Resurrection Plant Research Articles

Hydration-induced reversible deformation of biological materials

The influx and efflux of water in biological structures actuates reversible deformation and recovery processes that are crucial for mechanical functions in plants and animals. These processes utilize various mechanochemical mechanisms: swelling directed by the arrangement of cellulosic microfibrils in a bilayer construct, which generates different deformation patterns; lignification gradients; hierarchical foam-like inner structures, some of which also include swelling by hygroscopic cellulose inner cell layer; turgor pressure, which is activated by osmosis and acts at the cellular level, generating reversible motions. In this Review, we present representatives of each of these four mechanisms: pine cones, wheat awns, the twisted opening of Bauhinia pods and the seed of the stork’s bill; the resurrection plant; ice plant seed capsules and carrotwood seed pod; the wilting and redressing of plant stems. Natural polymeric materials produced by animals can also exhibit hydration-driven shape and strength recovery: bird feathers and hair are prime examples. Spider silk — a non-keratinous biopolymer — also exhibits humidity-driven reversible deformation. After describing these animal-based mechanisms, we outline bioinspired applications to actuate multifunctional and biocompatible smart materials, and indicate future directions of research with potential for new bioinspired designs. The influx and efflux of water in biological structures leads to reversible deformation, which has important functions in plants (for example, in seed protection and dispersal) and animals (for example, in the recovery of the strength and shape of feathers, and for reversible changes in silk and hair). Here the authors review the main hydration-induced deformation mechanisms and highlight applications inspired by these processes.

Ammonium metabolism in Selaginella bryopteris in response to dehydration-rehydration and characterisation of desiccation tolerant, thermostable, cytosolic glutamine synthetase from plant.

Water deficit (WD) has adverse effects on plant growth, and acclimation requires responses allowing primary metabolism to continue. Resurrection plants can serve as model system to gain insight into metabolic regulation during WD. We herein report the response of a resurrection lycophyte, Selaginella bryopteris, to dehydration-rehydration cycle with emphasis on ammonium metabolism. Dehydration of S. bryopteris fronds resulted in decrease of total protein and increase of free ammonium levels and the effect was reversed on rehydration. The proline content increased twice after 24 h of dehydration, which again recovered to background levels comparable to that at full turgor state. The specific activity of glutamine synthetase (GS) didn't change significantly till 6 h and then declined by 21% after 24 h of dehydration, whereas specific activities of glutamate synthase (GOGAT) and aminating glutamate dehydrogenase (GDH) were enhanced significantly during dehydration. The deaminating activity of GDH also increased during dehydration albeit at a slower rate. Immunoblot analysis indicated overexpression of GS and GDH polypeptides during dehydration and their levels declined on rehydration. The results suggested significant role of GDH along with GS/GOGAT in production of nitrogen-rich amino acids for desiccation tolerance. Unlike higher plants S. bryopteris expressed GS only in cytosol. The enzyme had pH and temperature optima of 5.5 and 60°C, respectively, and it retained 96% activity on preincubation at 60°C for 30 min indicating thermostability. Hence, like higher plants the cytosolic GS from S. bryopteris has a conserved role in stress tolerance.

The dehydration- and ABA-inducible germin-like protein CpGLP1 from Craterostigma plantagineum has SOD activity and may contribute to cell wall integrity during desiccation

Main conclusionCpGLP1 belongs to the large group of germin-like proteins and comprises a cell wall-localized protein which has superoxide dismutase activity and may contribute towards ROS metabolism and cell wall folding during desiccation.The plant cell wall is a dynamic matrix and its plasticity is essential for cell growth and processing of environmental signals to cope with stresses. A few so-called resurrection plants like Craterostigma plantagineum survive desiccation by implementing protection mechanisms. In C. plantagineum, the cell wall shrinks and folds upon desiccation to avoid mechanical and oxidative damage which contributes to cell integrity. Despite the high toxic potential, ROS are important molecules for cell wall remodeling processes as they participate in enzymatic reactions and act as signaling molecules. Here we analyzed the C. plantagineum germin-like protein 1 (CpGLP1) to understand its contribution to cell wall folding and desiccation tolerance. The analysis of the CpGLP1 sequence showed that this protein does not fit into the current GLP classification and forms a new group within the Linderniaceae. CpGLP1 transcripts accumulate in leaves in response to dehydration and ABA, and mannitol treatments transiently induce CpGLP1 transcript accumulation supporting the participation of CpGLP1 in desiccation-related processes. CpGLP1 protein from cell wall protein extracts followed transcript accumulation and protein preparations from bacteria overexpressing CpGLP1 showed SOD activity. In agreement with cell wall localization, CpGLP1 interacts with pectins which have not been reported for GLP proteins. Our data support a role for CpGLP1 in the ROS metabolism related to the control of cell wall plasticity during desiccation in C. plantagineum.

Efficient protein extraction for shotgun proteomics from hydrated and desiccated leaves of resurrection Ramonda serbica plants.

Resurrection plant Ramonda serbica is a suitable model to investigate vegetative desiccation tolerance. However, the detailed study of these mechanisms at the protein level is hampered by the severe tissue water loss, high amount of phenolics and polysaccharide, and possible protein modifications and aggregations during the extraction and purification steps. When applied to R. serbica leaves, widely used protein extraction protocols containing polyvinylpolypyrrolidone and ascorbate, as well as the phenol/SDS/buffer-based protocol recommended for recalcitrant plant tissues failed to eliminate persistent contamination and ensure high protein quality. Here we compared three protein extraction approaches aiming to establish the optimal one for both hydrated and desiccated R. serbica leaves. To evaluate the efficacy of these protocols by shotgun proteomics, we also created the first R. serbica annotated transcriptome database, available at http://www.biomed.unipd.it/filearrigoni/Trinity_Sample_RT2.fasta . The detergent-free phenol-based extraction combined with dodecyl-β-D-maltoside-assisted extraction enabled high-yield and high-purity protein extracts. The phenol-based protocol improved the protein-band resolution, band number, and intensity upon electrophoresis, and increased the protein yield and the number of identified peptides and protein groupsby LC-MS/MS. Additionally, dodecyl-β-D-maltoside enabled solubilisation and identification of more membrane-associated proteins. The presented study paves the way for investigating the desiccation tolerance in R. serbica, and we recommend this protocol for similar recalcitrant plant material.

Profiling of phenolic compounds in desiccation-tolerant and non-desiccation-tolerant Linderniaceae.

Craterostigma plantagineum and Lindernia brevidens are resurrection plants, so these plants can tolerate desiccation of their vegetative tissues. Different components and mechanisms contribute to desiccation tolerance and secondary plant metabolites, like phenolic compounds, may play a role during these processes. Secondary plant metabolites of the two resurrection plants, C. plantagineum and L. brevidens as well as the closely related desiccation sensitive species, L. subracemosa, were investigated regarding the polyphenol profile. Secondary plant compounds were extracted with acidified methanol and analysed with ultra-high-performance liquid chromatography electrospray ionisation mass spectrometry (UHPLC-ESI-MS). Phenolic compounds were identified by comparing of ultraviolet (UV) and MSn -spectra with published data. All compounds were quantified as verbascoside equivalents by external calibration at the compound specific wavelength. In total, eight compounds that belong to the subclass of phenylethanoid glycosides and one flavone, luteolin hexoside pentoside, were identified. Two of these compounds exhibited a fragmentation pattern, which is closely related to phenylethanoid glycosides. The predominantly synthesised phenylethanoid in all of the three plant species and in every stage of hydration was verbascoside. The total content of phenolic compounds during the three stages of hydration, untreated, desiccated, and rehydrated revealed differences especially between C. plantagineum and L. brevidens as the latter one lost almost all phenolic compounds during rehydration. The amount of verbascoside correlates with the degree of desiccation tolerance and verbascoside might play a role in the protective system in acting as an antioxidant.

Identification and characterization of CTP:phosphocholine cytidylyltransferase CpCCT1 in the resurrection plant Craterostigma plantagineum

Phosphatidylcholine is a major phospholipid which is shown to be involved in stress adaptation. Phosphatidylcholine increased during dehydration in Craterostigma plantagineum, and therefore we characterized CTP:phosphocholine cytidylyltransferase (CpCCT1), a key regulatory enzyme for phosphatidylcholine synthesis in plants. The CpCCT1 gene from the resurrection plant C. plantagineum was cloned and the amino acid sequence was compared with homologs from other species including yeast and rat. CCT proteins have conserved catalytic and membrane-binding domains while the N-terminal and C-terminal domains have diverged. The tissue specific expression analysis indicated that CpCCT1 is expressed in all tested tissues and it is induced by dehydration and in response to 0.5 M NaCl solutions. In plants exposed to low temperature in the dark, the CpCCT1 transcript increased after 4 h at 4 °C. CpCCT1 expression also increased during mannitol and sorbitol treatments in a concentration dependent manner. Phytohormones such as abscisic acid and indole-3-acetic acid also trigged transcript accumulation. Comparisons of transcript and protein accumulations for different treatments (except for dehydration) suggest transcriptional and translational control mechanisms. Analysis of promoter activity and polysome occupancy suggest that CpCCT1 gene expression is mainly under translational regulation during dehydration.

Field and acclimated metabolomes of a resurrection plant suggest strong environmental regulation in the extreme end of the species’ range

Plant secondary metabolites are significant mediators of the interactions of plants with their environment. The desiccation tolerant “resurrection plant” Myrothamnus flabellifolia Welw. is distributed throughout southern Africa and is vicariantly separated between arid Namibia and the comparatively mesic South Africa where it is subjected to contrasting climate regimes. Our earlier study indicated that these populations were metabolomically and phylogenetically distinct, leading us to hypothesise that the metabolic signature of the arid-adapted plants from Namibia was environmentally determined. To test this, we profiled the metabolomes of plants from both regions that had been sampled directly in the field (non-acclimated) with those of plants from the same regions that had been long-term acclimated in a greenhouse (acclimated). Long-term acclimation resulted in a convergence of the metabolic profiles of the plants collected from the different regions. However, while the South African plants demonstrated little difference between their acclimated and non-acclimated metabolomes, the metabolomes of the acclimated Namibian samples were distinct from those of the plants sampled in the field in Namibia. Further scrutiny of the metabolite differences between the acclimated and non-acclimated Namibian samples revealed several metabolites that were significantly more abundant in the field samples, and we propose that these might contribute to survival in this region. To further test the metabolomic response from a temporal perspective, we subjected the acclimated plants to short-term high-temperature treatment in climate chambers. However, this treatment had no significant impact on the metabolomes of the plants. Our findings suggest that long-term, rather than short-term, environmental conditions warrant large-scale reprogramming of the metabolome in M. flabellifolia, and that the climate conditions in the more arid region of the species’ range necessitate the production of particular phenolic metabolites.

Recovery of photosynthetic activity of resurrection plant Haberlea rhodopensis from drought- and freezing-induced desiccation

The recovery of photosynthetic activity during rehydration of Haberlea rhodopensis from drought- and freezing-induced desiccation were investigated. The water uptake during the initial 15 h was slow thus preventing cellular damages. The results showed faster recovery of quantum efficiency of PSII in plants rehydrated after freezing stress (RAF) compared to plants rehydrated after drought stress (RAD) and the most significant differences between them were evident after 9-15 h of rehydration. Following rehydration, PSI activity recovered faster compared to PSII and in contrast to PSII, its activity was higher in RAD compared to RAF plants. During the first hours of rehydration, prominent alterations in energy transfer between photosynthetic complexes occurred as revealed by 77 K fluorescence of isolated thylakoids. High proportion of thermal energy dissipation in dry plants and during the first hours of rehydration protects them from photooxidation; the role of PSII reaction center quenching during the recovery was suggested.

Vegetative desiccation tolerance in Eragrostiella brachyphylla: biochemical and physiological responses

Eragrostiella brachyphylla is an angiosperm desiccation-tolerant resurrection plant, which can survive during desiccation in the air-dry state and recover completely on availability of water. The present study was conducted to understand the vegetative desiccation tolerance of Eragrostiella brachyphylla by evaluating its ability to recover the physiological, biochemical and morphological functions post desiccation. In order to understand the responses of Eragrostiella brachyphylla to desiccation and subsequent rehydration experiments were conducted in the hydrated state (HS), desiccated state (DS) and rehydrated state (RS). Scanning electron microscopy revealed significant changes between the three stages in the internal ultra-structures of leaves and stems. Compared to the other states, photosynthetic parameters such as chlorophyll a, chlorophyll b, total chlorophylland total carotenoid contents decreased significantly in the desiccated state. Superoxide radical (O2•−) content also increased, resulting in an oxidative burst during desiccation. Consequently, antioxidant enzymes such as catalase (CAT) superoxide dismutase (SOD) peroxidase (APX) and glutathione reductase (GR) activities were found to be significantly elevated in the desiccated state to avoid oxidative damage. Increased malondialdehyde (MDA) content and relative electrolyte leakage (REL) during desiccation provide evidence for membrane damage and loss of cell-wall integrity. During desiccation, the contents of osmolytes represented by sucrose and proline were found to increase to maintain cell structure integrity. After rehydration, all physiological, biochemical and morphological properties remain unchanged or slightly changed when compared to the hydrated state. Hence, we believe that these unique adaptations contribute to the remarkable desiccation-tolerance property of this plant.

MicroRNA profiling the resurrection plant Haberlea rhodopensis unveils essential regulators of survival under severe drought

Small RNAs (sRNAs) are essential components of gene-regulatory networks, which guide plant development and tune it to environmental challenges. Though the past years have witnessed evidences on sRNA importance for stress response, there is scarce data on their involvement in resurrection plant survival under severe drought. Haberlea rhodopensis (hrh) is an angiosperm resurrection species, whose vegetative tissues can tolerate desiccation and recover upon rehydration. In this study, high-throughput sequencing sRNAs indicated a higher complexity of the sRNA population, especially of a 24 nt sRNA category, in the desiccated vegetative tissue of H. rhodopensis compared to unstressed tissues. The cross-species discovery was performed to predict 77 mature microRNAs (miRNAs), most of which were assigned to 23 high-confidence conserved miRNA families in the leaf tissue. Several members of the miR156/157, miR166, and miR399 families were found to be desiccation-responsive. The miR156/157 family members were found up-regulated upon dehydration and down-regulated upon rehydration, while the miR166 and miR399 family members followed an opposite trend of expression. A probable miR156/157 target, orthologous to the SQUAMOSA promoter binding protein-like, was reconstructed in H. rhodopensis based on genomic data available for this species and the closely related Boea hygrometrica. Reverse transcription quantittative PCR analysis confirmed the expression profile of hrh-miR156a-5p and hrh-miR157-5p established by sRNA sequencing and revealed an inverse expression pattern between these miRNAs and their targets in the desiccated tissue. Our study suggests that the miR156/157 and miR399 families are essential for plant survival under severe drought due to their ability to control plant development and growth by modulating transcription factor expression.

Shared up-regulation and contrasting down-regulation of gene expression distinguish desiccation-tolerant from intolerant green algae

Among green plants, desiccation tolerance is common in seeds and spores but rare in leaves and other vegetative green tissues. Over the last two decades, genes have been identified whose expression is induced by desiccation in diverse, desiccation-tolerant (DT) taxa, including, e.g., late embryogenesis abundant proteins (LEA) and reactive oxygen species scavengers. This up-regulation is observed in DT resurrection plants, mosses, and green algae most closely related to these Embryophytes. Here we test whether this same suite of protective genes is up-regulated during desiccation in even more distantly related DT green algae, and, importantly, whether that up-regulation is unique to DT algae or also occurs in a desiccation-intolerant relative. We used three closely related aquatic and desert-derived green microalgae in the family Scenedesmaceae and capitalized on extraordinary desiccation tolerance in two of the species, contrasting with desiccation intolerance in the third. We found that during desiccation, all three species increased expression of common protective genes. The feature distinguishing gene expression in DT algae, however, was extensive down-regulation of gene expression associated with diverse metabolic processes during the desiccation time course, suggesting a switch from active growth to energy-saving metabolism. This widespread downshift did not occur in the desiccation-intolerant taxon. These results show that desiccation-induced up-regulation of expression of protective genes may be necessary but is not sufficient to confer desiccation tolerance. The data also suggest that desiccation tolerance may require induced protective mechanisms operating in concert with massive down-regulation of gene expression controlling numerous other aspects of metabolism.

Desiccation does not drastically increase the accessibility of exogenous DNA to nuclear genomes: evidence from the frequency of endosymbiotic DNA transfer

BackgroundAlthough horizontal gene transfer (HGT) is a widely accepted force in the evolution of prokaryotic genomes, its role in the evolution of eukaryotic genomes remains hotly debated. Some bdelloid rotifers that are resistant to extreme desiccation and radiation undergo a very high level of HGT, whereas in another desiccation-resistant invertebrate, the tardigrade, the pattern does not exist. Overall, the DNA double-strand breaks (DSBs) induced by prolonged desiccation have been postulated to open a gateway to the nuclear genome for exogenous DNA integration and thus to facilitate the HGT process, thereby enhancing the rate of endosymbiotic DNA transfer (EDT).ResultsWe first surveyed the abundance of nuclear mitochondrial DNAs (NUMTs) and nuclear plastid DNAs (NUPTs) in five eukaryotes that are highly resistant to desiccation: the bdelloid rotifers Adineta vaga and Adineta ricciae, the tardigrade Ramazzottius varieornatus, and the resurrection plants Dorcoceras hygrometricum and Selaginella tamariscina. Excessive NUMTs or NUPTs were not detected. Furthermore, we compared 24 groups of desiccation-tolerant organisms with their relatively less desiccation-tolerant relatives but did not find a significant difference in NUMT/NUPT contents.ConclusionsDesiccation may induce DSBs, but it is unlikely to dramatically increase the frequency of exogenous sequence integration in most eukaryotes. The capture of exogenous DNA sequences is possible only when DSBs are repaired through a subtype of non-homologous end joining, named alternative end joining (alt-EJ). Due to the deleterious effects of the resulting insertion mutations, alt-EJ is less frequently initiated than other mechanisms.

Heterologous Expression of Dehydration-Inducible MfWRKY17 of Myrothamnus Flabellifolia Confers Drought and Salt Tolerance in Arabidopsis

As the only woody resurrection plant, Myrothamnus flabellifolia has a strong tolerance to drought and can survive long-term in a desiccated environment. However, the molecular mechanisms related to the stress tolerance of M. flabellifolia are largely unknown, and few tolerance-related genes previously identified had been functionally characterized. WRKYs are a group of unique and complex plant transcription factors, and have reported functions in diverse biological processes, especially in the regulation of abiotic stress tolerances, in various species. However, little is known about their roles in response to abiotic stresses in M. flabellifolia. In this study, we characterized a dehydration-inducible WRKY transcription factor gene, MfWRKY17, from M. flabellifolia. MfWRKY17 shows high degree of homology with genes from Vitis vinifera and Vitis pseudoreticulata, belonging to group II of the WRKY family. Unlike known WRKY17s in other organisms acting as negative regulators in biotic or abiotic stress responses, overexpression of MfWRKY17 in Arabidopsis significantly increased drought and salt tolerance. Further investigations indicated that MfWRKY17 participated in increasing water retention, maintaining chlorophyll content, and regulating ABA biosynthesis and stress-related gene expression. These results suggest that MfWRKY17 possibly acts as a positive regulator of stress tolerance in the resurrection plant M. flabellifolia.

Biotechnology and Drought Stress Tolerance in Plants

Drought stress in plants has become one of the major abiotic stress that limits the growth and development of plants which also contributes to low yields. Biotechnology which has new and emerging techniques can be use to solve the problem of drought stress in plants. This review aimed at identifying drought stress tolerance in plants at different stages, how plants respond to drought stress using different methods and the application of different biotechnology methods to improve drought tolerance in plants. Some important parameters about drought stress in plants such as drought tolerance mechanisms, plants responses to drought stress, gene regulation for drought stress tolerance in plants, effects of drought stress at different stages of plant growth and biotechnology methods in developing drought tolerance in plants was reviewed. The use of biotechnology methods such as classical breeding, use of genetic manipulation, genes from resurrection plants and Protoplast fusion was discussed. Drought stress affects our plants seriously and it leads to wilts, reduction of yields and death of plants at different developmental stages. Plants have developed different mechanisms to respond to drought stress but these mechanisms are not sufficient enough without the application of biotechnology to greatly improve the growth, development and increase yield in pants. The use of biotechnology greatly improves plants ability to tolerate drought stress depending on the plant species and period of exposure. The use of biotechnology methods has become very vital in improving plants drought stress so as to overcome the major problems of plants which includes increase in population and climatic change.

Freezing tolerance of photosynthetic apparatus in the homoiochlorophyllous resurrection plant Haberlea rhodopensis

Haberlea rhodopensis is unique among homoiochlorophyllous resurrection plants with its ability to tolerate also low temperatures at temperate climate. This study was carried out to elucidate the response and acclimation ability of photosynthetic apparatus to cold and the capacity to tolerate freezing temperatures. Cold acclimated plants experienced short-term freezing conditions under controlled-environment in climatic chamber and also long-term subzero winter temperatures in an ex-situ natural environment. Our results indicated strong freezing tolerance after cold acclimation. In fact, fresh leaves were exposed to and survived freezing stress under both controlled and ex-situ conditions, thus confirming their appropriate cold acclimation. Freezing temperatures induced desiccation of leaves and the corresponding ultrastructural changes in mesophyll cells under ex situ environmental conditions. However, while the complete rearrangement in the cells commenced at 20 % RWC under drought stress, this process started already at 60 % RWC under freezing conditions. The presence of epidermal channels on both leaf sides was observed and their role for the fast water loss is proposed. It was found that freezing-induced desiccation, reversible downregulation of photosynthesis, readjustments in the abundance/organization of the pigment protein complexes and the main photosynthetic proteins together with increased thermal energy dissipation during chilling and freezing temperatures enable plants to survive harsh winter conditions and their fast recovery with the onset of spring. Low temperature responses are discussed in comparison to desiccation-induced changes to point out both common and specific features.

Isolation of high-quality RNA from recalcitrant leaves of variegated and resurrection plants.

Resurrection plant Ramonda serbica is a suitable model to investigate mechanisms of desiccation tolerance, while variegated Pelargonium zonale has been proven to serve as an excellent model for the metabolite allocation between sink tissue and source tissue within the same organ. However, the genomes of these plants are still not sequenced, limiting their application in molecular studies. To investigate the transcript abundance by next-generation sequencing, high-quality RNA input is required. Leaves of both P. zonale and R. serbica are rich in polyphenols that interfere with high-quality RNA extraction by common protocols. Moreover, low water content and high amount of sugars and other osmoprotectants in desiccated R. serbica leaves present the additional challenge in total RNA extraction. Here, we evaluated and compared several already established TRIzol- and CTAB-based protocols aiming to develop the efficient, simple and low-cost methods for the extraction of the satisfactory yield RNA of great purity and integrity, required for the construction of high-quality cDNA libraries. Our results show that the CTAB-based protocol (i.e. CTAB 1b) enabled the extraction of high-quality RNA from photosynthetically active and non-photosynthetically active leaf sectors of P. zonale, with high RIN values. On the other hand, TRIzol-based protocol provided a high RNA yield with low contamination and high RNA integrity even in desiccated leaves of R. serbica. We envisage that the proposed protocol would be suitable for the RNA extractions from other desiccated organs (e.g. seeds, grains, pollen grains).

Barbacenia graminifolia, a resurrection plant with high capacity of water retention

Desiccation tolerance (DT) in vegetative tissues is not a common ability, especially in Angiosperms. Barbacenia genus is distributed in tropical seasonally dry environments, such as rock outcrops, in South America. Some of the Barbacenia species are described as DT and are able to tolerate drastic water loss of their tissues during the desiccation process and to reestablish their metabolism after rehydration. In order to better understand this ability, we evaluated aspects related to leaf water status, gas exchange, photosynthetic pigments content and chlorophyll a fluorescence of B. graminifolia, during 32 days of water deprivation followed by rehydration. Carbon assimilation (A) remained active until the 24th day, when volumetric soil moisture was below 10%. Leaf relative water content (RWC) remained constant during 28 days of water withholding, decreasing significantly after this period, followed by the lowest gas exchange parameters and maximum quantum efficiency of photosystem II (Fv/Fm), and the highest degradation rates of chlorophyll and carotenoids in the course of the desiccation period. After rehydration, RWC was rapidly recovered, as well as Fv/Fm and photosynthetic parameters. This time frame was not enough for total recovery of A rates due, probably, to the slow restoration of chlorophyll a content. We classify, therefore, the species as a resurrection plant. Despite the similar decrease of photosynthetic rates found in other DT species before reaching the desiccated state, B. graminifolia maintains CO2 assimilation even under low soil water availability (10%) as physiological strategy when submitted to severe water deficit.

MfPIF1 of Resurrection Plant Myrothamnus flabellifolia Plays a Positive Regulatory Role in Responding to Drought and Salinity Stresses in Arabidopsis.

Phytochrome-interacting factors (PIFs), a subfamily of basic helix-loop-helix (bHLH) transcription factors (TFs), play critical roles in regulating plant growth and development. The resurrection plant Myrothamnus flabellifolia possesses a noteworthy tolerance to desiccation, but no PIFs related to the response to abiotic stress have been functionally studied. In this study, a dehydration-inducible PIF gene, MfPIF1, was cloned and characterized. Subcellular localization assay revealed that MfPIF1 is localized predominantly in the nucleus. Overexpression of MfPIF1 in Arabidopsis thaliana led to enhanced drought and salinity tolerance, which was attributed to higher contents of chlorophyll, proline (Pro), soluble protein, and soluble sugar, activities of antioxidant enzymes as well as lower water loss rate, malondialdehyde (MDA) content, and reactive oxygen species (ROS) accumulation in transgenic lines compared with control plants. Moreover, MfPIF1 decreased stomatal aperture after drought and abscisic acid (ABA) treatment, and increased expression of both ABA biosynthesis and ABA-responsive genes including NCED3, P5CS, and RD29A. Overall, these results indicated that MfPIF1 may act as a positive regulator to drought and salinity responses, and therefore could be considered as a potential gene for plant genetic improvement of drought and salinity tolerance.

Effect of different priming treatments on seed germination of sago palm (Cycas revoluta L.)

King sago palm or sago cycas are the other name of Kangi palm ( Cycas revoluta ) sago palm has been used as an indoor and outdoor landscape plant for centuries. The present study was conducted to estimate the effect of different priming treatments on seed germination of sago palm ( Cycas revoluta L.) in the research area of Department of Horticulture PMAS, University of Arid Agriculture Rawalpindi, Pakistan. The Experiment consisted of ten treatments; the seeds without pulp were soaked in solution of 500, 750 and 1000 ppm GA 3 and 2%, 3% and 4% solution of KNO 3 for 24 hr at room temperature. In case of hot water treatment, seeds were primed at 80 o C, 90 o C and 100 o C for 30, 20 and 10 minutes respectively. The effect of different concentrations of gibberellic acid (GA 3 ), potassium nitrate (KNO 3 ) and hot water on various parameters like germination rate, germination percentage, germination value, decayed seed percentage, time of germination, number of leaves and seedling height were studied. Significant results of germination rate (55.56 days), germination value (192.19) were achieved from 500 ppm GA 3 . Maximum germination percentage (73.33%) and number of leaves (2) were observed in KNO 3 at 2% followed by 500 ppm GA 3 . Similarly lowest decayed seed percentage (26.66%) and time of germination (59.41 days) were noted in 2% KNO 3 . The seedling height was optimum (19.33 cm) in 3% KNO 3 followed by 2% KNO 3 . Best germination results were obtained due to permeability of hard seed coat made by low concentrations of priming treatments (KNO 3 @ 3%).

Born to revive: molecular and physiological mechanisms of double tolerance in a paleotropical and resurrection plant.

Resurrection plants recover physiological functions after complete desiccation. Almost all of them are native to tropical warm environments. However, the Gesneriaceae include four genera, remnant of the past palaeotropical flora, which inhabit temperate mountains. One of these species is additionally freezing-tolerant: Ramonda myconi. We hypothesise that this species has been able to persist in a colder climate thanks to some resurrection-linked traits. To disentangle the physiological mechanisms underpinning multistress tolerance to desiccation and freezing, we conducted an exhaustive seasonal assessment of photosynthesis (gas exchange, limitations to partitioning, photochemistry and galactolipids) and primary metabolism (through metabolomics) in two natural populations at different elevations. R.myconi displayed low rates of photosynthesis, largely due to mesophyll limitation. However, plants were photosynthetically active throughout the year, excluding a reversible desiccation period. Common responses to desiccation and low temperature involved chloroplast protection: enhanced thermal energy dissipation, higher carotenoid to Chl ratio and de-epoxidation of the xanthophyll cycle. As specific responses, antioxidants and secondary metabolic routes rose upon desiccation, while putrescine, proline and a variety of sugars rose in winter. The data suggest conserved mechanisms to cope with photo-oxidation during desiccation and cold events, while additional metabolic mechanisms may have evolved as specific adaptations to cold during recent glaciations.