Anti-senescence Activity Research Articles

New cytokinin derivatives – their discovery, development and use for micropropagation of endangered tree species

Elms (Ulmus sp.) are highly valuable trees for their great strength, tightly twisted grain, and durability, as well as for their cold and salt tolerance[1]. Wych elm (Ulmus glabra, Huds.) is a native species in Europe. In the Czech Republic, it is spread especially in mountain regions. During the years 1970–80, the second epidemic of Dutch elm disease destroyed most elm populations in Europe. The elm trees, which have survived the disease, are capable to maintain a high degree of resistance against the repeated infection. Micropropagation represents promising alternative of their vegetative reproduction. The wild service tree (Sorbus torminalis (L.) Crantz) is a slow-growing tree reaching maximum height of 20–25 m at around 80–100 years. According to the latest data, the species is also disappearing from forests of the Czech Republic and it is considered to be endangered. On the other hand, the wild service tree is rated as one of the most valuable hardwoods [2] with a great potential for wider use in forestry and forest ecology, and also for its importance in the timber industry. The in vitro induction of organogenesis, rooting and acclimatization of above mentioned elm species as well as wild service tree were optimalized and standartized. Widely used BAP is an important and affordable cytokinin routinely utilized for its effective stimulatory properties in micropropagation practice. On the other hand, BAP may negatively influence the growth, rooting and acclimatization processes in some crops [3].It is known that hydroxylated aromatic cytokinins (topolins) are more resistant to cytokinin oxidase (CKX), more stable and in some biological systems active at lower concetrations than the isoprenoid CKs. In addition, meta - topolin does not inhibit root formation which is a typical inconvenient effect of high concentrations of BAP. These properties might help to enhance the future productivity of plant tissue culture industry crops [3,4]. The development of other new CK derivatives exhibiting high morphogenetic activity might consequently be of a great practical importance in plant biotechnology.During our recent search for naturally occurring aromatic cytokinins (ARCKs) in plants, another new group of endogenous BAP derivatives –methoxytopolins – exhibiting high biological, especially anti-senescence (and surprisingly also anti-cancer) activity, was discovered. Based on these results, we synthesized several groups of their synthetic analogues that exhibited high activity in three different CK bioassays and showed the ability to activate cytokinin receptors and/or to inhibit CKX. Best compounds so far (6-(3-hydroxybenzylamino)purine (mT) and the 6-(3-methoxybenzylamino)purine-9-ribofuranoside (MeomTR)) were used for retardation of senescence during multiplication stage of micropropagation of above mentioned tree species as well as for rooting support. Subsequently, wide range of endogenous plant hormones (isoprenoid cytokinins, IAA, ethylene) were quantified (using UPLC-MS/MS and/or GC/FID, respectively) and compared in relation to cytokinin exogenously used. The results about optimal endogenous plant hormone concentrations and their dependence on different exogenous cytokinin used in the cultivation media, may improve in-vitro micropropagation efficiency as well as quality of ex vitro acclimatized plants of above mentioned elm species, wild service tree and possibly also of other tree species. This work was supported by the Ministry of Agriculture of the Czech Republic (Mze 0002070202, QI 92A247), Czech Ministry of Education (MSM 6198959216), ED0007/01/01 Centre of the Region Hana for Biotechnological and Agricultural Research.

The miR-17-92 Cluster of MicroRNAs Confers Tumorigenicity by Inhibiting Oncogene-Induced Senescence

In mammalian cells, activation of oncogenes usually triggers innate tumor-suppressing defense mechanisms, including apoptosis and senescence, which are compromised by additional mutations before cancers are developed. The miR-17-92 gene cluster, a polycistron encoding six microRNAs (miRNA), is frequently overexpressed in human cancers and has been shown to promote several aspects of oncogenic transformation, including evasion of apoptosis. In the current study, we show a new role of miR-17-92 in inhibiting oncogenic ras-induced senescence. Further dissection of the miRNA components in this cluster reveals that the miR-17/20a seed family accounts for this antisenescence activity. miR-17 and miR-20a are both necessary and sufficient for conferring resistance to ras-induced senescence by directly targeting p21(WAF1), a key effector of senescence. By contrast, these components are not essential for the ability of miR-17-92 to evade Myc-induced apoptosis. Moreover, disruption of senescence by miR-17-92 or its miR-17/20a components leads to enhanced oncogenic transformation by activated ras in primary human cells. Taken together with previous reports that miR-17-92 inhibits apoptosis by suppressing Pten via the miR-19 components, our results indicate that this miRNA cluster promotes tumorigenesis by antagonizing both tumor-suppressing mechanisms, apoptosis, and senescence, through the activities of different miRNA components encoded in this cluster.

An Energy-Sensor Network Takes Center Stage During Endothelial Aging

See related article, pages 1384–1393 Blood vessels form a critical interface between the environment and the organism by supplying nutrients, oxygen and macromolecules to all tissues and cells in the body. Endothelial cells (ECs) line the inner surface of the hierarchically branched blood vessel network and integrate functionally into different organs to support tissue growth and function in development, physiology, and disease. In healthy postnatal tissues, ECs are mostly quiescent and rarely migrate or proliferate. However, ECs possess a remarkable phenotypic plasticity in terms of being able to proliferate rapidly in response to vascular injury, tissue ischemia, or other stress conditions. This phenotypic plasticity progressively declines when ECs age and/or are permanently exposed to metabolic (eg, hyperglycemia) and environmental stressors (eg, oxidative stress) and coincides with the development of endothelial senescence.1 Cellular senescence is a stress response that is characterized by a robust inhibition of cell proliferation, which often becomes irreversible and independent of the initial stress signal.2 Senescence can be observed in most mammalian cells after extended propagation in culture and is related to the attrition of telomeres after repetitive cycles of cell divisions.2 In addition to telomere shortening, other stressors such as DNA damage, genomic instability, and oxidative stress can induce a similar growth arrest and trigger senescence.2 Senescent cells display characteristic alterations in cell morphology and gene expression that may weaken cellular functions. In ECs, these changes cause a phenotype that is proinflammatory, prothrombotic, and proatherosclerotic, which also negatively affects the vasodilatory, angiogenic, and regenerative properties of ECs and, thus, accelerates the development of several cardiovascular diseases.1 Despite advances in understanding the molecular mechanisms of endothelial senescence and vascular aging, the signaling networks governing the development and progression of EC senescence remain less well defined. In this issue of Circulation Research …

Water Dropwort (Ostericum sieboldii) and Sedum (Sedum sarmentosum) Delay H2O2-Induced Senescence in Human Diploid Fibroblasts

It is known that a close relationship exists among oxidative damage, senescence, and aging. Water dropwort (Ostericum sieboldii Miq. Nakai) and Sedum (Sedum sarmentosum Bunge) are popular green vegetables in Korea and are reported to have strong antioxidative activity. We investigated whether dropwort and Sedum have the potential to prevent aging using H(2)O(2)-induced prematurely senescent human diploid fibroblasts (HDFs). Dropwort and Sedum had similarly high contents of polyphenols, but dropwort had a flavonoid content about twofold higher than that of Sedum. Exposure of young HDFs to H(2)O(2) induced G2/M cell cycle arrest, positive senescence-associated (SA) beta-galactosidase (beta-gal) staining, and elevated p53, p21, and p16 protein levels. However, cotreatment with dropwort or Sedum ethanol extract significantly lowered p53, p21, and p16 levels and intracellular reactive oxygen species levels and attenuated the cell cycle arrest compared with H(2)O(2)-alone treatment. Interestingly, the increase in p16 level was prevented more quickly and clearly by dropwort treatment than Sedum treatment. The number of SA beta-gal-positive cells at 7 days after treatment was significantly reduced in dropwort-treated cells compared to H(2)O(2) alone-treated cells, whereas it was slightly reduced in Sedum-treated cells with no significance. In conclusion, dropwort showed a potential anti-senescence activity in H(2)O(2)-treated HDFs, which might be mediated by reducing p16, p21, and p53 levels and oxidative stress.

Delayed leaf senescence by exogenous lyso-phosphatidylethanolamine: Towards a mechanism of action

Exogenous application of the lysophospholipid, lyso-phosphatidylethanolamine (LPE) is purported to delay leaf senescence in plants. However, lyso-phospholipids are well known to possess detergent-like activity and application of LPE to plant tissues might be expected to rather elicit a wound-like response and enhance senescence progression. Since phosphatidic acid (PA) accumulation and leaf cell death are a consequence of wounding, PA- and hormone-induced senescence was studied in leaf discs from Philodendron cordatum (Vell.) Kunth plants in the presence or absence of egg-derived 18:0-LPE and senescence progression quantified by monitoring both lipid peroxidation (as the change in malondialdehyde concentration), and by measuring retention of total chlorophyll (Chl(a+b)) and carotenoids (C(c+x)). Only abscisic acid (ABA) stimulated lipid peroxidation whereas ABA, 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor to ethylene (ETH), and 16:0-18:2-PA stimulated loss of chloroplast pigments. Results using primary alcohols as attenuators of the endogenous PA signal confirmed a role for PA as an intermediate in both ABA- and ETH-mediated senescence progression. Exogenous 18:0-LPE did not appear to influence senescence progression and was unable to reverse hormone-induced senescence progression. However, when supplied together with 16:0-18:2-PA at 1:1 (mol:mol), activity of phosphatidylglycerol (PG) hydrolase, chlorophyllase (E.C. 3.1.1.14), and progression of leaf senescence were negated. This apparent anti-senescence activity of exogenous 18:0-LPE was associated with induction of the pathogenesis-related protein, extracellular acid invertase (Ac INV, E.C. 3.2.1.26) suggesting that 18:0-LPE like 16:0-18:2-PA functions as an elicitor.

Reaction of carnosine with aged proteins: another protective process?

Cellular aging is often associated with an increase in protein carbonyl groups arising from oxidation- and glycation-related phenomena and suppressed proteasome activity. These "aged" polypeptides may either be degraded by 20S proteasomes or cross-link to form structures intractable to proteolysis and inhibitory to proteasome activity. Carnosine (beta-alanyl-l-histidine) is present at surprisingly high levels (up to 20 mM) in muscle and nervous tissues in many animals, especially long-lived species. Carnosine can delay senescence in cultured human fibroblasts and reverse the senescent phenotype, restoring a more juvenile appearance. As better antioxidants/free-radical scavengers than carnosine do not demonstrate these antisenescent effects, additional properties of carnosine must contribute to its antisenescent activity. Having shown that carnosine can react with protein carbonyls, thereby generating "carnosinylated" polypeptides using model systems, we propose that similar adducts are generated in senescent cells exposed to carnosine. Polypeptide-carnosine adducts have been recently detected in beef products that are relatively rich in carnosine, and carnosine's reaction with carbonyl functions generated during amino acid deamidation has also been described. Growth of cultured human fibroblasts with carnosine stimulated proteolysis of long-labeled proteins as the cells approached their "Hayflick limit," consistent with the idea that carnosine ameliorates the senescence-associated proteolytic decline. We also find that carnosine suppresses induction of heme-oxygenase-1 activity following exposure of human endothelial cells to a glycated protein. The antisenescent activity of the spin-trap agent alpha-phenyl-N-t-butylnitrone (PBN) towards cultured human fibroblasts resides in N-t-butyl-hydroxylamine, its hydrolysis product. As hydroxylamines are reactive towards aldehydes and ketones, the antisenescent activity of N-t-butyl-hydroxylamine and other hydroxylamines may be mediated, at least in part, by reactivity towards macromolecular carbonyls, analogous to that proposed for carnosine.

Inhibitory Effect of Coronamic Acid Derivatives on Senescence in Cut Carnation Flowers

(+)-(1R,2S)-Allocoronamic acid, (−)-(1S,2R)-allocoronamic acid, and their racemate showed an inhibitory effect on senesence in cut carnation flowers. This antisenescent activity was based on the inhibition of endogenous ethylene formation catalyzed by an ethylene-forming enzyme.

NITROGUANIDINES, A NEW FAMILY OF PGRs, INHIBIT SENESCENCE OF LEAVES AND VEGETABLES

Nitroguanidines are a new family of synthetic plant growth regulators (Speltz, Walworth, and Pavlista 1986. US Patent #4, 594, 092) These compounds have cytokinin-like activity such as delaying senescence. Three compounds are AC239, 604, AC243, 419 and AC132, 654 The first two are phenyl and the latter is a benzyl nitroguanidine. Examples of anti-senescence activity of these compounds are: 1. sunflower leaves, 2. tobacco leaves, 3. leafy lettuce, 4. kale, 5. collards, and 6. Swiss chard. The senescence of cut ornamental flowers is also inhibited. Examples are gladiolus and daffodils. Along with delaying senescence, AC239, 604, for example, increased leaf size, thereby, increasing yield of leaf crops such as tobacco (Pavlista and Templeton. 1987. PGRSA Proc.) and lettuce.

Anti-senescence Activity of Chemicals Applied to Kentucky Bluegrass

This study was conducted to determine the potential anti-senescence activity of certain chemicals by monitoring changes in gross. CO2 exchange with senescence of excised leaves of Kentucky bluegrass (Poa pratensis L.). One day following foliar applications of benzyladenine (BA), triadimefon, and propiconazole, with and without chelated Fe (8% Fe phosphate citrate), Kentucky bluegrass leaves were excised, floated on distilled water in petri dishes, and placed in a darkened growth chamber. Gross CO2 exchange rates (CER) were recorded 1, 4, 7, and 10 days after excision (DAE). Foliar applications of Fe, BA, triadimefon, or propiconazole applied alone induced an anti-senescence response. Combinations of Fe with the chemicals delayed excision-induced leaf senescence, but no significant increase in anti-senescence activity was obtained from the Fe and chemical combinations as compared to the materials applied alone. Chemical names used: N-(phenylmethyl)-1H-purin-6-amine (benzyladenine, BA); 1-(4-Chlorophenoxy)-3,3-dimethyl-1(1H-1,2,4-triazol-1yl)-2-butanone (triadimefon);1-[[2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-yl]methyl]-1H-1,2,4-triazole (propiconazole).

Effect of fungicides on the physiology of plants. Part IV: Protection of cellular organelles of senescent wheat leaves by carbendazim

AbstractWheat leaves (cv. Kormoran) floated on water and kept in darkness turned yellow. This induced senescence was accompanied by a loss of electrolytes and amino acids, and by disorganisation of all cellular organelles except cell walls. Treatment with a solution of carbendazim (20 μg ml−1) prevented the leakage of electrolytes and disorganisation of cell organelles. At 100 μg ml−1, the fungicide did not prevent the damage caused by senescence but stimulated the loss of electrolytes from the leaves. It is proposed that one of the major mechanisms of the antisenescent activity of carbendazim is its protective effect on membranes.

The Influence of Aliphatic Alcohols on Leaf Senescence

Because of the effects of ethanol used as a solvent in other experiments, the action of aliphatic alcohols on leaf senescence in the dark has been studied systematically. These compounds both maintain chlorophyll and prevent proteolysis in the dark, much as do the cytokinins and other senescence-delaying substances. The activity of the straight-chain alcohols increases in a log-linear fashion with increasing chain length up to 1-octanol. Introduction of a branch in the chain or of a second OH group greatly decreases, or in some cases annuls, the antisenescence activity. In all cases, the action on senescence is closely (although not always exactly) paralleled by opening of the stomata. Abscisic acid and exposure to high concentrations of osmoticum, both of which close the stomata, antagonize the action of the alcohols. Some interactions with other agents are noted. The effects are compared with reported effects on seed germination, on hemolysis and animal membranes, and especially on permeability to K(+) ions, and a tentative basis for the mechanism of action is advanced.

Antisenescent Activity of Natural Cytokinins

AbstractThe antisenescent activity of naturally occurring cytokinins (bases and ribosides) has been evaluated by measuring chlorophyll retention in detached wheat (Triticum vulgare) leaf segments. 6‐(3‐Methyl‐2‐butenylamino)‐2‐methylthiopurine (ms2ip) was the most active cytokinin followed by 6‐(4‐hydroxy‐3‐methyl‐trans‐2‐butenylamino)purine (tZ). 6‐(4‐Hydroxy‐3‐methyl‐cis‐2‐butenylamino)‐9‐β‐D‐ribofuranosylpurine (cZR), 6‐(4‐hydroxy‐3‐methyl‐trans‐2‐butenylamino)‐2‐methylthio‐9β‐D‐ribofuranosylpurine (MstZR), and 6‐(4‐hydroxy‐3‐methyl‐cis‐2‐butenylamino)‐2‐methylthio‐9‐β‐D‐ribofuroanosylpurine (mscZR) were essentially inactive. 9‐Ribosyl substitution did not affect the activity of tZ, (±)‐6‐(4‐hydroxy‐3‐methylbutylamino)purine (DHZ), or 6‐(3‐methyl‐2‐butenylamino)purine (2ip), but lowered the activity of 6‐(o‐hydroxybenzylamino)purine (OHBA) and 6‐(4‐hydroxy‐3‐methyl‐cis‐2‐butenylamino)purine (cZ). 2‐Methylthio substitution increased the activity of 2ip and DHZ, decreased the activity of tZ, and had no effect on the activity of cZ. The activities of the simultaneously substituted 2‐methylthio‐9‐ribosyl compounds are lower than those of their corresponding unsubstituted or 2‐methylthio substituted bases with the exception of DHZ.Structure‐activity relationships for chlorophyll retention did not parallel many of the relationships found for callus tissue growth stimulation.