Developmental studies in orchid flowers IV: Cypripedioid species

The floral development of four species of Cypripediaceae (sensu Rasmussen 1985) was studied by means of scanning electron microscopy, with special attention to the early development of the organs that constitute the gynostemium. At the ventral base of the gynostemium a prominent structure was observed. It is most probably a vestige of the median adaxial stamen a₃ based on its early initiation and place of origin. In Cypripedium calceolus the median carpel primordium is, according to expectation, initiated slightly earlier than the lateral carpel primordia, and later develops into the largest stigma lobe. Interestingly, Cypripedium irapeanurn shows an opposite sequence in the initial phase of the carpel development in that the primordia of the lateral carpels are initiated before the primordium of the median carpel.     

Developmental studies in orchid flowers II: Orchidoid species

The floral development of 11 species of Orchidoideae (sensu Rasmussen 1985) was studied by means of SEM, paying special attention to the early development of the gynostemium and its appendages. In contrast to the staminodes found in epidendroid and vandoid orchids, the 'auricles' of the tribe Orchideae are developed on the dorsal side of the fertile anther and therefore are not interpreted as staminodes. Presumed vestiges of the staminodes corresponding to those of the Epidendroideae and Vandoideae are differentiated in early developmental stages, but remain inconspicuous structures later on. The three-lobed rostellum originates entirely from the median carpel. The outstanding systematic position of the tribe Orchideae is briefly discussed.     

Developmental studies in orchid flowers I: Epidendroid and vandoid species

The floral development of 47 epidendroid and vandoid orchids was studied by means of scanning electron microscopy, paying special attention to the early development of the gynostemium (column) and its appendages. The following main conclusions are drawn: the lateral appendages of the adult gynostemium are homologous with the two lateral stamens of the inner whorl; their primordia are present even in species which lack prominent appendages in the adult gynostemium (incorporation of the sta-minodial primordia into the gynostemium during development). Ventral appendages observed in some species are supposed to be vestiges of the adaxial stamens on account of their early initiation. It is confirmed that the rostellum is the upper part of the median stigma lobe and that the lip corresponds to the inner median tepal. The affinities of the epidendroid and vandoid orchids are briefly discussed.     

Floral morphology and ontogeny in Orchidaceae subtribe Disinae

Floral morphology and ontogeny in Orchidaceae subtribe Disinae. The flower structure and development of 24 species of the orchid subtribe Disinae are described and illustrated by drawings and scanning electron micrographs with special attention being paid to the gynostemium. The morphogenesis of this subtribe is fundamentally similar to that of the closely related tribe Orchideae. This includes the initiation of the auricles on the anther base in a dorsolateral position, and hence their interpretation as being mere appendages of the filament. The keel connecting the petals and the gynostemium plus its protrusion is considered homologous to the inner lateral staminodeS. Presumed vestiges of the adaxial staminodes were detected in one specieS. A peculiarity of the Disinae is that the entire apex of the median carpel develops into the rostellum, whereas its stigmatic portion emerges from the median carpel below the rostellum in later stages. The main diagnostic feature of the group is the reflexed position of the mature anther. However, it is shown here that this anther movement occurs in the later stages and that the initial anther is erect.     

Floral morphology of southern African Orchideae. II. Habenariinae

The floral morphology of the southern African genera of Orchideae-Habenariinae (Bonatea, Cynorkis, Habenaria, Platycoryne, Stenoglottis, Centrostigma and Roe-perocharis) is surveyed paying special attention to the gynostemium. Ontogenetic data are provided for the species from which adequate material was available. It is shown that the floral architecture is essentially an elaboration and complication of that found in the better known Orchidinae. The structural similarities are particularly evident in the early ontogeny. Although the tribe Orchideae is commonly said to have gynostemia with erect anthers, a few Habenariinae are reported here to have reflexed anthers. In most cases both 'auricles' (filament excrescences) and 'basal bulges' (staminodes) are united to form the lateral gynostemium appendages. The primordia of both structures are clearly recognizable in the early ontogeny in all species studied. In Habenaria dregeana the basal bulges are only basally fused to the auricles, but in their main portion become adnate to the lip and petal bases: the auricles then solely form the lateral gynostemium appendages. It is suspected that this occurs also in other species not studied here. Systematic and phylogenetic aspects of the southern African representatives of the Habenariinae are discussed: the generic separation of Bonatea, Platycoryne and Centrostigma from Habenaria does not appear justified. Cynorkis, Roeperocharis and Stenoglottis are morphologically dissimilar to Habenaria. Based on the findings in the southern African taxa the status of the Habenariinae, Orchidinae, Orchideae and Diseae is discussed: there is no clear distinction between Habenariinae and Orchidinae; while the Diseae seem to represent a monophyletic group, the Orchideae are possibly polyphyletic.     

寒兰花器官发生及花发育过程的研究

为了揭示寒兰的成花机理,利用石蜡切片和花芽实体解剖记录了濒危植物寒兰花芽分化和发育的过程,并着重观察唇瓣和合蕊柱早期及中期的发育(在合蕊柱伸长之前)。结果表明:寒兰花芽分化沿着花序轴从下往上可分为4个阶段:花序原基分化,花原基分化,花被片分化和合蕊柱形成。唇瓣分化分为3个阶段:褶片分化,侧裂片分化和色块形成。唇瓣侧裂片和褶片产生较晚,与退化雄蕊可能没有关系。在合蕊柱形成过程中,首先分化出花药,随后分化产生中心皮顶部,侧心皮顶部,并形成花柱道,最终分化出蕊喙和黏盘。     

Floral morphology of southern African Orchideae. I. Orchidinae

The floral morphology of the southern African genera of Orchidaceae-Orchideae-Orchidinae ( Brachycorythis, Schwartzkopffia, Neobolusia, Schizochilus, Holothrix and Bartholina ) is surveyed paying special attention to the gynostemium. Ontogenetic data are provided for a number of species that appear to be essential in formulating a proper interpretation of the gynostemium. The floral architecture is shown to be basically similar to that of the (much better known) European representatives of the subtribe. This, however, does not fully apply to the homology of the lateral gynostemium appendages ("auricles"): In Brachycorythis, Neobolusia and Schizochilus these develop like in Orchis and Dactylorhiza. Their prominent sculptured portions originate from dorsal stamen outgrowths and correspond to filament excrescences. Structures obviously homologous to lateral inner stamens can be recognized in the early ontogeny, but are in the mature flower incorporated in the 'arch' connecting the lip with the gynostemium. In contrast, in Holothrix and Bartholina the gynostemium appendages correspond entirely to staminodes, while the filament excrescences are missing. It is also shown that the 'concave' stigma said to be characteristic of the Orchidinae is in fact ± convex or even pad-like, but is generally positioned in a cavity under the rostellum. The 'erect' anther (the main diagnostic feature of the Orchideae) is reflexed up to 45° in some taxa. Affinities of the genera are briefly discussed. The generic separation of Schwartzkopffia and Neobolusia from Brachycorythis does not appear justified. Neobolusia virginea is obviously misplaced in the respective genus, and eventually merits generic status. The affinities of Schizochilus remain ± obscure at the moment. Bartholina appears to be merely a small group of specialized Holothrix species.     

The gynostemium of Hemipiliopsis purpureopunctata and Senghasiella glaucifolia, two taxonomically disputed species of Habenariinae (Orchidaceae)

The gynostemium structure and ontogeny of two taxonomically disputed orchids, Hemipiliopsis (= Habenaria ) purpureopunctata and Senghasiella (= Habenaria ) glaucifolia , are described and illustrated by scanning electron micrographs. The early gynostemium ontogeny of Hemipiliopsis purpureopunctata is shown to be fundamentally similar to that of the species of the tribe Orchideae that have been previously studied. This includes the initiation sequence of sepals, petals and lip, form and orientation of anthers, three-lobed condition of median carpel apex, and presence of auricles and basal bulges. During the later developmental stages some differences occur. The stigma processes of Senghasiella glaucifolia are united into a tongue-shaped organ, and the lateral rostellum lobes of Hemipiliopsis purpureopunctata protrude forwards with their viscidia positioned above the spur-mouth. Based on gynostemium characters, the generic rank of Hemipiliopsis was confirmed, but that of Senghasiella was not supported.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 147 , 191–196.     

Flower development and anatomy of Clusia valerioi,a Central American species of Clusiaceae offering floral resin

The present paper is part of a study dealing with various aspects of reproduction of two Costa Rican Clusia species offering resin as a floral reward. It provides data on the floral development and flower (especially stamen and staminode) anatomy of one of the species, Clusia valerioi. In the early stages, both male and female flowers develop in the same manner. The bracts are distinguished by a decussate arrangement from the five sepals and five petals, which emerge in a spiral manner. In the male flowers the apical meristem forms five meristematic mounds (common stamen primordia) that are pentagonally arranged around the apical meristem in epipetalous position. From these mounds, the primordia of the proper stamina emerge in 3–5 whorls. Direction is centrifugal. In the centre, five hemispherical bulges arise which develop into carpel primordia. These, however, cease growth, stay rudimentary and are hidden by the stamens in the mature male flower. The adult stamens consist mainly of a thick angular filament column, while the two anthers situated at the flattened top are very small. One anther is annular and surrounds a second, hemispherical one right in the centre. At the periphery, these two pollen sacs (provided with a distinct wall of customary anatomy) are surrounded by a ring-like protuberance of the filament. The resin canals are situated at the periphery of the filament. Their schizogenous development is documented in cross sections. At anthesis, the resin is released from the ring-like filament protuberance by burst of the single-layered epidermis. In the female flower, the five meristematic mounds produce two whorls of staminode primordia. The development of the staminodes does not essentially differ from that of the fertile stamens, but some staminodes lack the central pollen sac and the other tissues do not develop into pollen grains. An attempt is made to derive the peculiar stamen morphology of Clusia valerioi and similar species from conventional stamens. Three hypotheses are proposed and discussed.     

Floral organogenesis of Potamogeton distinctus A. Benn. (Potamogetonaceae)

The floral organogenesis of Potamogeton distinctus A. Benn. was observed under the scanning electron microscope (SEM). The floral buds are first initiated on the lower portion of inflorescence in alternating whorls of three. Each of the floral buds is subtended by a bract primordium during the early stages. The primordia of the floral appendages arise on the floral bud acropetally. Two lateral tepals are first initiated and then two median ones soon after. Stamens are normally initiated as elongate primordia opposite the tepals, with the two lateral stamens preceding the median ones. The two carpel primordia arise alternating with the stamens. In some flowers, one of the two gynoecial primordia becomes inactive soon after they are initiated, or only one carpel primordium is initiated. The present observation of the gynoecial development supports the viewpoint that the evolution of flower in Potamogeton involves a reduction in number of parts. The existence of bract primordium during the early stages in many species of Potamogeton indicates that the absence of bractin mature flowers should be the result of reduction.     

LRP1, a gene expressed in lateral and adventitious root primordia of arabidopsis.

We describe a gene that is expressed in lateral and adventitious root primordia of Arabidopsis. The gene was identified by expression of a transposon-borne promoterless beta-glucuronidase gene in lateral root primordia. The gene, designated LRP1 for lateral root primordium 1, and its corresponding cDNA were cloned and sequenced. The expression pattern of the gene in lateral root primordia was confirmed by in situ hybridization with LRP1 cDNA probes. The LRP1 gene encodes a novel protein. LRP1 expression is activated during the early stages of root primordium development and is turned off prior to the emergence of lateral roots from the parent root. Insertion of the transposon in the LRP1 gene disrupted its expression. To evaluate the homozygous insertion line for a mutant phenotype, several aspects of wild-type lateral root development were analyzed. A mutant phenotype has not yet been identified in the insertion line; however, there is evidence that the gene belongs to a small gene family. LRP1 provides a molecular marker to study the early stages of lateral and adventitious root primordium development.     

The floral morphology and ontogeny of some Chinese representatives of orchid subtribe Orchidinae

The flower structure and development of ten species in six genera of the orchid subtribe Orchidinae are described and illustrated by scanning electron micrographs. Particular attention is given to the structure of the gynostemium, which for most species is interpreted from ontogenetic data. All the species studied here share a series of features, e.g. the sequence of tepal and anther initiation, the shape and position of the anther, the presence of auricles and basal bulges, the three-lobed condition of the median carpel apex and the lateral lobes of the median carpel embracing the basal ends of the thecae. However, the form and structure of the three carpel apices are most varied in the later development stages or in the adult flower. The genus Hemipilia shows a series of peculiar characters that are quite different from those of the other genera in Orchidinae. The peculiar structure and development of the viscidia in both Amitostigma and Neottianthe indicate that both of them are different from other genera in Orchidinae. The adult floral morphology shows that the genera Galearis and Chusua are not congeneric with Orchis. The separation of the lateral lobes of the rostellum in most genera studied here as well as in the Brachycorythis group from South Africa suggests that this is the ancestral state in the subtribe Orchidinae. In contrast, the conjoining of lateral lobes in Dactylorhiza and Orchis is suggested as a derived character.     

LEAF DEVELOPMENT IN DOXANTHA UNGUIS-CATI (BIGNONIACEAE)

Leaf structure in Doxantha unguis-cati is polymorphic. The usual mature compound leaf is composed of two lanceolate leaflets and a terminal tripartite spine-tendril. Leaf primordia are initiated simultaneously in pairs on opposite flanks of the shoot apical meristem by periclinal cell divisions in the third subsurface layer of the peripheral flank meristem. Two leaflet primordia are the first lateral appendages of the compound leaf. Initiation of these leaflet primordia occurs on the adaxial side of a compound leaf primordium 63–70 μm long. Lamina formation is initiated at the base of a leaflet primordium 70–90 μm long and continues acropetally. Mesophyll differentiation occurs in later stages of development of leaflets. The second pair of lateral appendages of the leaf primordium differentiate as prongs of the tendril. Initiation of the second pair of lateral appendages occurs on the adaxial side of a primordium approximately 168 μm long. Acropetal procambialization and vacuolation of cells extend to the apex of tendrils about 112 μm long, restricting the tendril meristem to the adaxial side of the primordium and resulting in curvature of the tendril. The tendril meristem is gradually limited to a more basipetal position as elongation of apical cells continues. Initiatory divisions and early ontogenetic stages of leaflets and tendrils are similar. Their ontogeny differs when the lateral primordia are approximately 70 μm long. Marginal and submarginal initials differentiate within leaflets but not in tendrils. Apical growth of tendrils ceases very early in ontogeny as compared with leaflets.     

Floral development of dioecious species and trends of floral evolution in Piper sensu lato

The initiation of the floral parts (mainly stamens and carpels) is described for the four dioecious species of Piper: Piper polysyphorum C. DC, P. bavinum C. DC., P. pedicellatum C. DC., P. pubicatulum C. DC. The initiation order resembles that in the perfect flowers of some species, such as P. amalago. The carpels are initiated simultaneously, in most cases, as three primordia. In P. polysyphorum , carpel tips split into two lobes, so that finally a four- or five-lobed stigma will be formed when the ovary is fully developed. The staminodes (exactly, staminodial primordia) in the female flowers are initiated in the same order as the stamens in the male flowers and remain until the ovaries are enclosed. The unisexual flowers have stamens reduced to three or two. The reduction of stamen or staminode (staminodial primordium) number is accompanied by the change of their positions from opposite the carpels to alternate. After the initiation of the staminodes, or, exactly staminodial primordia, in the female flowers, the central part of the floral apex forms a ring meristem which is triangular. The carpel primordia (often three) are initiated on the three points of the ring meristem. The evolutionary trends of the flowers of Piper sensu lato are discussed.     

Expression studies on AUX1-like genes in Medicago truncatula suggest that auxin is required at two steps in early nodule development

Medicago truncatula contains a family of at least five genes related to AUX1 of Arabidopsis thaliana (termed MtLAX genes for Medicago truncatula-like AUX1 genes). The high sequence similarity between the encoded proteins and AUX1 implies that the MtLAX genes encode auxin import carriers. The MtLAX genes are expressed in roots and other organs, suggesting that they play pleiotropic roles related to auxin uptake. In primary roots, the MtLAX genes are expressed preferentially in the root tips, particularly in the provascular bundles and root caps. During lateral root and nodule development, the genes are expressed in the primordia, particularly in cells that were probably derived from the pericycle. At slightly later stages, the genes are expressed in the regions of the developing organs where the vasculature arises (central position for lateral roots and peripheral region for nodules). These results are consistent with MtLAX being involved in local auxin transport and suggest that auxin is required at two common stages of lateral root and nodule development: development of the primordia and differentiation of the vasculature.     

Activation of seminal root primordia during wheat domestication reveals underlying mechanisms of plant resilience

Seminal roots constitute the initial wheat root system and provide the main route for water absorption during early stages of development. Seminal root number (SRN) varies among species. However, the mechanisms through which SRN is controlled and in turn contribute to environmental adaptation are poorly understood. Here, we show that SRN increased upon wheat domestication from 3 to 5 due to the activation of 2 root primordia that are suppressed in wild wheat, a trait controlled by loci expressed in the germinating embryo. Suppression of root primordia did not limit water uptake, indicating that 3 seminal roots is adequate to maintain growth during seedling development. The persistence of roots at their primordial state promoted seedling recovery from water stress through reactivation of suppressed primordia upon rehydration. Our findings suggest that under well‐watered conditions, SRN is not a limiting factor, and excessive number of roots may be costly and maladaptive. Following water stress, lack of substantial root system suppresses growth and rapid recovery of the root system is essential for seedling recovery. This study underscores SRN as key adaptive trait that was reshaped upon domestication. The maintenance of roots at their primordial state during seedling development may be regarded as seedling protective mechanism against water stress.     

长角凤仙花（凤仙花科）的花器官发生和发育

以不同发育时期的长角凤仙花Impatiens longicornuta Y.L.Chen（凤仙花科Balsaminaceae）为材料,利用扫描电镜技术观察了其花器官的分化及其发育过程。长角凤仙花为两侧对称花,具2枚侧生萼片,唇瓣囊状,旗瓣具鸡冠状突起,雄蕊5枚,子房上位,5心皮5室。其花器官分化顺序为向心式,萼片—花瓣—雄蕊—雌蕊原基。2枚侧生萼片先发生,然后近轴萼片（即唇瓣）原基和2枚前外侧萼片原基近同时发生;但是这3枚萼片原基的发育不同步,远轴的2枚前外侧萼片原基的发育渐渐滞后,然后停止发育,最后渐渐为周围组织所吸收,直至消失不见。花瓣原基中,旗瓣原基最先发生,4个侧生花瓣原基相继成对发生,且之后在基部成对愈合形成翼瓣;5枚雄蕊原基几乎同时发生,5个心皮原基轮状同时发生。本文结果支持凤仙花属植物为5基数的花,并进一步证实了唇瓣的萼片来源;此外,研究结果表明花器官早期发育资料对植物系统与进化研究具有重要参考价值。     

台闽苣苔（苦苣苔科）花部器官的形态发生

在扫描电镜下对台闽苣苔 (T .oldhamii (Hemsl.)Solereder)进行了花部器官形态发生的观察 ,为探索该类群的个体发育、类群间的系统发育关系和进化趋势提供依据。研究发现该属植物萼片、花冠和雄蕊发生式样均为五数花类型 ,它们各自来源于花原基上分化出来的萼片原基、花冠原基和雄蕊原基 ;花冠与雄蕊的两侧对称性与花冠上唇生长稍快和退化雄蕊原基发育迟滞相关 ;萼片原基的发生和发育的顺序是不一致的 :萼片原基发生的式样为近轴中原基—远轴 2原基— 2侧原基 ,发育式样则为近轴中萼片— 2侧萼片—远轴 2萼片 ,花蕾时为镊合状排列。花冠裂片原基的发生和发育式样是一致的 ,即远轴中裂原基 (下唇中裂片 )—远轴 2侧裂原基 (下唇 2侧裂片 )—近轴 2裂原基 (上唇 2裂片 )。花蕾期卷迭式为覆瓦状排列 ,从外向内 :下唇中裂片—下唇 2侧裂片—上唇 2裂片或下唇 2侧裂片—上唇 2裂片—下唇中裂片。雄蕊原基与花冠裂片原基互生 ,前方雄蕊原基在发生上稍迟于后方雄蕊原基 ,后者与退化雄蕊原基几乎同时发生 ,但较小 ,并与近轴心皮 (或柱头上唇 )对生。将该属与玄参科 (Scrophulari aceae)的地黄属 (Rehmannia)、苦苣苔科 (Gesneriaceae)的异叶苣苔属 (Whytockia)和尖舌苣苔属 (Rhynchoglossum)的花部器官比较发现