Floral Senescence Research Articles

Co-silencing of the Mirabilis antiviral protein (MAP) permits virus-induced gene silencing (VIGS) of other genes in Four O’Clock plants (Mirabilis jalapa)

SummaryVirus-induced gene silencing (VIGS) is a powerful and rapid technique for the analysis of gene function during plant growth and development. We attempted to use VIGS for the functional analysis of genes associated with floral senescence and abscission in Four O’Clock plants (Mirabilis jalapa). Plants infected with a Tobacco Rattle Virus (TRV) vector containing a fragment of the phytoene desaturase (PDS) gene did not show the expected photo-bleaching phenotype. We hypothesised that the failure of VIGS in this species might be due to the presence of the Mirabilis antiviral protein (MAP) which is known to have potent activity in preventing viral infection. Plants infected with a TRV vector containing fragments of both the PDS and MAP genes showed the typical photo-bleaching phenotype in photosynthetic tissues, and this was accompanied by reductions in the abundance of PDS and MAP transcripts. We also demonstrated reduced transcript abundance (and the expected phenotypes) when VIGS with a TRV-MAP vector was used to silence the chlorata42 (Ch42) and the proliferating cell nuclear antigen (PCNA) genes. Silencing of the 3,4-dihydroxy-L-phenylalanine 5-glucosyl transferase (DOPA5GT) gene reduced pigmentation in stems, leaves, and flowers. This is the first direct demonstration of the role of an enzyme that has been proposed to be a key step in the synthesis of betalain pigments. Co-silencing of endogenous anti-viral proteins may increase the range of taxa that are amenable to the use of VIGS for functional gene analysis.

Rapid floral senescence following male function and breeding systems of some tropical orchids

No comparative study of floral senescence following male function among a range of tropical orchid genera has previously been undertaken. The timing and pattern of floral senescence and occurrence of fruit formation were studied following self-, geitonogamous and cross-pollination in 14 epiphytic and two terrestrial orchid species to determine their breeding system and assess the occurrence of floral abscission following pollinaria removal. Both pollination and pollinaria removal caused rapid floral senescence, and the pattern and timing of the floral changes were the same in all treatments. Six Dendrobium species and Pelatantheria insectifera were self-incompatible (SI) and eight other species, including one terrestrial species, were self-compatible (SC). Capsules produced from outcrossing in four SC species, Phalaenopsis cornu-cervi, Eria pubescens, Cleisostoma appendiculatum and Arundina graminifolia, were larger and heavier than those produced after selfing. Reductions in flower life span following pollinaria removal were positively correlated with flower size and longevity of unpollinated flowers but not with position in the inflorescence or nature of the breeding system. Rapid flower senescence following pollinaria removal reported here suggests that it may be widespread in tropical species. The significant association of the response with size of flowers and inflorescences among the species studied suggests that the cost of flower maintenance outweighs the benefit of remaining open for female function after pollinaria have been removed. Both SC and SI species were found among tropical orchids, but variation in capsule size following self- and cross-pollination indicates that there may be a reduction in seed production following selfing, even in SC species, and that fruit formation alone should not be taken as reliable evidence of full self-compatibility.

Is there an important role for reactive oxygen species and redox regulation during floral senescence?

Senescence is a highly regulated process terminating with programmed cell death (PCD). Floral senescence, and in particular petal senescence, forms an interesting model to study this process in that floral lifespan is species specific and linked to biological function. A feature of petal senescence is a rise in reactive oxygen species (ROS) and a change in redox balance. A key question is whether this is merely a consequence of de-regulation of antioxidant systems as cells enter PCD, or whether the rise in ROS may have a regulatory or signalling function. An important division in the physiology of floral senescence is between species in which ethylene is a key regulator, and those in which it appears not to perform an important regulatory role. Another important question we can therefore ask is whether the redox and ROS changes have the same significance in species with different physiologies. Transcriptomic studies in ethylene-sensitive and -insensitive species allow us to further determine whether changes in the activity of ROS-scavenging enzymes are transcriptionally regulated during floral senescence. Finally, it is important to assess how a signalling role for ROS or redox status would fit with known plant growth regulator (PGR) control of floral senescence.

A UNIVERSAL PRIMER FOR ISOLATION OF FRAGMENTS OF A GENE ENCODING PHYTOENE DESATURASE FOR USE IN VIRUS-INDUCED GENE SILENCING (VIGS) STUDIES

We have been using Virus-Induced Gene Silencing (VIGS) to test the function of genes that are candidates for involvement in floral senescence. Although VIGS is a powerful tool for assaying the effects of gene silencing in plants, relatively few taxa have been studied using this approach, and most that have are in the Solanaceae. We typically use silencing of phytoene desaturase (PDS) in preliminary tests of the feasibility of using VIGS. Silencing this gene, whose product is involved in carotene biosynthesis, results in a characteristic photobleaching phenotype in the leaves. We have found that efficient silencing requires the use of fragments that are more than 90% homologous to the target gene. To simplify testing the effectiveness of VIGS in a range of species, we designed a set of universal primers to a region of the PDS gene that is highly conserved among species, and that therefore allows an investigator to isolate a fragment of the homologous PDS gene from the species of interest. We report the sequences of these primers and the results of VIGS experiments in horticultural species from the Asteraceae, Leguminosae, Balsaminaceae and Solanaceae.

A THIDIAZURON PULSE TREATMENT DELAYS LEAF AND FLOWER SENESCENCE IN IRIS

Thidiazuron (N-phenyl-N'-1,2,3-thiadiazol-5-ylurea, TDZ), a non-metabolized phenyl urea compound with cytokinin-like activity, is a potent inhibitor of leaf senescence in cut flowers. In the present study, we determined the potential for TDZ to delay both leaf and flower senescence on cut iris 'Discovery' stems. We found that a postharvest pulse with 200, 500 or 1000 μM TDZ for 6, 12 or 24 hours at 20°C prevented leaf yellowing and extended flower life by 0.6-1.5 days (12-34%) relative to control (0 μM TDZ) stems. Treatment with TDZ also increased the length of shoots on which flowers develop by 0.7-2.5 cm (8-30%) over control stems. The benefits of TDZ treatment were maintained even when flowers were held dry for 3 days at 0°C after pulsing. Treating flowers with 500 μM TDZ in combination with 350 mg/L GA 3 further increased floral shoot growth and led to more complete flower opening. The extension in flower life may be a direct effect of TDZ treatment in delaying floral senescence or a reflection of improved carbohydrate supply from leaf tissues. Our findings highlight the potential use for TDZ as a postharvest pulse treatment to improve the opening and longevity of iris flowers.

Petunia floral volatile benzenoid/phenylpropanoid genes are regulated in a similar manner

Petunia (Petunia x hybrida cv 'Mitchell Diploid' [MD]) flowers emit high levels of multiple floral volatile benzenoid/phenylpropanoid (FVBP) compounds from anthesis to senescence in a concerted manner. Here we show seven genes responsible for the production of emitted FVBPs share similar transcript accumulation profiles through an analysis of four expression criteria. As a group, the FVBP gene transcripts accumulate to high levels in petal limb tissue of MD flowers from anthesis to senescence. Two to four hours of exogenous ethylene exposure reduces transcript levels of all FVBP genes examined, but 2h of treatment will not accelerate senescence or reduce volatile emissions in MD flowers. The FVBP genes show two obvious rhythmic patterns of transcript accumulation; however, corresponding enzyme activities of a subset of FVBP gene products do not. Together, these results depict floral volatile benzenoid/phenylpropanoid biosynthesis as a specific system with multiple regulatory features. One such feature is the highly regulated transcript accumulation of the FVBP genes. Additionally, ethylene may have a regulatory role in the FVBP system prior to a floral senescence program.

Floral longevity and scent respond to pollen manipulation and resource status in the tropical orchid Myrmecophila christinae

Floral longevity (FL) is a key aspect in plant reproductive ecology. Despite this, the effect of resource status on FL has usually been ignored, and never has resource status been linked to the effects of pollen manipulation on FL. In addition, immediate changes in floral scent characteristics subsequent to pollen addition/removal have not been looked at. Here we use the tropical orchid Myrmecophila christinae to address the following: (1) Does flower bud removal (resource status change) increase FL? (2) Does pollen manipulation (addition/removal) decrease FL, and do such effects interact with plant resource status? (3) Are there rapid changes in floral scent production and composition after pollen manipulation? To answer the first question, we removed 50% of the flower buds on 24 plants (24 more were controls). To test the second question, 1 month after removing buds, one of four flowers on each inflorescence received one of the following treatments: no manipulation, pollinia removal, pollination, or pollination + pollinia removal. Finally, to answer the third question, one of four flowers on each of 15 plants (different site) received one of the above-mentioned pollen treatments. Flowers were collected 2, 4, and 6 h after manipulation to measure scent production/composition. Results showed that flowers on bud-removed plants remained open significantly longer relative to those on control plants, and that pollination significantly decreased FL. Additionally, scent production increased throughout the morning and responded differently depending on the pollen manipulation treatment; scent composition on the other hand, remained relatively unchanged throughout the sampling period. By studying both floral scent and physical changes in M. christinae, this study intends to offer a more integrated view of floral senescence within the context of resource and pollen status conditions.

활성산소종이 무궁화 꽃의 노화에 미치는 영향

To understand the effect of reactive oxygen species (ROS) on floral senescence in Hibiscus syriacus L., we have investigated change in relative water potential, malondialdehyde (MDA) content, <TEX>H_2O_2</TEX> content and the activity of antioxidative enzymes in the petals during flower opening and senescence. Hibiscus flowers were achieved full bloom at early morning and started to in-rolling and showed petal in-rolling over than 50% at 24 h and 36 h after full bloom, respectively. The flower was a decrease in fresh weight by 30% and showed water loss with floral senescence. MDA content and activity of antioxidative enzymes such as APX, GR and CAT were showed no significant change until 36 h after full bloom. In the flower 48 h after full bloom that showed complete petal in-rolling and wilting, however, activity of antioxidative enzymes and <TEX>H_2O_2</TEX> content was greatly increased as compared with 0 h after full bloom. These results suggest that reactive oxygen species are related to accelerating the later senescence more than inducing the early senescence during Hibiscus flower senescence.

Characterisation of respiration, ethylene production, and carbohydrate contents during flower opening in Epidendrum ibaguense

SummaryThe opening of flowers in Epidendrum ibaguense is characterised by continuous drops in respiration, ethylene production, and 1-aminocyclopropone-1-carboxylate (ACC) oxidase activity from the bud stage to fully open. Later, an increase in ethylene production and ACC oxidase activity occurred, suggesting autocatalytic production of ethylene, beginning at an early stage of senescence. Regardless of developmental stage, the main non-structural carbohydrates in flowers were non-reducing sugars [23.7% (w/w) fresh weight (FW)]. Starch accounted for 3.1% (w/w) FW and reducing sugars for 0.7% (w/w) FW. No depletion in the level of any carbohydrate was observed throughout senescence. At the beginning of floral senescence, a sharp increase occurred in the activities of acid and alkaline invertases, suggesting a role for both enzymes in the cleavage of sucrose. However, no major changes in sucrose synthase activity were found during flower development.

Pollination-induced floral senescence in orchids: Status of oxidative stress

The orchid flowers may stay fresh in unpollinated state from few weeks to months but show rapid senescence upon pollination. Metabolic changes related to this phenomenon are less well understood in orchid flowers. Presently, two orchid species, Aerides multiflora Roxb. and Rhynchostylis retusa (L.) Bl., varying in their floral life span were evaluated for their postpollination-induced responses, involving the oxidative stress. The unpollinated flowers of A. multiflora stayed fresh for 17 days and attained senescence in 5 days after pollination (DAP), while those of R. retusa. remained fresh for 24 days and showed senescence in 7 DAP. After pollination, wilting began in 2 to 3 days in A. multiflora and 3 to 4 days in R. retusa. There was a higher electrolyte leakage accompanied by a concomitant increase in the levels of malondialdehyde (MDA) and hydrogen peroxide (H2O2), indicators of oxidative damage in all the organs after pollination while ascorbic acid decreased significantly. The flowers of A. multiflora showed a greater electrolyte leakage, MDA and H2O2 contents as compared to those of R. retusa. Ascorbic acid content, on the other hand, was lower in A. multiflora than in R. retusa, suggesting a higher oxidative damage to the floral organs in the former species. An application of triiodobenzoic acid ( an auxin inhibitor; 0.25 mM) and silver nitrate (ethylene inhibitor; 0.25 mM) to pollinated flowers partially prevented the oxidative damage and consequently the senescence, suggesting the involvement of these hormones. AgNO3 was more effective in delaying senescence.

Effects of various chemical agents and early ethylene production on floral senescence of Hibiscus syriacus L.

To understand the factors that induce floral senescence in Hibiscus syriacus L., we have investigated the effects of various chemical agents on flower senescence at two different flowering stages, before and after full bloom, as well as the relationship between flower longevity and endogenous ethylene production before full bloom. Treatments with ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC), and ethephon enhanced floral senescence, while aminoethoxyvinylglycine (AVG) promoted flower longevity regardless of treatment timing. Although ethanol slightly extended flower longevity, abscisic acid (ABA), nitric oxide, boric acid and sucrose, which have been reported to affect flower longevity or senescence, had no effect on H. syriacus floral senescence. The polyamine spermine (SPM), methylglyoxal-bis(guanylhydrazone) (MGBG), an inhibitor of SPM biosynthesis, and cycloheximide (CHI) accelerated flower senescence when applied before full bloom, but had no effect when applied after full bloom. SPM, MGBG and CHI treatments resulted in enhanced ethylene production during flower opening, and the promotion of flower senescence is mediated by ethylene production prior to full bloom. Furthermore, endogenous ethylene, spontaneously produced before blooming, was closely associated with floral senescence. These results suggest that ethylene production during flower opening plays a key role in determining the timing of Hibiscus flower senescence.

GA 4+7 plus BA enhances postproduction quality in pot tulips

Previously we reported that postproduction quality of pot ‘Seadov’ tulip ( Tulipa gesneriana) was significantly increased by GA 4+7 plus BA in a manner dependent on the concentration and stage of flower development at application. In these experiments, we extended the survey to 20 tulip cultivars to further evaluate the effects of GA 4+7 plus BA sprays for enhancing postproduction flower and leaf quality. The senescence symptom of the cultivars fell into three categories: wilting, wilting-abscission (abscission shortly after tepal wilting) and abscission (abscission without wilting), with the majority of the cultivars belonging to the wilting and wilting-abscission categories. Pots bearing six plants were sprayed with a range of GA 4+7 plus BA concentrations at marketable stage and placed in a simulated consumer environment (SCE). GA 4+7 plus BA significantly enhanced individual flower and postproduction longevity, but the effect was dependent upon the senescence category of the cultivar. In general, GA 4+7 plus BA increased individual flower and postproduction longevity of wilting-type cultivars at concentrations above 10 mg L −1, while longevity of wilting-abscission-type cultivars was only enhanced by 50 mg L −1. Abscission-type cultivars were not affected by any concentrations of GA 4+7 plus BA. Regardless of floral senescence category, leaf yellowing was significantly reduced by GA 4+7 plus BA sprays in those cultivars showing postproduction leaf yellowing. GA 4+7 plus BA did not induce leaf and stem elongation in most cultivars. Only ‘Yellow Baby’, the shortest cultivar, showed elongation of stem and leaf by GA 4+7 plus BA at concentrations above 25 mg L −1. Spray applications of GA 4+7 plus BA can be useful to enhance flower and leaf quality in pot tulips.

Enhanced expression of serine proteases during floral senescence in Gladiolus

Programmed cell death during senescence in plants is associated with proteolysis that helps in remobilization of nitrogen to other growing tissues. In this paper, we provide one of the few reports for the expression of specific serine proteases during senescence associated proteolysis in Gladiolus grandiflorus flowers. Senescence in tepals, stamens and carpels results in an increase in total protease activity and a decrease in total protein content. Of the total protease activity, serine proteases account for about 67–70% while cysteine proteases account for only 23–25%. In-gel assays using gelatin as a substrate and specific protease inhibitors reveal the enhanced activity of two trypsin-type serine proteases of sizes 75 kDa and 125 kDa during the course of senescence. The activity of the 125 kDa protease increases not only during tepal senescence but also during stamen and carpel senescence indicating that it is responsive to general senescence signals.

Programmed cell death during floral development and senescence

Programmed cell death during floral development and senescence

Temperature-Mediated Relationship Between Western Flower Thrips (Thysanoptera: Thripidae) and Chrysanthemum

Modeling the effect of temperature on the sustainability of insect-plant interactions requires assessment of both insect and plant performance. We examined the effect of temperature on western flower thrips, Frankliniella occidentalis (Pergande), a generalist herbivore with a high reproductive rate, and chrysanthemum inflorescences, a high quality but relatively fixed, ephemeral resource for thrips population growth. We hypothesized that different thrips versus plant responses to temperature result in significant statistical interaction of temperature with thrips abundance and flower damage attributes over time. Experiments were conducted at five temperatures between 20.7 and 35.3 degrees C, with thrips infestation and time after infestation as main effects. Only minor, uncontrolled variations in relative humidity and light intensity may otherwise have influenced the results. High temperatures lead to an initially rapid increase in density of thrips followed by abrupt declines in abundance. The rate of floral senescence increased with temperature and thrips infestation, as indicated by a reduced fresh biomass and greater leaching of yellow pigments. Multiple regression indicated that indices of plant damage responded more directly to thrips density at low than high temperature, supporting the conclusion that temperature affected the outcome beyond what was predictable simply from differential plant and insect optima. The relative intensity of damage caused by individual thrips decreased with increasing temperature, likely caused by thrips competition and reduced survival, growth, and fecundity on depleted inflorescences. Reduced per capita damage at high temperature may be common in insects exploiting fixed plant resources that exhibit an accelerated rate of deterioration at high temperatures.

Thrips‐induced damage of chrysanthemum inflorescences: evidence for enhanced leakage of carotenoid pigments

AbstractThe present study quantifies the leakage of carotenoid pigments in senescing inflorescences of chrysanthemum, Dendranthema grandiflora Tzelev (Asteraceae), infested or not with western flower thrips, Frankliniella occidentalis Pergande (Thysanoptera: Thripidae). The extractability of pigments was evaluated at repeated intervals by measuring the absorbance of immersion and crude extracts of inflorescences, using 447 nm as a diagnostic wavelength (absorption peak of lutein, a predominant carotenoid pigment in chrysanthemum with yellow inflorescences). The absorbance of immersion extracts increased over time and was higher for inflorescences infested with thrips than control inflorescences; the opposite trends were observed for crude extracts of inflorescences. These results suggest that both natural and thrips‐induced senescence of chrysanthemum inflorescences are characterized by enhanced extractability of pigments in organic solvents, most likely resulting from a disruption of cellular membranes. Thin layer chromatography analysis confirmed the presence of lutein in immersion extracts of thrips‐infested inflorescences, providing further support to the hypothesis that the mechanical damage caused by thrips is linked with a leakage of cellular content. An enhanced extractability of pigments in organic solvents may be a widespread phenomenon characterizing floral senescence in non‐climacteric plants.

Changes in abscisic acid and flower pigments during floral senescence of petunia

The present work was focused on abscisic acid (ABA) changes in three differently coloured petunias during flower development and senescence. The ABA content was studied in correlation with changes of flower pigments and other phytohormones. The variations of anthocyanins and endogenous hormones were induced by treatments with 1 or 2 mM amino-oxyacetic acid (AOA), 50, 100 &mu;M thidiazuron (TDZ) and 50 &mu;M 6-benzyladenine (BA). ABA content decreased during bud development and increased during senescence. The AOA reduced the anthocyanins content and avoided ABA increase, while the cytokinins (BA and TDZ) did not significantly affected anthocyanin contents but increased ABA content. TDZ doubled the ABA content compared to the control. However, the treatments did not affected flower life, confirming the secondary role of ABA during flower senescence.

Ripening in the tomato Green-ripe mutant is inhibited by ectopic expression of a protein that disrupts ethylene signaling

To achieve full ripening, climacteric fruits, such as tomato require synthesis, perception and signal transduction of the plant hormone ethylene. The nonripening phenotype of the dominant Green-ripe (Gr) and Never-ripe 2 (Nr-2) mutants of tomato is the result of reduced ethylene responsiveness in fruit tissues. In addition, a subset of ethylene responses associated with floral senescence, abscission, and root elongation are also impacted in mutant plants, but to a lesser extent. Using positional cloning, we have identified an identical 334-bp deletion in a gene of unknown biochemical function at the Gr/Nr-2 locus. Consistent with a dominant gain of function mutation, this deletion causes ectopic expression of Gr/Nr-2, which in turn leads to ripening inhibition. A CaMV35::GR transgene recreates the Gr/Nr-2 mutant phenotype but does not lead to a global reduction in ethylene responsiveness, suggesting tissue-specific modulation of ethylene responses in tomato. Gr/Nr-2 encodes an evolutionary conserved protein of unknown biochemical function that we associate here with ethylene signaling. Because Gr/Nr-2 has no sequence homology with the previously described Nr (Never-ripe) ethylene receptor of tomato we now refer to this gene only as GR. Identification of GR expands the current repertoire of ethylene signaling components in plants and provides a tool for further elucidation of ethylene response mechanisms and for controlling ethylene signal specificity in crop plants.

Programmed cell death in floral organs: how and why do flowers die?

Flowers have a species-specific, limited life span with an irreversible programme of senescence, which is largely independent of environmental factors, unlike leaf senescence, which is much more closely linked with external stimuli. Life span of the whole flower is regulated for ecological and energetic reasons, but the death of individual tissues and cells within the flower is co-ordinated at many levels to ensure correct timing. Some floral cells die selectively during organ development, whereas others are retained until the whole organ dies. Pollination is an important floral cell death trigger in many species, and its effects are mediated by the plant growth regulator (PGR) ethylene. In some species ethylene is a major regulator of floral senescence, but in others it plays a very minor role and the co-ordinating signals involved remain elusive. Other PGRs such as cytokinin and brassinosteroids are also important but their role is understood only in some specific systems. In two floral cell types (the tapetum and the pollen-tube) there is strong evidence for apoptotic-type cell death, similar to that in animal cells. However, in petals there is stronger evidence for an autophagous type of cell death involving endoplasmic reticulum-derived vesicles and the vacuole. Proteases are important, and homologues to animal caspases, key regulators of animal cell death, exist in plants. However, their role is not yet clear. There are similarities to cell death in other plant organs, and many of the same genes are up-regulated in both leaf and petal senescence; however, there are also important differences for example in the role of PGRs. Understanding gene regulation may help to understand cell death in floral organs better, but alone it cannot provide all the answers.

Regulation of volatile benzenoid biosynthesis in petunia flowers

The petunia flower has served as a model for the study of several physiological processes including floral development, self-incompatibility, anthocyanin biosynthesis and ethylene signalling during senescence. More recently, Petunia hybrida 'Mitchell' has been used to understand the complex regulation of volatile benzenoid biosynthesis, which occurs predominantly in flower petal tissues. Benzenoid biosynthesis is temporally and circadian controlled and is tightly down-regulated by ethylene during floral senescence. Using targeted transcriptomics and gene knockouts, both biosynthetic genes and a transcription factor regulating benzenoid synthesis have been recently discovered and characterized. It appears that benzenoid production is regulated predominantly by transcriptional control of the shikimate pathway, benzenoid biosynthesis genes and S-adenosyl-methionine cycle genes.