Laticifer starch grain morphology and laticifer evolution in Euphorbia (Euphorbiaceae)

The micromorphology of starch grains in the nonarticulated laticifer was examined in 200 taxa of succulent and nonsucculent Euphorbia. Rod, spindle, osteoid, discoid and intermediate shapes were found in latex. These unusual starch grain shapes are assumed derivatives from more rounded grains present in other angiospermous cells. Unbranched, rod–shaped grains were present in latex of annual and perennial herbaceous taxa. Spindle, osteoid, and discoid shapes, often branched, occurred in xerophytic, succulent taxa. Leafy taxa in several subgenera possessed rod–shaped grains. Taxa of the primitive subgenus, Esula , possessed the shortest rod–shaped grains derived from rounded grains common in parenchyma. Length of rod–shaped grains increased through herbaceous subgenera and culminated in Poinsettia where grain length may be extremely great. Dwarf or shrubby succulents with thickened roots have osteoid grains. Shrubby or arborescent coralline and cactiform species, specialized taxa, possessed large branched grains. Grain morphology of Euphorbia was compared with that from latex of other genera of the Euphorbiaceae. These in–depth analyses of laticifer plastids demonstrates the applicability of starch grain morphology for interpreting the progressive evolution of the nonarticulated laticifer as a cell type within the genus Euphorbia.     

Scanning electron microscopy of starch grains from latex of Euphorbia terracina and E. tirucalli

Summary The morphology of starch grains isolated from the latex of 2 species of Euphorbia was compared by scanning electron microscopy. In E. terracina they are elongated and greater, in diameter at the midregion than at the tips while in E. tirucalli they are osteoid. Starch grains varied in size in both, species although in E. tirucalli the largest grains, which measured 49 , were approximately twice the length of those in E. terracina (27 ).     

A COMPARISON OF ALPHA-AMYLASES FROM THE LATEX OF THREE SELECTED SPECIES OF EUPHORBIA (EUPHORBIACEAE)

A technique for the partial purification of α-amylases from latex of Euphorbia heterophylla, E. marginata, and E. tirucalli is described. The enzymes were found to be similar to other higher plant amylases using the criteria of molecular weight, pH characteristics, kinetics, number of isozymes, and blue value-reducing value patterns. Carbohydrases other than α-amylases were not detectable in latex. The amylases were employed to examine their capacity to digest latex starch grains which are common components of the laticiferous cell in this genus. Laticifer starch grains are not susceptible to in vitro amylolysis. Removal of the starch grain membrane with Triton X-100, damaging the grain, or treating the grains with α-amylases from diverse biological sources had little effect upon hydrolysis. Grains incubated with pullulanase followed by α-amylase caused a slight but significant increase in hydrolysis of raw laticifer starch grains. These studies indicate that the nonarticulated laticifer in Euphorbia is a cul de sac for certain primary and secondary metabolic products and that the indigestible and morphologically complex starch grains in the latex have evolved to function in a secondary role within the laticifer.     

Accumulation of non-utilizable starch in laticifers of Euphorbia heterophylla and E. myrsinites

Starch biosynthesis and degradation was studied in seedlings and mature plants of Euphorbia heterophylla L. and E. myrsinites L. Mature embryos, which lack starch grains in the non-articulated laticifers, develop into seedlings that accumulate starch rapidly when grown either in the light or the dark. Starch accumulation in laticifers of dark-grown seedlings was ca. 47 and 43% of total starch in light-grown controls in E. heterophylla and E. myrsinites, respectively. In light-grown seedlings, starch was present in laticifers as well as parenchyma of stems and leaves, whereas in dark-grown seedlings starch synthesis was almost exclusively limited to laticifers. In 7-month-old plants placed into total darkness, the starch in chyma was depleted within 6 d, whereas starch in laticifers was not mobilized. The starch content of latex in plants during development of floral primordia, flowering, and subsequent fruit formation remained rather constant. The results indicate that laticifers in seedlings divert embryonal storage reserves to synthesize starch even under stress conditions (darkness) in contrast to other cells, and that starch accumulated in laticifers does not serve as a metabolic reserve. The laticifer in Euphorbia functions in the accumulation and storage of secondary metabolites yet retains the capacity to produce, but not utilize starch, a primary metabolite.     

CHARACTERIZATION OF STARCH GRAINS IN THE NONARTICULATED LATICIFER OF EUPHORBIA PULCHERRIMA (POINSETTIA)

Starch grain morphology in laticifer amyloplasts of Euphorbia pulcherrima Willd. (poinsettia) was examined for evidence of starch metabolism in vegetative and flowering plants. Laticifer starch grains in vegetative plants were rod shaped with lengths ranging from 3 to 60 μm. Average grain size was significantly larger in stems than leaves, and in older than younger tissues. Starch grain length frequency was unimodal and approximated a normal probability distribution in stems, but was skewed positively toward smaller grains in leaves. Frequency distributions were shifted toward larger grains in older tissues. Under short-day photoperiod (flowering) conditions, round starch grains formed in latex of stems, and the average length of rod-shaped grains decreased in latex of stems and leaves. Round grains did not occur in laticifers of leaves or bracts. Round starch grains often occurred in aggregates of two or more subunits. Changes in size and shape of latex starch grains indicate that amyloplasts in fully differentiated laticifers metabolize starch. Identification of metabolically active amyloplasts in differentiated laticifers suggests that the function of these organelles may involve starch mobilization under certain physiological conditions.     

Euphorbia venkatarajui sp. nov. (Euphorbiaceae) from Eastern Ghats of Andhra Pradesh,India

Euphorbia venkatarajui, a new succulent species of Euphorbiaceae, is described from Kurnool district of Andhra Pradesh state, India. The new species belongs to the subgenus Euphorbia, and it closely resembles Euphorbia gokakensis S.R. Yadav, Malpure and Chandore and E. caducifolia Haines., but differs in certain distinct characters.     

Euphorbia gokakensis sp. nov. (Euphorbiaceae) from sandstone formations in Karnataka,India

Euphorbia gokakensis, a new succulent species of Euphorbiaceae, is described from the Belgaum district of Karnataka, India. The new species belongs to Euphorbia subgen. Euphorbia, and closely resembles Euphorbia caducifolia Haines. However, it is distinguished by its characteristic dwarf habit forming a compact cushion that hardly exceeds 50 cm in height.     

LATEX AND LATICIFER STARCH CONTENT OF DEVELOPING LEAVES OF EUPHORBIA PULCHERRIMA

Laticifer starch accumulation was compared to laticifer growth for developing leaves of Euphorbia pulcherrima Willd. (poinsettia). Measurements of the laticifer-specific triterpenol, cycloartenol, in latex and in whole leaf extracts were used to calculate the total latex volume in leaves of different developmental stages. Latex volume and starch concentration in the latex were used to determine total laticifer starch and to compare laticifer growth and starch synthesis. Young leaves contained the highest latex and laticifer starch contents on dry wt and leaf area bases. In older expanding leaves, laticifer growth produced an increase in total latex volume accompanied by an increase in total laticifer starch. Laticifer growth and starch accumulation stopped upon cessation of leaf expansion. Starch concentration was similar in latex from all leaves, but differed between plant organs. Thus, laticifer starch accumulation correlated with laticifer growth, but mobilization of the starch out of the laticifer was not observed in old or senescent leaves. This is evidence that laticifer starch grains function within the laticifer independently of degradation or export to other cell types.     

Protozoans—the first food of larval herring (Clupea harengus L.)?

In short-run experiments herring larvae at the end of the yolk sac stage (S_L 6.5 to 8.5 m) were fed with maize and potato starch to investigate the effect of particle size on food selection. About 20% of the larvae ingested these particles during the experiments. In the case of maize starch (3 to 26 μm grain size) the size classes from 14 to 25 μm and in the case of potato starch (5 to 80 μm) the size classes larger than 29 μm were preferred. The highest numbers of ingested grains per larva were 150 maize starch grains and 57 potato starch grains. The selective uptake of these size classes leads to the conclusion that planktonic organisms in this size range—in other words mostly protozoans—may play an important role as a first food source of herring larvae.     

PLASTIDS IN LATICIFERS OF PAPAVER. I. DEVELOPMENT AND CYTOCHEMISTRY OF LATICIFER PLASTIDS IN P. SOMNIFERUM L. (PAPAVERACEAE)

Plastids were observed in all stages of laticifer differentiation in Papaver somniferum L. Plastids in laticifer initials were present as proplastids that later developed electron-dense inclusions, but never possessed the thylakoids or starch grains that characterize chloroplasts in other cells. Electron-dense inclusions in laticifer plastids were membrane-bound and appeared to arise from the accumulation of material within an invagination of the inner plastid membrane. Cytochemical studies of these plastid inclusions indicated that their matrix was not composed of crystalline protein, α-amylose, amylopectin or polysaccharide. The results suggest that the electron-dense, membrane-bound inclusions in laticifer plastids may be composed of lipoprotein.     

Taxonomic revision and phytogeographic studies in Euphorbia (Euphorbiaceae) in the Khorassan provinces of Iran

This study is focused on the genus Euphorbia L. in a part of northeast Iran, viz. the three Khorassan provinces. Since there are many taxa of Euphorbia in Iran which are used in different industries and have significant effects on human and non‐human life it is important to revise their taxonomy. With about 90 species, following Turkey with 91 species, Iran is the second richest country for Euphorbia in Asia. Of these, 30 species are distributed in the Khorassan provinces. This is the first comprehensive work on the genus in this region. According to ‘Flora Iranica’, there are 17 species of Euphorbia in northeast Iran, while according to our results, there are 30 species of Euphorbia in the Khorassan provinces alone. In addition to various new taxonomic and biogeographic results, a new species, viz. E. chamanbidensis, is described. Euphorbia chamanbidensis is closely related to E. aucheri, but seed micro‐morphological characters differentiate them. Two identification keys to the Euphorbia species of the studied area are provided, one based on macro‐morphological characters and another based on seed micro‐morphological characters. Phytogeographic analysis and distribution maps for all species are also presented.     

ULTRASTRUCTURE OF NON-ARTICULATED LATICIFERS IN MATURE EMBRYOS AND SEEDLINGS OF ASCLEPIAS SYRIACA L. (ASCLEPIADACEAE)

The protoplast of the non-articulated branched laticifer in the embryo and seedling of Asclepias syriaca L. was studied at the ultrastructural level and was found to differ from that of adjacent cell types. Embryonal laticifers possess numerous vesicles with electron-dense contents, but lack a large organized central vacuole. Plastids have few lamellae, possess phytoferritin, and accumulate small amounts of starch. Other organelles and membrane systems are similar to those in other cells. After germination, laticifers develop numerous elongated vacuoles by dilation of endoplasmic reticulum. Nuclei in laticifers within the hypocotyl of seedlings are highly lobed and possess dilated perinuclear spaces. Plastids and other organelles are similar to those observed in the protoplast of laticifers in the embryo. The latex or rubber component of the laticifer is not apparent in mature embryos of 72-hr seedlings.     

Stem surface injuries of 20 species of succulent Euphorbia (Euphorbiacae) from South Africa

Cactus and succulent Euphorbia plants have green stems that are exposed to sunlight over long periods. Previous research demonstrated that barking injuries occur to stem surfaces of 20 species of cacti in the Americas. For these 20 cactus species the amounts of injuries were related to annual amounts of sunlight exposure on surfaces. Cacti with many injuries had high mortality rates. Data herein show that stem surfaces of 20 species of Euphorbia in South Africa have identical surface injuries as for cacti. Euphorbia plants at 30°S show a mean ratio of scale and bark injuries of 3.5:1 of equatorial-facing to polar-facing surfaces, a ratio is similar to the 4:1 of annual sunlight exposure ratio at that latitude. Results show that Euphorbia stems have injuries on younger tissues than cactus species. Thus, Euphorbia stems are more sensitive than cactus stems. Euphorbia species with most stem injuries had smooth (non-undulate) surfaces, a one-celled epidermal cell layer only, cortex cells that abutted the epidermis, and initial injuries that involved only epidermal cells. This is the first report of identical stem surface injuries to Euphorbia species that are identical to surface injuries to cactus species worldwide. Moreover, the amounts on stem injuries on Euphorbia and long-lived, columnar cactus species are highly correlated with relative amounts of sunlight on stem surfaces over the annual cycle. These results suggest that these species are good bio-indicators of annual sunlight exposure.     

Aristolochia bidoupensis sp. nov. from southern Vietnam

Aristolochia bidoupensis Do sp. nov. is newly described. This new species, currently only known from southern Vietnam, is most similar to Aristolochia faviogonzalezii (northern Vietnam) and A. moupinensis (China), but can be distinguished from the latter two by the following characters: flowers terminal, axillary, solitary, peduncle 1.3–1.5 cm long, bracteole ovate, 3–4 × 2–3 mm, limb discoid‐shaped with three expanded lobes, not revolute, internal surface uniformly dark purple, smooth, throat uniformly golden without dots. Morphological characters such as a 3‐lobed gynostemium and a 3‐lobed limb place the new species in A. subgen. Siphisia.     

陕西分布10种大戟属植物茎叶形态结构比较

利用石蜡切片法、叶表皮装片法对陕西分布10种大戟属植物茎叶的形态结构进行了比较观察。结果表明:(1)10种植物叶的上下表皮细胞形态、气孔分布及大小等指标存在明显差异,茎的结构在各种之间也存在一定差异。(2)用Statistica 6.0分析软件对所测的性状特征值进行了主成分分析和聚类分析,结果发现,在10种植物中,甘遂与其他种的亲缘关系最远,南大戟与华北大戟的亲缘关系较近,斑地锦与地锦草亲缘关系最近。该研究结果为大戟属植物的分类研究奠定了理论依据。     

A Phylogeny of Euphorbieae Subtribe Euphorbiinae (Euphorbiaceae) Based on Molecular Data

Phylogenetic relationships within Euphorbiinae were inferred from our analysis of the 3′; end of the chloroplast gene ndhF. A sampling of that subtribe covered 88 species; 3 closely related species from the subtribes Anthosteminae and Neoguillauminiinae and the tiribe Hippomaneae were included as outgroups. A phylogenetic assessment was carried out using the parsimony approach. The relationships revealed via these ndhF data supported the monophyly of subg.Esula, subg.Chamaesyce, subg.Euphorbia, and subg.Lacanthis. However, the polyphyly of subg.Agaloma, subg.Lyciopsis, and subg.Eremophyton also was strongly suggested. The African succulent Euphorbiinae can be divided into primarily two independent groups: 1) spiny succulents, which form a strongly supported clade with three subclades (subg.Euphorbia, subg.Lacanthis, andMonadenium+Synadenium); and 2) non-spiny succulents, which consist of sect.Meleuphorbia, sect.Medusae, sect.Anthacantha, sect.Trichadenia, sect.Pseudeuphorbium, sect.Treisia, and sect.Pseudacalypha. In the ndhF tree, the subg.Esula clade is placed as a sister to the rest of the Euphorbiinae. Thus, the origin of theEuphorbia s.I. should be sought within the herbaceous species of subg.Esula. The core North American endemicEuphorbia groups --Agaloma, Chamaesyce, andPoinsettia — are monophyletic and independent of the South American subg.Agaloma. Instead, they are derived from the AfricanEuphorbia subg.Lyciopsis andEremophyton. The Eurasian subg.Esula clade forms two subclades, which are concordant to sect.Esula and sect.Tithymalus.     

Nickel localization in tissues of different hyperaccumulator species of Euphorbiaceae from ultramafic areas of Cuba

Pantropical species of the genera Phyllanthus and Euphorbia and the Cuban endemic genus Leucocroton from the Euphorbiaceae family, were selected for nickel localization microanalysis. Scanning Electron Microscopy coupled with Energy Dispersive X-ray Microanalysis (SEM-EDX) was used for qualitative detection of nickel in the selected Ni-hyperaccumulator species: Euphorbia helenae, Leucocroton linearifolius, L. flavicans Phyllanthus orbicularis, P. discolor and P. xpallidus, all collected from Cuban ultramafic soils. The leaves and stems from the Euphorbiaceae species analyzed were the organs with higher nickel accumulation. Elemental mapping of leaves and stem tissues from these species have been compared. The highest Ni concentrations were found in the laticifer tubes of stems and the epidermis tissues of leaves in all the analyzed species, suggesting a general pattern of the Euphorbiaceae family for nickel accumulation. The high nickel concentrations and its rather homogeneous distribution found in leaves of these Ni-hyperaccumulating plants suggest a possible role in protection mechanisms against environmental stress, such as UV irradiation.     

Effects of floral restrictiveness and stigma size on heterospecific pollen receipt in a prairie community

Plant species vary greatly in the degree to which floral morphology restricts access to the flower interior. Restrictiveness of flower corollas may influence heterospecific pollen receipt, but the impact of floral morphology on heterospecific pollen transfer has received little attention. We characterized patterns of pollinator visitation and quantities of conspecific and heterospecific pollen receipt for 29 species with a range of floral morphologies in a prairie community dominated by the introduced plant Euphorbia esula (leafy spurge) which has an unrestrictive morphology. Pollinator overlap was significantly greater between Euphorbia and other unrestrictive flowers than restrictive flowers. Compared to flowers with restrictive morphologies, unrestrictive flowers received significantly more Euphorbia pollen, more heterospecific pollen from other sources, and a greater diversity of pollen species, but not more conspecific pollen. However, stigmatic surface area was significantly larger for flowers with unrestrictive morphologies, and the density of Euphorbia and other heterospecific pollen per stigmatic area did not significantly differ between flower types. These findings suggest that the smaller stigma size in restrictive flowers partly accounts for their decreased heterospecific pollen receipt, but that restrictiveness also allows species to increase the purity of pollen loads they receive. Given that restrictive flowers receive fewer heterospecific pollen grains but at a higher density, the effect of restrictiveness on fecundity depends on whether absolute quantity or density of heterospecific pollen affects fecundity more. Our results also indicate that abundant neighbors are not necessarily important heterospecific pollen sources since Euphorbia pollen was rarely abundant on heterospecifics.