Manifestation Of Senescence Research Articles

Exogenous Melatonin Alleviated Leaf Yellowing via Inhibiting Respiration and Ethylene Biosynthesis during Shelf Life in Pakchoi.

Postharvest yellowing of leafy plant is a manifestation of senescence, and melatonin (MT) is known to delay leaf senescence in some higher plants. Herein, we investigated the effect of exogenous MT treatment on postharvest pakchoi by monitoring the ethylene biosynthesis and respiratory metabolism. Results showed that exogenous MT effectively extended the shelf life, delayed leaf yellowing, minimized the alteration in Fv/Fm ratio and maintained higher integrity of chloroplast in pakchoi. There was a significant correlation between yellowing index, respiration rate and ethylene production. MT treatments greatly delayed the yellowing process of pakchoi that was associated with the reduced activity of glycolysis pathway and tricarboxylic acid cycle (TCA), increased proportion of pentose phosphate pathway (PPP) in respiratory metabolism, as manifested by the lower activity of phosphohexose isomerase (PHI), succinate dehydrogenase (SDH) and cytochrome C oxidase (COX), downregulated the expression of their corresponding genes, but enhanced the activity and expression level of 6 phosphogluconate dehydrogenase (6PGDH). MT also markedly maintain chlorophyll content by inhibiting ethylene production and action during shelf life, likely a consequence of reduced activities of 1-aminocyclopropane-1-carboxylate (ACC) synthase (ACS) and ACC oxidase (ACO), as well as the expression levels of their related genes. These results collectively indicate that melatonin alleviated leaf yellowing of postharvest pakchoi might be attributed to the suppression of the ethylene biosynthesis and respiratory metabolism, and our findings contribute to provide a good candidate measure for extending shelf life and reducing postharvest loss of pakchoi.

AFT survival model to capture the rate of aging and age-specific mortality trajectories among first-allogeneic hematopoietic stem cells transplant patients.

Accelerated failure time (AFT) model is commonly applied in engineering studies to address the failure rate of a machine. In humans, survival profile of transplant patients is among the rare scenarios whereby AFT is applicable. To date, it is uncertain whether reliable risk estimates and age-specific mortality trajectories have been published using conventional statistics approach. By investigating mortality trajectory, the rate of aging d(log(μ(x)))/dx of Hematopoietic Stem Cells Transplants (HSCTs) patients who had underwent first-allogeneic transplants can be obtained, and to unveil the possibility of elasticity of human aging rate in HSCTs. A modified parametric frailty survival model was introduced to the survival profiles of 11,160 patients who had underwent first-allogeneic HSCTs in the United States between 1995 and 2006; data was shared by Center for International Bone and Marrow Transplant Research. In comparison to stratification, the modification permits two entities in relation to time to be presented; age and calendar time. To consider its application in empirical studies, the data contains arbitrary right-censoring, a statistical condition which is preferred by choice in many transplant studies. The finalized multivariate AFT model was adjusted for clinical and demographic covariates, and age-specific mortality trajectories were presented by donor source and post-transplant time-lapse intervals. Two unexpected findings are presented: i) an inverse J-shaped hazard in unrelated donor-source t≤100-day; ii) convergence of unrelated-related hazard lines in 100-day<t ≤ 365-day suggests maximum manifestation of senescence among survivors. Analyses of long-term survivors (t>365-day) must consider for periodic medical improvements, and transplant year as a standalone time-variable is not sufficient for statistical adjustment in the finalized multivariate model. In relevance to clinical studies, biennial event-history analysis and age-specific mortality trajectories of long-term survivors provide a more relevant intervention audit report for transplant protocols than the popular statistical presentation; i.e. survival probabilities among donor-source.

Relevance of hypercholesterolemia to fetal and pediatric atherosclerosis.

Ubiquitous atherosclerotic changes in fetal and pediatric subjects demonstrate the fundamental importance of repetitive hemodynamic stresses and cannot be explained on the basis of the hypercholesterolemic/lipid hypothesis because serum cholesterol levels at this age lie within allegedly "desirable blood levels." This fact, inconsistent with the lipid hypothesis, renders absurd the widespread dietary restriction of cholesterol and animal fats as prevention of atherosclerosis. Iatrogenic effects of atherosclerosis in humans and its experimental production in herbivores at serum cholesterol levels below infant levels strongly support the "vascular fatige" concept and negate the lipid hypothesis. Neither is atherosclerosis a manifestation of senescence because age is merely a time factor indicating the duration of exposure to hemodynamic stresses that are variable with time and location.

Does bristlecone pine senesce?

We evaluated hypotheses of senescence in old trees by comparing putative biomarkers of aging in Great Basin bristlecone pine (Pinus longaeva) ranging in age from 23 to 4713 years. To test a hypothesis that water and nutrient conduction is impaired in old trees we examined cambial products in the xylem and phloem. We found no statistically significant age-related changes in tracheid diameter, or in several other parameters of xylem and phloem related to cambial function. The hypothesis of continuously declining annual shoot growth increments was tested by comparing trees of varying ages in regard to stem unit production and elongation. No statistically significant age-related differences were found. The hypothesis that aging results from an accumulation of deleterious mutations was addressed by comparing pollen viability, seed weight, seed germinability, seedling biomass accumulation, and frequency of putative mutations, in trees of varying ages. None of these parameters had a statistically significant relationship to tree age. Thus, we found no evidence of mutational aging. It appears that the great longevity attained by some Great Basin bristlecone pines is unaccompanied by deterioration of meristem function in embryos, seedlings, or mature trees, an intuitively necessary manifestation of senescence. We conclude that the concept of senescence does not apply to these trees.

Lipofuscin: mechanisms of formation and increase with age.

Lipofuscin (age pigment) is a brown-yellow, electron-dense, autofluorescent material that accumulates progressively over time in lysosomes of postmitotic cells, such as neurons and cardiac myocytes. The exact mechanisms behind this accumulation are still unclear. This review outlines the present knowledge of age pigment formation, and considers possible mechanisms responsible for the increase of lipofuscin with age. Numerous studies indicate that the formation of lipofuscin is due to the oxidative alteration of macromolecules by oxygen-derived free radicals generated in reactions catalyzed by redox-active iron of low molecular weight. Two principal explanations for the increase of lipofuscin with age have been suggested. The first one is based on the notion that lipofuscin is not totally eliminated (either by degradation or exocytosis) even at young age, and, thus, accumulates in postmitotic cells as a function of time. Since oxidative reactions are obligatory for life, they would act as age-independent enhancers of lipofuscin accumulation, as well as of many other manifestations of senescence. The second explanation is that the increase of lipofuscin is an effect of aging, caused by an age-related enhancement of autophagocytosis, a decline in intralysosomal degradation, and/or a decrease in exocytosis.

Differential survival and natural selection: their impact upon aging and cancer mortality

Evidence for natural selection is often presented from the perspective of evolution. However, evolution is not the purpose of natural selection. Natural selection might also impact upon the manifestation of senescence via differential survival. The relationship between age-specific cancer mortality rates and corresponding age group population size in the USA from 1951 to 1989 for age groups over age 45 was examined. Rising age-specific cancer mortality rates among elderly men were increasingly correlated with growing age group population size with increasing age. This relationship was not observed in women. Since an age-specific rate should be independent of age group population size, this finding suggests that successive cohorts of elderly USA men were not comparable with respect to their susceptibility to cancer mortality. Differential survival, which effects men more than women, and its selective culling effect upon the surviving gene pool in an aging population may account for some of the observed increasing cancer mortality rates among elderly men. If so, evidence of natural selection can also be presented from the perspective of manifestation rates for some disorders associated with senescence.

Differential survival, natural selection, and the manifestation of senescence

Evidence for natural selection is typically sought by searching for changes in organisms over generations (that is, evolution). However, evolution may represent but one biological manifestation of the force of natural selection. Although its evolutionary influence diminishes with aging, natural selection might also impact upon the manifestation of senescence via differential survival. Annual population estimates in the United States from 1951 to 1990 for age groups over 60 years old were analyzed. The rate of increase in the size of these age groups increased with increasing age. Since birth rates in developed countries have declined, this finding is a direct manifestation of differential survival over time. Correspondingly, increasing mortality rates from many disorders associated with senescence have been shown to be correlated with increasing age group population size. These observations suggest that natural selection, via differential survival, has had a demonstrable impact upon manifestation rates of the disorders of senescence.

Relationship between changes in lipid with ageing of cassava roots and senescence parameters

The roots of cassava ( Manihot esculenta) display parenchyma discoloration soon after unearthing. The progressive change in this parameter of senescence was evaluated and its relationship with simultaneous changes in lipid composition in the ageing of the roots were studied in two consecutive years. In total, seven phospholipids were measured, and of these phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol and diphosphatidylglycerol showed concerted changes in content and proportion. These changes were correlated with the root discoloration. Overall decreases in total phospholipids and glyceroglycolipids contents, and increases in the ratio of total sterol containing lipids to total phospholipids and to total glyceroglycolipids, suggest alterations of membranes, similar to those occurring in other senescent plant organs. The results indicate a causal relationship between the changes in lipids and the parenchyma discoloration that occur in cassava roots after unearthing. The hypothesis that considers cassava discoloration as a manifestation of senescence, is supported.

The influence of senescence on thyroid function: functional changes evaluated with I131.

THE functional status of the thyroid gland in old age and its role in the genesis of some of the manifestations of senescence have been subjects of speculation for many years. It has been recognized that some of the features of senescence are similar to those of the hypothyroid state: thus dryness of the skin, diminished motor activity, impaired muscle strength, diminished cold tolerance and sparseness of the hair are common to both. Lorand (1) commented on the similarity of ageing to hypothyroidism and others (2) have suggested thyroid hormone therapy for the aged. Carlson (3), in a recent review of thyroid function during ageing, states that there is no convincing proof that secretion of thyroid hormone decreases with advancing age. In a previous publication from this laboratory (4) thyroid secretion rate, determined by the goiter prevention assay, was less in senescent rats than in younger mature animals.