Different Stages Of Senescence Research Articles

Senescent endothelial cells: a potential target for diabetic retinopathy.

Diabetic retinopathy (DR) is a diabetic complication that results in visual impairment and relevant retinal diseases. Current therapeutic strategies on DR primarily focus on antiangiogenic therapies, which particularly target vascular endothelial growth factor and its related signaling transduction. However, these therapies still have limitations due to the intricate pathogenesis of DR. Emerging studies have shown that premature senescence of endothelial cells (ECs) in a hyperglycemic environment is involved in the disease process of DR and plays multiple roles at different stages. Moreover, these surprising discoveries have driven the development of senotherapeutics and strategies targeting senescent endothelial cells (SECs), which present challenging but promising prospects in DR treatment. In this review, we focus on the inducers and mechanisms of EC senescence in the pathogenesis of DR and summarize the current research advances in the development of senotherapeutics and strategies that target SECs for DR treatment. Herein, we highlight the role played by key factors at different stages of EC senescence, which will be critical for facilitating the development of future innovative treatment strategies that target the different stages of senescence in DR.

Dynamic 3D genome reorganization during senescence: defining cell states through chromatin.

Cellular senescence, a cell state characterized by growth arrest and insensitivity to growth stimulatory hormones, is accompanied by a massive change in chromatin organization. Senescence can be induced by a range of physiological signals and pathological stresses and was originally thought to be an irreversible state, implicated in normal development, wound healing, tumor suppression and aging. Recently cellular senescence was shown to be reversible in some cases, with exit being triggered by the modulation of the cell's transcriptional program by the four Yamanaka factors, the suppression of p53 or H3K9me3, PDK1, and/or depletion of AP-1. Coincident with senescence reversal are changes in chromatin organization, most notably the loss of senescence-associated heterochromatin foci (SAHF) found in oncogene-induced senescence. In addition to fixed-cell imaging, chromatin conformation capture and multi-omics have been used to examine chromatin reorganization at different spatial resolutions during senescence. They identify determinants of SAHF formation and other key features that differentiate distinct types of senescence. Not surprisingly, multiple factors, including the time of induction, the type of stress experienced, and the type of cell involved, influence the global reorganization of chromatin in senescence. Here we discuss how changes in the three-dimensional organization of the genome contribute to the regulation of transcription at different stages of senescence. In particular, the distinct contributions of heterochromatin- and lamina-mediated interactions, changes in gene expression, and other cellular control mechanisms are discussed. We propose that high-resolution temporal and spatial analyses of the chromatin landscape during senescence will identify early markers of the different senescence states to help guide clinical diagnosis.

Changes in volatile profile and related gene expression during senescence of tobacco leaves.

Volatile organic compounds are critical for food flavor and play important roles in plant-plant interactions and plants' communications with the environment. Tobacco is well-studied for secondary metabolism and most of the typical flavor substances in tobacco leaves are generated at the mature stage of leaf development. However, the changes in volatiles during leaf senescence are rarely studied. The volatile composition of tobacco leaves at different stages of senescence was characterized for the first time. Comparative volatile profiling of tobacco leaves at different stages was performed using solid-phase microextraction coupled with gas chromatography/mass spectrometry. In total, 45 volatile compounds were identified and quantified, including terpenoids, green leaf volatiles (GLVs), phenylpropanoids, Maillard reaction products, esters, and alkanes. Most of the volatile compounds showed differential accumulation during leaf senescence. Some terpenoids, including neophytadiene, β-springene, and 6-methyl-5-hepten-2-one, increased significantly with the progress of leaf senescence. Hexanal and phenylacetaldehyde also showed increased accumulation in leaves during senescence. The results from gene expression profiling indicated that genes involved in metabolism of terpenoids, phenylpropanoids, and GLVs were differentially expressed during leaf yellowing. Dynamic changes in volatile compounds during tobacco leaf senescence are observed and the integration of gene-metabolites datasets offers important readouts for the genetic control of volatile production during the process of leaf senescence. © 2023 Society of Chemical Industry.

Anthocyanin Biosynthesis Associated with Natural Variation in Autumn Leaf Coloration in Quercus aliena Accessions.

Quercus aliena is an economically important tree species and one of the dominant native oak species in China. Although its leaves typically turn yellow in autumn, we observed natural variants with red leaves. It is important to understand the mechanisms involved in leaf color variation in this species. Therefore, we compared a Q. aliena tree with yellow leaves and three variants with red leaves at different stages of senescence in order to determine the causes of natural variation. We found that the accumulation of anthocyanins such as cyanidin 3-O-glucoside and cyanidin 3-O-sambubiglycoside had a significant effect on leaf coloration. Gene expression analysis showed upregulation of almost all genes encoding enzymes involved in anthocyanin synthesis in the red-leaved variants during the early and main discoloration stages of senescence. These findings are consistent with the accumulation of anthocyanin in red variants. Furthermore, the variants showed significantly higher expression of transcription factors associated with anthocyanin synthesis, such as those encoded by genes QaMYB1 and QaMYB3. Our findings provide new insights into the physiological and molecular mechanisms involved in autumn leaf coloration in Q. aliena, as well as provide genetic resources for further development and cultivation of valuable ornamental variants of this species.

Changes in the biochemical characteristics and volatile fingerprints of atemoya during postharvest ripening at room temperature

In order to determine the best shelf life of the atemoya, the changes in the biochemical characteristics in five different stages of senescence were investigated. During postharvest ripening at room temperature, the firmness decreased rapidly after harvest and the fruit weight loss and browning degree increased from the earliest green-colored stage onward. The total soluble solid concentrations (TSSC) and titratable acidity (TA) increased continuously throughout maturation, and the peak respiratory and ethylene production rates occurred on the 3d and 5th day of postharvest, respectively. Phenylalanine ammonialyase (PAL) activity steadily increased, catalase and polyphenol oxidase (PPO) activities decreased significantly on the 1st day and then gradually increased, and peroxidase activities increased during the initial 3 days, and then decreased at later stages. The volatile fingerprints of flesh samples from the five senescence stages were successfully established using gas chromatography-ion mobility spectrometry (GC-IMS) combined with principal component analysis, and 32 typical target compounds and 35 indeterminate compounds were obtained. The results provide a theoretical basis for the development of innovative preservation methods for atemoya.

Ultraviolet radiation accelerates photodegradation under controlled conditions but slows the decomposition of senescent leaves from forest stands in southern Finland

Depending on the environment, sunlight can positively or negatively affect litter decomposition, through the ensemble of direct and indirect processes constituting photodegradation. Which of these processes predominate depends on the ecosystem studied and on the spectral composition of sunlight received. To examine the relevance of photodegradation for litter decomposition in forest understoreys, we filtered ultraviolet radiation (UV) and blue light from leaves of Fagus sylvatica and Betula pendula at two different stages of senescence in both a controlled-environment experiment and outdoors in four different forest stands (Picea abies, Fagus sylvatica, Acer platanoides, Betula pendula). Controlling for leaf orientation and initial differences in leaf chlorophyll and flavonol concentrations; we measured mass loss at the end of each experiment and characterised the phenolic profile of the leaf litter following photodegradation. In most forest stands, less mass was lost from decomposing leaves that received solar UV radiation compared with those under UV-attenuating filters, while in the controlled environment UV-A radiation either slightly accelerated or had no significant effect on photodegradation, according to species identity. Only a few individual phenolic compounds were affected by our different filter treatments, but photodegradation did affect the phenolic profile. We can conclude that photodegradation has a small stand- and species-specific effect on the decomposition of surface leaf litter in forest understoreys during the winter following leaf fall in southern Finland. Photodegradation was wavelength-dependent and modulated by the canopy species filtering sunlight and likely creating different combinations of spectral composition, moisture, temperature and snowpack characteristics.

Organ-specific distribution and non-enzymatic conversions indicate a metabolic network of phenylphenalenones in Xiphidium caeruleum

We investigated the organ-specific phytochemistry of the inflorescences, leaves at different stages of senescence, and roots of Xiphidium caeruleum (Haemodoraceae) and elucidated the structure of six undescribed compounds. Among these, a phenylcarbamoylnaphthoquinone (PCNQ), representing the first member of a class of undescribed phenylphenalenone-derived nitrogenous compounds, was identified and its spontaneous formation elaborated. Starting from phenylbenzoisochromenone glucosides, the reaction cascade proceeds through oxidative decarboxylation and several oxidation steps to an anhydride, which is further converted to a carboxy-phenylnaphthoquinone. In the presence of amino acids, this carboxy-phenylnaphthoquinone readily reacts to PCNQs. Hence, the carboxy-phenylnaphthoquinone was hypothesized to be involved in plant defense because of its reactivity towards amino acids. It was also hypothesized that reduced levels of the corresponding glucosidic phenylbenzoisochromenone precursors in older leaves may foster pathogen-driven senescence.

Mitochondria change dynamics and morphology during grapevine leaf senescence.

Leaf senescence is the last stage of development of an organ and is aimed to its ordered disassembly and nutrient reallocation. Whereas chlorophyll gradually degrades during senescence in leaves, mitochondria need to maintain active to sustain the energy demands of senescing cells. Here we analysed the motility and morphology of mitochondria in different stages of senescence in leaves of grapevine (Vitis vinifera), by stably expressing a GFP (green fluorescent protein) reporter targeted to these organelles. Results show that mitochondria were less dynamic and markedly changed morphology during senescence, passing from the elongated, branched structures found in mature leaves to enlarged and sparse organelles in senescent leaves. Progression of senescence in leaves was not synchronous, since changes in mitochondria from stomata were delayed. Mitochondrial morphology was also analysed in grapevine cell cultures. Mitochondria from cells at the end of their growth curve resembled those from senescing leaves, suggesting that cell cultures might represent a useful model system for senescence. Additionally, senescence-associated mitochondrial changes were observed in plants treated with high concentrations of cytokinins. Overall, morphology and dynamics of mitochondria might represent a reliable senescence marker for plant cells.

Discrimination of floor cover of dry deciduous forest using Hyperion (EO-1) data

A study was conducted to analyze high spectral reflectance data of the floor cover of dry deciduous forests (Shoolpaneshwar wildlife sanctuary, Gujarat, India) during the summer season. Hyperion data and field data were acquired in the month of April, 2006 (dry/summer season) when the vegetation was in different stages of senescence. Variations in spectral characteristics of different types of leaf litter were seen. Spectral reflectance curves were different for different thicknesses of leaf litter. Altitude also had an impact on the reflectance curves. Spectra of bare soil is easily separable from the ones covered by litter. Descriptive spectra were extracted for four cover types such as Tectona grandis L., Dendrocalamus strictus Nees., mixed deciduous species and bare soil. Continuum removal spectra were also extracted for these four types. Sharp absorption features were seen in VIS and SWIR-II wavelengths which were absent in the spectra of bare soil, indicating the ability of Hyperion data to discriminate dry forest floor from bare soil. The three cover types are also distinctly separable. SWIR-II wavelengths are more sensitive to the type of floor cover indicating its distinctiveness. Results are discussed highlighting the potential of Hyperion data in deciphering floor cover characteristics in the dry season.

Movement by mating females of a host alternating aphid: a response to leaf fall

Autumn remigrants of the host alternating bird cherry‐oat aphid, Rhopalosiphum padi, colonise individual plants of the winter host, Prunus padus. However, they do not select leaves at different stages of senescence, which is surprising as leaf fall is a definitive deadline for production and development of mating females. For successful development mating females should be mobile and have the capacity to evaluate leaf senescence. Although remigrants do not selectively colonise leaves at different stages of senescence, mating females were found in very low numbers on leaves that were about to be shed. In choice test and olfactometer bioassays, abscising leaves were avoided by mating females. In the field mature leaves were available for colonisation during the period of leaf fall of P. padus. We conclude that mating females abandon abscising leaves in favour of leaves at an earlier stage of senescence, increasing the time available for mating. Our results support the role of remigrants as pioneers which identify good winter host plants, and of mating females as mobile searchers for optimal feeding and mating sites.

The effect of organic matter on sedimentary phosphorus release in an Australian reservoir

Australian reservoirs, compared to much of the world, are subjected to extreme arid and semi-arid climatic conditions where dam volumes can range from near-empty to full, often with rapid filling events. P-release, after re-flooding of desiccated sediments, can be important to water quality, and can be further influenced by dried macrophyte, exposed as water recedes and incorporated into sediments. P-release from Lake Rowlands (New South Wales, Australia) sediments was studied under different aerobic and sterile conditions with five carbon source amendments to the sediment (the macrophyte Isoetes sp. in different stages of senescence and acetate). Sedimentary P-release involved a complex array of factors modified by aerobic, biotic and abiotic processes, organic matter breakdown, iron content of sediments and turbulence. Under aerobic conditions, P-release from sterile non-amended sediments and sterile macrophyte-amended sediments was greater than from non-sterile sediments. Under anaerobic conditions, P-release was maximal from non-sterile macrophyte-amended sediments, probably via pathways involving fermentative Fe3+-reducing bacteria where electrons are transferred from organic matter to amorphous Fe(OOH) leading to Fe2+ and consequent release of P. Macrophyte addition (whether fresh or dried) enhanced P-release under anaerobic compared with aerobic conditions. P-release from acetate-amended sediments appeared to involve acetate aerobes. The re-flooding of sediments, therefore, has the potential to create conditions that are conducive to aerobic sedimentary P-release and should be taken into account in management strategies adopted for reservoirs where levels are likely to fluctuate.

Changes in Blue-Green and Chlorophyll Fluorescence Emission and Fluorescence Ratios during Senescence of Tobacco Plants

Blue-green fluorescence and the red/far-red chlorophyll (Chl) fluorescence emission spectra of green tobacco leaves and of aurea leaves in different stages of senescence were measured using excitation at 355 nm in order to test the suitability of the fluorescence ratios green/red and green/far-red together with other ratios as stress and pigment indicators. Young yellowish-green leaves of the aurea mutant tobacco showed a much higher blue-green fluorescence emission and lower chlorophyll fluorescence as compared to the green wild type tobacco. As a consequence, the fluorescence intensity ratios blue/green ( F440/ F520), blue/red ( F440/ F690), blue/far-red ( F440/ F740), green/red ( F520/ F690) and green/far-red ( F520/ F740), as determined from the measured fluorescence emission spectra of the adaxial and abaxial leaf sides, were quite different for both leaf types and were functions of the content of chlorophylls and carotenoids. As chlorophyll levels decreased in senescing leaves of the aurea tobacco plant, the Chl a/ b ratio remained high at 3.3 to 4.0, while the ratio of chlorophylls to carotenoids declined slightly. In contrast, the Chl fluorescence ratios ( R fd 690-values, F v / F m and F v / F 0) as physiological indicators continuously declined, indicating a successive loss of photosynthetic activity. Values of the chlorophyll fluorescence ratio F690/ F740 for adaxial and abaxial leaf-sides increased with yellowing, whereas F440/ F520 tended to decrease with the senescence-induced decline in Chl content. F440/ F690 and F520/ F690 were found to increase after an initial decrease, with leaf age and senescence. The same trend was found for F440/ F740 and F520/ F740, which exhibited maximum sensitivity with respect to Chl breakdown. Whereas the F690/ F740 ratio for abaxial versus adaxial leaf surfaces correlated linearly, with the abaxial leaf-side values always being higher than the adaxial leaf-side, values for both sides corresponded in a curvilinear fashion with leaf Chl content. Changes during early stages of leaf development were seen not only in the most commonly used red/far-red ratio, F690/ F740, but to some extent also in F440/ F520. The results indicate that changes in photosynthetic activity due to senescence and Chl breakdown can easily be detected and qualified via fluorescence ratios that are based on the UV-A excited fluorescence bands F440, F520, F690 and F740. These ratios provide a solid basis for the laser-induced remote sensing of the state of health and Chl content of vegetation. The fluorescence ratios green/red and green/far-red were found to be very suitable complementary indicators of early stress events in plants.

Chlorophyll breakdown in senescing barley leaves as correlated with phaeophorbidea oxygenase activity

Activities of phaeophorbide a oxygenase (PaO), a key enzyme of the catabolic pathway of chlorophyll (Chi) were measured in membrane preparations from barley primary leaves at different stages of senescence. Under conditions of natural senescence, degreening began about 3 weeks after sowing; it took about 2 weeks and coincided with appearance and level of PaO activity. Premature, accelerated Chl breakdown in detached leaves induced to senesce in darkness was also well correlated with PaO activity. In detached and darkened leaves treatment with cytokinin delayed the loss of Chl as well as the appearance of PaO activity. Treatment of detached leaves with abscisic acid caused the acceleration of degreening in conjunction with increased PaO activity, but only when incubations were performed under photoperiod. Jasmonic acid methylester caused a most rapid breakdown of Chl in detached leaves kept under photoperiod. In this case the real activities of PaO could not be determined because the membrane preparations contained an inhibitory factor. Heat shock accelerated breakdown of Chl and also caused the appearance of increased activities of PaO. Effects of inhibitors of cytoplasmic protein synthesis suggest that the PaO protein is newly synthesized upon the induction of senescence. They also suggest that PaO is not the sole pace-making protein of the catabolic pathway.

Response of a lizard species to the senescence of a dominant plant in the Sonoran desert

:Animal species often respond to changes in the plant community during ecological succession. I discovered such a response in the distribution of a lizard (Urosaurus ornatus, tree lizard) associated with different stages of senescence of saguaro cactus (Carnegiea gigantea). From 1986 through 1995, I periodically assessed the distribution and numbers of tree lizards in the mesquite (Prosopis juliflora), palo verde (Circidium microphylum), and saguaro association in the Saguaro National Park, Arizona. Many of the lizards use saguaro cactus as vantage points for territory defense, feeding and oviposition. Two study plots contained 137 sites which consisted of living, dead standing, and dead prone saguaro cactus. Plots were surveyed for tree lizards in 1986, 1987, 1988, 1992, and 1995. In each year, a site was counted as used by lizards if a resident lizard (captured during two or more census periods) was present. During the study, only 3/91 (3.3%) living cactus were ever used by lizards. In contrast, 73% (27/37) of dead standing saguaro and 12.5% (4/32) of dead prone cactus were used in at least one year of the study. Living saguaro comprised an average of 63% of all sites, dead standing was 19%, and dead prone was 18%. An average of 79% of all lizard records were from the use of dead standing cactus. Only 7% of lizard records were from living saguaro. Analysis of the pattern of use of the classes of cactus showed a highly significant saguaro effect, no significant differences in use among years, and no significant saguaro class by year interaction. Saguaro cactus provide opportunities for exploitation of a distinct microhabitat resource (primarily dead standing cactus) by tree lizards. It appears that dead saguaro are quickly recognized and exploited by tree lizards, which allows an expansion of the territory and home range boundaries of individual lizards.

Unstable cytoplasms in Hawaiian strains of Neurospora intermedia

By subjecting a large sample of natural isolates of N. intermedia to prolonged serial subculturing, 26 cytoplasmic variants have been identified. These variants show senescence, and finally death at some strain-specific point in the subculture series. All senescent strains are from the Hawaiian archipelago, where their incidence in natural populations is high. Senescent cultures can be female-fertile. Random ascospore analyses show that (i) senescence is maternally inherited; (ii) different stages of senescence give different proportions of senescent progeny; and (iii) ascospores from one cross show different degrees of senescence. These results indicate that senescence is determined by a genetic factor which re sides in the cytoplasm. This factor promotes instability of the cytoplasm, resulting initially in cytoplasmic heterogeneity shown by ascus and conidium sampling, and finally in death. Molecular studies to be published elsewhere show that the progression through senescence to death is correlated with the occurence of abnormalities in cytochrome content and mitochondrial DNA. The Hawaiian word kalilo (dying), symbolised [kal], is proposed to denote these cytoplasms.