Loss of flower bud vigour in the Mediterranean shrub,Cistus albidus L. at advanced developmental stages

To better understand aging in perennials, age‐related changes in the physiology of leaves and flower buds of the Mediterranean shrub, Cistus albidus L. were evaluated. Two groups of different ages (5 and 10 years old), both at advanced developmental stages but of similar size, were compared. Total plant biomass, biomass produced per apical meristem and levels of cytokinins, abscisic acid and jasmonic acid in leaves and flower buds, as well as flower production, were measured. No differences in plant size, vegetative growth rates and levels of phytohormones in leaves were observed between 5‐ and 10‐year‐old plants. However, they showed significant differences in flower bud development; the older plants having reduced vigour, with 29.6% of flowers reaching anthesis compared to 52.5% in the younger plants. Furthermore, endogenous concentrations of zeatin and abscisic acid in flower buds at stage I (start of flower organ formation) were 61% and 41%, respectively, smaller in 10‐ than in 5‐year‐old plants. At stage II (with all flower organs formed), zeatin and abscisic acid concentrations decreased by ca. 90% and 80%, respectively, but differences between age groups were still evident (60% and 29% for zeatin and abscisic acid, respectively). Jasmonic acid levels in flower buds decreased by 80% from stage I to II, but did not differ between age groups. Despite reductions in flower bud vigour, total number of flowers per individual was not significantly different between age groups, so that an age‐related loss in reproductive vigour at the organ level did not lead to a decrease in flower production at the whole plant level.     

Florivores on the dioecious shrub Eurya japonica and the preferences and performances of two polyphagous geometrid moths on male and female plants

Flowers of dioecious plants have sexually dimorphic traits that may affect florivore performances, and florivores may have preferences to plant sex that are correlated with their performance on different plant sexes. We investigated the florivory on a polygamodioecious evergreen shrub Eurya japonica in Japan to reveal florivores and their feeding patterns involved in sexually biased florivory on E. japonica flowers. Flowers of E. japonica were infested by lepidopteran and dipteran larvae and hemipteran insects. Lepidopteran larvae were chewers, dipteran larvae were gall makers and hemipteran insects were suckers. Chewed flowers were most frequent among infested flowers. Of florivores, lepidopteran larvae, mostly of Geometridae, were the important florivore that damaged flowers by chewing. Florivores infested male flower buds more often than female flower buds, but only a geometrid larvae Chloroclystis excise, which exclusively uses flower buds, showed the biased infection on male flowers. Rearing experiments for two other geometrid moths which use both leaves and flowers showed that the preference and performance of Ourapteryx nivea that fed mainly leaves did not differ between the plant sexes, whereas the development of Alcis angulifera larvae which fed both leaves and flowers was slower when they fed female than male leaves and flower buds. In addition, A. angulifera larvae fed fewer flower buds on female than on male plants. These results show that the male‐biased florivory on E. japonica trees is attributed mainly to the specialist florivore and also feeding preference for male flowers in an opportunistic florivore that feed both leaves and flowers.     

Plant responses to insect herbivore damage are modulated by phosphorus nutrition

Interactions between plants and their herbivores are often multidimensional, complicating interpretation of herbivore‐impact studies. A previous study, directed toward understanding variation in incidences of flower bud abscission among cotton plants attacked by Lygus plant bugs, revealed an unanticipated correlation between levels of phosphorus nutrition and the propensity of plants to abscise developing flower buds. Here, we further investigate the relationship between phosphorus nutrition and cotton [Gossypium hirsutum Tod. (Malvaceae)] plant responses to herbivory by tarnished plant bugs, Lygus hesperus Knight (Hemiptera: Miridae). Complementary experimental approaches and survey data both suggest that levels of phosphorus nutrition falling within the normal range of variation can influence the manner by which plants respond to herbivory. In particular, higher levels of phosphorus nutrition resulted in elevated bud abscission rates when buds were damaged. Interestingly, increased levels of abscission under high‐phosphorus regimes did not translate into a decrease in overall cotton lint yield, suggesting that the ‘phosphorus effect’ may ultimately reflect how environmentally contingent differences in the allocation of vegetative vs. reproductive investments can provide parallel pathways to equal yields.     

Sexual differences in flower defense and correlated male‐biased florivory in a plant–florivore system

Male‐biased florivory is a prominent phenomenon in the interaction between plants and florivores, and is potentially related to the evolution of flower traits and sex expression; however, its adaptive significance is not well understood. We studied florivory in the geometrid moth Chloroclystis excisa utilizing flower buds of a sexually polymorphic shrub, Eurya japonica, to reveal relationships between flower sex and moth oviposition preference, moth larval performance, and plant phenolics composition. In the field, C. excisa exploited flower buds on male and hermaphrodite trees but never those on female trees. In the laboratory, moths showed a strong oviposition preference for male over female flower buds, and larvae did not survive on female buds. Mortality was caused solely by feeding on the calyx covering the female bud. Female calyces contained higher concentrations of total phenolics and condensed tannins than did male calyces. These results suggest that substantial sexual differences in defense against florivory may have evolved in association with the differentiation of flower sexes and that a strong preference for the weakly defended flower sex may have evolved in florivores as a counter‐adaptation.     

Altered expression of CmNRRa changes flowering time of Chrysanthemum morifolium

Flowering time is an important ornamental trait for chrysanthemum (Chrysanthemum morifolium, Dendranthema x grandiflorum) floricultural production. In this study, CmNRRa, an orthologous gene of OsNRRa that regulates root growth in response to nutrient stress in rice, was identified from Chrysanthemum and its role in flowering time was studied. The entire CmNRRa cDNA sequence was determined using a combinatorial PCR approach along with 5′ and 3′ RACE methods. CmNRRa expression levels in various tissues were monitored by real‐time RT‐PCR. CmNRRa was strongly expressed in flower buds and peduncles, suggesting that CmNRRa plays a regulatory role in floral development. To investigate the biological function of CmNRRa in chrysanthemums, overexpression and knockdown of CmNRRa were carried out using transgenic Chrysanthemum plants generated through Agrobacterium‐mediated transformation. CmNRRa expression levels in the transgenic plants were assayed by real‐time RT‐PCR and Northern blot analysis. The transgenic plants showed altered flowering times compared with nontransgenic plants. CmNRRa‐RNAi transgenic plants flowered 40–64 days earlier, while CmNRRa‐overexpressing plants exhibited a delayed flowering phenotype. These results revealed a negative effect of CmNRRa on flowering time modulation. Alteration of CmNRRa expression levels might be an effective means of controlling flowering time in Chrysanthemum. These results possess potential application in molecular breeding of chrysanthemums that production year‐round, and may improve commercial chrysanthemum production in the flower industry.     

Modification of flower sex and acid phosphatase activity by phthalimides in female plants of Morus nigra L.

Phthalimide treatments at 125, 250 and 500 mg 1^–1 to female plants of dioecious Morus nigra L. induced intersex and male flowers. Qualitative and quantitative analyses of acid phosphatase in male and female flower buds showed that the male flower had significantly higher levels of the enzyme activity than the female flower buds. The level of acid phosphatase activity significantly increased in intersex and male flowers induced on female plants after phthalimide treatments.     

Structure and development of ‘witches' broom’ galls in reproductive organs of Byrsonima sericea (Malpighiaceae) and their effects on host plants

Galls are anomalies in plant development of parasitic origin that affect the cellular differentiation or growth and represent a remarkable plant–parasite interaction. Byrsonima sericea DC. (Malpighiaceae) is a super host of several different types of gall in both vegetative and reproductive organs. The existence of galls in reproductive organs and their effects on the host plant are seldom described in the literature. In this paper, we present a novel study of galls in plants of the Neotropical region: the ‘witches' broom’ galls developed in floral structures of B. sericea. The unaffected inflorescences are characterised by a single indeterminate main axis with spirally arranged flower buds. The flower buds developed five unaffected brownish hairy sepals and five pairs of elliptical yellow elaiophores, five yellow fringed petals, 10 stamens and a pistil with superior tricarpellar and trilocular ovary. The affected inflorescences showed changes in architecture, with branches arising from the main axis and flower buds. The flower buds exhibited several morphological and anatomical changes. The sepals, petals and carpels converted into leaf‐like structures after differentiation. Stamens exhibited degeneration of the sporogenous tissue and structures containing hyphae and spores. The gynoecium did not develop, forming a central meristematic region, from which emerges the new inflorescence. In this work, we discuss the several changes in development of reproductive structures caused by witches' broom galls and their effects on reproductive success of the host plants.     

The boron transporter BnaC4.BOR1;1c is critical for inflorescence development and fertility under boron limitation in Brassica napus

Boron (B) is an essential micronutrient for plants, but the molecular mechanisms underlying the uptake and distribution of B in allotetraploid rapeseed (Brassica napus) are unclear. Here, we identified a B transporter of rapeseed, BnaC4.BOR1;1c, which is expressed in shoot nodes and involved in distributing B to the reproductive organs. Transgenic Arabidopsis plants containing a BnaC4.BOR1;1c promoter‐driven GUS reporter gene showed strong GUS activity in roots, nodal regions of the shoots and immature floral buds. Overexpressing BnaC4.BOR1;1c in Arabidopsis wild type or in bor1‐1 mutants promoted wild‐type growth and rescued the bor1‐1 mutant phenotype. Conversely, knockdown of BnaC4.BOR1;1c in a B‐efficient rapeseed line reduced B accumulation in flower organs, eventually resulting in severe sterility and seed yield loss. BnaC4.BOR1;1c RNAi plants exhibited large amounts of disintegrated stigma papilla cells with thickened cell walls accompanied by abnormal proliferation of lignification under low‐B conditions, indicating that the sterility may be a result of altered cell wall properties in flower organs. Taken together, our results demonstrate that BnaC4.BOR1;1c is a AtBOR1‐homologous B transporter gene expressing in both roots and shoot nodes that is essential for the developing inflorescence tissues, which highlights its diverse functions in allotetraploid rapeseed compared with diploid model plant Arabidopsis.     

Floral and growth responses in Chenopodium rubrum L. to an extract from flowering Nicotiana tabacum L.

Flowering of Chenopodium rubrum seedling plants was obtained in continuous light after application of fractions of a partially purified extract from leaves of flowering Maryland Mammoth tobacco (Nicotiana tabacum). The stage of flowal differentiation was dependent on the age of the Chenopodium plants used for the bioassay. Apices of plants treated with the extract at the age of four or seven days showed an advanced branching of the meristem or the beginning of formation of a terminal flower; treatment with the extract of plants 12 d old resulted in rapid formation of flower buds in all assay plants. Non-treated control plants kept in continuous light remained fully vegetative. The effects of the extract on flowering were associated with pronounced growth effects. Floral differentiation was preceeded by elongation of the shoot apex. Extension of all axial organs occurred, while growth of leaves, including leaf primordia, was inhibited. The pattern of growth after application of the flower-inducing substance(s) did not resemble the effects of the known phytohormones, but showed some similarities to growth changes resulting from photoperiodic induction of flowering.     

Identification of the carotenoid modifying gene PALE YELLOW PETAL 1 as an essential factor in xanthophyll esterification and yellow flower pigmentation in tomato (Solanum lycopersicum)

Xanthophylls, the pigments responsible for yellow to red coloration, are naturally occurring carotenoid compounds in many colored tissues of plants. These pigments are esterified within the chromoplast; however, little is known about the mechanisms underlying their accumulation in flower organs. In this study, we characterized two allelic tomato (Solanum lycopersicum L.) mutants, pale yellow petal (pyp) 1‐1 and pyp1‐2, that have reduced yellow color intensity in the petals and anthers due to loss‐of‐function mutations. Carotenoid analyses showed that the yellow flower organs of wild‐type tomato contained high levels of xanthophylls that largely consisted of neoxanthin and violaxanthin esterified with myristic and/or palmitic acids. Functional disruption of PYP1 resulted in loss of xanthophyll esters, which was associated with a reduction in the total carotenoid content and disruption of normal chromoplast development. These findings suggest that xanthophyll esterification promotes the sequestration of carotenoids in the chromoplast and that accumulation of these esters is important for normal chromoplast development. Next‐generation sequencing coupled with map‐based positional cloning identified the mutant alleles responsible for the pyp1 phenotype. PYP1 most likely encodes a carotenoid modifying protein that plays a vital role in the production of xanthophyll esters in tomato anthers and petals. Our results provide insight into the molecular mechanism underlying the production of xanthophyll esters in higher plants, thereby shedding light on a longstanding mystery.     

Changes in polyamine pattern mediates sex differentiation and unisexual flower development in monoecious cucumber (Cucumis sativus L.)

Changes in the levels of polyamines are associated with fundamental physiological processes such as embryogenesis, induction of flowering, fruit development and ripening, senescence, and responses to environmental stresses, but the role of polyamines in sex differentiation and unisexual flower development has not been deeply studied. To extend the knowledge on the regulatory mechanisms of flowering in monoecious plant (producing unisexual flowers), we investigated the morphogenesis and free polyamine levels in Cucumis sativus during sex differentiation and unisexual flower development in vitro using histocytological and biochemical methods. As shown in our study, floral development in vitro was undisturbed and flowers of both sexes were produced. Sex differentiation relied on preventing the development of generative organs of the opposite sex, as we observed carpel repression in male flowers and stamen repression in female flowers. Pollen viability was negatively correlated with female flower development on the same node. Biochemical analysis revealed increased accumulation of aliphatic amines (tri, tetra‐amines) in generative (flower buds and flowers) compare to vegetative (axillary buds and leaves) organs. Undifferentiated floral buds contained elevated levels of agmatine, cadaverine, spermidine and spermine. Sex differentiation was associated with significantly decreased levels of agmatine and cadaverine. Our results showed that female flowers contained higher levels of total polyamine than male flowers. The increased level of cadaverine was associated with macrogametogenesis and female flower maturation. Putrescine was important for male flower development. Such results support the hypothesis that aliphatic amines are involved in unisexual flower development.     

Key‐factor/key‐stage analysis of long‐term life table data for a fruit gall midge,Asphondylia sphaera (Diptera: Cecidomyiidae)

1. Population dynamics of Asphondylia sphaera Monzen (Diptera: Cecidomyiidae), a species that induces fruit galls on Ligustrum japonicum (Oleaceae), was studied from 1970 to 1996 in broad‐leaved evergreen forests in Kagoshima, southern Japan. The numbers of fruit galls and emerging adults fluctuated greatly from year to year along with alternate year flowering of the host plant. 2. To detect density‐dependent and independent forces operating on the A. sphaera population and to assess the relative strength of top‐down and bottom‐up effects, we used the method of Key‐factor/key‐stage analysis, which allowed us to avoid various problems of the conventional key‐factor analysis. 3. Five factors and seven stages were distinguished in the life tables. Key‐factor/key‐stage analysis indicated that the number of flower buds made the largest contribution to the annual changes in total survival rate by operating through the proportion of eggs and first instars that survived abortion of host flower buds and flowers, which contributed most to density‐dependency. 4. The population dynamics of A. sphaera has been strongly influenced by the bottom‐up effects of both the abundance of flower buds and the abortion of flowers of L. japonicum. 5. A top‐down effect of Bracon asphondyliae Maeto (Hymenoptera: Braconidae) was weakly density‐dependent and contributed less to the total survival rate. Abiotic factors, such as summer and winter temperatures and the effect of typhoons were negligible.     

Cold deacclimation mechanisms and reacclimation potential in flower buds of blackcurrant (Ribes nigrum)

As a consequence of global climate change, cold acclimation and deacclimation cycles are becoming increasingly frequent during winter in temperate regions. However, little is known about plant deacclimation and in particular reacclimation mechanisms, although deacclimation resistance and the ability to reacclimate may have wide‐ranging consequences regarding plant productivity in a changing climate. Here, we report time‐dependent responses of freezing tolerance, respiration rates, metabolite contents (high‐resolution magic angle spinning NMR) and fatty acid levels (gas chromatography) in flower buds of two ecodormant Ribes nigrum cultivars exposed to three different deacclimation temperatures followed by a reacclimation treatment at 4°C. The data reveal that despite differences in the progression of deacclimation, the capacity of blackcurrant flower buds to reharden in late winter is virtually non‐existing, implying that increasingly irregular temperature patterns is critical for blackcurrant fruit yield. The early phase of deacclimation is associated with a transient increase in respiration and decreasing contents of amino acids, tricarboxylic acid (TCA) cycle intermediates and sugars, indicating an increased need for carbon sources and respiratory energy production for the activation of growth. Decreasing sugar levels may additionally cause loss of freezing tolerance. Deacclimation also involves desaturation of membrane lipids, which likely also contributes to decreased freezing tolerance but may also reflect biosynthesis of signaling molecules stimulating growth and floral organ differentiation. These data provide new insights into the under‐researched deacclimation mechanisms and the ability of blackcurrant to reacclimate following different advancements of deacclimation and contribute to our understanding of plant responses to increasingly irregular temperature patterns.     

Trehalose 6‐phosphate is involved in triggering axillary bud outgrowth in garden pea (Pisum sativum L.)

Trehalose 6‐phosphate (Tre6P) is a signal of sucrose availability in plants, and has been implicated in the regulation of shoot branching by the abnormal branching phenotypes of Arabidopsis (Arabidopsis thaliana) and maize (Zea mays) mutants with altered Tre6P metabolism. Decapitation of garden pea (Pisum sativum) plants has been proposed to release the dormancy of axillary buds lower down the stem due to changes in sucrose supply, and we hypothesized that this response is mediated by Tre6P. Decapitation led to a rapid and sustained rise in Tre6P levels in axillary buds, coinciding with the onset of bud outgrowth. This response was suppressed by simultaneous defoliation that restricts the supply of sucrose to axillary buds in decapitated plants. Decapitation also led to a rise in amino acid levels in buds, but a fall in phosphoenolpyruvate and 2‐oxoglutarate. Supplying sucrose to stem node explants in vitro triggered a concentration‐dependent increase in the Tre6P content of the buds that was highly correlated with their rate of outgrowth. These data show that changes in bud Tre6P levels are correlated with initiation of bud outgrowth following decapitation, suggesting that Tre6P is involved in the release of bud dormancy by sucrose. Tre6P might also be linked to a reconfiguration of carbon and nitrogen metabolism to support the subsequent growth of the bud into a new shoot.     

Effect of defoliation by checkerspot caterpillars (Euphydryas phaeton) and sawfly larvae (Macrophya nigra and Tenthredo grandis) on their host plants (Chelone spp.)

Summary The effect of defoliation by herbivores, checkerspot caterpillars (Euphydryas phaeton) and sawfly larvae (Macrophya nigra and Tenthredo grandis), on the reproductive output of turtlehead (Chelone spp.) was examined. Defoliation prior to development of flower buds reduced the number of reproductive stalks, flower buds, flowers and seed capsules. Severe herbivory, after flower buds appeared, decreased the final number of seed capsules and seeds per capsule. The availability of the host plants to the herbivores was a function of prior defoliation and environmental conditions. Sawfly larvae, by defoliating the plants in midsummer, forced prediapause checkerspot caterpillars to wander in search of food plants. Decimation of these perenials by postdiapause checkerspot caterpillars in a dry spring retarded growth of turtlehead and, consequently, most of the plants were not available for egg-laying by sawflies and checkerspots.     

Effect of modified endogenous ethylene production on sex expression, bisexual flower development and fruit production in melon (Cucumis melo L.)

Members of the Cucurbitaceae family display a range of sexual phenotypes including various combinations of male, female, or bisexual flowers. Ethylene appears to be a key hormone regulating the sex determination process. Application of ethylene, or inhibition of ethylene action, increases or decreases the number of pistil-bearing buds, respectively. Elevated levels of ethylene production and expression of genes for ethylene biosynthesis, have been correlated with pistillate flower production. In this study, we sought to determine the effect of modified endogenous ethylene production on sex expression by constitutively expressing ACS (1-aminocyclopropane-1-carboxylate synthase), the first committed enzyme for ethylene biosynthesis, in transgenic melons (Cucumis melo L.). Most melon genotypes are andromonoecious, where an initial phase of male flowers is followed by a mixture of bisexual and male flowers. ACS melon plants showed increased ethylene production by leaves and flower buds, and increased femaleness as measured by earlier and increased number of bisexual buds. ACS melons also had earlier and increased number of bisexual buds that matured to anthesis, suggesting that ethylene is important not only for sex determination, but also for development of the bisexual bud to maturity. Field studies showed that ACS melons had earlier mature bisexual flowers, earlier fruit set, and increased number of fruit set on closely spaced nodes on the main stem. These results provide a direct demonstration of the importance of endogenous ethylene production for female reproductive processes in melon.