Oogenesis in the Apogamous Fern Pteris cretica

The events that characterize egg formation and maturation inPteris cretica were investigated using transmission electronmicroscopy and electron microscope microprobe analysis. Theydid not differ significantly from those described for sexuallyreproducing ferns. The significance of these findings is discussedin relation to current theories concerning phase change in ferns. Pteris cretica, fern, apogamy, agamospory, transmission electron microscopy, oogenesis     

Phytochelatins are involved in differential arsenate tolerance in Holcus lanatus

Arsenate tolerance is conferred by suppression of the high-affinity phosphate/arsenate uptake system, which greatly reduces arsenate influx in a number of higher plant species. Despite this suppressed uptake, arsenate-tolerant plants can still accumulate high levels of As over their lifetime, suggesting that constitutive detoxification mechanisms may be required. Phytochelatins are thiol-rich peptides, whose production is induced by a range of metals and metalloids including arsenate. This study provides evidence for the role of phytochelatins in the detoxification of arsenate in arsenate-tolerant Holcus lanatus. Elevated levels of phytochelatin were measured in plants with a range of tolerance to arsenate at equivalent levels of arsenate stress, measured as inhibition of root growth. The results suggest that arsenate tolerance in H. lanatus requires both adaptive suppression of the high-affinity phosphate uptake system and constitutive phytochelatin production.     

The spores of Pteris cretica complex (Pteridaceae-Pteridophyta) in America

Spore morphology in the Pteris cretica complex, including Pteris brasiliensis, P. ciliaris, P. cretica, P. denticulata var. denticulata, P. denticulata var. tristicula, P. ensiformis, P. multifida and P. mutilata was examined using light and scanning electron microscope. The spores are trilete, triangular to circular in shape, with an equatorial thickening (= cingulum). Equatorial diameter ranges from 29 to 69 μm, and polar diameter from 18 to 53 μm. Exospore is proximally verrucate and distally rugate, with the exception of Pteris ensiformis, which has cones on both polar faces. Perispore is generally less than 1 μm thick, apparently single-layered in section, and translucent under light microscope. Spheroids were frequently observed on the surfaces of both perispore and exospore. Hyaline spores lacking cingulum were found in all specimens. Pteris brasiliensis, P. cretica and P. denticulata exhibit pronounced polymorphism and, in addition to trilete spores these taxa also produce atypical spores such as tetralete, monolete and intermediate types.     

Antheridia and Archegonia of the Apogamous Fern Pteris cretica

The external appearance of gametophytes and gametangia of Pteriscretica closely resembled those of sexually reproducing ferns.Antheridia were fully functional but archegonia were not. Despitethe formation of egg, ventral and neck canal cells, the flask-shapedarchegonia failed to open and Pteris spermatozoids failed toexhibit a chemotactic response to them. Cryo SEM revealed thatthe topmost cells of mature archegonia had collapsed, and thisis thought to account for the loss of archegonial function. Pteris cretica, fern, apogamy, antheridia, archegonia, cryo SEM     

大叶凤尾蕨的离体培养及植株再生

1　植物名称　大叶凤尾蕨 (Ｐｔｅｒｉｓｃｒｅｔｉｃａ)品种白斑大叶凤尾蕨 (ｃｖ .“Ａｌｂｏｌｉｎｅｎｅａｔａ”)。2　材料类别　叶背面成熟孢子。孢子囊群沿羽片顶部以下的叶缘连续分布 ,呈狭条形。供试植株来源于荷兰花卉市场的大叶凤尾蕨盆花。3　培养条件　 (1 )诱导孢子萌发培养基 :1 / 3ＭＳ ;(2 )初代培养基 :ＭＳ 6 ＢＡ 3 .0ｍｇ·Ｌ- 1 (单位下同 ) ＩＢＡ 3 .0 ;(3 )继代培养基 :ＭＳ 6 ＢＡ 1 .0 ＩＢＡ 1 .0 ;(4)生根培养基 :1 / 2ＭＳ ＮＡＡ 2 .0 ＩＡＡ2 .0 ;(5 )复壮培养基 :1 / 2ＭＳ 活性炭 2 0 ｇ·Ｌ- 1…     

Multifactorial Growth Responses in Holcus lanatus: Optima and Limiting Factors

A factorial, controlled-environment experiment employing fourlevels each of photosynthetically-active radiation (PAR), nutrientsupply and ambient temperature was conducted on the grass Holcuslanatus L. (Yorkshire fog). The back-transformed means of log total dry weight per plantat 28 d for the highest- and lowest-yielding treatments were533 mg and 1·8 mg respectively. An analysis of varianceshowed that all three environmental variables have strong andcomplex interaction with one another. Multivariable, polynomialresponse surfaces were fitted to answered questions such as:Where does maximal yield lie? How curved is the response? Howsteep are the gradients of yield against the three environmentalvariables? How sensitive are individual response curves to backgroundlevels of other factors? The direction of change in the logarithms of total dry weightand total leaf area was positive throughout with changes inPAR, nutrient supply and temperature, except at certain extremecombinations of factor values. For leaf area ratio, the directionof change with nutrient supply and temperature was also consistentlypositive, but with PAR it was consistently negative, creatingsaddle-point in the response surface. For all three yields variables, the response to all three factorsconsidered individually was relatively independent of variationsin the background levels of the remaining two. The ranking ofpercentage yields was particularly stable to such variationsin background, even under markedly sub-optimal combinationsof conditions. General conclusions regarding the significance of multivariatetests were drawn, with particular reference to the conduct ofinter-specific screening operations and the interpretation ofmulti-factor environment scenarios such as those involved inclimate change research.Copyright 1993, 1999 Academic Press Multifactorial experiment, temperature, photosynthetically-active radiation, mineral nutrients, response surfaces, optima, limiting factors, screening, climate change     

A new hypothesis for the origin of pentaploid Holcus from diploid Holcus lanatus L. and tetraploid Holcus mollis L. in France

The Holcus complex in France consists of two species, Holcus lanatus L. (Yorkshire fog; 2n= 2x= 14) and Holcus mollis L. (Creeping soft-grass; 2n= 4x= 28) and an interspecific hybrid H.m.×H.l. (2n= 5x= 35), which is morphologically similar to Holcus mollis. A heterologous rDNA probe from wheat was used to detect the corresponding region in Holcus (s. l.) genomic DNA'fragments, for six to eight plants from 13 populations located south-west of Paris. A restriction enzyme map of the ribosomal RNA genes (rDNA) in Holcus (s. l.) was also constructed. The length polymorphism detected in the IGS region was used as a DNA fingerprint for the identification of different cytotypes and species of the Holcus complex and for the typing and delimitation of individuals in populations. In the light of the results we reconsider the assumption that the pentaploid hybrid H.m.×H.l. is purely clonal. New hypotheses concerning the origin of the pentaploid hybrid and its reproduction are proposed, and the consequences for genetic diversity in natural populations discussed.     

Polymorphism and physiology of arsenate tolerance in Holcus lanatus L. from an uncontaminated site

The polymorphism of arsenate tolerance in a Holcus lanatus L. population from an uncontaminated soil was investigated and a high percentage of tolerant individuals (65%) was found in the population studied. Influx of arsenate was highly correlated to arsenate tolerance within the population, with the most tolerant individuals having the lowest rates of arsenate influx. Isotherms for the high affinity arsenate uptake systems were determined in six tolerant and six non-tolerant genotypes. Tolerant plants had the lowest rates of arsenate influx. This was achieved by adaptation of the V_max of arsenate influx with the V_max of the high affinity uptake system saturating at lower substrate concentrations in the tolerant plants. The polymorphism is discussed with relation to adaptation to the extreme environments to which the plants are subjected on mine-spoil soils.     

Ecotypes of Holcus lanatus Tolerant to Zinc Toxicity also Tolerate Zinc Deficiency

Genotypes tolerant to zinc (Zn) toxicity, if they accumulateZn in their roots, may grow better than Zn-sensitive genotypes,even in Zn-deficient soil. In the present study, Holcus lanatusL. ecotypes differing in tolerance to Zn toxicity were grownin Zn-deficient Laffer soil which was amended with Zn to createa range of conditions from Zn deficiency to Zn toxicity. IncreasingZn additions to the soil, up to the sufficiency level, improvedgrowth of all ecotypes. At toxic levels of added Zn, the Zn-sensitiveecotype suffered a greater decrease in growth than the Zn-tolerantecotypes. All ecotypes accumulated more Zn in roots than inshoots, with root concentrations exceeding 8 g Zn kg^-1dry weightin extreme cases. When grown in Zn-deficient or Zn-sufficientsoil (up to 0.5 mg Zn kg^-1soil added), ecotypes tolerant toZn toxicity took up more Zn, grew better and had greater rootand shoot Zn concentration than the control (Zn-sensitive ecotype).Zn-tolerant ecotypes transported more Zn, copper (Cu) and iron(Fe) from roots to shoots in comparison with the Zn-sensitiveecotype. The average Zn uptake rate from Zn-deficient soil (noZn added) was greater in the Zn-tolerant ecotypes than in theZn-sensitive ecotype. In conclusion, ecotypes of H. lanatusthat are tolerant to Zn toxicity also tolerate Zn deficiencybetter than the Zn-sensitive ecotype because of their greatercapacity for taking up Zn from Zn-deficient soil. This is thefirst report of the coexistence of traits for tolerance to Zntoxicity and Zn deficiency in a single plant genotype. Copyright2000 Annals of Botany Company Copper, heavy metal, Holcus lanatus, iron, zinc deficiency, zinc toxicity     

Copper- and arsenate-induced oxidative stress in Holcus lanatus L. clones with differential sensitivity

The biochemical responses of Holcus lanatus L. to copper and arsenate exposure were investigated in arsenate‐tolerant and ‐non‐tolerant plants from uncontaminated and arsenic/copper‐contaminated sites. Increases in lipid peroxidation, superoxide dismutase (SOD) activity and phytochelatin (PC) production were correlated with increasing copper and arsenate exposure. In addition, significant differences in biochemical responses were observed between arsenate‐tolerant and ‐non‐tolerant plants. Copper and arsenate exposure led to the production of reactive oxygen species, resulting in significant lipid peroxidation in non‐tolerant plants. However, SOD activity was suppressed upon metal exposure, possibly due to interference with metallo‐enzymes. It was concluded that in non‐tolerant plants, rapid arsenate influx resulted in PC production, glutathione depletion and lipid peroxidation. This process would also occur in tolerant plants, but by decreasing the rate of influx, they were able to maintain their constitutive functions, detoxify the metals though PC production and quench reactive oxygen species by SOD activity.     

Effects of indole-3-acetic acid on arsenic uptake and antioxidative enzymes in Pteris cretica var. nervosa and Pteris ensiformis

A hydroponic experiment was conducted to investigate the effects of indole-3-acetic acid (IAA) on arsenic (As) uptake and antioxidative enzymes in fronds of Pteris cretica var. nervosa (As hyperaccumulator) and Pteris ensiformis (non-hyperaccumulator). Plants were exposed to 2 mg L^?1 As(III), As(V) or dimethylarsinic acid (DMA) and IAA concentrations for 14 d. The biomass and total As in the plants significantly increased at 30 mg L^?1 IAA. Superoxide dismutase (SOD) activities significantly increased with IAA addition. Catalase (CAT) activities showed a significant increase in P. ensiformis exposed to three As species at 30 or 50 mg L^?1 IAA but varied in P. cretica var. nervosa. Peroxidase (POD) activities were unchanged in P. ensiformis except for a significant decrease at 50 mg L^?1 IAA under As(III) treatment. However, a significant increase was observed in P. cretica var. nervosa at 10 mg L^?1 IAA under As(III) or DMA treatment and at 50 mg L^?1 IAA under As(V) treatment. Under DMA stress, malondialdehyde contents in fronds of P. cretica var. nervosa showed a significant decrease at 10 mg L^?1 IAA but remained unchanged in P. ensiformis. Therefore, IAA enhanced As uptake and frond POD activity in P. cretica var. nervosa under As stress.     

Leaf growth in the fast-growing Holcus lanatus and the slow-growing Deschampsia flexuosa: tissue maturation

Inherent variation in the relative growth rate of grasses is negatively correlated with that in leaf mass per unit leaf area (LMA). To scrutinize this correlation, the LMA of two grass species was analysed. Changes in LMA and cell wall synthesis in leaf blades of the fast-growing grass Holcus lanatus and the slow-growing grass Deschampsia flexuosa were investigated above the elongation zone of the leaf blade. After the leaf had obtained its final length, in H. lantus final LMA values of 40-44 gm^-2 were obtained at full leaf length, whereas in D. flexuosa LMA values continued to rise to 110 gm^-2. During this period of tissue maturation the LMA value doubled in H. lanatus, whereas in D. flexuosa an increase of 30% was measured. Most of the cell walls could be hydrolysed with driselase, the residue was hydrolysed with sulphuric acid. Driselase hydrolysates were identical in sugar composition, whereas the sugars released by sulphuric acid treatment changed gradually in composition as the tissue matured. The major sites of cell wall deposition during cell maturation were the outer walls of epidermal cells, fibres adjacent to the epidermis and the mestome ring around the vascular bundles. Lignin deposition was restricted to the vascular bundles and lignin levels of the leaf blade did not exceed 0.9% of the total amount of cell wall polysaccharides. Lignin accumulation occurred mainly after the increase in LMA and is unlikely to affect measurably the growth of these leaves.     

The oviposition sites of five leafhopper species (Horn. Auchenorrhyncha) on Holcus mollis and H.lanatus

Abstract. 1. A study was made of the oviposition sites of five leafhopper species Diplocolenus abdominalis, Recilia coronifera, Errastunus ocellaris, Elymana sulphurella (Cicadellidae) and Dicranotropic hamata (Delphacidae) on the grasses Holcus mollis and H.lanatus.
2. Experiments were made in the laboratory, each insect species being provided simultaneously with a complete plant of both Holcus species.
3. Distribution of eggs within the leaf sheath and leaf blade, and their height above ground-level, were recorded.
4. The presence and size of egg groups were noted, as well as the angle of eggs to the longitudinal axis of the leaf.
5. On the basis of comparison of the vertical distribution of the eggs with availability of plant tissues, the five species can be divided into three groups: (a) D.abdominalis and R.coronifera , (b) D.hamata and E.ocellaris , (c) E.sulphurella. Species within a group, i.e. with similar distributions of eggs, have other features separating their oviposition sites.