Studies on Endogenous Hormones and Nutritional Physiology Related to the Premature Senescence of Super-hybrid Rice Liangyoupeijiu and Its Parents at Late Growth Stage

The amount of root bleeding sap, contents of chlorophyl , nutrients and hormones in flag leaves of a super-hybrid rice cultivar Liangyoupeijiu （LYPJ） and its parents 9311 and Pei’ai 64S after heading were measured in this study. The re-sults revealed that compared with 9311, the chlorophyl content of LYPJ reduced more quickly after heading, and then kept at a lower level, which was an obvious characteristic of premature senescence. The other physiological indices of LYPJ af-ter heading except abscisic acid （ABA） content in leaf and root also maintained at a lower level than 9311, while al the physiological indices of the sterile line Pei＇ai 64S were lower than LYPJ. So it was speculated that the early-aging characteristic of LYPJ may be inherited from Pei’ai 64S. Al the leaf and root early-aging traits reduced for LYPJ and its parent lines after heading, their leaf and root aged grad-ual y, which indicated that the above-ground （leaf） and under-ground （root） parts cor-related to each other closely, but there was not absolute correlations between them judged from the data.

Cisplatin-induced premature senescence with concomitant reduction of gap junctions in human fibroblasts

To examine the role of gap junctions in cell senescence,the changes of gap junctions in cisplatin-induced premature senescence of primary cultured fibroblasts were studied and compared with the replicative senescent human fibroblasts.Dye transfer assay for gap junction function and immunofluorescent staining for connexin 43 protein distribution were done respectively. Furthermore,cytofluorimetry and DAPI fluorescence staining were performed for cell cycle and apoptosis analysis. p53 gene expression level was detected with indirect immunofluorescence. We found that cisplatin (10 mM) treatment could block cell growth cycle at G1 and induced premature senescence. The premature senescence changes included high frequency of apoptosis,elevation of p53 expression,loss of membranous gap junctions and reduction of dye-transfer capacity. These changes were comparable to the changes of replicative senescence of human fibroblasts. It was also concluded that cisplatin could induce premature senescence concomitant with inhibition of gap junctions in the fibroblasts. Loss of functional gap junctions from the cell membrane may account for the reduced intercellular communication in the premature senescent fibroblasts. The cell system we used may provide a model useful for the study of the gap junction thus promoting agents against premature senescence.

Isolation and physiological characteristics of a premature senescence mutant in rice(Oryza sativa L.)

A rice pse（t） （premature senescence, tentatively） mutant line, was isolated from 4500 independent T-DNA inserted transgenic lines. The symptoms of premature senescence appeared more severely than those of the control plants （Zhonghua 11, japonica） at the last development stage. To characterize the mutant and provide basic information on the candidate genes by mapping to a physical region of 220-kb, experiments were carried out in two phytotrons under controlled temperature of 24 ℃ and 28 ℃, respectively. The content of chlorophyll, soluble protein and MDA （malondialdehyde）, net photosynthesis, the antioxidant enzyme activities of SOD （superoxide dismuase） （EC 1.15.1.1 ） and POD （peroxidase） （EC 1.11.1.7） and the peptidase activities of leaves were measured from top to bottom according to the leaf positions at the flowering stage. Compared with the control plant, the mutant showed the following characteristics： （1） Higher net photosynthesis rate （Pn） appeared in the 1st and 2nd leaves, contents of chlorophyll and soluble protein were also higher in the 1st leaf; （2） The activities of SOD, POD and peptidase were higher according to the leaf position from top to bottom; （3） The symptom of premature senescence was accelerated in the mutant at 28 ℃ treatment. The MDA content and the SOD and POD activities between the 24 ℃ and 28 ℃ treatment mutants were not significantly different. Content of chlorophyll and soluble protein of leaves mutant decreased rapidly at 28 ℃ treatment. The results show thatpse（t） is sensitive to high temperature. The probable function of PSE（T） is discussed.

Rice melatonin deficiency causes premature leaf senescence via DNA methylation regulation

In a study of DNA methylation changes in melatonin-deficient rice mutants,mutant plants showed premature leaf senescence during grain-filling and reduced grain yield.Melatonin deficiency led to transcriptional reprogramming,especially of genes involved in chlorophyll and carbon metabolism,redox regulation,and transcriptional regulation,during dark-induced leaf senescence.Hypomethylation of mCG and mCHG in the melatonin-deficient rice mutants was associated with the expression change of both protein-coding genes and transposable element-related genes.Changes in gene expression and DNA methylation in the melatonin-deficient mutants were compensated by exogenous application of melatonin.A decreased S-adenosyl-L-methionine level may have contributed to the DNA methylation variations in rice mutants of melatonin deficiency under dark conditions.

Defect in an immune regulator gene BrSRFR1 leads to premature leaf senescence in Chinese cabbage

Leaf senescence is the final stage of leaf development, where the nutrients and energy of senescent leaves are redistributed to developing tissues or organs for plant growth, reproduction, and defense. Outer leaves are photosynthetic organs that usually senesce at the late heading stage in Chinese cabbage, and premature leaf senescence often reduces leafy head yield and quality. In this study, 11 premature leaf senescence mutants were screened from an ethyl methanesulfonate-mutagenized population of the double haploid line ‘FT' in Chinese cabbage. At the early heading stage, the mutants exhibited edge yellowing within its outer leaves, and at the mature stage, its leafy head weight decreased significantly. Genetic analysis revealed that the mutated trait of all 11 mutants corresponds to single gene recessive inheritance. Semi-diallel cross tests showed that 5 of the 11 were allelic mutants. MutMap and Kompetitive Allele Specific PCR genotyping revealed that BraA01g001400.3C was the candidate gene, which is orthologous of Arabidopsis SUPPRESSOR OF rps4-RLD 1, encoding an immune regulator, so we named it as BrSRFR1. All the BrSRFR1 in the five allelic mutants exhibited single nucleotide polymorphisms at different positions on their exons and led to premature translation termination, which confirmed that defect in BrSRFR1 led to premature leaf senescence. These results verify the role of Br SRFR1 on leaf senescence and provide a new insight into the mechanisms of leaf senescence in Chinese cabbage, which reveals a novel function of SRFR1 in plant development.

Single base substitution in Os CDC48 is responsible for premature senescence and death phenotype in rice

A premature senescence and death 128 （psd128） mutant was isolated from an ethyl methane sulfonate-induced rice IR64 mutant bank. The premature senescence phenotype appeared at the six-leaf stage and the plant died at the early heading stage, psd128 exhibited impaired chloroplast develop- ment with significantly reduced photosynthetic ability, chlorophyll and carotenoid contents, root vigor, soluble protein content and increased malonaldehyde content. Furthermore, the expression of senescence-related genes was significantly altered in psd128. The mutant trait was controlled by a single recessive nuclear gene. Using map- based strategy, the mutation Oryza sativa cell division cycle 48 （OsCDC48） was isolated and predicted to encode a putative AAA-type ATPase with 809 amino-acid residuals. A single base substitution at position C2347T in psd128 resulted in a premature stop codon. Functional complementation could rescue the mutant phenotype. In addition, RNA interference resulted in the premature senescence and death phenotype. OsCDC48 was expressed constitutively in the root, stem, leaf and panicle. Subcellular analysis indicated that OsCDC48：YFP fusion proteins were located both in the cytoplasm and nucleus. OsCDC48 was highly conserved with more than 90% identity in the protein levels among plant species. Our results indicated that the impaired function of OsCDC48 was responsible for the premature senescence and death phenotype.

Effect of Saikokeishito, a Kampo medicine, on hydrogen peroxide-induced premature senescence of normal human dermal fibroblasts

OBJECTIVE： Saikokeishito（TJ-10） is a Kampo（traditional Japanese herbal） medicine, clinically used for hundreds of years in East Asia. Among its various mechanisms elucidated so far, TJ-10 inhibits the production of transforming growth factor-β1（TGF-β1） and development of pancreatic fi brosis in vivo. Oxidative damage of normal human dermal fi broblasts（NHDFs） in the corium is a cause of human dermal senescence. Our aim was to determine whether TJ-10 protects NHDFs from premature senescence by hydrogen peroxide（H2O2）. METHODS： Premature senescence was induced in NHDFs by 200 μmol/L H2O2 for 4 h. Cell viability and the expressions of p53, AMP-activated protein kinase α1（AMPKα1）, AMPKα2, and 14-3-3 protein sigma（14-3-3 σ） were measured in NHDFs treated with TJ-10 for 48 h before exposure to H2O2 for 4 h. RESULTS： Cell viability after treatment with 200 μmol/L H2O2 for 4 h was similar（about 80%） to after pre-treatment with TJ-10. Ascorbic acid as a control did not protect NHDFs from damage by 200 μmol/L H2O2. Treatment with 200 μmol/L H2O2 tended to up-regulate p53 and to down-regulate SIRT1 and AMPKα1, but had no effect on AMPKα2 and 14-3-3 σ expression. Pretreatment with TJ-10 inhibited H2O2-induced up-regulation of p53 and enhanced AMPKα1 expression. CONCLUSION： It is suggested that Saikokeishito has a protective effect on oxidative stressinduced senescence of NHDFs.

Identification and gene mapping of the starch accumulation and premature leaf senescence mutant ossac4 in rice

The rice mutant ossac4(starch accumulating 4)was raised from seeds of the rice(Oryza sativa L.)indica maintainer line Xinong 1B treated with ethyl methanesulfonate.The distal and medial portions of the second leaf displayed premature senescence in the ossac4 mutant at the four-leaf stage.Physiological and biochemical analysis,and cytological examination revealed that the ossac4 mutant exhibited the premature leaf senescence phenotype.At the four-leaf stage,the leaves of the ossac4 mutant exhibited significantly increased contents of starch compared with those of the wild type(WT).Quantitative real-time PCR analysis showed that the expression levels of photosynthesis-associated genes were down-regulated and the expression levels of glucose metabolism-associated genes were abnormal.Genetic analysis indicated that the ossac4 mutation was controlled by a single recessive nuclear gene.The OsSAC4 gene was localized to a 322.7-kb interval between the simple-sequence repeat marker XYH11-90 and the single-nucleotide polymorphism marker SNP5300 on chromosome 11.The target interval contained 20 annotated genes.The present results demonstrated that ossac4 represents a novel starch accumulation and premature leaf senescence mutant,and lays the foundation for cloning and functional analysis of OsSAC4.

Phenotypic characterization and fine mapping of mps1,a premature leaf senescence mutant in rice (Oryza sativa L.)

Leaves play a key role in photosynthesis in rice plants. The premature senescence of such plants directly reduces the accumulation of photosynthetic products and also affects yield and grain quality significantly and negatively. A novel premature senescence mutant, mps1（mid-late stage premature senescence 1）, was identified from a mutant library consisting of ethyl methane sulfonate（EMS） induced descendants of Jinhui 10, an elite indica restorer line of rice. The mutant allele, mps1, caused no phenotypic differences from the wild type（WT）, Jinhui 10, but drove the leaves to turn yellow when mutant plants grew to the tillering stage, and accelerated leaf senescence from the filling stage to final maturation. We characterized the agronomic traits, content of photosynthetic pigments and photosynthetic efficiency of mps1 and WT, and fine-mapped MPS1. The results showed that the MPS1-drove premature phenotype appeared initially on the leaf tips at the late tillering stage and extended to the middle of leaves during the maturing stage. Compared to the WT, significant differences were observed among traits of the number of grains per panicle（–31.7%） and effective number of grains per panicle（–38.5%） of mps1 individuals. Chlorophyll contents among the first leaf from the top（Top 1st）, the second leaf from the top（Top 2nd） and the third leaf from the top（Top 3rd） of mps1 were significantly lower than those of WT（P〈0.05）, and the levels of photosynthetic efficiency from Top 1st to the forth leaf from the top（Top 4th） of mps1 were significantly lower than those of WT（P〈0.01）. Results from the genetic analysis indicated that the premature senescence of mps1 is controlled by a recessive nuclear gene, and this locus, MPS1 is located in a 37.4-kb physical interval between the markers Indel145 and Indel149 on chromosome 6. Genomic annotation suggested eight open reading frames（ORFs） within this physical region. All of these results will provide informative references for the further researches involving functional analyses and molecular mechanism exploring of MPS1 in rice.

Mechanisms of melatonin in anti-aging and its regulation effects in radiation-induced premature senescence

Melatonin is an effective antioxidant hormone produced mainly by the pineal gland.Premature senescence refers to senescence induced by declined cell proliferation and physiological functions when cells are stimulated by nontelomeric signals.The anti-aging effect of melatonin is exerted by upregulating the expression of silent information regulator 1/Sirtuin 1(SIRT1),which reduces oxidative stress damage,decreases p53 activation,and inhibits the NF-κB pathway.Radiation can induce premature senescence through direct or indirect oxidative stress damage.The mechanism by which melatonin regulates radiation-induced premature senescence includes the inhibition of the p53-mediated senescence pathway through elimination of reactive oxygen species or p53 deacetylation induced by upregulation of SIRT1 expression.Melatonin exhibits different regulatory effects for different cells and types of radiation.

Blockade of integrin signaling reduces chemotherapy-induced premature senescence in collagen cultured bladder cancer cells

Background:Diminished sensitivity towards chemotherapy remains the major impediment to the clinical treatment of bladder cancer.However,the critical elements in control of chemotherapy resistance remain obscure.Methods:We adopted improved collagen gels and performed cytotoxicity analysis of doxorubicin(DOX)and mitomycin C(MMC)of bladder cancer cells in a 3D culture system.We then detected the expression of multidrug resistant gene ABCB1,dormancy-associated functional protein chicken ovalbumin upstream-transcription factor 1(COUPTF1),cell proliferation marker Ki-67,and cellular senescence marker senescence-associatedβ-galactosidase(SA-β-Gal)in these cells.We further tested the effects of integrin blockade or protein kinase B(AKT)inhibitor on the senescent state of bladder cancer.Also,we examined the tumor growth and survival time of bladder cancer mouse models given the combination treatment of chemotherapeutic agents and integrinα2β1 ligand peptide TFA(TFA).Results:Collagen gels played a repressive role in bladder cancer cell apoptosis induced by DOX and MMC.In mechanism,collagen activated the integrinβ1/AKT cascade to drive bladder cancer cells into a premature senescence state via the p21/p53 pathway,thus attenuating chemotherapy-induced apoptosis.In addition,TFA had the ability to mediate the switch from senescence to apoptosis of bladder cancer cells in xenograft mice.Meanwhile,TFA combined with chemotherapeutic drugs produced a substantial suppression of tumor growth as well as an extension of survival time in vivo.Conclusions:Based on our finding that integrinβ1/AKT acted primarily to impart premature senescence to bladder cancer cells cultured in collagen gel,we suggest that integrinβ1 might be a feasible target for bladder cancer eradication.

Chlorophyll Fluorescence and Membrane Lipid Peroxidation in the Flag Leaves of Different High Yield Rice Variety at Late Stage of Development Under Natural Condition

With indica ( Oryza sativa L.) hybrid Shanyou 63 as control, the hybrid rice varieties including Peiai 64S/E32, Peiai 64S/9311, X07S/Zihui 100, Guangyou 881 and japonica 9516 were used to study changes of chlorophyll content, photosynthetic response to light intensity and temperature, chlorophyll fluorescence characteristics and membrane lipid peroxidation in their flag leaves at the late stage of development under natural conditions in Nanjing. The results were as follows:. primary photochemical efficiency of PS II ( F-v / F-m), quantum yield of linear electron transport of PS II (phi(PSII)), electron transfer rate (ETR) in these rice varieties decreased with their decrease of chlorophyll content during this period. This kind of impediment to energy conversion induced the transfer of excessive energy to the reducing side of PS I, hence the accumulation of O-2(radical anion) and peroxidation of membrane lipid, and resulting in the accumulation of malondialdehyde (MDA), that is the destroys of photosynthetic pigments and membranes and the consequent, premature senescence. This phenomenon is variable conspicuously in different rice varieties. Under natural condition in Nanjing, F-v/F-m, phi(PSII), ETR and quenching coefficient ( qP) in japonica 9516 tolerant to photooxidation decreased less and the conversion capacity of light energy was stable, premature senescence was unlikely, and consequently the seed-setting rate was higher. While F-v/F-m, phi(PSII), ETR and photochemical qP in Shanyou 63 sensitive to photooxidation decreased more and therefore premature senescence was easy to happen, thus the seed-setting rate and yield were all reduced. The tolerance to photooxidation and premature senescence in other hybrids derived from typical two line or three line crossing laid in the middle. From the rice breeding for super-high-yield, on the basis of the good plant-type of current rice, considering both hybrid vigor and the prevention premature senescence, it would be a notable strategy to use japonica maternal line or maternal. lines with some japonica genotype as the sterile lines in rice breeding.

Transcriptional Analysis of Normal Human Fibroblast Responses to Microgravity Stress

To understand the molecular mechanism（s） of how spaceflight affects cellular signaling pathways, quiescent normal human WI-38 fibroblasts were flown on the STS-93 space shuttle mission. Subsequently, RNA samples from the spaceflown and ground-control cells were used to construct two cDNA libraries, which were then processed for suppression subtractive hybridization （SSH） to identify spaceflight-specific gene expression. The SSH data show that key genes related to oxidative stress, DNA repair, and fatty acid oxidation are activated by spaceflight, suggesting the induction of cellular oxidative stress. This is further substantiated by the up-regulation of neuregulin 1 and the calcium-binding protein calmodulin 2. Another obvious stress sign is that spaceflight evokes the Ras/mitogen-activated protein kinase and phosphatidylinositol-3 kinase signaling pathways, along with up-regulating several Gl-phase cell cycle traverse genes. Other genes showing upregulation of expression are involved in protein synthesis and pro-apoptosis, as well as pro-survival. Interactome analysis of functionally related genes shows that c-Myc is the ＂hub＂ for those genes showing significant changes. Hence, our results suggest that microgravity travel may impact changes in gene expression mostly associated with cellular stress signaling, directing cells to either apoptotic death or premature senescence.

Tacrolimus may play a role in dermatitis and radiation-induced skin injury through cellular senescence

Skin Exposure of skin to ionizing radiation can induce acute or chronic biological effects,resulting in radiation-induced skin injury(RSI).Premature cellular senescence,caused by oxidative stress and/or DNA damage from chemical or physical agents,leads to the decrease of cellular proliferation and physiological function.Persistent DNA damage and accumulation of senescent cells are associated with the progression of radiation-induced injury.Atopic dermatitis and RSI have similar inflammatory symptoms.The treatment of tacrolimus(TAC)in atopic dermatitis may be associated with premature cellular senescence.TAC can prevent the onset of cellular senes-cence by inactivating the p38 mitogen-activated protein kinase(p38 MAPK).The activation of p38 MAPK can induce the senescence-associated secretory phenotype(SASP)by enhancing the transcriptional activity of nuclear factor kappa-B(NF-κB),which ultimately leads to premature cellular senescence.FK506 binding protein 51(FKBP51)exhibits resistance to ionizing radiation,but the mechanism of TAC regulation of ionizing radiation-induced premature senescence still needs further study.This review discusses the mechanism of cellular senes-cence in RSI and the role of TAC in both dermatitis and RSI.