Reciprocal conversion between annual and polycarpic perennial flowering behavior in the Brassicaceae.

The development of perennial crops holds great promise for sustainable agriculture and food security. However, the evolution of the transition between perenniality and annuality is poorly understood. Here, using two Brassicaceae species, Crucihimalaya himalaica and Erysimum nevadense, as polycarpic perennial models, we reveal that the transition from polycarpic perennial to biennial and annual flowering behavior is a continuum determined by the dosage of three closely related MADS-box genes. Diversification of the expression patterns, functional strengths, and combinations of these genes endows species with the potential to adopt various life-history strategies. Remarkably, we find that a single gene among these three is sufficient to convert winter-annual or annual Brassicaceae plants into polycarpic perennial flowering plants. Our work delineates a genetic basis for the evolution of diverse life-history strategies in plants and lays the groundwork for the generation of diverse perennial Brassicaceae crops in the future.

The structure of B-ARR reveals the molecular basis of transcriptional activation by cytokinin.

The phytohormone cytokinin has various roles in plant development, including meristem maintenance, vascular differentiation, leaf senescence, and regeneration. Prior investigations have revealed that cytokinin acts via a phosphorelay similar to the two-component system by which bacteria sense and respond to external stimuli. The eventual targets of this phosphorelay are type-B ARABIDOPSIS RESPONSE REGULATORS (B-ARRs), containing the conserved N-terminal receiver domain (RD), middle DNA binding domain (DBD), and C-terminal transactivation domain. While it has been established for two decades that the phosphoryl transfer from a specific histidyl residue in ARABIDOPSIS HIS PHOSPHOTRANSFER PROTEINS (AHPs) to an aspartyl residue in the RD of B-ARRs results in a rapid transcriptional response to cytokinin, the underlying molecular basis remains unclear. In this work, we determine the crystal structures of the RD-DBD of ARR1 (ARR1RD-DBD) as well as the ARR1DBD-DNA complex from Arabidopsis. Analyses of the ARR1DBD-DNA complex have revealed the structural basis for sequence-specific recognition of the GAT trinucleotide by ARR1. In particular, comparing the ARR1RD-DBD and ARR1DBD-DNA structures reveals that unphosphorylated ARR1RD-DBD exists in a closed conformation with extensive contacts between the RD and DBD. In vitro and vivo functional assays have further suggested that phosphorylation of the RD weakens its interaction with DBD, subsequently permits the DNA binding capacity of DBD, and promotes the transcriptional activity of ARR1. Our findings thus provide mechanistic insights into phosphorelay activation of gene transcription in response to cytokinin.

A V-shaped association between high-density lipoprotein cholesterol levels and poor outcomes in patients after percutaneous coronary intervention.

BACKGROUND: High density lipoprotein cholesterol (HDL-C) is considered as "good cholesterol". Recent evidence suggests that a high HDL-C level may increase the risk of poor outcomes in some populations. PURPOSE: To investigate the association between HDL-C levels and poor outcomes in patients after percutaneous coronary intervention (PCI). METHODS: Patients undergoing PCI during January 2012 and December 2018 were consecutively recruited and divided into three groups with different HDL-C levels: HDL-C ≤ 25 mg/dL, 25 < HDL-C ≤ 60 mg/dL, HDL-C > 60 mg/dL by the restricted cubic spline (RCS) analysis and assessed for all-cause mortality (ACM). The association between HDL-C levels and poor outcomes was assessed by multivariable cox regression analysis. RESULTS: The patients were followed with a median duration of 4 years. Of the 7284 participants, 727 all-cause deaths and 334 cardiovascular deaths occurred. A V-shaped association of HDL-C with the prognosis was observed, patients with either excessively low or high HDL-C levels reporting a higher risk than those with midrange values. After adjustment for confounding factors, the former exhibited a higher cumulative rate of ACM and cardiovascular mortality (CM) than the latter [low HDL-C: for ACM, hazard ratio (HR), 1.96; 95%CI, 1.41, 2.73, P < 0.001; for CM, HR, 1.66; 95%CI, 1.03, 2.67; P = 0.037; high HDL-C: for ACM, HR, 1.73; 95%CI, 1.29, 2.32, P < 0.001; for CM, HR, 1.73; 95%CI, 1.16, 2.58; P = 0.007]. CONCLUSION: HDL-C levels display a V-shaped association with poor outcomes in patients after PCI, with excessively high or low HDL-C suggesting a higher mortality risk. An optimal HDL-C level may fall in the range of 25-60 mg/dL.

Stent-assisted coiling of intracranial carotid ophthalmic segment aneurysm segment aneurysms: Long-term follow-up from a single center.

Background: To evaluate the efficacy of stent-assisted coiling (SAC) for the treatment of carotid ophthalmic segment aneurysm segment aneurysms (OSAs) of the internal carotid artery (ICA) through detailed long-term follow-up of a large patient cohort. Methods: We retrospectively analyzed 88 consecutive patients with OSAs between January 2009 and January 2020 â€‹at our center. Angiographic results were evaluated using the modified Raymond grading system and clinical outcomes were evaluated using the mRS scale. The primary endpoints were major aneurysm recurrence and poor clinical outcomes for at least 18 months of follow-up. The patients were asked to attend clinical follow-up assessments and possibly undergo DSA or MR via telephone. Results: We enrolled 88 patients with 99 OSAs treated with coiling, of whom 76 were treated with SAC. The coiling procedures were successful in all 88 patients. Overall, complications occurred in 8 patients (9.1%). No procedure-related mortality was observed. 67 (76.1%) experienced immediate aneurysm occlusion at the end of the procedure. Long-term angiographic follow-up (18 months) was available in 45/88 aneurysms (51%) (average 18.7 â€‹± â€‹5.2 months). Four patients continued their follow-up for 5 years after initial aneurysm treatment. After a clinical follow-up time of 28.7 months (range, 12-51 months), 85 patients (95.5%) achieved favorable clinical outcomes (mRS scores of 0-2). Conclusions: This study indicates that SAC treatment is a safe and effective therapeutic alternative for ruptured and unruptured OSAs. The procedural risks are low with relatively long-term effectiveness.

Prognostic value of triglyceride glucose index in population at high cardiovascular disease risk.

BACKGROUND: Early identification of populations at high cardiovascular disease (CVD) risk and improvement of risk factors can significantly decrease the probability of CVD development and improve outcomes. Insulin resistance (IR) is a CVD risk factor. The triglyceride glucose (TyG) index is a simple and reliable index for evaluating IR. However, no clinical studies on the prognostic value of the TyG index in a high risk CVD population have been conducted. This study evaluated the relationship between the TyG index and prognosis in a high risk CVD population. METHODS: This study enrolled 35,455 participants aged 35-75 years who were at high CVD risk and visited selected health centers and community service centers between 2017 and 2021. Their general clinical characteristics and baseline blood biochemical indicators were recorded. The TyG index was calculated as ln[fasting triglyceride (mg/dl)× fasting blood glucose (mg/dl)/2]. The endpoints were all-cause death and cardiovascular death during follow-up. Cox proportional hazard models and restricted cubic spline (RCS) analysis were used to evaluate the correlation between the TyG index and endpoints. RESULTS: In the overall study population, the mean age of all participants was 57.9 ± 9.6 years, 40.7% were male, and the mean TyG index was 8.9 ± 0.6. All participants were divided into two groups based on the results of the RCS analysis, with a cut-off value of 9.83. There were 551 all-cause deaths and 180 cardiovascular deaths during a median follow-up time of 3.4 years. In the multivariate Cox proportional hazard model, participants with a TyG index ≥ 9.83 had a higher risk of all-cause death (Hazard ratio [HR] 1.86, 95% Confdence intervals [CI] 1.37-2.51, P<0.001) and cardiovascular death (HR 2.41, 95%CI 1.47-3.96, P = 0.001) than those with a TyG index < 9.83. Subgroup analysis revealed that there was no interaction between the TyG index and variables in all subgroup analyses. CONCLUSIONS: The high TyG index was associated with an increased risk of all-cause death and cardiovascular death in people at high risk of CVD. This finding demonstrates the value of the TyG index in the primary prevention of CVD. TRIAL REGISTRATION: retrospectively registered, the registration number is K2022-01-005 and the date is 2022.01.30.

The maturation and aging trajectory of Marchantia polymorpha at single-cell resolution.

Bryophytes represent a sister to the rest of land plants. Despite their evolutionary importance and relatively simple body plan, a comprehensive understanding of the cell types and transcriptional states that underpin the temporal development of bryophytes has not been achieved. Using time-resolved single-cell RNA sequencing, we define the cellular taxonomy of Marchantia polymorpha across asexual reproduction phases. We identify two maturation and aging trajectories of the main plant body of M. polymorpha at single-cell resolution: the gradual maturation of tissues and organs along the tip-to-base axis of the midvein and the progressive decline of meristem activities in the tip along the chronological axis. Specifically, we observe that the latter aging axis is temporally correlated with the formation of clonal propagules, suggesting an ancient strategy to optimize allocation of resources to producing offspring. Our work thus provides insights into the cellular heterogeneity that underpins the temporal development and aging of bryophytes.

Elevated branched-chain amino acid promotes atherosclerosis progression by enhancing mitochondrial-to-nuclear H2O2-disulfide HMGB1 in macrophages.

As the essential amino acids, branched-chain amino acid (BCAA) from diets is indispensable for health. BCAA supplementation is often recommended for patients with consumptive diseases or healthy people who exercise regularly. Latest studies and ours reported that elevated BCAA level was positively correlated with metabolic syndrome, diabetes, thrombosis and heart failure. However, the adverse effect of BCAA in atherosclerosis (AS) and its underlying mechanism remain unknown. Here, we found elevated plasma BCAA level was an independent risk factor for CHD patients by a human cohort study. By employing the HCD-fed ApoE-/- mice of AS model, ingestion of BCAA significantly increased plaque volume, instability and inflammation in AS. Elevated BCAA due to high dietary BCAA intake or BCAA catabolic defects promoted AS progression. Furthermore, BCAA catabolic defects were found in the monocytes of patients with CHD and abdominal macrophages in AS mice. Improvement of BCAA catabolism in macrophages alleviated AS burden in mice. The protein screening assay revealed HMGB1 as a potential molecular target of BCAA in activating proinflammatory macrophages. Excessive BCAA induced the formation and secretion of disulfide HMGB1 as well as subsequent inflammatory cascade of macrophages in a mitochondrial-nuclear H2O2 dependent manner. Scavenging nuclear H2O2 by overexpression of nucleus-targeting catalase (nCAT) effectively inhibited BCAA-induced inflammation in macrophages. All of the results above illustrate that elevated BCAA promotes AS progression by inducing redox-regulated HMGB1 translocation and further proinflammatory macrophage activation. Our findings provide novel insights into the role of animo acids as the daily dietary nutrients in AS development, and also suggest that restricting excessive dietary BCAA consuming and promoting BCAA catabolism may serve as promising strategies to alleviate and prevent AS and its subsequent CHD.

Mitochondria-derived H2O2 triggers liver regeneration via FoxO3a signaling pathway after partial hepatectomy in mice.

Reactive oxygen species (ROS) can induce oxidative injury and are generally regarded as toxic byproducts, although they are increasingly recognized for their signaling functions. Increased ROS often accompanies liver regeneration (LR) after liver injuries, however, their role in LR and the underlying mechanism remains unclear. Here, by employing a mouse LR model of partial hepatectomy (PHx), we found that PHx induced rapid increases of mitochondrial hydrogen peroxide (H2O2) and intracellular H2O2 at an early stage, using a mitochondria-specific probe. Scavenging mitochondrial H2O2 in mice with liver-specific overexpression of mitochondria-targeted catalase (mCAT) decreased intracellular H2O2 and compromised LR, while NADPH oxidases (NOXs) inhibition did not affect intracellular H2O2 or LR, indicating that mitochondria-derived H2O2 played an essential role in LR after PHx. Furthermore, pharmacological activation of FoxO3a impaired the H2O2-triggered LR, while liver-specific knockdown of FoxO3a by CRISPR-Cas9 technology almost abolished the inhibition of LR by overexpression of mCAT, demonstrating that FoxO3a signaling pathway mediated mitochondria-derived H2O2 triggered LR after PHx. Our findings uncover the beneficial roles of mitochondrial H2O2 and the redox-regulated underlying mechanisms during LR, which shed light on potential therapeutic interventions for LR-related liver injury. Importantly, these findings also indicate that improper antioxidative intervention might impair LR and delay the recovery of LR-related diseases in clinics.

Anisotropic cell growth at the leaf base promotes age-related changes in leaf shape in Arabidopsis thaliana.

Plants undergo extended morphogenesis. The shoot apical meristem (SAM) allows for reiterative development and the formation of new structures throughout the life of the plant. Intriguingly, the SAM produces morphologically different leaves in an age-dependent manner, a phenomenon known as heteroblasty. In Arabidopsis thaliana, the SAM produces small orbicular leaves in the juvenile phase, but gives rise to large elliptical leaves in the adult phase. Previous studies have established that a developmental decline of microRNA156 (miR156) is necessary and sufficient to trigger this leaf shape switch, although the underlying mechanism is poorly understood. Here we show that the gradual increase in miR156-targeted SQUAMOSA PROMOTER BINDING PROTEIN-LIKE transcription factors with age promotes cell growth anisotropy in the abaxial epidermis at the base of the leaf blade, evident by the formation of elongated giant cells. Time-lapse imaging and developmental genetics further revealed that the establishment of adult leaf shape is tightly associated with the longitudinal cell expansion of giant cells, accompanied by a prolonged cell proliferation phase in their vicinity. Our results thus provide a plausible cellular mechanism for heteroblasty in Arabidopsis, and contribute to our understanding of anisotropic growth in plants.

Common evolutionary trajectory of short life-cycle in Brassicaceae ruderal weeds.

Weed species are detrimental to crop yield. An understanding of how weeds originate and adapt to field environments is needed for successful crop management and reduction of herbicide use. Although early flowering is one of the weed trait syndromes that enable ruderal weeds to overcome frequent disturbances, the underlying genetic basis is poorly understood. Here, we establish Cardamine occulta as a model to study weed ruderality. By genome assembly and QTL mapping, we identify impairment of the vernalization response regulator gene FLC and a subsequent dominant mutation in the blue-light receptor gene CRY2 as genetic drivers for the establishment of short life cycle in ruderal weeds. Population genomics study further suggests that the mutations in these two genes enable individuals to overcome human disturbances through early deposition of seeds into the soil seed bank and quickly dominate local populations, thereby facilitating their spread in East China. Notably, functionally equivalent dominant mutations in CRY2 are shared by another weed species, Rorippa palustris, suggesting a common evolutionary trajectory of early flowering in ruderal weeds in Brassicaceae.

Study on environmental residues detection and cleaning method of 15 cytotoxic antineoplastic drugs in PIVAS of our hospital / 中国药房

OBJECTIVE To provide a method to reduce environmental residues for pharmacy intravenous admixture service （PIVAS）， and ensure the occupational health of medical staff. METHODS The residues of 15 cytotoxic antineoplastic drugs such as gemcitabine were detected by UPLC-Q-Orbitrap-HRMS. The cleaning process was optimized with the residual quantity as the index. Nitrogen blowing method was used for alcohol volatilization experiment. CCK-8 assay was used to detect the effect of chlorine-containing disinfectant on the toxicity of cytotoxic antitumor drugs. RESULTS The linear range of 15 cytotoxic antineoplastic drugs such as gemcitabine were 0.5-1 000 ng/mL. RSDs of intra-day and intra-day precision were no higher than 20.00%. Six drugs including gemcitabine， isocyclophosphamide and cyclophosphamide were detected in the PIVAS environment of our hospital， and the residue of cyclophosphamide was relatively high. The optimal cleaning procedure was cleaning once with water + cleaning once with 1 000 mg/L chlorine-containing disinfectant + cleaning once with 75% alcohol， wiping with dry gauze method. The results of alcohol volatilization test showed that there was no significant difference in drug residues between control group and 75% alcohol group （P＞0.05）. The results of CCK-8 test showed that compared with control group， the survival rates of the cells treated with 15 cytotoxic antineoplastic drugs were decreased significantly （P＜0.01）； the survival rates of the cells treated with 15 cytotoxic antineoplastic drugs+chlorine-containing disinfectant were significantly higher than those treated with 15 cytotoxic antineoplastic drugs （P＜0.01）. CONCLUSIONS A method for the simultaneous determination for residues of 15 cytotoxic antineoplastic drugs such as gemcitabine in PIVAS is successfully established； the optimal cleaning procedure can significantly reduce the residues of drugs， the use of chlorine- containing disinfectant can significantly reduce the toxicity of drug， and the residual drugs will not cause secondary contamination of the operating area with alcohol volatilization.

The sage genome provides insight into the evolutionary dynamics of diterpene biosynthesis gene cluster in plants.

The widely cultivated medicinal and ornamental plant sage (Salvia officinalis L.) is an evergreen shrub of the Lamiaceae family, native to the Mediterranean. We assembled a high-quality sage genome of 480 Mb on seven chromosomes, and identified a biosynthetic gene cluster (BGC) encoding two pairs of diterpene synthases (diTPSs) that, together with the cytochromes P450 (CYPs) genes located inside and outside the cluster, form two expression cascades responsible for the shoot and root diterpenoids, respectively, thus extending BGC functionality from co-regulation to orchestrating metabolite production in different organs. Phylogenomic analysis indicates that the Salvia clades diverged in the early Miocene. In East Asia, most Salvia species are herbaceous and accumulate diterpenoids in storage roots. Notably, in Chinese sage S. miltiorrhiza, the diterpene BGC has contracted and the shoot cascade has been lost. Our data provide genomic insights of micro-evolution of growth type-associated patterning of specialized metabolite production in plants.

The Formation of Hollow Trait in Cucumber (Cucumis sativus L.) Fruit Is Controlled by CsALMT2.

The hollow trait is crucial for commercial quality of cucumber (Cucumis sativus L.) fruit, and its molecular regulatory mechanism is poorly understood due to its environmental sensitivity. In the previous research, we obtained the hollow and the non-hollow materials of ecotype cucumbers of South China, which were not easily affected by the external environment through a systematic breeding method. In this study, first, we proposed to use the percentage of the hollow area as the criterion to compare the hollow characteristics between two materials, and to analyze the formation mechanism of early hollow trait from the perspective of cytology. The results showed that the hollow trait occurred in the early stage of fruit development, and formed with the opening of carpel ventral zipped bi-cell layer, which formed rapidly from 2 to 4 days, and then slowed to a constant rate from 14 to 16 days. Meanwhile, the different genetic populations were constructed using these materials, and fine mapping was performed by bulked segregant analysis (BSA) and kompetitive allele specific PCR (KASP) method. The Csa1G630860 (CsALMT2), encoding protein ALMT2, was determined as a candidate gene for regulating the hollow trait in fruit. Furthermore, the expression profile of CsALMT2 was analyzed by qRT-PCR and fluorescence in situ hybridization. The expression of CsALMT2 had obvious tissue specificity, and it was abundantly expressed in the ovule development zone inside the fruit. In the hollow material of cucumber fruit, the expression of CsALMT2 was significantly downregulated. The subcellular localization in tobacco leaves indicated that CsALMT2 was distributed on the plasma membrane. In conclusion, in this study, for the first time, we found the regulatory gene of hollow trait in cucumber fruit, which laid the foundation for subsequent research on the molecular mechanism of hollow trait formation in cucumber fruit, and made it possible to apply this gene in cucumber breeding.

FindIT2: an R/Bioconductor package to identify influential transcription factor and targets based on multi-omics data.

BACKGROUND: Transcription factors (TFs) play central roles in regulating gene expression. With the rapid growth in the use of high-throughput sequencing methods, there is a need to develop a comprehensive data processing and analyzing framework for inferring influential TFs based on ChIP-seq/ATAC-seq datasets. RESULTS: Here, we introduce FindIT2 (Find Influential TFs and Targets), an R/Bioconductor package for annotating and processing high-throughput multi-omics data. FindIT2 supports a complete framework for annotating ChIP-seq/ATAC-seq peaks, identifying TF targets by the combination of ChIP-seq and RNA-seq datasets, and inferring influential TFs based on different types of data input. Moreover, benefited from the annotation framework based on Bioconductor, FindIT2 can be applied to any species with genomic annotations, which is particularly useful for the non-model species that are less well-studied. CONCLUSION: FindIT2 provides a user-friendly and flexible framework to generate results at different levels according to the richness of the annotation information of user's species. FindIT2 is compatible with all the operating systems and is released under Artistic-2.0 License. The source code and documents are freely available through Bioconductor ( https://bioconductor.org/packages/devel/bioc/html/FindIT2.html ).

A robust mechanism for resetting juvenility during each generation in Arabidopsis.

Multicellular organisms undergo several developmental transitions during their life cycles. In contrast to animals, the plant germline is derived from adult somatic cells. As such, the juvenility of a plant must be reset in each generation. Previous studies have demonstrated that the decline in the levels of miR156/7 with age drives plant maturation. Here we show that the resetting of plant juvenility during each generation is mediated by de novo activation of MIR156/7 in Arabidopsis. Blocking this process leads to a shortened juvenile phase and premature flowering in the offspring. In particular, an Arabidopsis plant devoid of miR156/7 flowers even without formation of rosette leaves in long days. Mechanistically, we find that different MIR156/7 genes are reset at different developmental stages through distinct reprogramming routes. Among these genes, MIR156A, B and C are activated de novo during sexual reproduction and embryogenesis, while MIR157A and C are reset upon seed germination. This redundancy generates a robust reset mechanism that ensures accurate restoration of the juvenile phase in each plant generation.

Dynamic chromatin state profiling reveals regulatory roles of auxin and cytokinin in shoot regeneration.

Shoot regeneration is mediated by the sequential action of two phytohormones, auxin and cytokinin. However, the chromatin regulatory landscapes underlying this dynamic response have not yet been studied. In this study, we jointly profiled chromatin accessibility, histone modifications, and transcriptomes to demonstrate that a high auxin/cytokinin ratio environment primes Arabidopsis shoot regeneration by increasing the accessibility of the gene loci associated with pluripotency and shoot fate determination. Cytokinin signaling not only triggers the commitment of the shoot progenitor at later stages but also allows chromatin to maintain shoot identity genes at the priming stage. Our analysis of transcriptional regulatory dynamics further identifies a catalog of regeneration cis-elements dedicated to cell fate transitions and uncovers important roles of BES1, MYC, IDD, and PIF transcription factors in shoot regeneration. Our results, thus, provide a comprehensive resource for studying cell reprogramming in plants and provide potential targets for improving future shoot regeneration efficiency.

Successful Treatment with Integrated Chinese and Western Medicine for Massive Colchicine Overdose: A Case Report.

A 42-year-old male was hospitalized 13.5 hours after ingestion of 50 mg (approximately 0.7 mg/kg) colchicine in a suicide attempt. The patient developed gastrointestinal dysfunction, grade IV myelosuppression, and restrictive respiratory failure without occurrences of cardiovascular collapse or fatal dysrhythmias. Emergency treatment with integrated Chinese and Western medicine was started and the patient fully recovered without long-term complications. This report describes a massive overdose of colchicine successfully treated with integrated Chinese and Western medicine. Current treatment options are reviewed.

Pol IV and RDR2: A two-RNA-polymerase machine that produces double-stranded RNA.

DNA methylation affects gene expression and maintains genome integrity. The DNA-dependent RNA polymerase IV (Pol IV), together with the RNA-dependent RNA polymerase RDR2, produces double-stranded small interfering RNA precursors essential for establishing and maintaining DNA methylation in plants. We determined the cryo­electron microscopy structures of the Pol IV­RDR2 holoenzyme and the backtracked transcription elongation complex. These structures reveal that Pol IV and RDR2 form a complex with their active sites connected by an interpolymerase channel, through which the Pol IV­generated transcript is handed over to the RDR2 active site after being backtracked, where it is used as the template for double-stranded RNA (dsRNA) synthesis. Our results describe a 'backtracking-triggered RNA channeling' mechanism underlying dsRNA synthesis and also shed light on the evolutionary trajectory of eukaryotic RNA polymerases.

Cell division in the shoot apical meristem is a trigger for miR156 decline and vegetative phase transition in Arabidopsis.

What determines the rate at which a multicellular organism matures is a fundamental question in biology. In plants, the decline of miR156 with age serves as an intrinsic, evolutionarily conserved timer for the juvenile-to-adult phase transition. However, the way in which age regulates miR156 abundance is poorly understood. Here, we show that the rate of decline in miR156 is correlated with developmental age rather than chronological age. Mechanistically, we found that cell division in the apical meristem is a trigger for miR156 decline. The transcriptional activity of MIR156 genes is gradually attenuated by the deposition of the repressive histone mark H3K27me3 along with cell division. Our findings thus provide a plausible explanation of why the maturation program of a multicellular organism is unidirectional and irreversible under normal growth conditions and suggest that cell quiescence is the fountain of youth in plants.