Defining the limits of flowers: the challenge of distinguishing between the evolutionary products of simple versus compound strobili

Recent phylogenetic reconstructions suggest that axially condensed flower-like structures evolved iteratively in seed plants from either simple or compound strobili. The simple-strobilus model of flower evolution, widely applied to the angiosperm flower, interprets the inflorescence as a compound strobilus. The conifer cone and the gnetalean ‘flower’ are commonly interpreted as having evolved from a compound strobilus by extreme condensation and (at least in the case of male conifer cones) elimination of some structures present in the presumed ancestral compound strobilus. These two hypotheses have profoundly different implications for reconstructing the evolution of developmental genetic mechanisms in seed plants. If different flower-like structures evolved independently, there should intuitively be little commonality of patterning genes. However, reproductive units of some early-divergent angiosperms, including the extant genus Trithuria (Hydatellaceae) and the extinct genus Archaefructus (Archaefructaceae), apparently combine features considered typical of flowers and inflorescences. We re-evaluate several disparate strands of comparative data to explore whether flower-like structures could have arisen by co-option of flower-expressed patterning genes into independently evolved condensed inflorescences, or vice versa. We discuss the evolution of the inflorescence in both gymnosperms and angiosperms, emphasising the roles of heterotopy in dictating gender expression and heterochrony in permitting internodal compression.     

The influence of deer browsing on the reproductive biology of Canada yew (Taxus canadensis marsh.)

Summary Canada yew (Taxus canadensis) populations currently browsed by white-tailed deer (Odocoileus virginianus) or browsed by deer in the past had significantly lower production of male strobili, female strobili, and seeds than unbrowsed yew populations. Exclosure studies showed that protected yews produced significantly more male and female strobili than unprotected yews, but only after several years of protection. Seed production did not respond as readily to protection from deer perhaps because of reduced pollination levels in browsed yew populations. Previously unbrowsed yews were clipped at different levels of removal of available browse (control (no removal), 25%, 50%, 75%, and 100% removal) to simulate deer browsing. Reduction in male strobilus production was linearly related to clipping intensity in three years of observation. Female strobilus production was significantly reduced only at the 100% level of removal. Intermediate levels of clipping may have even stimulated production of female strobili. Analysis of covariance, with previous year's branch production as the covariate, showed no significant effect of clipping on male strobilus production except in the 100% removal group. Female strobilus production showed no such covariance with branch production. Effects of clipping on seed production could not be reliably assessed in 1984 and 1985 due to low seed production. Seed production in 1986 was significantly reduced only in the 100% removal group. Field observations of deer browsing of Canada yew indicate that 100% levels of removal are typical of natural levels of browsing.     

Biochemical Systematics of Gymnosperms (3)—On the Systematic Position of Tax aceae from Their Seed Protein Peptides and Needle Peroxidases

The major peptides in the seed of Taxus and Pseudotaxus have molecular weight about 31, 22 and 20 kilodaltons (Kd) shown by SDS polyacrylamide gel electrophoresis. The seed protein peptides of Cephalotaxus is very similar to those of Taxus and Pseudotaxus except a few bands of high molecular weight. Some considerable differences in peptide pattern exist between Amentotaxus and the three genera cited above. The former has a new major peptide, 33K, but lacks 22 K. The seed of Torreya does not contain peptide 44 K, although Torreya and Amentotaxus have many bands in common. To a certain extent, the seed protein peptides of Podocarpus nagi are similar to those of the above taxa. A great range of divergency in needle peroxidases among different genera of Taxaceae has been observed by using electrophoresis, while the zymogram of Cephalotaxus is somewhat similar to that of Taxus. Two series of protein data demonstrate, that there is an evolutionary tendency from Taxus to Torreya through Pseudotaxus and Amentotaxus within Taxaceae. And the Taxaceae is closely related to Cephalotaxus by way of Taxus. The systematic positionof the Taxaceae, therefore, should be placed under the Coniferales.     

Pollen productivity variations. Pollen-ovule ratio and sexual selection in Pinus roxburghii

Total pollen production, pollen-ovule ratio and the production of male-female strobili were recorded in Pinus roxburghii at two different altitudes during two successive years. The values of total pollen production per tree and per hectare varied between 1953.56 to 2727.16 2 10 9 and 2.91 to 4.26 2 10 14 (in 1999) at the lower altitude and 1247.5 to 1673.5 2 10 9 and 2.24 2 10 14 (in 1998) and 1599.89 to 2038.96 2 10 9 and 3.18 2 10 14 (in 1999) at the higher altitude. The pollen-ovule ratio in P. roxburghii has indicated the xenogamous type of breeding system The production of male and female cones per tree and per hectare ranged from 21.7 - 0.34 to 33.6 - 0.71 2 10 3 and 55.16 - 24.08 to 220.85 - 87.75 per tree and 32.55 to 70.56 2 10 5 and 2.76 to 26.50 2 10 3 per hectare respectively. However the production of female cones per 100 male cones oscillated between 0.25 to 0.66, which suggested the intense male competition among trees to pollinate their neighbours. A linear correlation was recorded between diameter and extent of the tree crown to the total production of strobili groups/strobili clusters, strobili, microsporophylls and pollen grains per individual tree. The ratio between the number of strobili per strobili group and the number of strobili groups per tree showed an inverse relationship; thus, the individuals with most strobili groups have the strobili groups with the least strobili and vice-versa. This ratio was also shown between the number of pollen grains per strobilus and the number of strobili per tree, as well as the number of pollen grains per strobili group and the number of strobili groups per tree.     

几种药用植物内生真菌抗真菌活性的初步研究

从三尖杉,南方红豆杉及香榧中分离出172株内生真菌,对其进行抗菌活性检测,结果表明共90株内生真菌对一种或多种植物病原真菌,如红色面孢霉（Neurospora sp.）,木霉(Trichoderma sp.）,镰刀菌（Fusarium sp.）等有抑制作用,来自三尖杉、南方红豆杉和香榧的抗菌活性菌株比例分别为40％,54.2%及57.1%。其中平板抑菌圈直径大于15mm的高抗菌株有35株。按Ainsworth等鉴定系统和方法进行鉴定,具有抗菌活性的内生真菌主要分布于心青霉属、镰孢菌属等18个属中。     

植物内生真菌抗肿瘤活性菌株的筛选*

从三尖杉、南方红豆杉及香榧中分离到172株植物内生真菌,利用抗肿瘤体外细胞毒筛选模型(MTT法)对其进行活性检测。结果表明,25株内生真菌(占总分离菌株的14.5%)对KB（人口腔上皮癌）或HL-60（人白血病）细胞具有显著的抑制活性。三尖杉、南方红豆杉及香榧内生真菌的抗肿瘤活性菌株占各供测菌株的3.3%, 19.6%和8.6%。其中7个菌株的细胞毒ID50为1,000以上,占总供测菌株的4.1%。抗肿瘤活性菌株主要分布在拟青霉属及头孢霉属中。     

Changes in growth conditions alter the male strobilus gene expression pattern in<Emphasis Type="Italic"> Cryptomeria japonica</Emphasis>

Two-year old saplings grown from cuttings of Cryptomeria japonica D. Don initiate strobilus development following treatment with gibberellic acid under long-day photoperiods. At 25 °C with a 14-h photoperiod in a phytotron, male strobili initiated normally; however, they remained green and fell from the saplings prematurely. To examine the change in male strobilus development at the molecular level, three genes expressed specifically in male strobili were analyzed. Two were MADS box genes homologous to the B-function genes in angiosperms, CjMADS1 and CjMADS2, and the third was Cry j I, which encodes an allergen protein, and this gene is expressed mainly in microspores. Under phytotron growing conditions, the homeotic genes were expressed constantly, which reflected the extended early developmental stage of male strobili. On the other hand, Cry j I expression was detected after a long delay just before strobilus development ceased. These results indicate that the expression of the genes related to male reproductive development in C. japonica is regulated by a factor(s) that is sensitive to environmental signals.Abbreviation GA₃ gibberellic acid     

Identification of QTLs associated with male strobilus abundance in Cryptomeria japonica

It has become increasingly important to understand the factors controlling the abundance of male strobili in Cryptomeria japonica since allergic reactions to the species?? pollen have become prevalent in Japan. There is considerable inter-annual variation in the abundance of male strobili, so it is important to investigate and validate quantitative trait loci (QTL) for strobili abundance across different years. Data on third generation families derived from an individual that produces abundant male strobili were studied using Kruskal?CWallis tests and Bayesian regression analysis, resulting in the detection of a single major QTL that was observed over multiple years. This QTL explained between 10.4 and 26.5?% of the phenotypic variation in male strobilus abundance. The consistency and significance of this QTL??s effects suggest that it has a major role in male strobilus production in C. japonica, although we also detected other QTLs, indicating that strobilus production is subject to complex and multifactorial regulation. These QTL may also affect precocity because we were unable to separate their effects from the genetic variability in male strobilus production. The major QTL that we detected occurs in a region homologous to a QTL detected in a previous study examining trees with a different genetic heritage following artificial induction of male strobilus production. This result further supports the importance of the QTL detected in the present study. Identifying the important genes in this QTL will therefore significantly increase our understanding of the genetic mechanisms of pollen production in C. japonica.     

Paratingia wudensis sp. nov., a whole noeggerathialean plant preserved in an earliest Permian air fall tuff in Inner Mongolia, China

Noeggerathiales are a little known group of Carboniferous and Permian plants of uncertain systematic position that have been variously considered to be ferns, sphenopsids, progymnosperms, or a separate group. These heterosporous plants carry adaxial sporangia on leaf-like or disk-shaped sporophylls that form cones. Leaves are pinnate with a rather stiff appearance, and pinnules can be attached in either two or four rows. In the present report, we present the top of a noeggerathialean plant with leaves and strobili attached, Paratingia wudensis Wang, Pfefferkorn et Bek sp. nov., from an earliest Permian volcanic ash fall tuff in Inner Mongolia. The excellent preservation allows the reconstruction of the whole plant, the complex three-dimensional leaves with anisophyllous pinnules, the heterosporous strobili, and the spores in situ. The homology of leaves and strobili can be elucidated and contributes to an understanding of the debated taxonomic position of Noeggerathiales. The "anisophyllous" leaves carry pinnules arranged in four rows. The strobili are bisporangiate and have disk-shaped sporophylls, each with one ring of 10-14 adaxial sporangia around the strobilus axis. Megaspores have an equatorial bulge. This new species expands the known diversity of Noeggerathiales. It grew in a peat-forming forest, thus changing earlier interpretations of the growth of noeggerathialean plants with anisophyllous pinnules.     

Morphological and ontogenetic studies on southern African podocarps. Shoot apex morphology and ovuliferous cone initiation

STOFFBERG, E., 1991. Morphological and ontogenetic studies on southern African podocarps. Shoot apex morphology and ovuliferous cone initiation. Four species of Podocarpus indigenous to southern Africa were investigated. The morphology of the primordium of the female cone is compared with that of the shoot apex. Rhythmic growth occurs in Podocarpus. The external morphology of bud scales protecting dormant shoot apices is described and illustrated. Female strobili of the three species of section Podocarpus studied are initiated in the axils of euphylls during the spring growth flush as laterally flattened triangular structures. The axillary position of a female cone indicates that it is a modified shoot. The first two cone bracts (prophylls) are formed approximately at right angles to the subtending bract (one or both are fertile), while the 3rd and 4th bracts originate on the anterior and posterior sides of the strobilus respectively. Two to four bracts per cone are formed, not in pairs–the phyllotaxis is spiral. In P.falcatus primordia of female strobili and vegetative branches could be distinguished only after emergence of the seed scale complex. Based on cell differentiation, well-defined cytological zones can be distinguished in the shoot apex and it is classified as being of the Abies-Cryptomeria-lype. Meristematic zones of cone primordia and vegetative branches are basically similar, although the former are less well defined. No gradual transition from a vegetative to a reproductive apex could be identified and it would seem that the fate of axillary buds are determined at the time of their origination or even before.     

Phyllotaxis, phenology and architecture in Cephalotaxus, Torreya and c(Coniferales)

In Amentotaxus, Cephalotaxus and Torreya there is a regular seasonal alternation of foliage leaves and bud-scales, with foliage leaves largely preformed, i.e. initiated in the season before they expand. On most plagiotropic shoots phyllotaxis in the production of foliage leaves may be either bijugate ( Cephulotaxus, Torreya ) or decussate ( Amentotaxus ). In bijugate phyllotaxis successive leaf pairs originate at an angle of about 68° to each other, i.e. approximately one-half of the 'ideal' or Fibonacci angle of 137.5°. Secondary leaf orientation in Cephulotaxus and Torreya , by twisting of the leaf base, produces the dorsiventrality of plagiotropic shoots, whereas in Amentotaxus secondary orientation involves a twisting of the stemc as well as the leaf base. In Cephalotaxus cc condition is constant in the production of the numerous but imprecise number of bud-scales and in the production of foliage leaves. However, in Torreya the phyllotaxis changes from bijugate in the production of foliage leaves to decussate in the production of bud-scales, which are constant in number (about eight pairs). This allows a precise analysis of the biphasic production of leaf primordia in the seasonal cycle. The phyllotactic change in Torreya may not be the result of reported changes in shoot apex dimensions since Cephalotaxus , with its constant phyllotaxis, has a comparable seasonal change in apex dimensions. Information on architecture, chirality and cone morphology is also included.     

Ancestral MADS box genes in Sugi, Cryptomeria japonica D. Don (Taxodiaceae), homologous to the B function genes in angiosperms.

In flowering plants, flower organ identity is controlled by the ABC genes, including several MADS box genes. We present two MADS box genes of a conifer, Cryptomeria japonica D. Don. The genes, CjMADS1 and CjMADS2, were related to the angiosperm B function genes which determine the identities of petals and stamens. A phylogenetic analysis showed that these genes form a new clade outside the angiosperm B group, that is, PISTILLATA (PI) and APETALA3 (AP3) lineages. CjMADS1 had a PI-group specific motif and CjMADS2 had AP3-group specific motifs at the C terminal end, respectively. CjMADS1 was expressed in male strobili (or cones) throughout its development, while CjMADS2 was transiently expressed during male strobilus development. The specific expression in the male reproductive organ indicated that the B function is maintained in gymnosperms. Our cladistic analysis suggests that the gene duplication event which generated B function gene lineages predates the divergence of angiosperms and gymnosperms and that the gene duplication which produced the two genes of C. japonica occurred in an ancestral conifer species.     

部分裸子植物假种皮微形态特征及其分类学意义

应用扫描电镜对红豆杉科、三尖杉科和罗汉松科植物假种皮的微形态特征进行了研究,结果表明：可以把红豆杉科植物分为两类,即具规则型网状纹饰的红豆杉属和具无规则型网状纹饰的白豆杉属、穗花杉属和榧树属。在后三属中,穗花杉属的穗花杉和白豆杉属的纹饰特征更为相近,同属厚网脊亚型。而云南穗花杉和榧树属的特征相近,属薄网脊亚型。假种皮表面纹饰特征显示不宜将红豆杉（T．chinensis）再分为两个独立的种,认为设立红豆杉和变种南方红豆杉（T．chinensisvar.mairei）的处理方式更加合理。三尖杉科（属）蓖子三尖杉（C．oliveri）假种皮纹饰的网脊、网底分化程度、细胞大小、单位面积细胞数和本届的其它植物差异很大,为建立蓖子三尖杉组提供了进一步的佐证。假种皮的微形态特征还支持把宽叶粗榧（C.sinensisvar.latifolia）上升为种C．latifolia的观点。罗汉松科假种皮纹饰类型的观察结果表明罗汉松属和陆均松属是自然分类群。尽管罗汉松属竹相组假种皮纹饰的网脊变异范围相对较大,但是变异范围仍在属内,不支持将其独立为新科的观点。假种皮的表面纹饰特征还表明三尖杉科和红豆杉科之间的联系密切。     

Morphogenesis of the reproductive shoots of Welwitschia mirabilis and Ephedra distachya (Gnetales), and its evolutionary implications

For decades, Gnetales appeared to be closely related to angiosperms, the two groups together forming the anthophyte clade. At present, molecular studies negate such a relationship and give strong support for a systematic position of Gnetales within or near conifers. However, previous interpretations of the male sporangiophores of Gnetales as pinnate with terminal synangia conflict with a close relationship between Gnetales and conifers. Therefore, we investigated the morphogenesis of the male reproductive structures of Welwitschia mirabilis and Ephedra distachya by SEM and light microscopy. The occurrence of reduced apices to both halves of the antherophores of W. mirabilis gives strong support for the assumption that the male ‘flowers’ of W. mirabilis represent reduced compound cones. We assume that each half of the antherophore represents a lateral male cone that has lost its subtending bract. Although both halves of the antherophores of Ephedra distachya lack apical meristems, the histological pattern of the developing antherophores supports interpreting them as reduced lateral male cones as well. Therefore, the male sporangiophores of Gnetales represent simple organs with terminal synangia. Although extant conifers do not exhibit terminal synangia, similar sporangiophores are reported for some Cordaitales, the hypothetical sister group of conifers. Moreover, several Paleozoic conifers exhibit male cones with terminal sporangia or synangia. Therefore, we propose that conifers, Cordaitales and Gnetales originated from a common ancestor that displayed simple sporangiophores with a terminal cluster of sporangia.     

云南铁杉开花结实特性及其与环境因子的关系

以进入生殖阶段的8个天然云南铁杉(Tsuga dumosa)种群为对象, 对开花、结实植株(24个样株)的生长量进行测定, 并采用标准枝法对不同树冠层次与方位的开花及结实数量进行调查, 研究了开花结实规律和对其有主要影响的环境因子。结果表明: 云南铁杉雌、雄球花比为1:2, 雌球花转化为果实的数量仅占28%, 胸径为7 cm (树龄约25年)的植株最早进入开花结实阶段, 胸径为25-30 cm的植株开花结实量最高, 胸径为89 cm (树龄约200年)的植株开花结实最晚; 树冠不同层次与方位上开花结实数量有着明显的差异; 相关性分析得出植株胸径与开花结实量极显著相关(p < 0.01)、与冠幅显著相关, 生境中林分郁闭度与开花结实量、株高、胸径之间均呈负相关关系, 其中与结实量的相关性达显著水平; 主成分分析得出植株开花及结实主要受到温度因子、水分因子、光照因子协同作用的影响。云南铁杉雌雄球花的比例偏雄性、结实周期长、结实方式不经济、灾害性天气的影响是造成该种群逐渐走向濒危的主要原因。因此, 采用人工促进天然更新、建立母树林和种子园以提高种子的质量, 对云南铁杉种群的恢复和保护具有重要意义。     

Avian Cone Photoreceptors Tile the Retina as Five Independent,Self-Organizing Mosaics

The avian retina possesses one of the most sophisticated cone photoreceptor systems among vertebrates. Birds have five types of cones including four single cones, which support tetrachromatic color vision and a double cone, which is thought to mediate achromatic motion perception. Despite this richness, very little is known about the spatial organization of avian cones and its adaptive significance. Here we show that the five cone types of the chicken independently tile the retina as highly ordered mosaics with a characteristic spacing between cones of the same type. Measures of topological order indicate that double cones are more highly ordered than single cones, possibly reflecting their posited role in motion detection. Although cones show spacing interactions that are cell type-specific, all cone types use the same density-dependent yardstick to measure intercone distance. We propose a simple developmental model that can account for these observations. We also show that a single parameter, the global regularity index, defines the regularity of all five cone mosaics. Lastly, we demonstrate similar cone distributions in three additional avian species, suggesting that these patterning principles are universal among birds. Since regular photoreceptor spacing is critical for uniform sampling of visual space, the cone mosaics of the avian retina represent an elegant example of the emergence of adaptive global patterning secondary to simple local interactions between individual photoreceptors. Our results indicate that the evolutionary pressures that gave rise to the avian retina''s various adaptations for enhanced color discrimination also acted to fine-tune its spatial sampling of color and luminance.     

A DEF/GLO-like MADS-box gene from a gymnosperm: Pinus radiata contains an ortholog of angiosperm B class floral homeotic genes.

The specification of floral organ identity during development depends on the function of a limited number of homeotic genes grouped into three classes: A, B, and C. Pairs of paralogous B class genes, such as DEF and GLO in Antirrhinum, and AP3 and PI in Arabidopsis, are required for establishing petal and stamen identity. To gain a better understanding of the evolutionary origin of petals and stamens, we have looked for orthologs of B class genes in conifers. Here we report cDNA cloning of PrDGL (Pinus radiata DEF/GLO-like gene) from radiata pine. We provide phylogenetic evidence that PrDGL is closely related to both DEF- and GLO-like genes of angiosperms, and is thus among the first putative orthologs of floral homeotic B function genes ever reported from a gymnosperm. Expression of PrDGL is restricted to the pollen strobili (male cones) and was not detected in female cones. PrDGL expression was first detected in emergent male cone primordia and persisted through the early stages of pollen cone bud differentiation. Based on the results of our phylogeny reconstructions and expression studies, we suggest that PrDGL could play a role in distinguishing between male (where expression is on) and female reproductive structures (where expression is off) in radiata pine. We speculate that this could be the general function of DEF/GLO-like genes in gymnosperms that may have been recruited for the distinction between stamens and carpels, the male and female reproductive organs of flowering plants, during the evolution of angiosperms out of gymnosperm-like ancestors.     

Within-crown distribution of male and female cones on clonal Sitka spruce trees

The within-crown distribution of cones (strobili) was mapped on 48 mature grafts of Sitka spruce [Picea schensis (Bong.) Carr.]. The total number of cones per tree was increased by a mainstem injection of 20 mg GA_4/7 and 8 mm wide bark ring. The cones and buds were classified as either lateral or terminal on each individual branch. The distribution of lateral female, terminal female, lateral male and terminal male cones, showed a general progression from the upper distal to lower proximal regions of the tree crown in all 12 clones. Evidence for preferential allocation of cones to particular branch types is presented. The region of the tree with the greates number of cones varied with treatment and reflected differences in the sex ratio of the individual trees. There is evidence for a relationship between branch length, position within the crown and the type of cone produced.     

Characterization of the expression patterns of LEAFY/FLORICAULA and NEEDLY orthologs in female and male cones of the conifer genera Picea, Podocarpus, and Taxus: implications for current evo-devo hypotheses for gymnosperms

The identity of genes causally implicated in the development and evolutionary origin of reproductive characters in gymnosperms is largely unknown. Working within the framework of plant evolutionary developmental biology, here we have cloned, sequenced, performed phylogenetic analyses upon and tested the expression patterns of LEAFY/FLORICAULA and NEEDLY orthologs in reproductive structures from selected species of the conifer genera Picea, Podocarpus, and Taxus. Contrary to expectations based on previous assessments, expression of LFY/FLO and NLY in cones of these taxa was found to occur simultaneously in a single reproductive axis, initially overlapping but later in mutually exclusive primordia and/or groups of developing cells in both female and male structures. These observations directly affect the status of the "mostly male theory" for the origin of the angiosperm flower. On the other hand, comparative spatiotemporal patterns of the expression of these genes suggest a complex genetic regulatory network of cone development, as well as a scheme of functional divergence for LFY/FLO with respect to NLY homologs in gymnosperms, both with clear heterochronic aspects. Results presented in this study contribute to the understanding of the molecular-genetic basis of morphological evolution in conifer cones, and may aid in establishing a foundation for gymnosperm-specific, testable evo-devo hypotheses.     

The influence of deer browsing on the reproductive biology of Canada yew (Taxus canadensis marsh.)

Summary Browsed Canada yew (Taxus canadensis) populations have a higher proportion of males and a lower proportion of monoecious plants than unbrowsed yew populations. The proportion of monoecious plants increases with time following protection from browsing suggesting that deer browsing causes male-biased sex expression in Canada yew. In contrast, results from comparing browsed and unbrowsed populations, exclosure studies, and browse simulation experiments indicate that strobilus ratios and phenotypic gender of browsed yews may be female-biased. In part, these results correspond to the influence of size on sex expression in Canada yew; small yews tend to be male, but if monoecious, have female-biased strobilus ratios. Large yews are monoecious, but have male-biased strobilus ratios. There is, however, no consistent relationship between size and gender in Canada yew, suggesting that in some circumstances, yews shift allocation to female function in response to browsing.