Onset of Phloem Export from Senescent Petals of Daylily

During senescence, petals of attached daylily (Hemerocallis hybrid cv Cradle Song) flowers lost 95% sugar and 65% dry weight over the first 24 h, with 30% of dry weight loss coming from nonsugar components. Detaching flowers did not delay senescence, but halted loss of carbohydrate and amino acid, suggesting that loss in the intact state was due to phloem export. Petal autolysis occurred mainly in the interveinal parenchyma, causing vascular strands to begin separating from the petal mass. Such vascular strands still stained with tetrazolium and accumulated sucrose, indicating a retained viability. Their sucrose accumulation rates were high in comparison with those of other plant tissues, and the accumulated product was mainly sucrose. Sucrose synthesis took place in the senescent petal, and sucrose was the principal sugar in phloem exudate, whereas hydroxyproline and glutamine were the main transport amino acids. [14C]Sucrose applied to attached senescent flowers was rapidly translocated to other parts of the plant, particularly developing flower buds. Thus, onset of phloem export allowed most of the soluble carbohydrate and amino acid in the senescing flower to be retrieved by the plant. Additional salvaged material came from proteins and possibly from structural carbohydrate. Over a 12-h period, the flower switched from acting as a strong carbohydrate sink during expansion to become a strong source during senescence. This rapid reversal offers potential for phloem transport studies.     

Physiological changes accompanying senescence in the ephemeral daylily flower

The daylily flower, Hemerocallis hybrid cv Cradle Song, develops from the opening bud to full senescence in 36 hours. Unlike other ephemeral flowers studied to date, it does not respond to ethylene, but other senescence phenomena are similar. There was a small respiration climacteric coinciding with early flower senescence, and it was also observed in isolated petals and petal slices. Cycloheximide abolished the climacteric and delayed senescence in all three systems. Petal apparent free space increased from 30% at bud opening to 38% at the onset of senescence, and sugar efflux increased from 0.2 to 2.8 milligrams per gram of fresh weight per hour during the same period. A sharp increase in ion efflux from 0.8 to 4.0 micromoles of NaCl equivalents per gram of fresh weight per hour, coinciding with the climacteric, was abolished by cycloheximide. Uptake of radiolabeled inorganic phosphate by petal slices from 100 micromolar solution increased during onset of senescence from 6 to 10 nmoles per gram of fresh weight per hour. Half was esterified; of this, 14% went into ATP, and the cellular energy charge remained high at 0.86 during senescence. The proportion incorporated into phospholipid (2.2%) did not change during senescence, but the proportion in phosphatidyl choline increased and in phosphatidyl glycerol decreased during senescence. The general phosphate ester pattern in presenescent slices closely resembled that in other plant tissues except that phospholipid precursors were more prominent (approximately 20% of total organic ³²P versus 5%). In senescent slices, the proportion of hexose phosphates decreased from 40 to 15% of total organic ³²P and that of phospholipid precursors increased to approximately 50%, suggesting that phospholipid synthesis was blocked early in senescence.     

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.     

Spatial and temporal distribution of mineral nutrients and sugars throughout the lifespan of <Emphasis Type="Italic">Hibiscus rosa-sinensis</Emphasis> L. flower

Although the physiological and molecular mechanisms of flower development and senescence have been extensively investigated, a whole-flower partitioning study of mineral concentrations has not been carried out. In this work, the distribution of sucrose, total reducing sugars, dry and fresh weight and macro and micronutrients were analysed in Hibiscus rosa-sinensis L. petals, stylestigma including stamens and ovary at different developmental stages (bud, open and senescent flowers). Total reducing sugars showed the highest value in petals of bud flowers, then fell during the later stages of flower development whereas sucrose showed the highest value in petals of senescent flowers. In petals, nitrogen and phosphorus content increased during flower opening, then nitrogen level decreased in senescent flowers. The calcium, phosphorus and boron concentrations were highest in ovary tissues whatever the developmental stage. Overall, the data presented suggests that the high level of total reducing sugars prior the onset of flower opening contributes to support petal cells expansion, while the high amount of sucrose at the time of petal wilting may be viewed as a result of senescence. Furthermore, this study discusses how the accumulation of particular mineral nutrients can be considered in a tissue specific manner for the activation of processes directly connected with reproduction.     

Characterization of proteolytic activity during senescence in daylilies

From 12 to 24 h after the opening of daylily flowers ( Hemerocallis hybrid cv. Stella d'Oro), the petals begin to degrade and the protein levels of soluble, microsomal‐ and plastid‐enriched fractions decrease by 50%, on a per petal basis. To help determine some of the components for the cell death program in daylily petals, we studied the mechanisms that regulate this loss of protein. Enzyme activities capable of digesting native daylily protein, gelatin, and azocasein markedly increase after flower opening, and their appearance is inhibited by the translation inhibitor, cycloheximide. Protein hydrolysis in vitro is prevented by inhibitors of cysteine, serine and metalloproteinases. Immunoblots using antibodies to ubiquitin pathway enzymes indicate that the ubiquitin system is not senescence specific. However, ion leakage is delayed by two inhibitors of the 26S proteasome. We propose that programmed cell death in daylily petals may involve the increase in activity of at least three classes of proteinases, and discuss the possibility that these proteinases may operate in concert with the ubiquitin pathway.     

Activities of Various Peptidases in the Senescing Petals of Tulip

The hydrolysis of seven peptidase substrates by petal extracts of tulip (Tulipa sp. cv. Guillaume Tell) was assayed at four stages in the life cycle of the petals. During senescence pronounced increases from three- to sixfold took place in all the activities. At the same time the amount of soluble protein decreased about 75% and there was a simultaneous increase in free amino acids. The activity levels (on a dry weight basis) in the petals at the beginning of withering were rather similar to those present in normal leaves. Despite their different pH-optima (5-9), all the peptidases probably act in the mobilization of protein amino acids in the senescing petals.     

Translocation of 14C-sucrose in Relation to Changes in Carbohydrate Content in Rose Corollas Cut at Different Stages of Development

The dry matter and carbohydrate contents of intact growing ‘Sonia’rose corollas were measured from an immature bud to full expansionof the petals. Reducing sugars and starch, but not sucrose,accumulated throughout most of the corolla development. Thesefindings were compared with the carbohydrate changes in thecorollas of flowers cut at different stages and allowed to agewith their stems either in water or in a sucrose-containingsolution. For a few days after cutting the carbohydrate metabolismof the cut flower roughly paralleled that of the intact floweruntil starch hydrolysed to maintain the soluble carbohydratepool. Feeding with the sucrose solution maintained the solublecarbohydrate levels and retarded the hydrolysis of starch. The cut flowers were fed with ¹⁴C-sucrose and the labelled metabolitesin the leaves and flowers were analysed. Active incorporationof ¹⁴C into ethanol-soluble carbohydrates, starch and ethanol-insolublematerial was found indicating that an active anabolic phaseprecedes the catabolic phase during the senescence of the cutflower. The findings are discussed in relation to the source-sinkhypothesis of flower development, with regard to the senescenceand growth of the corollas of cut and intact flowers respectively.     

Determination of subcellular concentrations of soluble carbohydrates in rose petals during opening by nonaqueous fractionation method combined with infiltration–centrifugation method

Petal growth associated with flower opening depends on cell expansion. To understand the role of soluble carbohydrates in petal cell expansion during flower opening, changes in soluble carbohydrate concentrations in vacuole, cytoplasm and apoplast of petal cells during flower opening in rose (Rosa hybrida L.) were investigated. We determined the subcellular distribution of soluble carbohydrates by combining nonaqueous fractionation method and infiltration–centrifugation method. During petal growth, fructose and glucose rapidly accumulated in the vacuole, reaching a maximum when petals almost reflected. Transmission electron microscopy showed that the volume of vacuole and air space drastically increased with petal growth. Carbohydrate concentration was calculated for each compartment of the petal cells and in petals that almost reflected, glucose and fructose concentrations increased to higher than 100 mM in the vacuole. Osmotic pressure increased in apoplast and symplast during flower opening, and this increase was mainly attributed to increases in fructose and glucose concentrations. No large difference in osmotic pressure due to soluble carbohydrates was observed between the apoplast and symplast before flower opening, but total osmotic pressure was much higher in the symplast than in the apoplast, a difference that was partially attributed to inorganic ions. An increase in osmotic pressure due to the continued accumulation of glucose and fructose in the symplast may facilitate water influx into cells, contributing to cell expansion associated with flower opening under conditions where osmotic pressure is higher in the symplast than in the apoplast.     

Identification of senescence-associated genes from daylily petals

The petals of daylily (Hemerocallis hybrid) have a genetically based program that leads to senescence and cell death ca. 24 h after the flower opens. In order to determine the components of this program, six cDNAs, whose levels increase during petal senescence, were isolated and sequenced and designated DSA3, 4, 5, 6, 12 and 15. All six DSAs are members of gene families and all but DSA5 and DSA6 have one to three other very similar genes. GenBank database homology searches indicate that DSA3 is most similar at the amino acid level to an in-chain fatty acid hydroxylase which is bound to cytochrome P450, DSA4 may be an aspartic proteinase, DSA5 is as yet unidentified, DSA6 is a putative S1-type nuclease, DSA12 is very similar to a cytochrome P450-containing allene oxide synthase, and DSA15 may be a fatty acid elongase. Except for DSA12, the genes are expressed at low levels in daylily roots. Levels of the DSA mRNAs in leaves are less than 4% of the maximum detected in petals, and there are no clear differences between younger and older leaves. With the exception of DSA4, accumulation of the DSA mRNAs is increased 3.2 to 43 times by a concentration of abscisic acid that causes premature senescence of the petals. The relationship of the putative DSA gene products to senescence and cell death of daylily petals is discussed.     

Combined Effects of Abscisic Acid and Sucrose on Growth and Senescence of Rose Flowers

The effects of sucrose and abscisic acid (ABA) and their interaction on development and senescence of petals were studied with leafless roses cultivar Super Star. Sucrose and ABA had opposing effects on the cut flowers. Sucrose retarded and ABA promoted processes associated with senescence: wilting, increase in pH, “blueing” and decrease in protein content of petals. These opposing effects are mutually antagonized when both chemicals are applied. ABA applied to flowers cut at the bud stage, promoted the rate of petal growth (but not their final size), increased respiration and caused a decrease in sucrose and an increase in level of reducing sugars. It is suggested that one way by which ABA accelerates senescence of cut roses is by promoting petal growth and respiration, thus decreasing the carbohydrate level in the petals and triggering the chain of metabolic processes leading to aging.     

Flower bud opening and senescence in roses (Rosa hybrida L.)

The flower is the most significant and beautiful part of plants. Flowers are very useful organs in plant developmental phenomenon. During flower bud opening, various events takes place in a well defined sequence, representing all aspects of plant development, such as cell division, cellular differentiation, cell elongation or expansion and a wide spectrum of gene expression. The complexity of flower bud opening illustrates that various biological mechanisms are involved at different stages. Senescence represents the ultimate stage of floral development and results in wilting or abscission of whole flower or flower parts. Senescence is an active process and governed by a well defined cell death program. Once a flower bud opens, the programmed senescence of petal allows the removal of a metabolically active tissue. In leaves, this process can be reversed, but in floral tissue it cannot, indicating that a highly controlled genetic program for cell death is operating. The termination of a flower involves at least two, sometimes overlapping, mechanisms. In one, the perianth abscises before the majority of its cells initiate a cell death program. Abscission may occur before or during the mobilization of food reserves to other parts of the plant. Alternatively, the petals may be more persistent, so that cell deterioration and food remobilization occur while the petals are still part of the flower. The overall pattern of floral opening varies widely between plant genera, therefore, a number of senescence parameters have been used to group plants into somewhat arbitrary categories. Opening and senescence of rose flower is still an unsolved jigsaw in the world of floriculture industry and the mechanism behind the onset of the very early events in the sequence still remains to be elucidated. Hence, for advancing the knowledge on the pertinent aspect of bud opening and senescence the literature has been cited under this review.     

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.     

Effects of Ethylene and Sucrose on Translocation of Dry Matter and 14C-Sucrose in the Cut Flower of the Glasshouse Carnation (Dianthus caryophyllus) During Senescence

The translocation and distribution of dry matter were studiedin the floral and vegetative parts of the cut carnation duringsenescence. The change in dry weights of the tissues and theamount of radioactivity recovered from them after feeding with¹⁴C-sucrose were measured. Treatments with ethylene and sucrosewere used to alter the rate of senescence of the flowers. Sucrosemoved through the stem relatively unchanged but was rapidlyinverted and metabolized in the petals. During natural ageing,¹⁴C moved from the stem to the flower and the movement was enhancedby exogenous sucrose, which also reduced the loss of dry matterin the petals and promoted their growth. Treatment with ethylenecaused petals to wilt and lose dry weight, and ovaries to enlargeand increase in dry weight. The distribution of radioactivityin flowers fed with 14C-sucrose before and after ethylene treatmentsupported the observation that dry matter was translocated betweenthe flower parts. The results indicate that a change in thesource-ink relationships of the flower parts contributes tothe factors that determine the rate of flower senescence.     

The role of fructan in flowering of Campanula rapunculoides

Inulin type fructan was detected in all vegetative organs of Campanula rapunculoides L. plants. All flower parts contained fructan at some developmental stage. A steady decrease was found in sepals during development. Petals, however, stored fructan in the bud stage. A rapid breakdown during opening of the flower resulted in high concentrations of glucose and especially fructose that may contribute to the osmotic driving force involved in petal expansion. Before complete shrivelling, the hexoses were apparently exported from flower parts. Fructans were hydrolysed and exported from the stamen and style tissue upon flower opening. Similarly, the major fructan reserves in the ovary were broken down almost simultaneously with those in other flower parts. Hexoses did not reach high levels in the ovary, probably because they were rapidly metabolized and/or incorporated by developing seeds.     

Analysis of nonstructural carbohydrates in storage organs of 30 ornamental geophytes by high-performance anion-exchange chromatography with pulsed amperometric detection

A comprehensive analysis of nonstructural carbohydrates in storage organs (bulbs and corms) of 30 ornamental geophytes was conducted by employing a variety of extraction techniques followed by high-performance anion-exchange chromatography with pulsed amperometric detection (HPAE-PAD). Among species, starch, fructan, glucomannan and soluble sugars accounted for 50-80% of storage organ dry weight (DW). Starch ranged from 24 to 760 mg g(-1) DW, fructan (commonly occurring with starch) from 25 to 500 mg g(-1) DW, and glucomannan from 15 to 145 mg g(-1) DW. An acid hydrolysis protocol for concurrent determination of fructan and glucomannan was developed. The average degree of polymerization (DP) of ethanol and water-soluble fructan and the man : glu ratio of glucomannan also varied between species. The 80% ethanol fraction contained soluble sugars and short-chain fructans (< 25 DP), whereas water extracts contained soluble sugars, fructans (both short- and long-chain, 相似文献   

Nitrogen metabolism and senescence-associated changes during growth of carnation flowers

Nitrogen metabolism including nitrate reductase (EC 1.6.6.1), glutamate dehydroge-nase (EC 1.4.1.2) and glutamate-oxalacetate aminotransferase (EC 2.6.1.1) activities were studied during growth of petals taken from carnation flowers ( Dianthus caryophyllus L. cv. Sir Arthur) together with senescence parameters (lipid hydroper-oxides, soluble amino acids and permeability). A slight decline in nitrogen percentage on a dry weight basis was found together with a sharp decrease in nitrate reduct-ase, glutamate-oxalacetate aminotransferase and glutamate dehydrogenase activities during the maximum growth phase, which was characterized by increase in respiration, dry weight, length, organic nitrogen and DNA per petal. Changes generally associated with senescence, like lipid hydroperoxide and soluble ammo nitrogen accumulation and increases in permeability began to appear already during early growth. The results indicate that permeability and proteolysis may be closely related. The possible significance of the decrease in nitrogen percentage and enzyme activities during growth of petals is discussed.     

Role of ethylene in the senescence of isolated hibiscus petals

Senescence of petals isolated from flowers of Hibiscus rosa-sinensis L. (cv Pink Versicolor) was associated with increased ethylene production. Exposure to ethylene (10 microliters per liter) accelerated the onset of senescence, as indicated by petal in-rolling, and stimulated ethylene production. Senescence was also hastened by basal application of 1-aminocyclopropane-1-carboxylic acid (ACC). Aminooxyacetic acid, an inhibitor of ethylene biosynthesis, effectively inhibited ethylene production by petals and delayed petal in-rolling. In marked contrast to these results with mature petals, immature petals isolated from flowers the day before flower opening did not respond to ethylene in terms of an increase in ethylene production or petal in-rolling. Furthermore, treatment with silver thiosulfate the day before flower opening effectively prevented petal senescence, while silver thiosulfate treatment on the morning of flower opening was ineffective. Application of ACC to both immature and mature petals greatly stimulated ethylene production indicating the presence of an active ethylene-forming enzyme in both tissues. Immature petals contained less free ACC than mature, presenescent petals and appeared to possess a more active system for converting ACC into its conjugated form. Thus, while the nature of the lack of responsiveness of immature petals to ethylene is unknown, ethylene production in hibiscus petals appears to be regulated by the control over ACC availability.     

Galactose metabolism in cell walls of opening and senescing petunia petals

Galactose was the major non-cellulosic neutral sugar present in the cell walls of ‘Mitchell’ petunia (Petunia axillaris × P. axillaris × P. hybrida) flower petals. Over the 24 h period associated with flower opening, there was a doubling of the galactose content of polymers strongly associated with cellulose and insoluble in strong alkali (‘residual’ fraction). By two days after flower opening, the galactose content of both the residual fraction and a Na₂CO₃-soluble pectin-rich cell wall fraction had sharply decreased, and continued to decline as flowers began to wilt. In contrast, amounts of other neutral sugars showed little change over this time, and depolymerisation of pectins and hemicelluloses was barely detectable throughout petal development. Size exclusion chromatography of Na₂CO₃-soluble pectins showed that there was a loss of neutral sugar relative to uronic acid content, consistent with a substantial loss of galactose from rhamnogalacturonan-I-type pectin. β-Galactosidase activity (EC 3.2.1.23) increased at bud opening, and remained high through to petal senescence. Two cDNAs encoding β-galactosidase were isolated from a mixed stage petal library. Both deduced proteins are β-galactosidases of Glycosyl Hydrolase Family 35, possessing lectin-like sugar-binding domains at their carboxyl terminus. PhBGAL1 was expressed at relatively high levels only during flower opening, while PhBGAL2 mRNA accumulation occurred at lower levels in mature and senescent petals. The data suggest that metabolism of cell wall-associated polymeric galactose is the major feature of both the opening and senescence of ‘Mitchell’ petunia flower petals.