Stages Of Floral Development Research Articles

Expression analysis of an APETALA1/FRUITFULL-like gene in Phalaenopsis sp. ‘Hatsuyuki’ (Orchidaceae)

Members of the APETALA1 (AP1)/FRUITFULL (FUL)-like gene family of MADS-box genes play important roles in controlling the development of floral organs. To understand the molecular mechanisms of floral development in orchid, we isolated and characterized a Phalaenopsis AP1/FUL-like gene, PhalFUL. The results of phylogenetic analysis indicated that PhalFUL is in the monocots group of AP1/FUL-like gene. PhalFUL transcripts were detected in the flower buds, but not in vegetative organs. Moreover, in situ hybridization experiments revealed PhalFUL hybridization signals in all floral organ primordia at a very early stage of floral development, and continued expression in the column of whorls 3 and 4 until late developmental stages. These expression patterns were similar to those of the FUL-like genes in Arabidopsis (FUL) and Antirrhinum (DEFH28), suggesting that the PhalFUL is similar in function to FUL and DEFH28.

Terpenoid, Benzenoid, and Phenylpropanoid Compounds in the Floral Scent of Vanda Mimi Palmer

Vanda Mimi Palmer is the product of a cross between Vanda Tan Chay Yan and Vanda tessellata. The flower of this hybrid produces a sweet-smelling fragrance during day time at the open-flower stage. This study aimed to investigate the floral scent constituents in Vanda Mimi Palmer. Scent emission analysis of this orchid was carried out at different time points in a 24-h cycle and also at different floral developmental stages. A comparison was also made on the volatiles emitted by Vanda Mimi Palmer and both of its parents. Gas chromatography-mass spectrometry (GC-MS) analysis showed that the scent of Vanda Mimi Palmer was dominated by terpenoid, benzenoid, and phenylpropanoid compounds. The identified terpenoids were ocimene, linalool oxide, linalool, and nerolidol; while the benzenoid and phenylpropanoid compounds were methylbenzoate, benzyl acetate, phenylethanol, and phenylethyl acetate. The emission of terpenoid, benzenoid, and phenylpropanoid compounds was developmentally and temporally regulated. Comparison of the volatiles emitted by both of its parents showed that the scent of Vanda Mimi Palmer is dissimilar to that of its fragrant parent, V. tessellata.

FLORAL BUD INITIATION AND DEVELOPMENT OF THREE PEAR TREE (PYRUS SP.) CULTIVARS IN TWO SUBTROPICAL REGIONS DURING THE SUMMER PERIOD

The flower formation in fruit trees is in the spring but actually begins in the previous summer. Flowers are induced in the apex of the buds, which were vegetative previously. After flower induction, which is still an unknown process, successive steps of physiological processes occur and morphological differentiation, when the apex becomes organized into a primordia of flower (or inflorescence). The first morphological change that occurs in the meristem is a 'broadening' of the apex, which also becomes convex, followed by its lengthening into a cylindrical shape and the formation of sepal primordia in the terminal flower (king flower). After this transformation, organ primordia become differentiated laterally. The time of floral bud formation in the fruit trees is of great importance, because it will determine the development level that these buds will reach before beginning the dormancy period, having a decisive effect on the quality of the produced inflorescence. The objective of this work was to investigate the time of floral bud initiation and development in three pear tree cultivars ('Packham's Triumph', 'Abate Fetel' and 'Housui') in two subtropical regions of Rio Grande do Sul state (Pelotas and Vacaria) during the growth period in 2007. To evaluate the floral bud initiation, terminal and axillary buds of long shoots and apical buds of spurs were collected from January 9 th , in a 15-day interval, until march 14 th , fixed in a solution of formalin, acetic acid and alcohol (FAA) and dissected under a stereoscopic microscopy in the Laboratory of Imunology and Electronic Microscopy at Embrapa Clima Temperado, Pelotas-RS. The time of floral bud initiation did not practically differ between the two regions to the three cultivars observed. However, the time of floral bud initiation differed between cultivars and, also, the three cultivars presented a differentiated behavior in the flower bud development. In the beginning of the observations, the spur buds of 'Housui' had already initiated and presented in more advanced stages of floral development than the other two cultivars. The floral initiation in the 'Packham's' spur buds and in the 'Housui' terminal buds occurred in late January. The spur buds of 'Abate Fetel', terminal buds of 'Packham's' and axillary buds of 'Housui' were initiated in early February. In the middle of March, the spurs of 'Housui' and 'Packham's' and the terminal buds of 'Housui' reached the carpel primordia stage.

Cryptic dioecy in Mussaenda pubescens (Rubiaceae): a species with stigma-height dimorphism.

Evolutionary transitions from heterostyly to dioecy have been proposed in several angiosperm families, particularly in Rubiaceae. These transitions involve the spread of male and female sterility mutations resulting in modifications to the gender of ancestral hermaphrodites. Despite sustained interest in the gender strategies of plants, the structural and developmental bases for transitions in sexual systems are poorly understood. Here, floral morphology, patterns of fertility, pollen-tube growth and floral development are investigated in two populations of the scandent shrub Mussaenda pubescens (Rubiaceae), native to southern China, by means of experimental and open-pollinations, light microscopy, fluorescence microscopy and scanning electron microscopy combined with paraffin sectioning. Mussaenda pubescens has perfect (hermaphroditic) flowers and populations with two style-length morphs but only weak differentiation in anther position (stigma-height dimorphism). Experimental pollinations demonstrated that despite morphological hermaphroditism, the species is functionally dioecious. The long-styled (L) morph possesses sterile pollen and functions as a female, whereas the short-styled (S) morph is female sterile and functions as a male. Self- and intra-morph pollinations of the S-morph were consistent with those expected from dimorphic incompatibility. The two populations investigated were both S-morph (male) biased. Investigations of early stages of floral development indicated patterns typical of hermaphroditic flowers, with no significant differences in organ growth between the floral morphs. Meiosis of microspore mother cells was of the simultaneous type with tetrads isobilateral in shape. The tapetal cells in anther walls of the L-morph became vacuolized during meiosis I, ahead of the uninucleate microspore stage in the S-morph. In the L-morph, the microspore nucleus degenerated at the tetrad stage resulting in male sterility. Microsporogenesis and male gametophyte development was normal in the S-morph. Failure in the formation of megaspore mother cells and/or the development of megagametophytes resulted in female sterility in the S-morph, compared with normal megasporogenesis in the L-morph. In M. pubescens, cryptic dioecy has evolved from stigma-height dimorphism as a result of morph-specific sterility mutations.

Crocins transport in Crocus sativus: The long road from a senescent stigma to a newborn corm

Saffron, the desiccated stigmas of Crocus sativus, is highly appreciated by its peculiar colour, flavour and aroma. The main compounds that accumulated throughout stigma development in C. sativus are crocetin, its glucoside derivatives, crocins, and picrocrocin, all of which increased as stigmas reached a fully developed stage. After anthesis, and in the absence of fertilization, the flower enters in a senescence programme, which represents the ultimate stage of floral development and results in wilting of whole flower. The programmed senescence of flowers allows the removal of a metabolically active tissue. We studied the composition of saffron apocarotenoids during the senescence of C. sativus flowers, and observed that changes in crocins were due to their transport from the senescent stigma to the ovaries and the developing corm. Afterwards, deglucosylation of crocins in these tissues results in crocetin accumulation. This mobilization mimics the export to storage cells (resorbed) of different compounds during leaf senescence avoiding loss of nutrients in leaves that would otherwise be cycled back into the soil system through leaf litter decomposition. In C. sativus, the resorbed apocarotenoids are stored within the developing corm, where they are not further detected in the advanced stages of development, suggesting that they are metabolized during the early and active phases of corm development, where the glucose molecules from crocins might contribute to cell initiation and elongation.

Characterization and expression analysis of PhalLFY, a homologue in Phalaenopsis of FLORICAULA/LEAFY genes

FLORICAULA/LEAFY (FLO/LFY) homologues are floral meristem identifying genes and play a key role in flower development among diverse species. Phalaenopsis is one of the world's most popular flowers. To understand the molecular mechanism of the reproduction process, PhalLFY, a FLO/LFY homologue gene was cloned from Phalaenopsis hybrida (cv.wedding promenade) and its expression pattern was analysed during vegetative as well as reproductive development. The full cDNA of PhalLFY was 1655 bp in length with an open reading frame (ORF) of 1422 bp encoding 424 amino acids. The analysis based on amino acid sequence alignment showed that PhalLFY shared a high degree of similarity to LFY-like (68%) from Anacamptis, LFY-like (61%) from Hyacinthus, RFL (60%) from Oryza sativa and LFY (54%) from Arabidopsis. A transient expression assay using PhalLFY/GFP fusion protein showed that PhalLFY was nucleus-localized protein. Semi-quantitative RT-PCR analysis and in situ hybridization results showed that PhalLFY was expressed both in the vegetative organs as well as the reproductive organs. Its transcripts accumulated at higher levels in the stem during the transition from vegetative to reproductive growth, especially in the inflorescence meristems, floral meristems, floral primordia and all floral organs during the floral developmental stage of P. hybrida. Moreover, PhalLFY transcript was lower in the young phase than in the mature phase. These results suggest that PhalLFY is a FLO/LFY homologue probably involved in the control of Phalaenopsis reproductive development.

Floral development, stigma receptivity and pollen viability in eight Nolana (Solanaceae) species

Nolana L.f. is a large, diverse genus in the Solanaceae endemic to the coastal deserts of Peru and Chile. Floral development studies were conducted in eight species (Nolana adansonii, N. aticoana, N. elegans, N. humifusa, N. ivaniana, N. laxa, N. plicata, and N. rupicola) as a precursor to breeding efforts and studies of interspecific sexual compatibility. Levels of stigma receptivity and pollen viability were evaluated at different stages during flower development. Species were found to be receptive to pollination over a wide range of floral developmental stages, including stages prior to anthesis. Pollen was found to remain viable throughout the open flower period and into senescence. Floral development keys were developed which provide a visual reference correlating morphological appearance of buds and flowers of each species at each developmental stage, and their corresponding durations and levels of stigma receptivity.

Cloning and Characterization of Prunus serotina AGAMOUS, a Putative Flower Homeotic Gene

Members of the AGAMOUS subfamily of MADS-box transcription factors play an important role in regulating the development of reproductive organs in flowering plants. To help understand the mechanism of floral development in black cherry (Prunus serotina), PsAG (a putative flower homeotic identity gene) was isolated, and its MIKC-type structure was shown to be a homolog of the Arabidopsis thaliana AG gene. It was a single-copy gene in black cherry. A phylogenetic tree derived from the protein sequence indicated PsAG to be a C-function flower homeotic gene with a high similarity to other AG homologs, such as those from Prunus persica and Prunus mume. PsAG met the criteria for AG subfamily gene structure with a typical MIKC structure. In situ hybridization showed that PsAG was expressed mainly in the floral meristem, such as stamen and carpel primordia during the early stage of floral development, and transcript of PsAG accumulated in the tissues of the ovary, stigma, style, and stamens. When the flowers matured, PsAG had enhanced expression in ovary, style, and stigma, with decreased expression in the stamen. PsAG continued to be expressed in the ovule at the late stage of flower development. The developmental patterns of expression were consistent with those of AG and homologs from other species. Both phylogenetic analysis and expression-pattern data suggest that PsAG was the black cherry homolog of Arabidopsis AG. An RNAi construct with a partial PsAG gene was constructed for black cherry transformation.

Environmental regulation of floral anthocyanin synthesis in Ipomoea purpurea

Responses of metabolites to environmental fluctuations may play large roles in biological adaptation, yet how these responses initiate in the natural environment and the molecular mechanisms remain unclear. Synthesis of floral anthocyanins, as typical examples of secondary metabolites, is known to respond to the physical environment and therefore an ideal system for understanding the process of the environmental regulation. Here, by simultaneous monitoring of six natural environmental variables and anthocyanin content of daily opening flowers throughout a natural flowering season ( approximately 50 days) of Ipomoea purpurea, we have identified significant and positive correlations of temperature (3-days ago) and ultraviolet (UV) light intensity (5-days ago) with the floral anthocyanin content. We sequenced all known (seven structural and three regulatory) anthocyanin genes in I. purpurea flowers and examined their transcript quantities in the natural environment across eight floral developmental stages (covering 0-96 h before anthesis). The anthocyanin gene expression patterns corroborated with the inferred effects from the time-series data, and further showed that the positive UV effect became negative on transcript levels about 36 h before anthesis. With falling natural temperature, content of the principal anthocyanin declined, whereas that of an alternative anthocyanin with fewer glucose and caffeic acid moieties increased. Our data suggest that environmental regulation of the anthocyanin pathway may account for more than half of the flux variation in the floral limb, and is influenced mainly by daily average temperature and UV light intensity that modulate anthocyanin transcript levels (most likely via myb1) at floral developmental stages.

Altered expression of wheat AINTEGUMENTA homolog, WANT-1, in pistil and pistil-like transformed stamen of an alloplasmic line with Aegilops crassa cytoplasm

Homeotic transformation of stamens into pistil-like structures, called pistillody, has been reported in some alloplasmic common wheat lines with Aegilops crassa cytoplasm. An alloplasmic line of Chinese Spring ditelosomic 7BS (CSdt7BS) with Ae. crassa cytoplasm lacking the long arm of the chromosome 7B shows pistillody, and the pistils and transformed stamens are sterile due to abnormal ovule development. To elucidate the molecular mechanism of the ovule abnormality, we compared the expression profiles of floral organs between euplasmic and alloplasmic CSdt7BS lines. Two differential display methods of mRNA profiling demonstrated that Ae. crassa cytoplasm largely affects nuclear gene expression profiles of common wheat. Of the differentially expressed genes, a wheat AINTEGUMENTA (ANT) homolog, WANT-1, was preferentially expressed in pistils but not in stamens, and accumulation of the transcript was limited to ovule primordia at the floral organ development stage. In alloplasmic wheat, WANT-1 expression was patchy and weak at the ovule-development stages. On the other hand, no significant difference in gene expression patterns of wheat AGAMOUS (AG) homologs (WAG-1 and WAG-2) was observed between fertile and sterile pistils. These results indicated that alteration of gene expression after initiation of ovule primordia results in abnormal ovule development, and that the aberrant ovule formation is at least partly associated with the weak expression of WANT-1 around ovule primordia in alloplasmic wheat with Ae. crassa cytoplasm.

Silencing the hydroxyproline-rich glycopeptide systemin precursor in two accessions of Nicotiana attenuata alters flower morphology and rates of self-pollination.

Systemins and their hydroxyproline-rich glycopeptide systemin (ppHS) subfamily members are known to mediate antiherbivore defenses in some solanaceous taxa but not others; functions other than in defense remain largely unexplored. Nicotiana attenuata's ppHS is known not to function in herbivore defense. NappHS transcripts are abundant in flowers, particularly in pistils, and when two N. attenuata accessions from Utah and Arizona were transformed to silence NappHS by RNAi (IRsys), seed capsule production and seed number per capsule were reduced in both accessions. These reductions in reproductive performance could not be attributed to impaired pollen or ovule viability; hand-pollination of all IRsys lines of both accessions restored seed production per capsule to levels found in wild-type plants. Rather, changes in flower morphology that decreased the efficiency of self-pollination are likely responsible: IRsys plants of both accessions have flowers with pistils that protrude beyond their anthers. Because these changes in flower morphology are reminiscent of CORONATINE-INSENSITIVE1-silenced N. attenuata plants, we measured jasmonates (JAs) and their biosynthetic transcripts in different floral developmental stages, and found levels of JA-isoleucine (Ile)/leucine and threonine deaminase transcripts, which are abundant in wild-type pistils, to be significantly reduced in IRsys buds and flowers. Threonine deaminase supplies Ile for JA-Ile biosynthesis, and we propose that ppHS mediates JA signaling during flower development and thereby changes flower morphology. These results suggest that the function of ppHS family members in N. attenuata may have diversified to modulate flower morphology and thereby outcrossing rates in response to biotic or abiotic stresses.

Water deficits promote flowering in Rhododendron via regulation of pre and post initiation development

Flowering is generally considered to be advanced by water deficits in many woody perennial species. A long-standing paradigm being that as a plant senses severe environmental conditions resources are diverted away from vegetative growth and towards reproduction before death. It is demonstrated that in Rhododendron flowering is promoted under water deficit treatments. However, the promotion of flowering is not achieved via an increase in floral initiation, but through separate developmental responses. If regulated deficit irrigation (RDI) is imposed prior to the time of initiation, fewer vegetative nodes are formed before the apical meristems switch to floral initiation, and chronologically, floral initiation occurs earlier. Both RDI and partial rootzone drying (PRD) treatments stimulate the development of more flowers on each inflorescence if the treatments are continued after the plant has undergone floral initiation. However, floral initiation is inhibited by soil water deficits. If the soil water deficit continues beyond the stages of floral development then anthesis can occur prematurely on the fully formed floral buds without a need for a winter chilling treatment. It is hypothesised that inhibition of floral initiation in plants experiencing severe soil water deficits results from the inhibitory action of ABA transportation to the apical meristem from stressed roots. It is demonstrated that ABA applications to well-watered Rhododendron inhibit floral initiation.

In planta localisation patterns of MADS domain proteins during floral development in Arabidopsis thaliana

BackgroundMADS domain transcription factors play important roles in various developmental processes in flowering plants. Members of this family play a prominent role in the transition to flowering and the specification of floral organ identity. Several studies reported mRNA expression patterns of the genes encoding these MADS domain proteins, however, these studies do not provide the necessary information on the temporal and spatial localisation of the proteins. We have made GREEN FLUORESCENT PROTEIN (GFP) translational fusions with the four MADS domain proteins SEPALLATA3, AGAMOUS, FRUITFULL and APETALA1 from the model plant Arabidopsis thaliana and analysed the protein localisation patterns in living plant tissues by confocal laser scanning microscopy (CLSM).ResultsWe unravelled the protein localisation patterns of the four MADS domain proteins at a cellular and subcellular level in inflorescence and floral meristems, during development of the early flower bud stages, and during further differentiation of the floral organs. The protein localisation patterns revealed a few deviations from known mRNA expression patterns, suggesting a non-cell autonomous action of these factors or alternative control mechanisms. In addition, we observed a change in the subcellular localisation of SEPALLATA3 from a predominantly nuclear localisation to a more cytoplasmic localisation, occurring specifically during petal and stamen development. Furthermore, we show that the down-regulation of the homeodomain transcription factor WUSCHEL in ovular tissues is preceded by the occurrence of both AGAMOUS and SEPALLATA3 proteins, supporting the hypothesis that both proteins together suppress WUSCHEL expression in the ovule.ConclusionThis approach provides a highly detailed in situ map of MADS domain protein presence during early and later stages of floral development. The subcellular localisation of the transcription factors in the cytoplasm, as observed at certain stages during development, points to mechanisms other than transcriptional control. Together this information is essential to understand the role of these proteins in the regulatory processes that drive floral development and leads to new hypotheses.

Functional transition in the floral receptacle of the sacred lotus (Nelumbo nucifera): from thermogenesis to photosynthesis.

The receptacle of the sacred lotus is the main source of heat during the thermogenic stage of floral development. Following anthesis, it enlarges, greens and becomes a fully functional photosynthetic organ. We investigated development of photosynthetic traits during this unusual functional transition. There were two distinct phases of pigment accumulation in receptacles. Lutein and photoprotective xanthophyll cycle pigments accumulated first with 64 and 95% of the maximum, respectively, present before anthesis. Lutein epoxide comprised 32% of total carotenoids in yellow receptacles, but declined with development. By contrast, more than 85% of maximum total chlorophyll, β-carotene and Rubisco were produced after anthesis, and were associated with significant increases in maximum electron transport rates (ETR) and photochemical efficiency (Fv/Fm). Leaves and mature receptacles had similar Rubisco content and ETRs (>200 μmol m-2 s-1), although total chlorophyll and total carotenoid contents of leaves were significantly higher than those of green receptacles. Receptacle δ13C before anthesis was similar to that of leaves; consistent with leaf photosynthesis being the source of C for these tissues. In contrast, mature receptacles had significantly lower δ13C than leaves, suggesting that 14-24% of C in mature receptacles is the result of refixation of respired CO2.

Floral Organogenesis of Triglochin maritimum Linn.（Juncaginaceae）

The floral organogenesis of Triglochin maritimum Linn.was observed under scannning electron microscope(SEM).Floral development of T.maritimum consists of the sequential initiation of alternating,trimerous whorls of floral appendages in centripetal and acropetal succession:two whorls of tepals,two of stamens,and two of carpels in the typical monocotyledonous pattern.Our observation did not find an association of the tepal and stamen primordia(the "CA complex").The common base of the stamen and its opposing tepal in later stage maybe a result of subsequent intercarary upgrowth,which is secondary result.There are differences in position,timing and rates of development between whorl of tepals and stamens.Differential timing and rates of growth of the inner tepals and outer stamens result in the former appearing to be located internal to the latter in the mature flower.In the late stage of floral development,we observed the decreasing case of the number of carpel.It seems that the present observation of T.maritimum does not support the interpretation of the flower of Triglochin as a reduced lateral branch of the inflorescence,though a more detailed study would be requried to confirm this.

In vitro hermaphrodism induction in date palm female flower

This study explores and reports on the gain brought to the morphogenetic aptitude of female date palm inflorescences through in vitro hermaphrodism induction. It investigates the main factors involved in the process of sex modification through hormonal induction, such as the floral developmental stage and hormone combination and concentration. It demonstrates that the vestigial stamens (staminodes) of female date palm flowers display a new and high capacity to proliferate under particular in vitro conditions, without blocking carpel's development, leading to morphologically typical hermaphrodite flowers. This de novo activation of repressed stamens was found to occur rapidly. The isolated pollen mother cells appear in the obtained anther's locules and undergo an ordinary microsporogenesis process. The data show that hermaphrodism induction depended heavily on both the growth regulators applied and the flower's developmental stage. They also confirm the early theory that suggests that dioecious plants come from a hermaphrodite ancestor. Such hermaphrodism control can provide new prospects and opportunities for the investigation of the in vitro self-fertilization process. It can also be useful in improving the understanding of the genetic mechanism involved in sex organ development in date palm.

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.

Synchronicity of thermogenic activity, alternative pathway respiratory flux, AOX protein content, and carbohydrates in receptacle tissues of sacred lotus during floral development

The relationships between heat production, alternative oxidase (AOX) pathway flux, AOX protein, and carbohydrates during floral development in Nelumbo nucifera (Gaertn.) were investigated. Three distinct physiological phases were identified: pre-thermogenic, thermogenic, and post-thermogenic. The shift to thermogenic activity was associated with a rapid, 10-fold increase in AOX protein. Similarly, a rapid decrease in AOX protein occurred post-thermogenesis. This synchronicity between AOX protein and thermogenic activity contrasts with other thermogenic plants where AOX protein increases some days prior to heating. AOX protein in thermogenic receptacles was significantly higher than in post-thermogenic and leaf tissues. Stable oxygen isotope measurements confirmed that the increased respiratory flux supporting thermogenesis was largely via the AOX, with little or no contribution from the cytochrome oxidase pathway. During the thermogenic phase, no significant relationship was found between AOX protein content and either heating or AOX flux, suggesting that regulation is likely to be post-translational. Further, no evidence of substrate limitation was found; starch accumulated during the early stages of floral development, peaking in thermogenic receptacles, before declining by 89% in post-thermogenic receptacles. Whilst coarse regulation of AOX flux occurs via protein synthesis, the ability to thermoregulate probably involves precise regulation of AOX protein, most probably by effectors such as alpha-keto acids.

Carbohydrate mobilization and gene regulatory profile in the pseudobulb of Oncidium orchid during the flowering process

The pseudobulb of Oncidium orchid is a storage organ for supplying water, minerals and carbohydrates to the developing inflorescence. Different patterns of mannan, starch and pectin metabolism were observed in the pseudobulb of three developmental stages by histochemical staining and high performance anion exchange chromatographic (HPAEC) analysis. Copious pectin was strongly stained by ruthenium red in young pseudobulbs demonstrating that mannan and pectin were preferentially accumulated in the young pseudobulb sink at inflorescence pre-initiation stage. Concomitant with the emergence of the inflorescence, mannan and pectin decreased gradually and converted to starch. The starch, synthesized at the inflorescence developing stage, was eventually degraded at the floral development stage. A systematic survey on the subtractive EST (expression sequence tag) library of pseudobulb in the inflorescence pre-initiation stage revealed the presence of five groups of gene homologues related to sucrose, mannan, starch, pectin and other carbohydrate metabolism. The transcriptional level of 13 relevant genes related to carbohydrate metabolism was characterized from pseudobulbs of three different developmental stages. The specific activities of the enzymes encoded by these genes were also assayed. The expression profiles of these genes show that the transcriptional levels largely correlated with the enzyme activities, which were associated with the respective carbohydrate pools. These results demonstrated a novel functional profile of polysaccharide mobilization pathway as well as their relevant gene expression in the pseudobulb of Oncidium orchid during the flowering process.

Photoinhibition and changes in pigments associated with bract browning in waratahs (Telopea spp., Proteaceae)

SummaryThe relationship between chronic or long-term photoinhibition, pigment changes, and bract browning in ‘Fire and Brimstone’, ‘Olympic Flame’ and ‘Wirrimbirra White’ waratahs [Telopea speciosissima (Smith) R.Br.] was investigated. Plants were grown under full sun, or under 50% shade-cloth over 2 years, with photoinhibition and pigment changes measured in the bracts and leaves at three stages of floral development (tight bud, juvenile open bud, and mature flower). Photoinhibition of waratah bracts was reduced by shading when applied either from flower initiation in late Summer, or from bud expansion in late Winter, until flower maturity in Spring. Outer bracts showed photoinhibition from the tight bud stage of flower development, and inner bracts from the juvenile open stage, while leaves were not affected. Photoinhibition, measured as pre-dawn photochemical efficiency (PE; Fv/Fm), declined in proportion to bract browning. Bracts on waratah plants kept under shade maintained higher chlorophyll, carotenoid, and anthocyanin levels than bracts exposed to full sun, and thus had a more intense flower colour. A significant decrease in bract pigmentation, combined with photoinhibition, indicates that photodamage occurs in bracts exposed to full sun. Leaf browning did not occur, and waratah leaves maintained a higher chlorophyll concentration than bracts in both full sun and shade conditions. Protection from photoinhibition was correlated with the level of UV-absorbing pigments.