FT overexpression induces precocious flowering and normal reproductive development in Eucalyptus

Eucalyptus trees are among the most important species for industrial forestry worldwide. However, as with most forest trees, flowering does not begin for one to several years after planting which can limit the rate of conventional and molecular breeding. To speed flowering, we transformed a Eucalyptus grandis × urophylla hybrid (SP7) with a variety of constructs that enable overexpression of FLOWERING LOCUS T (FT). We found that FT expression led to very early flowering, with events showing floral buds within 1–5 months of transplanting to the glasshouse. The most rapid flowering was observed when the cauliflower mosaic virus 35S promoter was used to drive the Arabidopsis thaliana FT gene (AtFT). Early flowering was also observed with AtFT overexpression from a 409S ubiquitin promoter and under heat induction conditions with Populus trichocarpa FT1 (PtFT1) under control of a heat‐shock promoter. Early flowering trees grew robustly, but exhibited a highly branched phenotype compared to the strong apical dominance of nonflowering transgenic and control trees. AtFT‐induced flowers were morphologically normal and produced viable pollen grains and viable self‐ and cross‐pollinated seeds. Many self‐seedlings inherited AtFT and flowered early. FT overexpression‐induced flowering in Eucalyptus may be a valuable means for accelerating breeding and genetic studies as the transgene can be easily segregated away in progeny, restoring normal growth and form.     

Dormancy and Flowering Are Regulated by the Reciprocal Interaction Between Cytokinin and Gibberellin in <Emphasis Type="Italic">Zantedeschia</Emphasis>

Floral productivity of Zantedeschia is dependent on the conversion rate of buds to shoots, which is controlled by varying intensities of para- (apical dominance), endo- (dormancy), and ecodormancy. We present evidence of cross-talk between cytokinin and gibberellin in their complementary roles to alleviate bud dormancy and enhance flowering in a perennial geophyte. We assessed the impact of cytokinin and gibberellin, applied alone and in sequential combinations, on bud fate during three phases along the ontogeny of growth, which coincide with the progressive transition of buds from apical dominance to dormancy. Given that cytokinin can stimulate branching and gibberellin can induce flowering in Zantedeschia, we measured these phenotypic responses as parameters of bud commitment. The efficacy of cytokinin alone to stimulate branching declined with the transition to dormancy (phase 1 = 3.8 ± 0.2 shoots; phase 3 = 1.0 ± 0.3 shoots). To sustain branching during this transition, a sequential application of gibberellin was necessary. Gibberellin alone failed to stimulate branching. The efficacy of gibberellin alone to stimulate flowering diminished with the transition to dormancy. Any flowering during this transition occurred only after the sequential application of cytokinin. Cytokinin alone failed to stimulate flowering. Alleviating bud dormancy and enhancing flowering in Zantedeschia, achieved by the reciprocal cross-talk between cytokinin and gibberellin, contributes to the pool of evidence drawing common mechanisms between dormancy and flowering and may have commercial implications.     

A possible role for flowering locus T‐encoding genes in interpreting environmental and internal cues affecting olive (Olea europaea L.) flower induction

Olive (Olea europaea L.) inflorescences, formed in lateral buds, flower in spring. However, there is some debate regarding time of flower induction and inflorescence initiation. Olive juvenility and seasonality of flowering were altered by overexpressing genes encoding flowering locus T (FT). OeFT1 and OeFT2 caused early flowering under short days when expressed in Arabidopsis. Expression of OeFT1/2 in olive leaves and OeFT2 in buds increased in winter, while initiation of inflorescences occurred i n late winter. Trees exposed to an artificial warm winter expressed low levels of OeFT1/2 in leaves and did not flower. Olive flower induction thus seems to be mediated by an increase in FT levels in response to cold winters. Olive flowering is dependent on additional internal factors. It was severely reduced in trees that carried a heavy fruit load the previous season (harvested in November) and in trees without fruit to which cold temperatures were artificially applied in summer. Expression analysis suggested that these internal factors work either by reducing the increase in OeFT1/2 expression or through putative flowering repressors such as TFL1. With expected warmer winters, future consumption of olive oil, as part of a healthy Mediterranean diet, should benefit from better understanding these factors.     

Pollen movement to flowering canopies of pistillate individuals of three rain forest tree species in tropical Australia

This study measured the quantities of effective pollen vectors and their pollen loads arriving at the canopies of dioecious tropical rain forest trees in north-east Queensland. Population flowering synchrony, effective pollinator populations and pollen loads transferred between staminate and pistillate trees were compared among three insect-pollinated tree species. All three were visited by a wide range of insects, 75% of which (mostly 3–6 mm long) carried conspecific pollen. Fewer than 8% of individual insects were found to be carrying single-species pollen exclusively and none could be described as specialist pollen foragers. The introduced honeybee carried greater quantities of pollen than any native species but was not necessarily a reliable pollinator. The brief flowering periods in Neolitsea dealbata (3–4 weeks) and Litsea leefeana (4–5 weeks) populations were synchronized among individuals. Flowering in the Diospyros pentamera population extended over 15 weeks and most individuals were in flower for most of this period. Staminate trees began flowering earlier, produced more flowers and attracted relatively more insects than did pistillate trees, suggesting a density-dependent response of pollinators to flowering performance. Pollen was trapped in greater quantities on insects at staminate trees than at pistillate trees. Insect numbers increased at peak flowering periods and Diptera were the most abundant flower visitors. Anthophilous Coleoptera were more numerous at staminate than at pistillate trees in all three tree species populations. Larger quantities of pollen were mobilized during peak flowering times although the greatest quantities were transferred to pistillate canopies towards the end of the population flowering periods. Diptera carried pollen more often to pistillate N. dealbata and L. leefeana trees than did other groups whereas Coleoptera carried pollen more often to pistillate D. pentamera trees. The two contrasting flowering performances in the three tree species are discussed with reference to mechanisms that facilitate pollen transfer between staminate and pistillate trees.     

Sarcodontia pachyodon: a Canker and White‐rot Agent of Plane‐trees

Some lignivorous hymenomycete fungi are capable of causing both cankers and decay in stemwood of adult trees. Recently in Tuscany (Italy), Platanus x acerifolia trees were found colonized by Sarcodontia pachydon (Polyporales, Meruliaceae), a fungus associated with white rot and stem cankers on different host tree species. Because the relationship S. pachyodon‐plane‐tree was only preliminary studied, we decided to investigate whether isolates obtained from this host are distinct from those commonly collected from oaks. For this purpose, isolates obtained from plane‐tree and from holm oak (Quercus ilex) were compared by in vitro test and molecular markers. Results showed that fungal isolates did not differ in growth nor in wood degradation, also molecular tests revealed relative similarity among fungal samples.     

The Cold Awakening of <Emphasis Type="Italic">Doritaenopsis</Emphasis> ‘Tinny Tender’ Orchid Flowers: The Role of Leaves in Cold-induced Bud Dormancy Release

Massive flowering of tropical Phalaenopsis orchids is coordinated by the cold-induced release of reproductive bud dormancy. Light and temperature are the two key factors integrated by the dormancy mechanism to both stop and reactivate the meristem development of many other angiosperm species, including fruit trees and ornamental plants. It is well established that leaves and roots play a major role in inducing flower development; however, currently, knowledge of molecular events associated with reproductive bud dormancy release in organs other than the bud is limited. Using differential gene expression, we have shown that the leaves of a hybrid of Phalaenopsis species, Doritaenopsis ‘Tinny Tender’, undergo major metabolic modifications. These changes result in the production of sucrose and amino acids, both of which can sustain bud outgrowth, and auxin and ethylene, which may play important roles in awaking the dormant buds. Intake of abscisic acid and synthesis of the hormone jasmonate may also explain the inhibition of vegetative growth that coincides with bud growth. Interestingly, many genes that were upregulated by cold treatment are homologous for genes involved in flower induction and vernalization in Arabidopsis, indicating that processes regulating flowering induction and those regulating reproductive bud dormancy release may use similar pathways and effector molecules.     

武夷山不同龄级香果树开花物候及其生殖特性

该研究采用固定样地观测研究了不同龄级香果树的开花物候和生殖特性,分析了物候指数与生殖构件之间的相关性。结果表明：香果树单花花期一般为5~9 d,平均为6.79 d,随着树龄增大,其单花花期呈幂函数增长趋势;不同树龄香果树的始花期不同,但终花期基本一致;随着树龄的增大,始花期逐渐提前,花期持续时间延长。20~50 a树龄的香果树始花期约为8月9日,花期持续时间最短,仅为36 d。110~140 a树龄的香果树始花期约为7月15日,花期持续时间为61 d;对于单株母树来讲,香果树的花枝数,花朵总数以及果实总数随着树龄的增大均显著增加;单花枝产花量随着树龄的增加呈上升趋势,单花枝产果实数量呈先上升后下降的趋势;香果树花枝和单花枝产花量在树冠方位上的分布由大到小依次为南>东/西>北、上>中>下,但单花枝果实数量则表现出不同规律,即东>南>西>北、中>下>上。香果树具有花多果少现象,开花物候指数与生殖构件数量间的相关性分析表明,其花期持续时间与花枝数、花数和果实数均存在极显著正相关关系,始花期与生殖构件数量呈极显著负相关关系,而物候指数与香果树树龄亦存在显著相关关系。     

Species of street tree is important for southern hemisphere bird trophic guilds

Abstract Urban environments are highly modified with unique assemblages of bird species. Much of the research on urban bird assemblages comes from the northern hemisphere. Southern hemisphere bird assemblages differ from northern hemisphere assemblages in that they contain a large proportion of nectarivores. In this study we focus on bird use of street trees in Australia. We investigate the relative influence of tree species (plane tree, Platanus x acerifolia; red gums, Eucalyptus camaldulensis; jacaranda, Jacaranda mimosifolia; bottlebrush, Callistemon citrinus), season and the environment surrounding street trees, on the abundance and species richness of birds in Adelaide, South Australia. Our study considers birds in terms of granivore, nectarivore and insectivore trophic guilds. Nectarivores accounted for the greatest proportion of observations, in terms of abundance, in each of the tree species investigated. Species of street tree was a significant influence on bird use of the trees for all birds and each dietary guild. Red gums were used more than the other tree species by nectarivores, while plane trees were used more than the other trees by insectivores. Use of the tree species by granivores varied with the season. The measures of the environment surrounding street trees were largely unimportant with the exception of traffic for nectarivores in some cases. Urban avifauna use street trees and the species of tree will strongly influence its use by birds. However, the pattern of use of street tree species varied at different times of year and differed between different trophic guilds of birds. The dominance of nectarivores in the southern avifauna will likely produce different patterns of urban environment use to northern hemisphere avifaunas.     

Non‐continuous reproductive phenology of animal‐dispersed species in young forest restoration plantings

Tree species that produce resources for fauna are recommended for forest restoration plantings to attract pollinators and seed dispersers; however, information regarding the flowering and fruiting of these species during early growth stages is scarce. We evaluated the reproductive phenology of animal‐dispersed tree species widely used in Atlantic Forest restoration. We marked 16 animal‐dispersed tree species in 3‐ to 8‐year‐old forest restoration plantings in Itu‐São Paulo, southeast Brazil. We noted the age of the first reproductive event, flowering and fruiting seasonality, percentage of trees that reached reproductive stages, and intensity of bud, flower, and fruit production for each species. Flowering and fruiting are seasonal for most species; only two, Cecropia pachystachya and Ficus guaranitica, exhibited continuous flowering and fruiting throughout the year; we also identified Schinus terebinthifolia and Dendropanax cuneatus fruiting in the dry season during resource scarcity. Therefore, we recommend all as framework species, that is, species that are animal‐dispersed with early flowering and fruiting potential, for forest restoration. Further, we recommend identifying and planting similar animal‐dispersed tree species that produce fruits constantly or in the dry season to maximize fauna resource availability throughout the year in tropical forest restoration plantings. Abstract in Portuguese is available with online material     

Changes in Dormancy and Sensitivity to Vernalization in Axillary Buds of Satsuma Mandarin Examined in vitro During the Annual Cycle

Effect of season and the presence of fruit on bud-endodormancyand the flowering response to low temperature treatments weredetermined using bud cultures of Owari satsuma mandarin (Citrusunshiu Marc). Bud dormancy was deeper in fruiting as comparedto defruited trees. In fruiting trees, the intensity of buddormancy was highest in spring, decreased to a low value byearly Jul. and then increased until early winter. This increasein dormancy during summer and early autumn did not occur innon-fruiting trees. No flowers formed in buds cultured betweenMay and Sep. Both in fruiting and defruited trees, buds becamecompetent to show a vernalization response to chilling by theend of Oct., at the time they also became capable of sproutingin vitro at low temperature (15/10 °C). There was a directeffect of fruit on the buds which persisted long after fruitremoval and resulted in a reduction of the flowering responseto chilling.Copyright 1995, 1999 Academic Press Citrus flowering, Citrus unshiu Marc., dormancy, flower induction, flowering, in vitro flowering, satsuma mandarin, vernalization     

Flowering pathway is regulated by bulb size in Lilium longiflorum (Easter lily)

Lilium longiflorum (Easter lily) vegetative propagation occurs through production of underground bulbs containing apical and axillary meristems. In addition, sexual reproduction is achieved by flowering of elongated shoots above the bulb. It is generally accepted that L. longiflorum has an obligatory requirement for vernalisation and that long day (LD) regime hastens flowering. However, the effect of bulb size and origin, with respect to axillary or apical meristems on flowering, as well as the interactions between these meristems are largely unknown. The aim of this study was to explore the effect of bulb size, vernalisation and photoperiod on L. longiflorum flowering. To this end, we applied vernalisation and photoperiod treatments to the different bulb sizes and used a system of constant ambient temperature of 25 °C, above vernalisation spectrum, to avoid cold‐dependent floral induction during plant growth. Vernalisation and LD hasten flowering in all bulbs. Large, non‐vernalised bulbs invariably remained at a vegetative stage. However, small non‐vernalised bulbs flowered under LD conditions. These results demonstrate for the first time that cold exposure is not an obligatory prerequisite for L. longiflorum flowering, and that an alternative flowering pathway can bypass vernalisation in small bulbs. We suggest that apical dominance interactions determine the distinct flowering pathways of the apical and axillary meristems. Similar floral induction is achieved in propagated bulblets from scaling. These innovative findings in the field of geophyte floral induction represent valuable applicative knowledge for lily production.