Senescence in European Middle Pleistocene hominids: The Atapuerca evidence

The mandibular specimens AT-250 and AT-793 (individual IV) and AT-888 (individual XXI) from the Atapuerca Middle Pleistocene sample show a combination of traits interpreted as evidence of senescence. In order to explore age-related mandibular changes relevant to the interpretation of the Atapuerca hominids, the sample of known age and sex from Spitalfields (London) and the Neolithic sample from Abu Hureyra (Syria) were used as a baseline. Results obtained indicate that the occurrence of an enlarged and posteriorly located mental foramen, in association with high alveolar resorption in AT-250 and AT-888, support the hypothesis of senescence in individuals IV and XXI from the Atapuerca sample. The findings suggest that European Middle Pleistocene populations lived long enough to reach senescence. The age at death for Middle Pleistocene hominids and Neanderthals has previously been estimated at around 40–45 years in the oldest specimens. The appearance of senescence processes before this age is indicative of higher rates of morphological aging in the clade which gave rise to Neanderthals. The anatomical significance of ageing features when considered in the context of craniofacial remodelling can help in the understanding of the taxonomic status of these morphological traits.     

The Control of Leaf Senescence in Kleinia articulata by Photoperiod

Experiments with attached and detached leaves of K. articulatahave shown that senescence rates are determined by the daylengthprevailing during early growth (leaf-expansion stage) and thatthis effect is lasting, long days leading to early leaf death.Daylength also affects longevity after full expansion has occurred,long days hastening senescence. Tests with numerous plant-growthregulators have revealed beneficial effects of gibberellic acid,while kinetin is detrimental to survival at 50 ppm. Entire detachedleaves and isolated petioles behave similarly to leaves on theplant, but leaf discs do not behave in the same way. Other parametersaffected by daylength include: leaf shape, the capacity of leavesto form roots, and enlargement of mesophyll cells normal tothe leaf surface.     

The Control of Flower Senescence in Petunia (Petunia hybrids)

Petunia corollas wilt and abscise between one and two weeksafter detachment when maintained in distilled water in vialsat 18 °C. The onset of wilting is brought forward substantiallyby the application of 1-aminocyclopropane-1-carboxylic acid(ACC) either to the vial solution or to the stigmatic surface.Both pollination and stigma removal also shorten the time tothe onset of wilting, colour change and to abscission. In thecase of stigma removal, the life span of the corolla is shortestwhen the treatment is made at the time of flower detachment(day 0), whereas pollination has the greatest effect if it occurson day 1. Stigma damage still has an effect on corolla senescenceeven when stigma and style are removed, as long as they havebeen left in place for a few hours after treatment. Evidencefrom several experiments shows that a 17 h period is sufficientfor the full effect to be shown, and that probably there aresome effects on the corolla even if the damaged stigma is onlyleft in position for 3–6 h. Treatments which advance corolladeath (to day 3) also advance the peak of ethylene productionby the pistil (to day 1) and the corolla (to day 2). The useof silver thiosulphate (STS) overcomes all manipulative andchemical treatments used, and greatly extends vase life. Theextension occurs even when STS application is delayed for 24h, i.e. after the peak of ethylene production by the pistiland after any senescence signal has arrived at the corolla.In this case, however, the time to first morphological changeis largely unaffected, but the STS greatly extends the timeperiod between first morphological change and corolla death.The evidence suggests that early symptoms of senescence e.g.colour change and slight loss of turgor, do not automaticallylead to corolla abscission. Petunia hybrida, abscission, ACC, STS, pollination, flower senescence, ethylene     

Adaptive Introgression Facilitates Adaptation to High Latitudes in European Aspen (Populus tremula L.)

Understanding local adaptation has become a key research area given the ongoing climate challenge and the concomitant requirement to conserve genetic resources. Perennial plants, such as forest trees, are good models to study local adaptation given their wide geographic distribution, largely outcrossing mating systems, and demographic histories. We evaluated signatures of local adaptation in European aspen (Populus tremula) across Europe by means of whole-genome resequencing of a collection of 411 individual trees. We dissected admixture patterns between aspen lineages and observed a strong genomic mosaicism in Scandinavian trees, evidencing different colonization trajectories into the peninsula from Russia, Central and Western Europe. As a consequence of the secondary contacts between populations after the last glacial maximum, we detected an adaptive introgression event in a genome region of ∼500 kb in chromosome 10, harboring a large-effect locus that has previously been shown to contribute to adaptation to the short growing seasons characteristic of Northern Scandinavia. Demographic simulations and ancestry inference suggest an Eastern origin—probably Russian—of the adaptive Nordic allele which nowadays is present in a homozygous state at the north of Scandinavia. The strength of introgression and positive selection signatures in this region is a unique feature in the genome. Furthermore, we detected signals of balancing selection, shared across regional populations, that highlight the importance of standing variation as a primary source of alleles that facilitate local adaptation. Our results, therefore, emphasize the importance of migration–selection balance underlying the genetic architecture of key adaptive quantitative traits.     

The Effect of the Autumn Senescence of Leaves on the Internal Cycling of Nitrogen for the Spring Growth of Apple Trees

The internal cycling of nitrogen (N) has been studied in applerootstocks grown in sand culture and subjected to a constantN supply, or defoliation, or withholding the N supply in theautumn in order to manipulate the amount of N stored over thewinter. The trees subsequently received either no N or 8–0mol N m^–3 (labelled with ¹⁵N to 498 atom%) with the irrigationthe following spring in order to determine the effect of thecurrent N supply on the remobilization of N for leaf growth. Provision of an autumnal N supply delayed leaf senescence andreduced the amount of N withdrawn from leaves from 156 mg Nplant^–1 to 91 mg N plant^–1. Loss of protein ribulose1,5-bisphosphate carboxylase/oxygenase (RUBISCO) accounted for83–87% of the soluble protein N lost during leaf senescence,there being a preferential loss of RUBISCO compared with othersoluble leaf proteins. Remobilization of N from perennial woody tissues (stems androots) in the spring was used predominantly for leaf growth.The amount of N remobilized depended upon the size of the Nstore, but was unaffected by the current N supply, demonstratingthat fertilization of trees does not alter the efficiency withwhich they cycle N. Degradation of RUBISCO in the autumn accountedfor between 32% and 48% of the N subsequently remobilized forleaf growth the following spring, suggesting that RUBISCO hasa role as a summer store for N. Key words: Malus domestica, Borkh, nitrogen, senescence, ribulose 1, 5-bisphosphate carboxylase, oxygenase, storage, remobilization     

The Role of Extracellular Vesicles in Senescence

Cells can communicate in a variety of ways, such as by contacting each other or by secreting certain factors. Recently, extracellular vesicles (EVs) have been proposed to be mediators of cell communication. EVs are small vesicles with a lipid bilayer membrane that are secreted by cells and contain DNA, RNAs, lipids, and proteins. These EVs are secreted from various cell types and can migrate and be internalized by recipient cells that are the same or different than those that secrete them. EVs harboring various components are involved in regulating gene expression in recipient cells. These EVs may also play important roles in the senescence of cells and the accumulation of senescent cells in the body. Studies on the function of EVs in senescent cells and the mechanisms through which nonsenescent and senescent cells communicate through EVs are being actively conducted. Here, we summarize studies suggesting that EVs secreted from senescent cells can promote the senescence of other cells and that EVs secreted from nonsenescent cells can rejuvenate senescent cells. In addition, we discuss the functional components (proteins, RNAs, and other molecules) enclosed in EVs that enter recipient cells.     

The Metabolism of Oat Leaves during Senescence: III. The Senescence of Isolated Chloroplasts

The changes in chlorophyll and protein in senescing chloroplasts isolated from the first leaves of 7-day-old oat (Avena sativa) seedlings have been investigated. In darkness the chlorophyll in these plastids is highly stable, losing only 5 to 10% of its content after 7 days at 26 C. This result contrasts with the behavior of chlorophyll in intact leaves, in which about 80% of the pigment would have disappeared in that time. The protein is less stable than the chlorophyll, though more stable than in the leaf; probably a small amount of protease is present in the plastids. Some protein is also being synthesized in the chloroplasts along with its breakdown; gains of up to 38% in protein and 13% in chlorophyll were observed under different conditions. l-Serine, which actively promotes senescence in the leaf, has only a very slight effect on the chloroplasts, and kinetin antagonizes it. Kinetin also has a small but significant effect in preserving the protein from breakdown. Acid pH somewhat promotes the breakdown, both of chlorophyll and protein. A loss of chlorophyll and protein comparable to that occurring in the senescence of the leaf could not be induced in the chloroplasts by suspending them in malate, in cytoplasmic extract, or in any of a number of enzymes tested alone. Incubation with a mixture of four enzymes was the only treatment which approximated the senescent process in the leaf, causing 34% loss of chlorophyll at pH 5 and 40% loss of protein at pH 7.4, both in 72 hours.In white light, the chlorophyll and the carotenoids, but not the protein, disappear rapidly. This disappearance was shown to be prevented in an atmosphere of nitrogen or in air by a number of reducing agents, of which ascorbic acid was the most effective. It is, therefore, ascribed to photooxidation rather than to normal senescence.     

The Control of Apical Bud Growth and Senescence by Auxin and Gibberellin in Genetic Lines of Peas

Pea (Pisum sativum L.) lines G2 (dwarf) and NGB1769 (tall) (Sn Hr) produce flowers and fruit under long (LD) or short (SD) days, but senesce only under LD. Endogenous gibberellin (GA) levels were inversely correlated with photoperiod (over 9-18 h) and senescence: GA20 was 3-fold and GA1 was 10- to 11-fold higher in flowering SD G2 shoots, and the vegetative tissues within the SD apical bud contained 4-fold higher levels of GA20, as compared with the LD tissues. Prefloral G2 plants under both photoperiods had GA1 and GA20 levels similar to the flowering plants under LD. Levels of indole-3-acetic acid (IAA) were similar in G2 shoots in LD or SD; SD apical bud vegetative tissues had a slightly higher IAA content. Young floral buds from LD plants had twice as much IAA as under SD. In NGB1769 shoots GA1 decreased after flower initiation only under LD, which correlated with the decreased growth potential. We suggest that the higher GA1 content of G2 and NGB1769 plants under SD conditions is responsible for the extended vegetative growth and continued meristematic activity in the shoot apex. This and the increased IAA level of LD floral buds may play a role in the regulation of nutrient partitioning, since more photosynthate partitions of reproductive tissue under LD conditions, and the rate of reproductive development in LD peas is faster than under SD.     

Metabolism of Oat Leaves during Senescence : VIII. The Role of L-Serine in Modifying Senescence

The mechanism whereby l-serine specifically promotes the dark senescence of detached oat (Avena) leaves has been examined. The fact that this promotion is strong in darkness but very weak in white light has been explained, at least in part, by the finding that added serine is partly converted to reducing sugars in light. Labeled serine gives rise to ¹⁴C-sugars and ¹⁴CO₂. In the absence of CO₂, serine does cause chlorophyll loss in light and undergoes a decreased conversion to sugar.     

核因子Y在细胞衰老中的作用

核因子Ｙ(ｎｕｃｌｅａｒｆａｃｔｏｒＹ ,ＮＦ Ｙ)也称作ＣＢＦ(ＣＣＡＡＴｂｏｘｂｉｎｄｉｎｇｆａｃｔｏｒ)、ＣＰ1 ,是结合ＣＣＡＡＴ盒的转录因子。它能识别真核基因启动子区域的 5′ ＣＴＧＡＴＴＧＧＹＹＲＲ 3′或 5′ ＹＹＲＲＣＣＡＡＴＣＡＧ 3′共有序列。有功能的ＮＦ Ｙ是一个异源三聚体蛋白 ,它包含三个不同的亚单位Ａ、Ｂ、Ｃ。细胞衰老是由细胞分裂的次数决定的。控制细胞分裂的机制之一是调控Ｇ1 /Ｓ期的基因表达。当细胞衰老时 ,由于Ｇ1 /Ｓ基因调控的转变 ,细胞不能进入Ｓ期而只停留在Ｇ1期。ＮＦ Ｙ正是通过与Ｇ1 /Ｓ…     

Control of Rooting and the Pattern of Senescence in Detached White Mustard Cotyledons

Senescence of detached mustard cotyledons was greatest in full light or at low light intensity but was reduced at intermediate light intensities. The location of yellowing in the blade depended on the conditions in which it was maintained after excision. Cotyledons cultured at full light intensity in the absence of exogenous nutrients formed roots at the base and yellowed around the margins. Reduction in light intensity and increasing nutrient concentrations resulted in an increasing proportion of the cotyledons yellowing from the base upwards, and fewer developed roots. At low light intensity with high nutrient levels rooting was suppressed and basal senescence predominated. The location of yellowing in the cotyledon may be associated with mobilisation gradients induced by the differential effects of light and mineral nutrient level on root initiation and blade growth.     

Hypobaric Control of Ethylene-Induced Leaf Senescence in Intact Plants of Phaseolus vulgaris L

A controlled atmospheric-environment system (CAES) designed to sustain normal or hypobaric ambient growing conditions was developed, described, and evaluated for its effectiveness as a research tool capable of controlling ethylene-induced leaf senescence in intact plants of Phaseolus vulgaris L.

Senescence was prematurely-induced in primary leaves by treatment with 30 parts per million ethephon. Ethephon-derived endogenous ethylene reached peak levels within 6 hours at 26°C. Total endogenous ethylene levels then temporarily stabilized at approximately 1.75 microliters per liter from 6 to 24 hours. Thereafter, a progressive rise in ethylene resulted from leaf tissue metabolism and release. Throughout the study, the endogenous ethylene content of ethephon-treated leaves was greater than that of nontreated leaves.

Subjecting ethephon-treated leaves to atmospheres of 200 millibars, with O₂ and CO₂ compositions set to approximate normal atmospheric partial pressures, prevented chlorophyll loss. Alternately, subjecting ethephon-treated plants to 200 millibars of air only partially prevented chlorophyll loss. Hypobaric conditions (200 millibars), with O₂ and CO₂ at normal atmospheric availability, could be delayed until 48 hours after ethephon treatment and still prevent most leaf senescence. In conclusion, hypobaric conditions established and maintained within the CAES prevented ethylene-induced senescence (chlorosis) in intact plants, provided O₂ and CO₂ partial pressures were maintained at levels approximating normal ambient availability.

An unexpected increase in endogenous ethylene was detected within nontreated control leaves 48 hours subsequent to relocation from winter greenhouse conditions (latitude, 42°00″ N) to the CAES operating at normal ambient pressure. The longer photoperiod and/or higher temperature utilized within the CAES are hypothesized to influence ethylene metabolism directly and growth-promotive processes (e.g. response thresholds) indirectly.

     

The Crosstalk between Cytokinin and Auxin Signaling Pathways in the Control of Natural Senescence of Arabidopsis thaliana Leaves

Russian Journal of Plant Physiology - Natural senescence of leaves is a regular physiological process subjected to a certain genetic program and controlled by various phytohormones. Cytokinins...