leaf tissue underwent considerable shrinkage and collapse on desiccation but was supported by a framework of vascular and sclerenchymous tissue, which is responsible for the fan-like shape of the leaves. In addition, the leaf ribs were covered with wax and an internal wax cuticle was observed. Biochemical analysis showed that the cyanidin 3-glucoside content increased on desiccation as did the trehalose and sucrose contents. Salt deposits were observed at the apices of desiccated leaves in the proximity of hydathode-like structures. We propose that this might regulate the leaf salt content since decreased intracellular cation concentration was observed in desiccated leaves. We believe that these unique adaptations contribute to the remarkable desiccation-tolerance properties of this plant.
Open Access
Determination of a robust metabolic barcoding model for chemotaxonomy in Aizoaceae species : expanding morphological and genetic understanding
(2016) Hilgart, Amelia; Gammon, David W; Farrant, Jill M
The use of metabolic fingerprints as taxonomic markers is becoming more common. Many studies have found that by comparing the vast metabolic fingerprints of closely related species to each other, secondary metabolites tend to be unique to the samples of individual species and are identified in clustering algorithms as the variables responsible for species-specific clustering. A holistic approach to metabolic fingerprinting was thus employed to assess the stability of various metabolomic markers and finally to distinguish taxonomically difficult Aizoaceae species. Many secondary metabolites are not constitutively produced. Because at least some Aizoaceae species facultatively use crassulacean acid metabolism (CAM), there was a potentially interesting molecular switch that could be monitored for transitions in metabolic fingerprints. In order to contextualise the changes in carbon uptake, 20 different climate, nutrient, physiological, and other variables were monitored over the course of 12 months to build up a store of species-specific information to use in model optimisation across 5 Aizoaceae species (Galenia africana, Aridaria noctiora, Carpobrotus edulis, Ruschia robusta, and Tetragonia fruticosa) using two Crassulaceae species as CAM controls (Cotyledon orbiculata and Tylecodon wallichii ). Metabolic fingerprints of the leaves of various Aizoaceae species were generated using LC/TOFMS, following which Principal Components Analysis (PCA) was used to identify the LC-MS ions which distinguished the species from each other, or in statistical terms, were informative. Once isolated, this subset of informative data was established as metabolic barcodes for the identification of the study species. A machine learning algorithm, Random Forest, was used to build a classification model based on the metabolic barcodes which was then trained on various trends from the factors monitored over the year. The use of these trends in the development of a classification model based on metabolic barcodes resulted in a highly robust classification model for species identification. Clustering analysis of a subset of ions which corresponded to compounds previously isolated from Aizoaceae species did not show species-specific clustering and was inevitably biased by compounds from species with a greater number of studies focusing on compound isolation. Ideally, this model should be expanded to include other species from the Aizoaceae family to further check robustness of the model. Application of this model to these and other species could facilitate not only species identification and distribution, but also the identification of novel chemical constructs associated with particular species.