THE FLORAL AND EXTRA-FLORAL NECTARIES OF PASSIFLORA. I. THE FLORAL NECTARY

Floral nectary development and nectar secretion in three species of Passiflora were investigated with light and electron microscopy. The nectary ring results from the activity of an intercalary meristem. Increased starch deposition in the amyloplasts of the secretory cells parallels maturation of the nectary phloem. Large membrane-bound protein bodies are observed consistently in phloem parenchyma cells, but their function is presently unknown. The stored starch serves as the main source of nectar sugars at anthesis. Plastid envelope integrity is maintained during starch degradation, and there is no evidence of participation of endoplasmic reticulum or Golgi in the secretion of pre-nectar. It is concluded that in these starchy nectaries granulocrine secretion, commonly reported for floral nectaries, does not occur.     

THE FLORAL AND EXTRA-FLORAL NECTARIES OF PASSIFLORA. II. THE EXTRA-FLORAL NECTARY

Extra-floral nectaries of nine species of Passiflora were studied with light and electron microscopy prior to and during secretion. There is no evidence of ER or Golgi participation in the secretion of nectar. The vascular tissue supplying the nectary is characterized by companion and phloem parenchyma cells which are usually larger than the sieve elements, a configuration similar to that found in leaf minor veins. In the petiolar nectaries, large masses of membrane-bound protein are commonly found in these cells. This protein is absent in laminar nectaries.     

Structure and biology of nectaries in Tabebuia serratifolia Nichols (Bignoniaceae)

THOMAS, V. & DAVE, Y., 1992. Structure and biology of nectaries in Tabebuia serratifolia Nichols (Bignoniaceae) . Tabebuia has both floral and extrafloral nectaries, situated on the petiole, bract, calyx, around the ovary and on the pericarp. The floral nectary present around the ovary base is differentiated into epidermis, secretory zone and sub-secretory zone. It is supplied by phloem strands up to the secretory zone. A mature extrafloral nectary consists of a single large basal cell and a head comprising a layer of vertically arranged elongated cells. Starch, protein and lipid are present in the floral nectary. The major insect visitors to both types of nectaries are honey bees, houseflies and ants.     

Floral nectar production and carbohydrate composition and the structure of receptacular nectaries in the invasive plant <Emphasis Type="Italic">Bunias orientalis</Emphasis> L. (Brassicaceae)

The data relating to the nectaries and nectar secretion in invasive Brassicacean taxa are scarce. In the present paper, the nectar production and nectar carbohydrate composition as well as the morphology, anatomy and ultrastructure of the floral nectaries in Bunias orientalis were investigated. Nectary glands were examined using light, fluorescence, scanning electron and transmission electron microscopy. The quantities of nectar produced by flowers and total sugar mass in nectar were relatively low. Total nectar carbohydrate production per 10 flowers averaged 0.3 mg. Nectar contained exclusively glucose (G) and fructose (F) with overall G/F ratio greater than 1. The flowers of B. orientalis have four nectaries placed at the base of the ovary. The nectarium is intermediate between two nectary types: the lateral and median nectary type (lateral and median glands stay separated) and the annular nectary type (both nectaries are united into one). Both pairs of glands represent photosynthetic type and consist of epidermis and glandular tissue. However, they differ in their shape, size, secretory activity, dimensions of epidermal and parenchyma cells, thickness of secretory parenchyma, phloem supply, presence of modified stomata and cuticle ornamentation. The cells of nectaries contain dense cytoplasm, plastids with starch grains and numerous mitochondria. Companion cells of phloem lack cell wall ingrowths. The ultrastructure of secretory cells indicates an eccrine mechanism of secretion. Nectar is exuded throughout modified stomata.     

Extrafloral Nectaries in Acacia mangium

Our microscopy studies describe the anatomy of extrafloral nectaries on the abaxial side of the basal part of every leaf stalks of Acacia mangium. The lens-like nectary expands with the development of the leafstalk, peaks at the stage at which the leafstalk itself has reached its mature size. The nectary is composed of numerous small parenchyma cells and a nectar cavity in which the nectar is pooled. Those small parenchyma cells are divided into nectariferous tissue and epithelial cells, which line the lumen of the nectar cavity, and secretes the nectar into the same. Each nectary is surrounded by several vascular bundles, which probably afford the nectar. In addition to the microscopic observation, the chemical constituents of the nectar are analyzed by NMR, and it mainly consists of sugars with 60 % sucrose, 25 % glucose and 15 % fructose.     

ONTOGENY AND STRUCTURE OF THE SECONDARY PHLOEM IN EPHEDRA

The secondary phloem in Ephedra is atypical of the gymnosperms in general and exhibits several angiosperm-like characteristics. The ray system of the conducting phloem consists of parenchymatous, multiseriate rays. The axial system contains parenchyma cells, sieve cells, and unusual albuminous cells reminiscent of the specialized parenchyma cells found in some angiosperms. These cell types may intergrade with each other. P-protein in the developing sieve element appears early in the form of a single, ovoid slime body. Later, smaller slime bodies appear and quickly disperse. In the mature sieve element the single, ovoid slime body is lost, and P-protein is then evident in the form of a parietal cylinder, thread-like strands, amorphose globules, or a slime plug. Necrotic-appearing nuclei are commonly found in mature sieve cells.     

Occurrence,structure, ontogeny and biology of nectaries inKigelia pinnata DC

The occurrence, morphology, ontogeny, structure and preliminary nectar analysis of floral and extrafloral nectaries are studied inKigelia pinnata of the Bignoniaceae. The extrafloral nectaries occur on foliage leaves, sepals and outer wall of the ovary, while the floral nectary is situated around the ovary base as an annular, massive, yellowish ring on the torus. The extrafloral nectaries originate from a single nectary initial. The floral nectary develops from a group of parenchymatous cells on the torus. The extrafloral nectaries are differentiated into multicellular foot, stalk and cupular or patelliform head. The floral nectary consists of parenchymatous tissue. The floral nectaries are supplied with phloem tissue. The secretion is copious in floral nectary. Function of the nectary, preliminary nectar analysis, and symbiotic relation between nectaries and animal visitors are discussed.     

Anatomical and developmental studies on floral nectaries in Cardiospermum species: an approach to the evolutionary trend in Paullinieae

Floral nectaries are a widespread trait in the Sapindaceae. However, until now only a few data on nectaries and their evolutionary shifts are available for most taxa. This research focuses on the anatomy and development of floral nectaries in two endemic species, Cardiospermum heringeri and C. integerrimum. The nectary consists of two horn-like lobes, located at the base of the androgynophore. Anatomically, it is characterized by three components: uniseriate epidermis, sub-epidermal secretory tissue and vascular tissue. The epidermis contains many nectarostomata involved in the exudation process. The secretory parenchyma is composed of small thin-walled cells, relatively lightly stained, and idioblasts containing oxalate druses. Vascular tissue supplying the nectary consists exclusively of phloem. From an early stage of development, the nectary lobes in both species are associated with the base of the posterior petals, but each organ originates independently of one another. These results plus additional morphological observations of nectary lobes in some species of Cardiospermum, Serjania, Paullinia and Urvillea were analyzed within the framework of phylogenetic knowledge.     

Floral nectaries in Sapindaceae <Emphasis Type="Italic">s.s.</Emphasis>: morphological and structural diversity,and their systematic implications

We investigated the morphology and structure of the floral nectary in 11 Neotropical genera belonging to the subfamilies Dodonaeoideae and Paullinioideae (Sapindaceae) from southern South America representing three tribes (Dodonaeaeae, Paullinieae, and Melicocceae), in relation to other floral traits in species with contrasting morphological flower characteristics. Nectary organization was analyzed under light, stereoscopic, and scanning electron microscopes; Diplokeleba floribunda N.E. Br. was also observed using transmission electron microscopy. Our comparative data may contribute to the understanding of floral nectary evolution and systematic value in this family. The nectaries were studied in both staminate and pistillate flowers. All the floral nectaries are typical of Sapindaceae: extrastaminal, receptacular, structured, and persistent. The anatomical analysis revealed a differentiated secretory parenchyma and an inner non-secretory parenchyma; the nectary is supplied by phloem traces and, less frequently, by phloem and xylem traces. Nectar is secreted through nectarostomata of anomocytic type. The anatomical analysis showed the absence of nectary in the three morphs of Dodonaea viscosa flowers. Nectary ultrastructure is described in D. floribunda. In this species, the change in nectary color is related to progressive accumulation of anthocyanins during the functional phase. We found relatively small variation in the nectary structural characteristics compared with large variation in nectary morphology. The latter aspect agreed with the main infrafamilial groupings revealed by recent phylogenetic studies, so it is of current valuable systematic importance for Sapindaceae. In representatives of Paullinieae, the reduction of the floral nectary to 4–2 posterior lobes should be interpreted as a derived character state.     

垂柳花蜜腺的发育解剖学研究

垂柳雌花蜜腺一枚,位于于房与花序轴之间,多呈扁平广卵形,由分泌表皮、泌蜜组织和维管束组成。雄花蜜腺呈基部相连的两枚突起,一枚位于花丝与花序轴之间,基部宽扁,上部棒状;另一枚位于花丝与苞片之间,棒状,仅由分泌表皮和泌蜜组织组成。雌、雄花蜜腺均起源于花托表面2—3层细胞。在蜜腺发育过程中,雌、雄花蜜腺泌蜜组织细胞的液泡发生规律性变化．雌花蜜腺为淀粉型蜜腺,而雄花蜜腺为非淀粉型蜜腺。雌、雄花蜜腺的原宜汁分别由蜜腺维管束韧应部或花丝维管束韧皮部提供,其蜜计最后均由分泌表皮细胞和变态气孔排出。     

NEC1, a novel gene, highly expressed in nectary tissue of Petunia hybrida

To study the molecular regulation of nectary development, we cloned NEC1, a gene predominantly expressed in the nectaries of Petunia hybrida, by using the differential display RT-PCR technique. The secondary structure of the putative NEC1 protein is reminiscent of a transmembrane protein, indicating that the protein is incorporated into the cell membrane or the cytoplast membrane. Immunolocalization revealed that NEC1 protein is present in the nectaries. Northern blot analyses showed that NEC1 is highly expressed in nectary tissue and weakly in the stamen. GUS expression driven by the NEC1 promoter revealed GUS activity in the outer nectary parenchyma cells, the upper part of the filament and the anther stomium. The same expression pattern was observed in Brassica napus. GUS expression was observed as blue spots on the surface of very young nectaries that do not secrete nectar and do accumulate starch. GUS expression was highest in open flowers in which active secretion of nectar and starch hydrolysis had taken place. Ectopic expression of NEC1 resulted in transgenic plants that displayed a phenotype with leaves having 3-4 times more phloem bundles in mid-veins than the wild-type Petunia. The possible role of NEC1 gene in sugar metabolism and nectar secretion is discussed.     

SOME ULTRASTRUCTURAL ASPECTS OF METAPHLOEM SIEVE ELEMENTS IN THE AERIAL STEM OF THE HOLOPARASITIC ANGIOSPERM EPIFAGUS VIRGINIANA (OROBANCHACEAE)

A light and electron microscope investigation was conducted on phloem in the aerial stem of Epifagus virginiana (L.) Bart. Tissue was processed at field collection sites in an effort to overcome problems resulting from manipulation. At variance with earlier accounts, Epifagus phloem consists of sieve elements, companion cells, phloem parenchyma cells, and primary phloem fibers. The sieve elements possess simple sieve plates and the phloem is arranged in a collateral type of vascular bundle. In addition, this constitutes the first study on phloem ultrastructure in the aerial stems of a holoparasitic dicotyledon, an entire plant which could be viewed as an “ideal sink.” Epifagus phloem possesses unoccluded sieve plate pores in mature sieve elements and a total lack of P-protein in sieve elements at all stages of development. Mature sieve elements lack nuclei. Plastids were rarely observed in mature sieve elements. Vacuoles with intact tonoplasts were encountered in some mature sieve elements. Otherwise, the ultrastructural features of sieve elements appear to differ little from those described by investigators of non-parasitic species.     

Expression of the phloem lectin is developmentally linked to vascular differentiation in cucurbits

The conducting elements of phloem in angiosperms are a complex of two cell types, sieve elements and companion cells, that form a single developmental and functional unit. During ontogeny of the sieve element/companion cell complex, specific proteins accumulate forming unique structures within sieve elements. Synthesis of these proteins coincides with vascular development and was studied in Cucurbita seedlings by following accumulation of the phloem lectin (PP2) and its mRNA by RNA blot analysis, enzyme-linked immunosorbent assay, immunocytochemistry and in␣situ hybridization. Genes encoding PP2 were developmentally regulated during vascular differentiation in hypocotyls of Cucurbita maxima Duch. Accumulation of PP2 mRNA and protein paralleled one another during hypocotyl elongation, after which mRNA levels decreased, while the protein appeared to be stable. Both PP2 and its mRNA were initially detected during metaphloem differentiation. However, PP2 mRNA was detected in companion cells of both bundle and extrafascicular phloem, but never in differentiating sieve elements. At later stages of development, PP2 mRNA was most often observed in extrafascicular phloem. In developing stems of Cucurbita moschata L., PP2 was immunolocalized in companion cells but not to filamentous phloem protein (P-protein) bodies that characterize immature sieve elements of bundle phloem. In contrast, PP2 was immunolocalized to persistent ␣ P-protein bodies in sieve elements of the extrafascicular phloem. Immunolocalization of PP2 in mature wound sieve elements was similar to that in bundle phloem. It appears that PP2 is synthesized in companion cells, then transported into differentiated sieve elements where it is a component of P-protein filaments in bundle phloem and persistent P-protein bodies in extrafascicular phloem. This differential accumulation in bundle and extrafascicular elements may result from different functional roles of the two types of phloem. Received: 31 July 1996 / Accepted: 27 August 1996     

A DEVELOPMENTAL STUDY OF EXTRAFLORAL NECTARIES IN SLIPPER SPURGE (PEDILANTHUS TITHYMALOIDES,EUPHORBIACEAE)

Slipper spurge (Pedilanthus tithymaloides) bears one or two stalked extrafloral nectaries on either side of the leaf base and one at the leaf tip. The mature nectary is differentiated into multicellular zones: head, neck, and stipe. The nectary arises as a small group of meristematic cells with densely staining cytoplasm and nuclei. The columnar secretory cells show changes in their chemical nature at different developmental stages of the nectary. There is a basipetal sequence in the development and decay of the tissues in the nectary. Decay of the nectary begins at the head, abscission occurs at the line between stipe and neck regions, and the scars of the fallen nectaries are left when the stipe cells also collapse.     

Adenosine triphosphatase in the phloem of Cucurbita

Summary The distribution of adenosine triphosphatase (ATPase) activity in the phloem of petioles and minor veins of Cucurbita maxima has been studied using a lead phosphate precipitation procedure. ATPase activity was localized in sieve elements, companion cells and parenchyma cells. Activity was found at the cell surfaces, associated with the dispersed P-protein of mature sieve elements, in mitochondria, sieve-element reticulum, and at specific regions of the cell walls. It is suggested that the ATPase at the phloem cell surfaces may function in intercellular transport of assimilates or ions, and that the ATPase activity associated with the P-protein may function in the translocation process or in callose deposition.     

Cytochemical localization of adenosine triphosphatase in the phloem of Pisum sativum and its relation to the function of transfer cells

The cytochemical localization of ATPase in differentiating and mature phloem cells of Pisum sativum L. has been studied using a lead precipitation technique. Phloem transfer cells at early stages of differentiation exhibit strong enzyme activity in the endoplasmic reticulum (ER) and some reaction product is deposited on the vacuolar and plasma membranes. As the phloem transfer cells mature and develop their characteristic wall structures, strong enzyme activity can be observed in association with the plasma membranes and nuclear envelopes. Mature phloem transfer cells with elaborate cell-wall ingrowths show ATPase activity evenly distributed on plasma-membrane surfaces. Differentiating sieve elements show little or no enzyme activity. When sieve elements are fully mature they have reaction product in the parietal and stacked cisternae of the ER. There is no ATPase activity associated with P-protein at any stage of sieve-element differentiation or with the sieve-element plasma membranes. It is suggested that the intensive ATPase activity on the plasma membranes of the transfer cells is evidence for a transport system involved in the active movement of photosynthetic products through these cells.Key to labeling in the figures ER endoplasmic reticulum - P parenchyma cell - PP P-protein - SE sieve element - SPP sieve-plate pore - TC transfer cell     

Anatomical and ultrastructural changes of the floral nectary ofPisum sativum L. during flower development

Summary The floral nectary ofPisum sativum L. is situated on the receptacle at the base of the gynoecium. The gland receives phloem alone which departed the vascular bundles supplying the staminal column. Throughout the nectary, only the companion cells of the phloem exhibited wall ingrowths typical of transfer cells. Modified stomata on the nectary surface served as exits for nectar, but stomatal pores developed well before the commencement of secretion. Furthermore, stomatal pores on the nectary usually closed by occlusion, not by guard-cell movements. Pore occlusion was detected most frequently in post-secretory and secretory glands, and less commonly in pre-secretory nectaries. A quantitative stereological study revealed few changes in nectary fine structure between buds, flowers secreting nectar, and post-secretory flowers. Dissolution of abundant starch grains in plastids of subepidermal secretory cells when secretion commenced suggests that starch is a precursor of nectar carbohydrate production. Throughout nectary development, mitochondria were consistently the most plentiful organelle in both epidermal and subepidermal cells, and in addition to the relative paucity of dictyosomes, endoplasmic reticulum, and their associated vesicles, the evidence suggests that floral nectar secretion inP. sativum is an energy-requiring (eccrine) process, rather that granulocrine.Abbreviations ER endoplasmic reticulum - GA glutaraldehyde - SEM scanning electron microscopy     

Floral nectary structure and nectar composition in Eccremocarpus scaber (Bignoniaceae), a hummingbird-pollinated plant of central Chile

Surface features, anatomy, and ultrastructure of the floral nectary of Eccremocarpus scaber (Bignoniaceae), pollinated predominantly by the largest-known hummingbird (Patagona gigas gigas), were studied together with nectar sugar content and secretion rate. The annular disk nectary comprises epidermis, secretory and ground parenchyma with intercellular spaces, and branched vascular bundles terminating in the secretory parenchyma where only phloem is found. Amyloplasts and vacuoles increase in size throughout development, the latter becoming sites of organelle degradation. Transferlike cells in nectary phloem and P-proteinlike fibrillar material in phloem parenchyma were observed. Flowers produced around 32 μl of nectar (mostly after anthesis) with 11 mg of sugar composed of fructose, glucose, sucrose, and maltose in a ratio of 0.34:0.32:0.17:0.17. Morphological studies as well as the presence of maltose and glucose in nectar suggest storage of the originally phloem-derived sugars as starch with its subsequent hydrolysis. The low sucrose/hexose ratio (0.25) and high nectary secretion force (nectar per flower biomass) observed places E. scaber close to large-bodied bat-pollinated plants. A hypothesis based on nectar origin and nectar secretion is advanced to explain pollinator-correlated variation in sucrose/hexose ratio.     

MORPHOLOGY AND ANATOMY OF FLORAL AND EXTRAFLORAL NECTARIES IN CAMPSIS (BIGNONIACEAE)

The genus Campsis (Bignoniaceae), with one New World and one Old World species, is unusual among temperate plants in having five distinct nectary sites. Multiple nectaries occur at all four of the extrafloral sites (petiole, calyx, corolla, fruit), representing an advanced strategy for ant attraction. The morphology and anatomy of the extrafloral nectaries in both species are uniform for the petioles, calyces, and young fruits; those on the outer corolla lobes are of slightly different forms. The generalized structure consists of one layer of basal cells, and a one- to two-layered secretory cup. Because of their small size, there is no vascular tissue in them. The large, vascularized (phloem only) floral nectary is an annular structure subtending the ovary.     

新疆鼠尾草花蜜腺的发育解剖学研究

新疆鼠尾草（Salvia deserta Schang）花蜜腺位于子房基部的花托上,为盘状的花托蜜腺,其顶部裂成4片,其裂片大小不等,比例悬殊。蜜腺由产蜜组织和分泌表皮构成,又为结构蜜腺。组织化学染色显示淀粉粒动态明显,因此又属淀粉蜜腺。在发育的过程中细胞液泡化动态明显,且淀粉粒和蛋白质具有明显的消长变化,但PAS反应和苏木精脂类染色无明显变化。其泌蜜过程可能为：原蜜汁由邻近的韧皮部提供,经薄壁细胞运送至产蜜组织,在产蜜组织中进一步积聚、合成后,最终蜜汁通过变态气孔和分泌表皮细胞的角质层泌出。