Development of leucine aminopeptidase activity during daylily flower growth and senescence

The possibility that exopeptidases, i.e. aminopeptidases and carboxypeptidases, in addition to the previously studied endopeptidase might also be developmentally regulated in daylily petals was examined. The level of leucine aminopeptidase and endopeptidase activities changed after the flower was fully open while that of carboxypeptidase activity remained relatively unchanged throughout senescence. Leucine aminopeptidase activity seemed to increase after the flower was fully open and peaked several hours earlier than endopeptidase did. Taken together, it is postulated that leucine aminopeptidase might play a role in protein turnover during flower opening and in the initiation of protein hydrolysis associated with petal senescence while the endopeptidase could be responsible for the breakdown of the bulk of proteins at the later stages. The drop in leucine aminopeptidase activity associated with the onset of daylily petal senescence was effectively halted by a cycloheximide treatment of cut daylily flowers for 24 h which was previously shown to prolong the vase life of the flowers and prevent protein loss from the petals. Apart from both being developmentally regulated in daylily petals, the leucine aminopeptidase activity and the previously studied endopeptidase are different in several aspects. They appear to have different pH optima, 8 for leucine aminopeptidase and 6.2 for endopeptidase. Unlike the endopeptidase activity, no new leucine aminopeptidase isozymes appeared during petal senescence, and the leucine aminopeptidase did not appear to belong to the cysteine class of proteolytic enzymes.     

Flower senescence in daylily (Hemerocallis)

This paper reviews recent developments in the use of molecular probes for analyzing the genetic makeup of somatic hybrids. Successful application of somatic hybridization to the interspecific transfer of traits encoded in the nucleus is still having limited success. A major difficulty is hybrid infertility, particularly in hybrids between sexually incompatible species. The formation of asymmetric hybrids is being explored as an approach for improving hybrid fertility. Evaluation of the degree of chromosome elimination and chromosome stability and instability in asymmetric hybrids is difficult when the traditional approaches of chromosome counting and isozyme analysis are used. Two new approaches are resolving this difficulty. The use of species-specific repetitive DNA probes in dot blotting and in situ hybridization to chromosomes is providing quantitative data on chromosome elimination and allows detection of translocations. Use of restriction fragment length polymorphism (RFLP) probes for analysis of hybrids between genetically mapped species makes it possible to account for the presence or absence of individual chromosomes and chromosomes arms. Wider use of such molecular probes should greatly improve our understanding of the genetics of both symmetric and asymmetric somatic hybrids and may lead to new strategies for the effective interspecific transfer of nucleus-encoded traits by protoplast fusion.     

Possible involvement of abscisic acid in senescence of daylily petals

Daylily flowers (Hemerocallis hybrid, cv. Stella d'Oro) senesce and die autonomously over a 24 h period after opening. Investigations were performed to determine some of the mechanisms that lead to death of the petals. The flowers are insensitive to ethylene, but exogenous ABA prematurely upregulates events that occur during natural senescence, such as loss or differential membrane permeability, increases in lipid peroxidation and the induction of proteinase and RNase activities. Furthermore, the same patterns of proteinase and RNase activities appearing on activity gels during natural senescence are induced prematurely by ABA. The mRNA profile from ABA-treated, prematurely senescing petals visualized by differential display shows a high degree of similarity to the mRNA profile of naturally senescing petals 18 h later. In addition, endogenous ABA increases before flower opening and continues to increase during petal senescence. An osmotic stress by sorbitol increases endogenous levels of ABA and upregulates the same parameters of senescence as those occurring during natural senescence and after application of ABA. The mRNA profile from sorbitol-treated, prematurely senescing petals, but somewhat less similarity to mRNA from ABA-treated petals. The possibility is discussed that ABA is a constituent of the signal transduction chain leading to programmed cell death of daylily petals.     

Ethylene and flower senescence

The end of the relatively short life of carnations held in air is associated with climacteric rises in ethylene production and respiration, and coordinate rises in activity of the enzymes of the ethylene biosynthetic pathway. Carnation sensescence is associated with derepression of specific genes, increased polyribosome activity, and major changes in patterns of protein synthesis. Isotopic competition assays indicate the presence in carnation petals of ethylene binding activity with the expected characteristics of the physiological ethylene receptor. Inhibition of ethylene production and/or ethylene binding (whether in selected varieties, or by treatment with chemicals) results in longer-lived carnations. Examination of other flowers shows that the carnation is not a universal paradigm for flower senescence. The response to ethylene varies widely, and in many species petal wilting occurs without any apparent involvement of ethylene.     

Molecular changes accompanying senescence and immortalization of cultured human mammary epithelial cells

Limits on the proliferative potential of cultured normal human cells may be consequences of pathways that exist to suppress tumorigenicity. Human mammary epithelial cells (HMEC) employ several mechanisms to prevent unlimited growth. One mechanism may be activated by stress, and is associated with upregulated expression of p16(INK4a). In serum-free medium, some HMEC arise spontaneously which do not express p16. These "post-selection" HMEC are capable of long-term proliferation, but ultimately cease growth when their telomeres become very short. As they approach a growth plateau, termed agonescence, post-selection HMEC populations accumulate chromosome abnormalities. In contrast to the crisis exhibited by cells lacking functional p53, agonescent cells can be maintained as viable cultures. Although transduction of hTERT, the catalytic subunit of telomerase, into post-selection cells can, by itself, efficiently produce immortality and avoid agonescence, the errors that produce telomerase reactivation during carcinogenesis are not known. The block to endogenous telomerase reactivation in HMEC is extremely stringent. However, if one predisposing error is present, the probability greatly increases that additional error(s) required for immortalization may be generated by genomic instability encountered during agonescence. In p53(+) HMEC immortalized after chemical carcinogen exposure, the events involved in overcoming agonescence can be temporally separated from activation of telomerase. We have used the term "conversion" to describe the gradual process that leads to telomerase activation, telomere length stabilization, decreased p57 (KIP2) expression, and increased ability to grow uniformly well in the presence or absence of TGF beta. In the presence of active p53, conversion may represent a rate-limiting step in immortal transformation.     

Correlated evolution of senescence and ephemeral substrate use in the Sordariomycetes

Evolutionary theory predicts that senescence--a decline in reproduction and survival with increasing age--can evolve as a trade-off between investment in reproduction on one side and in somatic maintenance and repair on the other. The ecology of a species is crucial because it provides the external causes of death that determine the statistical limit to a species' lifespan. Filamentous fungi are generally believed to be nonsenescent, and there are indeed spectacular examples of very old fungal individuals in nature. However, some fungi utilize ephemeral resources, and therefore, senescence is expected to have evolved, like in the coprophilic Podospora anserina, the only well-studied filamentous fungus with intrinsic senescence. Here, we hypothesize that rapid senescence is more common in fungi than generally believed and that the phylogenetic distribution of senescence correlates with ecology. We collected lifespan data for a set of Sordariomycetes and constructed phylogenies based on several nuclear sequences. Several of the strains were from the CBS culture collection, originally isolated from various substrates, some of which ephemeral. In addition, we isolated new strains from short-lived substrates. Senescence was observed throughout the phylogeny. Correlation tests support the hypothesis that in the Sordariomycetes, senescence is a trait that has arisen in response to ephemeral substrates, and that it has evolved repeatedly and independently along the phylogeny.     

Role of cytokinins in carnation flower senescence

Stem and leaf tissues of carnation (Dianthus caryophyllus) plants appear to contain a natural antisenescence factor since removal of most of these tissues from cut carnation flowers hastened their senescence. However, kinetin (5-10 μg/ml) significantly delayed senescence of flowers with stem and leaf tissues removed. In addition, the life span of cut flowers with intact (30-cm) stems was increased with kinetin treatment. Peak ethylene production by presenescent flowers was reduced 55% or more with kinetin treatment and was delayed by 1 day. Kinetin-treated flowers were less responsive to applied ethylene (100 μl/l for 3 hours) than untreated flowers. Possible natural roles of cytokinins in carnation flower senescence are discussed.     

Pollination-induced flower senescence: a review

Ethylene has long been implicated in the control of the senescence of many cut flower species, but the control of senescence in relation to wild species has received much less attention. The longevity of individual flowers varies greatly from species to species; in some each flower is open for just a few hours, whilst in others the flower may persist for several weeks, or even months. The functional life of the flower may be terminated by petal wilting, abscission or a colour change of all, or part, of the perianth. In some species pollination appears to reduce floral longevity whilst in others, particularly those species having short-lived flowers, the pattern of flower development and senescence appears unaffected by pollination.Examples of the various pollination-induced strategies shown by plants are presented and the role of ethylene and other potential mediators of senescence in these processes discussed.     

甘肃黄花烟草愈伤组织在生长与衰老期间呼吸途径的动态变化

实验结果表明：烟划愈伤组织在生长和衰老期间,总呼吸速率（Ｖｔ）分别在１１ｄ和１９ｄ出现２次呼吸跃升;细胞色素途径的运行（ρ＇Ｖｃｙｔ）与Ｖｔ的变化几乎一致,表明细胞色素途径仍组织主要的电子传递途径;交替途径容量（Ｖａｌｔ）及其与Ｖｔ的比值（Ｖａｌｔ／Ｖｔ）：在１５ｄ前不断上升,而在１５－１９ｄ之间处于稳定水平后下降。交替途径运行（ρＶａｌｔ）及其对Ｖｔ的贡献（ρＶａｌｔ／Ｖｔ）却与Ｖａｌｔ变化趋势     

Effect of gibberellic acid on carnation flower senescence: evidence that the delay of carnation flower senescence by gibberellic acid depends on the stage of flower development

Gibberellic acid at concentrations of 10^–5 M and 10^–4 M delayed the senescence of cut carnation flowers, when applied continuously via the stem, to flowers between the closed brush and fully open stages of development. Older flowers with reflexed petals were unresponsive. Treatment with paclobutrazol, an inhibitor of GA biosynthesis, prevented tight buds from opening fully, reduced the longevity of partially open flowers, but was ineffective when applied continuously to fully open flowers. Gibberellic acid-treated flowers did not show simultaneous petal inrolling, a known indicator of senescence, and the time to complete petal drying was extended. Gibberellic acid modified the climacteric ethylene rise in a manner consistent with the extension of longevity. These results provide evidence for a correlative role of gibberellins in flower development.Abbreviations GA₃ gibberellin A₃ - GLC gas liquid chromatography     

Delay of Iris flower senescence by protease inhibitors

Visible senescence of the flag tepals in Iris x hollandica (cv. Blue Magic) was preceded by a large increase in endoprotease activity. Just before visible senescence about half of total endoprotease activity was apparently due to cysteine proteases, somewhat less than half to serine proteases, with a minor role of metalloproteases. Treatment of isolated tepals with the purported serine protease inhibitors AEBSF [4-(2-aminoethyl)-benzenesulfonyl fluoride] or DFP (diisopropyl-fluorophosphate) prevented the increase in endoprotease activity and considerably delayed or prevented the normal senescence symptoms. The specific cysteine protease-specific E-64d reduced maximum endoprotease activity by 30%, but had no effect on the time to visible senescence. Zinc chloride and aprotinin reduced maximum endoprotease activity by c. 50 and 40%, respectively, and slightly delayed visible senescence. A proteasome inhibitor (Z-leu-leu-Nva-H) slightly delayed tepal senescence, which indicates that protein degradation in the proteasome may play a role in induction of the visible senescence symptoms. It is concluded that visible senescence is preceded by large-scale protein degradation, which is apparently mainly due to cysteine- and serine protease activity, and that two (unspecific) inhibitors of serine proteases considerably delay the senescence symptoms.     

乙烯在切花衰老中的作用(综述)

切花衰老是基因表达激活和蛋白质合成受到高度调控的过程。切花衰老所伴随的生理生化变化包括水解酶活性上升、大分子物质降解、呼吸作用增强和类似呼吸跃变的乙烯合成剧增等。乙烯的生成及其作用是切花衰老研究中十分重要的内容。本文综述乙烯在切花衰老过程中调控作用的研究现状。     

Polyamines and carnation flower senescence: Endogenous levels and the effect of applied polyamines on senescence

The polyamines putrescine and spermine were effective in delaying the senescence of carnation buds, but were ineffective when applied to flowers of which the petals had already opened, and were 90° with respect to the stem. Higher levels of endogenous putrescine were detected in the open flowers than in the buds, and this may explain the negative effect obtained when polyamines were applied to open flowers that were picked for commercial distribution.Abbreviations AOA amino-oxyacetic acid - AVG amino-ethoxyvinyl-glycine - SAM S-adenosyl methionine - STS silver thiosulphate     

Delay of Iris flower senescence by cytokinins and jasmonates

It is not known whether tepal senescence in Iris flowers is regulated by hormones. We applied hormones and hormone inhibitors to cut flowers and isolated tepals of Iris × hollandica cv. Blue Magic. Treatments with ethylene or ethylene antagonists indicated lack of ethylene involvement. Auxins or auxin inhibitors also did not change the time to senescence. Abscisic acid (ABA) hastened senescence, but an inhibitor of ABA synthesis (norflurazon) had no effect. Gibberellic acid (GA₃) slightly delayed senescence in some experiments, but in other experiments it was without effect, and gibberellin inhibitors [ancymidol or 4‐hydroxy‐5‐isopropyl‐2‐methylphenyltrimethyl ammonium chloride‐1‐piperidine carboxylate (AMO‐1618)] were ineffective as well. Salicylic acid (SA) also had no effect. Ethylene, auxins, GA₃ and SA affected flower opening, therefore did reach the flower cells. Jasmonates delayed senescence by about 2.0 days. Similarly, cytokinins delayed senescence by about 1.5–2.0 days. Antagonists of the phosphatidylinositol signal transduction pathway (lithium), calcium channels (niguldipine and verapamil), calmodulin action [fluphenazine, trifluoroperazine, phenoxybenzamide and N‐(6‐aminohexyl)‐5‐chloro‐1‐naphtalenesulfonamide hydrochloride (W‐7)] or protein kinase activity [1‐(5‐isoquinolinesulfonyl)‐2‐methylpiperazine hydrochloride (H‐7), N‐[2‐(methylamino)ethyl]‐5‐isoquinolinesulfonamide hydrochloride (H‐8) and N‐(2‐aminoethyl)‐5‐isoquinolinesulfonamide dihydrochloride (H‐9)] had no effect on senescence, indicating no role of a few common signal transduction pathways relating to hormone effects on senescence. The results indicate that tepal senescence in Iris cv. Blue Magic is not regulated by endogenous ethylene, auxin, gibberellins or SA. A role of ABA can at present not be excluded. The data suggest the hypothesis that cytokinins and jasmonates are among the natural regulators.