Mechanisms Of Desiccation Tolerance Research Articles

Organ-specific proteomes of Selaginella convoluta provide insights into its desiccation tolerance mechanisms

Selaginella convoluta is a desiccation-tolerant lycophyte capable of enduring water deprivation by arresting its metabolism when dry and reactivating it upon rehydration. Mechanisms to mitigate the harmful effects of desiccation have been investigated in an evolutionary context; however, plants have additional species-specific strategies refined by environmental conditions. Previous metabolome analysis pointed out S. convoluta as a source of chemodiversity. Shotgun proteomic analysis, conducted using an Orbitrap Elite and analyzed with PatternLab for proteomics, compared shoots and roots under two hydration conditions. Our approach identified 1,176 proteins. Proteins associated with photosynthesis, stress, and defense (primarily Reactive Oxygen Species scavengers and chaperones) were enriched in the shoots’ proteome in both hydrated and desiccated states. Post-hydration, roots exhibited exclusive proteins involved in defense, metabolism, and protein trafficking (notably 14-3-3-like proteins, and a putative Bet_v_1 domain-containing protein, which was 15.6 times more abundant in dehydrated roots). These results demonstrate that S. convoluta, when harvested in its dried state from its natural habitat, serves as a valuable source of molecular data, reflecting a realistic multifactorial environmental scenario.

Measurement of the rotational relaxation time of intracellular water in dried yeast and Jurkat cells by near infrared spectroscopy

Molecular mobility of intracellular water is a crucial parameter in the study of the mechanism of desiccation tolerance. As one of the parameters that reflecting molecular mobility, the viscosity of intracellular water has been found intimately related with the protection of the phospholipid membrane because it quantifies the diffusion ability of water and mass in the intracellular environment. In this work we measured the intracellular water relaxation time, which can be translated into water viscosity, by using a previously established NIR-dielectric method to monitor the drying process of baker's yeast and Jurkat cells with different desiccation tolerance. We found that intracellular saccharide can significantly decrease the intracellular water viscosity. Also, the intracellular water diffusion coefficient obtained from this method were found in good agreement with other reports.

Effect of glutathione-transport-related gene gsiD on desiccation tolerance of Cronobacter sakazakii and its related regulatory mechanism.

The outstanding desiccation tolerance of Cronobacter sakazakii (C. sakazakii) enables long-term persistence in food products with low-water activity to increase the infection risk, especially in low-birth-weight, immuno-compromised neonates, and infants less than 4 weeks of age. In our previous study, the disruption of glutathione transport-related gene gsiD by transposon was found to significantly increase its inactivation rate under drying stress challenges. However, the mechanism underlying the association between glutathione transport and desiccation tolerance of C. sakazakii remains to be clarified. In this study, the mechanism underlying their association was investigated in detail by constructing the gsiD gene deletion mutant. gsiD gene deletion was found to cause the dysfunction of the glutathione transport system GsiABCD and the limitation of glutathione import. The resulting decrease in intracellular glutathione caused the decreased potassium ions uptake and increased potassium ions efflux, inhibited the proline synthesis process, limited extracellular glutathione utilization, increased oxidant stress, reduced biofilm formation, and increased outer membrane permeability, which may be the main reasons for the significant reduction of the desiccation tolerance of C. sakazakii.IMPORTANCEContributing to its superior environmental adaptability, Cronobacter sakazakii can survive under many abiotic stress conditions. The outstanding desiccation tolerance makes this species persist in low-water activity foods, which increases harm to humans. For decades, many studies have focused on the desiccation tolerance of C. sakazakii, but the existing research is still insufficient. Our study found that gsiD gene deletion inhibited glutathione uptake and further decreased intracellular glutathione content, causing a decrease in desiccation tolerance and biofilm formation and an increase in outer membrane permeability. Moreover, the expression level of relative genes verified that gsiD gene deletion made the mutant not conducive to surviving in dry conditions due to restricting potassium ions uptake and efflux, inhibiting the conversion of glutamate to compatible solute proline, and increasing the oxidative stress of C. sakazakii. The above results enrich our knowledge of the desiccation tolerance mechanism of C. sakazakii.

Specific metabolic and cellular mechanisms of the vegetative desiccation tolerance in resurrection plants for adaptation to extreme dryness.

Substantial advancements have been made in our comprehension of vegetative desiccation tolerance in resurrection plants, and further research is still warranted to elucidate the mechanisms governing distinct cellular adaptations. Resurrection plants are commonly referred to as a small group of extremophile vascular plants that exhibit vegetative desiccation tolerance (VDT), meaning that their vegetative tissues can survive extreme drought stress (> 90% water loss) and subsequently recover rapidly upon rehydration. In contrast to most vascular plants, which typically employ water-saving strategies to resist partial water loss and optimize water absorption and utilization to a limited extent under moderate drought stress, ultimately succumbing to cell death when confronted with severe and extreme drought conditions, resurrection plants have evolved unique mechanisms of VDT, enabling them to maintain viability even in the absence of water for extended periods, permitting them to rejuvenate without harm upon water contact. Understanding the mechanisms associated with VDT in resurrection plants holds the promise of expanding our understanding of how plants adapt to exceedingly arid environments, a phenomenon increasingly prevalent due to global warming. This review offers an updated and comprehensive overview of recent advances in VDT within resurrection plants, with particular emphasis on elucidating the metabolic and cellular adaptations during desiccation, including the intricate processes of cell wall folding and the prevention of cell death. Furthermore, this review highlights existing unanswered questions in the field, suggests potential avenues for further research to gain deeper insights into the remarkable VDT adaptations observed in resurrection plants, and highlights the potential application of VDT-derived techniques in crop breeding to enhance tolerance to extreme drought stress.

Insights into the chaotropic tolerance of the desert cyanobacterium Chroococcidiopsis sp. 029 (Chroococcidiopsales, Cyanobacteria).

The mechanism of perchlorate resistance of the desert cyanobacterium Chroococcidiopsis sp. CCMEE 029 was investigated by assessing whether the pathways associated with its desiccation tolerance might play a role against the destabilizing effects of this chaotropic agent. During 3 weeks of growth in the presence of 2.4 mM perchlorate, an upregulation of trehalose and sucrose biosynthetic pathways was detected. This suggested that in response to the water stress triggered by perchlorate salts, these two compatible solutes play a role in the stabilization of macromolecules and membranes as they do in response to dehydration. During the perchlorate exposure, the production of oxidizing species was observed by using an oxidant-sensing fluorochrome and determining the expression of the antioxidant defense genes, namely superoxide dismutases and catalases, while the presence of oxidative DNA damage was highlighted by the over-expression of genes of the base excision repair. The involvement of desiccation-tolerance mechanisms in the perchlorate resistance of this desert cyanobacterium is interesting since, so far, chaotropic-tolerant bacteria have been identified among halophiles. Hence, it is anticipated that desert microorganisms might possess an unrevealed capability of adapting to perchlorate concentrations exceeding those naturally occurring in dry environments. Furthermore, in the endeavor of supporting future human outposts on Mars, the identified mechanisms might contribute to enhance the perchlorate resistance of microorganisms relevant for biologically driven utilization of the perchlorate-rich soil of the red planet.

Desiccation tolerance mechanisms of resurrection plant Selaginella pulvinata

The resurrection plant Selaginella pulvinata possesses an extraordinary ability to survive longterm desiccation, with the capacity to recover to normal growth after four years in a desiccated state. To understand the phenomenon, we investigated morphology, cytology, physiology, and performed PacBio single-molecule, real-time (SMRT) sequencing and Illumina RNA-sequencing of S. pulvinata during dehydration and rehydration. The full-length transcriptome dataset of S. puvinata consisted of 78,914 isoforms, and 75,819 isoforms (96.07%) were functionally annotated. The mapping rate of RNA-seq was 86.83–93.46% when utilizing the full-length transcriptome dataset as a reference. A total of 17,934 differentially expressed genes (DEGs) were identified during dehydration and rehydration. During dehydration, swollen chloroplasts and mitochondria, as well as vacuolation occupied space in desiccated cells, which cooperated with dense cytoplasm to inhibit the collapse and folding of desiccated cells. Accumulation and up-regulated gene expressions of osmotic agent and protective proteins contributed to the formation of vacuolation and dense cytoplasm. To reduce ROS damage during dehydration, two strategies were employed in S. pulvinata, i.e., reducing ROS production and scavenging ROS. Reducing exposure area, inactive PSII and down-regulated gene expression in photosynthesis decreased ROS production caused by excessive light absorption. Increased activities and up-regulated gene expressions in antioxidant enzyme system promoted ROS scavenging. ABA signaling pathway was hypothesized to play an important regulatory role in the desiccation tolerance of S. pulvinata due to significant ABA accumulation and up-regulated expressions of related genes during dehydration. Moreover, the comparative transcriptome analysis revealed that the pathways involved in dehydration and rehydration of the resurrection species S. pulvinata, S. lepidophylla and S. sellowii were consistent, indicating the similar desiccation tolerance mechanisms existing in the different resurrection species of Selaginella. Our study preliminarily revealed the desiccation tolerance mechanisms of S. pulvinata, which holds significant potential for inspiring biotechnological strategies aimed at enhancing drought tolerance in crops.

Tripogon loliiformis tolerates rapid desiccation after metabolic and transcriptional priming during initial drying

Crop plants and undomesticated resilient species employ different strategies to regulate their energy resources and growth. Most crop species are sensitive to stress and prioritise rapid growth to maximise yield or biomass production. In contrast, resilient plants grow slowly, are small, and allocate their resources for survival in challenging environments. One small group of plants, termed resurrection plants, survive desiccation of their vegetative tissue and regain full metabolic activity upon watering. However, the precise molecular mechanisms underlying this extreme tolerance remain unknown. In this study, we employed a transcriptomics and metabolomics approach, to investigate the mechanisms of desiccation tolerance in Tripogon loliiformis, a modified desiccation-tolerant plant, that survives gradual but not rapid drying. We show that T. loliiformis can survive rapid desiccation if it is gradually dried to 60% relative water content (RWC). Furthermore, the gene expression data showed that T. loliiformis is genetically predisposed for desiccation in the hydrated state, as evidenced by the accumulation of MYB, NAC, bZIP, WRKY transcription factors along with the phytohormones, abscisic acid, salicylic acid, amino acids (e.g., proline) and TCA cycle sugars during initial drying. Through network analysis of co-expressed genes, we observed differential responses to desiccation between T. loliiformis shoots and roots. Dehydrating shoots displayed global transcriptional changes across broad functional categories, although no enrichment was observed during drying. In contrast, dehydrating roots showed distinct network changes with the most significant differences occurring at 40% RWC. The cumulative effects of the early stress responses may indicate the minimum requirements of desiccation tolerance and enable T. loliiformis to survive rapid drying. These findings potentially hold promise for identifying biotechnological solutions aimed at developing drought-tolerant crops without growth and yield penalties.

Analysis of the trehalose synthesis pathway of Physarum polycehalum

Desiccation is a severe survival problem for organisms. We have been studying the desiccation tolerance mechanisms in the true slime mold Physarum polycephalum. We measured the trehalose content of P. polycephalum vegetative cells (plasmodia) and drought cells (sclerotia). Surprisingly, we found that the content in sclerotia was about 473-fold greater than in the plasmodia. We then examined trehalose metabolism-related genes via RNAseq, and consequently found that trehalose 6-phosphate phosphorylase (T6pp) expression levels increased following desiccation. Next, we cloned and expressed the genes for T6pp, trehalose 6-phosphate synthase/phosphatase (Tps/Tpp), maltooligosyltrehalose trehalohydrolase (TreZ), and maltooligosyltrehalose synthase (TreY) in E. coli. Incidentally, TreY and TreZ clones have been reported in several prokaryotes, but not in eukaryotes. This report in P. polycephalum is the first evidence of their presence in a eukaryote species. Recombinant T6pp, TreY, and TreZ were purified and confirmed to be active. Our results showed that these enzymes catalyze reactions related to trehalose production, and their reaction kinetics follow the Michaelis-Menten equation.The t6pp mRNA levels of the sclerotia were about 15-fold higher than in the plasmodia. In contrast, the expression levels of TreZ and TreY showed no significant change between the sclerotia and plasmodia. Thus, T6pp is probably related to desiccation tolerance, whereas the contribution of TreY and TreZ is insufficient to account for the considerable accumulation of trehalose in sclerotia.

Antioxidative Defense, Suppressed Nitric Oxide Accumulation, and Synthesis of Protective Proteins in Roots and Leaves Contribute to the Desiccation Tolerance of the Resurrection Plant Haberlea rhodopensis.

The desiccation tolerance of plants relies on defense mechanisms that enable the protection of macromolecules, biological structures, and metabolism. Although the defense of leaf tissues exposed to solar irradiation is challenging, mechanisms that protect the viability of the roots, yet largely unexplored, are equally important for survival. Although the photosynthetic apparatus in leaves contributes to the generation of oxidative stress under drought stress, we hypothesized that oxidative stress and thus antioxidative defense is also predominant in the roots. Thus, we aimed for a comparative analysis of the protective mechanisms in leaves and roots during the desiccation of Haberlea rhodopensis. Consequently, a high content of non-enzymatic antioxidants and high activity of antioxidant enzymes together with the activation of specific isoenzymes were found in both leaves and roots during the final stages of desiccation of H. rhodopensis. Among others, catalase and glutathione reductase activity showed a similar tendency of changes in roots and leaves, whereas, unlike that in the leaves, superoxide dismutase activity was enhanced under severe but not under medium desiccation in roots. Nitric oxide accumulation in the root tips was found to be sensitive to water restriction but suppressed under severe desiccation. In addition to the antioxidative defense, desiccation induced an enhanced abundance of dehydrins, ELIPs, and sHSP 17.7 in leaves, but this was significantly better in roots. In contrast to leaf cells, starch remained in the cells of the central cylinder of desiccated roots. Taken together, protective compounds and antioxidative defense mechanisms are equally important in protecting the roots to survive desiccation. Since drought-induced damage to the root system fundamentally affects the survival of plants, a better understanding of root desiccation tolerance mechanisms is essential to compensate for the challenges of prolonged dry periods.

Desiccation tolerance of Termitidae termites in relation to their nest type.

The family Termitidae is renowned for its diverse nesting behaviors, with the evolution of epigeal and arboreal nests hypothesized to increase desiccation stress due to greater exposure to air. However, these nests may also alleviate desiccation stress through humidity regulation. To explore the implications of acquiring epigeal and arboreal nests, we investigated desiccation tolerance traits in 16 Termitidae termite species with varying nest types and analyzed trait correlations. Principal component analysis revealed that termites constructing epigeal and arboreal nests exhibited reduced water loss rates and enhanced survival under desiccated conditions. Furthermore, termites building arboreal nests displayed a notably higher water content. Redundancy analysis demonstrated that nest types accounted for a substantial portion (57.2%) of the observed variation in desiccation tolerance. These findings support the hypothesis that epigeal and arboreal nests in termites are associated with increased desiccation stress and increased desiccation tolerance. These findings highlight the role of nest type in influencing desiccation tolerance mechanisms and water regulation strategies in termites.

Transcriptomic analysis reveals novel desiccation tolerance mechanism of Cronobacter based on type VI secretion system inhibition

Cronobacter malonaticus (C. malonaticus) is a food-borne pathogen inducing severe infections both in infants and adults, and it could survive in dry powdered infant formula (PIF) for a long time, implying its strong tolerance to desiccation. However, the thorough molecular mechanism of resistance to desiccation remains elusive. When C. malonaticus was exposed to desiccation conditions (7, 15, and 30 d), transcriptomic analysis provided a universal adaptation strategy to withstand desiccation with the increased compatible solutes accumulation, activated stress resistance-related regulators, suppressed protein export and bacterial secretion system, and reduced other unessential survival functions including adhesion, invasion, virulence, and flagellar motility. Importantly, type VI secretion system (T6SS) genes exhibited significantly downregulated expressions, as well as markedly increased survival and viability of their mutants after desiccation treatment, revealing the negative regulation of T6SS in desiccation tolerance. Meanwhile, the decreased expressions of T6SS structure genes in other six species further confirmed the vital role of T6SS in desiccation tolerance of Cronobacter spp. Thus, our studies present a novel hypothesis of desiccation resistance in Cronobacter based on type VI secretion system inhibition, causing the reduction of macromolecule secretion such as effectors and hyperosmolality development within the cytomembrane, which allow Cronobacter to survive in desiccation.

Construction and analysis of protein–protein interaction networks based on nuclear proteomics data of the desiccation-tolerant Xerophyta schlechteri leaves subjected to dehydration stress

ABSTRACT In order to understand the mechanism of desiccation tolerance in Xerophyta schlechteri, we carried out an in silico study to identify hub proteins and functional modules in the nuclear proteome of the leaves. Protein–protein interaction networks were constructed and analyzed from proteome data obtained from Abdalla and Rafudeen. We constructed networks in Cytoscape using the GeneMania software and analyzed them using a Network Analyzer. Functional enrichment analysis of key proteins in the respective networks was done using GeneMania network enrichment analysis, and GO (Gene Ontology) terms were summarized using REViGO. Also, community analysis of differentially expressed proteins was conducted using the Cytoscape Apps, GeneMania and ClusterMaker. Functional modules associated with the communities were identified using an online tool, ShinyGO. We identified HSP 70–2 as the super-hub protein among the up-regulated proteins. On the other hand, 40S ribosomal protein S2–3 (a protein added by GeneMANIA) was identified as a super-hub protein associated with the down-regulated proteins. For up-regulated proteins, the enriched biological process terms were those associated with chromatin organization and negative regulation of transcription. In the down-regulated protein-set, terms associated with protein synthesis were significantly enriched. Community analysis identified three functional modules that can be categorized as chromatin organization, anti-oxidant activity and metabolic processes.

Core cellular and tissue-specific mechanisms enable desiccation tolerance in Craterostigma.

Resurrection plants can survive prolonged life without water (anhydrobiosis) in regions with seasonal drying. This desiccation tolerance requires the coordination of numerous cellular processes across space and time, and individual plant tissues face unique constraints related to their function. Here, we analyzed the complex, octoploid genome of the model resurrection plant Craterostigma (C. plantagineum), and surveyed spatial and temporal expression dynamics to identify genetic elements underlying desiccation tolerance. Homeologous genes within the Craterostigma genome have divergent expression profiles, suggesting the subgenomes contribute differently to desiccation tolerance traits. The Craterostigma genome contains almost 200 tandemly duplicated early light-induced proteins, a hallmark trait of desiccation tolerance, with massive upregulation under water deficit. We identified a core network of desiccation-responsive genes across all tissues, but observed almost entirely unique expression dynamics in each tissue during recovery. Roots and leaves have differential responses related to light and photoprotection, autophagy and nutrient transport, reflecting their divergent functions. Our findings highlight a universal set of likely ancestral desiccation tolerance mechanisms to protect cellular macromolecules under anhydrobiosis, with secondary adaptations related to tissue function.

Transcriptional profiling analysis providing insights into desiccation tolerance mechanisms of the desert moss Syntrichia caninervis.

Syntrichia caninervis is a desiccation tolerant moss and is the dominant bryophyte found in biological soil crusts in the Gurbantunggut desert. In this study, we assessed the transcriptome profiles of S. caninervis gametophytes during the dehydration-rehydration (D-R) process (across 9 time points) using Illumina sequencing. In total, 22489 transcripts were identified, including 5337 novel transcripts, that mapped to the reference genome. A total of 12548 transcripts exhibited significant alterations in the D-R samples compared with the control samples. The differentially expressed transcripts (DETs) possessed several enriched Gene Ontology terms, such as "water stress response", "oxidation-reduction process", "membrane metabolism", "photosynthesis", and "transcription factor activity". Moreover, during early dehydration stress, the DETs were significantly enriched in stress-related pathways from the Kyoto Encyclopedia of Genes and Genomes, such as "phenylpropanoid biosynthesis", "alpha-linolenic acid metabolism", and "fructose and mannose metabolism". Photosynthesis-related transcripts (e.g., ScPsa H, ScRubisco, and ScLhcb1) were inhibited during the dehydration treatment and significantly accumulated during the late rehydration period. Most transcripts from the late embryogenesis abundant proteins (LEA) and early light-inducible protein (ELIP) families strongly accumulated at the late dehydration stage. These pathways were positively correlated with the content changes of absolute water content and Fv/Fm values, alongside peroxidase and superoxide dismutase activities. Seven transcription factor families, including AP2-ERF, bHLH, G2-like, MYB, NAC, WRKY, and bZIP, were enriched in DETs during D-R treatment. This study is the first transcriptome analysis using the S. caninervis genome for gene annotation and multigroup D-R treatment points. Our results demonstrated the detailed dynamic changes in the transcriptome of S. caninervis during the D-R process. These results also improve understanding of desiccation tolerant plants' adaptations to desiccation stress at the transcription level and provide promising gene resources for transgenic crop breeding.

Influence of desiccation and water deficit on the initial development of seedlings of Tabebuia aurea (Silva Manso) Beth. Hook. and S. Moore (Bignoniaceae)

Desiccation tolerance mechanisms are one of the main factors related to the ability to survive water deficit conditions imposed by abiotic stress. Thus, the objective of this work was to evaluate the desiccation tolerance and the influence of water deficit on the initial development of Tabebuia aurea (Silva Manso) Benth. & Hook.f. ex S. Moore. The seedlings were divided into two treatments the control and those that were submitted to 50% desiccation. The control groups received water daily over a period of 30 days, while the groups that underwent water deficit had water suspension for 14 days, totaling two cycles of water deficit over a period of 30 days. The results of this study indicate that seedlings of T. aurea survive desiccation and present less development, whether of the stem, roots, number of leaves, stem diameter when subjected to desiccation and consequent water deficit. Thus, these results indicate that the reduction in early development is related to the perception and attenuation of stressful conditions imposed by the abiotic environment during development.

Coevolution of tandemly repeated hlips and RpaB-like transcriptional factor confers desiccation tolerance to subaerial Nostoc species

Desert-inhabiting cyanobacteria can tolerate extreme desiccation and quickly revive after rehydration. The regulatory mechanisms that enable their vegetative cells to resurrect upon rehydration are poorly understood. In this study, we identified a single gene family of high light-inducible proteins (Hlips) with dramatic expansion in the Nostoc flagelliforme genome and found an intriguingly special convergence formed through four tandem gene duplication. The emerged four independent hlip genes form a gene cluster (hlips-cluster) and respond to dehydration positively. The gene mutants in N. flagelliforme were successfully generated by using gene-editing technology. Phenotypic analysis showed that the desiccation tolerance of hlips-cluster-deleted mutant decreased significantly due to impaired photosystem II repair, whereas heterologous expression of hlips-cluster from N. flagelliforme enhanced desiccation tolerance in Nostoc sp. PCC 7120. Furthermore, a transcription factor Hrf1 (hlips-cluster repressor factor 1) was identified and shown to coordinately regulate the expression of hlips-cluster and desiccation-induced psbAs. Hrf1 acts as a negative regulator for the adaptation of N. flagelliforme to the harsh desert environment. Phylogenetic analysis revealed that most species in the Nostoc genus possess both tandemly repeated Hlips and Hrf1. Our results suggest convergent evolution of desiccation tolerance through the coevolution of tandem Hlips duplication and Hrf1 in subaerial Nostoc species, providing insights into the mechanism of desiccation tolerance in photosynthetic organisms.

De novo transcriptome assembly and analysis of genes involved in desiccation tolerance in Grimmia pilifera

The anatomically simple plants that transition from the aquatic to the terrestrial have a certain mechanism to deal with the damage caused by the changing living environment. Grimmia pilifera is a type of resurrection plants that can survive a long period of desiccation. To understand the molecular mechanisms of desiccation tolerance, nine cDNA libraries were constructed in triplicate from mRNA obtained from G. pilifera for the 0 h, 6 h and 18 h desiccation treatment. RNA-Seq generated ∼ 666 million reads which were assembled into 135,850 unigenes. The differentially expressed genes (DEGs) were identified between different period of time of desiccation. Gene ontology analysis showed that a significant number of genes involved in water deprivation, chloroplast organization, xyloglucan metabolic process, regulation of signaling pathway. In addition, genes involved in osmotic stress, oxidative stress, accumulation of soluble matter, such as gene encoding antioxidant enzymes, trehalose synthase and channel protein, were up-regulated in response to drought stress. These results will be helpful for further studying on the molecular mechanisms of desiccation responses in G. pilifera.

Responses of primary photosynthetic processes to repetitive rehydration differ in two representatives of Svalbard moss flora

Global warming in polar regions brings a risk of more frequent and long-lasting dry periods due to warmer and windier climate during polar summers. Mosses are well adapted to desiccation-rehydration events and they have evolved remarkable constitutive and inducible mechanisms of desiccation tolerance. In our study, Sanionia uncinata and Racomitrium lanuginosum were collected in Svalbard and used for laboratory-based repetitive 32-h-lasting rehydration cycles with continuous monitoring of restoration of their primary photosynthetic processes measured by chlorophyll fluorescence parameters. Immediately after the addition of water to dry thalli, potential quantum yield of PSII (FV/FM) was about 50% of its maximum reached after 32 h of rehydration. In a course of time of rehydration, both species showed an increase in FV/FM and effective quantum yield (FPSII) following a S-curve relationship. Non-photochemical quenching did not show clear trend with the rehydration time, It differed between the two species and showed both decrease and increase with the time of rehydration. Relative chlorophyll fluorescence decrease (RFd), which is considered a vitality indicator, increase with the time of rehydration showing similar trends in the first and the third cycle of rehydration. The results indicate that both Sanionia uncinata and Racomitrium lanuginosum are resistant to desiccation since FV/FM and FPSII recovered fully after 32 h of rehydration and there we only minor differences in the two parameters between the first and third rehydration cycle.

Deciphering endurance capacity of mango tree (Mangifera indica L.) to desiccation stress using modern physiological tools

• Mango plant can maintain its canopy coolness during desiccation period by its ability to with draw water during water limiting conditions. • Mango plant can maintain its carboxylation capacity during hotter period of the day. • Crucial components of photosynthesis, PSII efficiency is maintained during desiccation period, thereby preventing the plants from desiccation damage and providing tolerance mechanisms. • Mango plant can maintain its structural attributes (mainly by maintaining turgidity due to water retention capacity) such as convex hull area, which also supports desiccation tolerance mechanisms. Capacity of mango tree to withstand drought (absence of soil moisture) can be attributed to stress resilient physiological processes inside the cell and also at whole plant level. To test this hypothesis, photosynthetic traits were recorded over the period of time. Further, desiccation tolerance of photosystem II (PSII) in excised mango leaves were measured by employing chlorophyll fluorescence imaging system. Beside this, the capacity of mango tree to keep its canopy cool was monitored in every 10 min interval throughout the day during dry and rainy season in the field by employing thermal imaging system. Finally, phenomics platform was used to monitor depletion of tissue moisture level as well as changes in structural attributes during desiccation in excised shoots of the tree. It was inferred that mango tree can maintain its carboxylation efficiency over the period of time. IR studies confirmed that mango tree maintained its canopy coolness during dry season. In addition, the chlorophyll fluorescence experiments revealed that mango leaves retained 50% of initial PSII efficiency for as many as 4 days after desiccation and chlorophyll fluorogram also depicted the observations. Phenomics studies concluded that mango twig retained tissue water content even up to the 164 h of desiccation with gradual decrease in canopy area. Hence, it is interpreted that these physiological resilience are amongst the various reasons for evergreen feature of mango tree which has tendency to survive severe soil moisture deficit particularly during the summer in tropical and subtropical regions, which has been revealed for first time using phenomics platform.

Reactivation of the Photosynthetic Apparatus of Resurrection Plant Haberlea rhodopensis during the Early Phase of Recovery from Drought- and Freezing-Induced Desiccation.

Haberlea rhodopensis is a unique desiccation-tolerant angiosperm that also survives winter frost. As, upon freezing temperatures, H. rhodopensis desiccates, the taxon is proposed to survive low temperature stress using its desiccation tolerance mechanisms. To reveal the validity of this hypothesis, we analyzed the structural alterations and organization of photosynthetic apparatus during the first hours of recovery after drought- and freezing-induced desiccation. The dynamics of the ultrastructure remodeling in the mesophyll cells and the restoration of the thylakoid membranes shared similarities independent of the reason for desiccation. Among the most obvious changes in thylakoid complexes, the proportion of the PSI-LHCII complex strongly increased around 70% relative water content (RWC), whereas the proportion of Lhc monomers decreased from the beginning of rehydration. We identified enhanced levels of cyt b6f complex proteins that contributed to the enhanced electron flow. The high abundance of proteins related to excitation energy dissipation, PsbS, Lhcb5, Lhcb6 and ELIPs, together with the increased content of dehydrins contributed to the preservation of cellular integrity. ELIP expression was maintained at high levels up to 9 h into recovery. Although the recovery processes from drought- and freezing-induced desiccation were found to be similar in progress and time scale, slight variations indicate that they are not identical.