Inferring the geometry of fourth-period metallic elements in arabidopsis thaliana seeds using synchrotron-based multi-angle X-ray fluorescence mapping

BACKGROUND: Improving our knowledge of plant metal metabolism is facilitated by the use of analytical techniques to map the distribution of elements in tissues. One such technique is X-ray fluorescence (XRF), which has been used previously to map metal distribution in both two and three dimensions. One of the difficulties of mapping metal distribution in two dimensions is that it can be difficult to normalize for tissue thickness. When mapping metal distribution in three dimensions, the time required to collect the data can become a major constraint. In this article a compromise is suggested between two- and three-dimensional mapping using multi-angle XRF imaging. METHODS: A synchrotron-based XRF microprobe was used to map the distribution of K, Ca, Mn, Fe, Ni, Cu and Zn in whole Arabidopsis thaliana seeds. Relative concentrations of each element were determined by measuring fluorescence emitted from a 10 microm excitation beam at 13 keV. XRF spectra were collected from an array of points with 25 or 30 microm steps. Maps were recorded at 0 and 90 degrees , or at 0, 60 and 120 degrees for each seed. Using these data, circular or ellipsoidal cross-sections were modelled, and from these an apparent pathlength for the excitation beam was calculated to normalize the data. Elemental distribution was mapped in seeds from ecotype Columbia-4 plants, as well as the metal accumulation mutants manganese accumulator 1 (man1) and nicotianamine synthetase (nasx). CONCLUSIONS: Multi-angle XRF imaging will be useful for mapping elemental distribution in plant tissues. It offers a compromise between two- and three-dimensional XRF mapping, as far as collection times, image resolution and ease of visualization. It is also complementary to other metal-mapping techniques. Mn, Fe and Cu had tissue-specific accumulation patterns. Metal accumulation patterns were different between seeds of the Col-4, man1 and nasx genotypes.     

霍山石斛组培苗移栽后微观结构与微区元素的变化研究

采用扫描电镜及X射线能谱仪技术,研究霍山石斛组培苗移栽后各器官组织的微观结构和所含元素的变化,以了解霍山石斛组培苗生长发育以及药效成分的状况。结果表明:(1)霍山石斛组培苗移栽2个月后,根增粗近1倍,具有根被,且根被细胞壁的网络状增厚更加明显,表皮、皮层、中柱发育分化更加完善,Mg、Si、Cl、S、K、Ca元素含量提高,其中Ca增长了2.76倍。(2)茎表面纵向凹陷增多,内部结构致密,维管束发育较为完善,细胞内充满物质,Mg、Si、Cl、S、K、Ca、Fe、Cu、Zn元素含量增多,尤其是K和Fe分别增长了3.25倍和4.61倍。(3)叶增厚,具有了角质层,气孔形状更加饱满,叶肉细胞内含物丰富,Mg、Si、Cl、S、K、Ca、Fe、Mn、Zn的含量显著上升,其中K升高了17倍。(4)与根、叶相比,茎中所富集的元素种类最多。研究认为,霍山石斛试管苗移栽后,生长发育趋向完善,各项功能增强,细胞内含物质增多,元素成分丰富并且含量提高,体现出对移栽环境的良好适应性。     

Cesium toxicity in Arabidopsis

Cesium (Cs) is chemically similar to potassium (K). However, although K is an essential element, Cs is toxic to plants. Two contrasting hypotheses to explain Cs toxicity have been proposed: (1) extracellular Cs+ prevents K+ uptake and, thereby, induces K starvation; and (2) intracellular Cs+ interacts with vital K(+)-binding sites in proteins, either competitively or noncompetitively, impairing their activities. We tested these hypotheses with Arabidopsis (Arabidopsis thaliana). Increasing the Cs concentration in the agar ([Cs](agar)) on which Arabidopsis were grown reduced shoot growth. Increasing the K concentration in the agar ([K](agar)) increased the [Cs](agar) at which Cs toxicity was observed. However, although increasing [Cs](agar) reduced shoot K concentration ([K](shoot)), the decrease in shoot growth appeared unrelated to [K](shoot) per se. Furthermore, the changes in gene expression in Cs-intoxicated plants differed from those of K-starved plants, suggesting that Cs intoxication was not perceived genetically solely as K starvation. In addition to reducing [K](shoot), increasing [Cs](agar) also increased shoot Cs concentration ([Cs](shoot)), but shoot growth appeared unrelated to [Cs](shoot) per se. The relationship between shoot growth and [Cs](shoot)/[K](shoot) suggested that, at a nontoxic [Cs](shoot), growth was determined by [K](shoot) but that the growth of Cs-intoxicated plants was related to the [Cs](shoot)/[K](shoot) quotient. This is consistent with Cs intoxication resulting from competition between K+ and Cs+ for K(+)-binding sites on essential proteins.     

Bundle sheath cells of small veins in maize leaves are the location of uptake from the xylem.

Rb(+) as a tracer for K(+) was used to test the hypothesis that uptake of K(+) from xylem vessels of small veins into the symplast of maize leaves occurs at the xylem/bundle sheath cell interface. 22.5 min after immersing cut leaves into 20 mM RbCl+1 mM KCl, Rb(+) appeared in the cells of the leaves. Sections of these leaves were freeze-dried. In cryo-thin sections (5 microm), (85)Rb(+) and (41)K(+) content was determined by laser microprobe mass analysis with a large resolution of about 1 microm. Determining the ratio of (85)Rb(+) to (41)K(+) in the cell walls and cytosols of bundle sheath cells, mesophyll cells, and in the cells between the xylem elements resulted in the following picture: In small veins, Rb(+) entered the symplast directly at the xylem/bundle sheath cell interface.     

中国660种陆生植物叶片8种元素含量特征

对全国范围内120个样点660种陆生植物共1781个植物样本的叶片S、K、Na、Fe、Ca、SiO2、Al、Mn含量特征进行了研究。各元素的平均含量大小顺序为KCaSiO2NaSAlFeMn,总体上属于KCa型。与世界陆生植物平均元素含量相比较,我国植物叶片Na的含量偏高。除Ca在草本植物中的含量低于木本植物外,为满足快速生长的需要,S、K、Na、Fe、Ca、SiO2的含量草本植物木本植物、落叶植物常绿植物、阔叶植物针叶植物,而Mn的含量在这些功能组却刚好相反,Al的含量变化不大。S、K、SiO2在针叶林中的含量最低,S、Na、Fe在荒漠植物中的含量最高。Ca与SiO2、Al,以及Mn与除Al之外的其他6种元素之间均呈极显著负相关(P0.01),除此之外,植物元素含量间的相关关系都为极显著正相关(P0.01)。植物叶片元素含量与植物所处的地理位置的相关分析表明,S、K、Na、Fe、Ca、SiO2含量随纬度的增加而增加,Al、Mn随纬度的增加而减少;S、K、Na、Fe、SiO2、Al随经度的增加而减少,Mn随经度的增加而增加,而Ca与经度间相关性不显著。     

Mineral composition and accumulation of silicon in tissues of blueberry (Vaccinum corymbosus cv. Bluecrop) cuttings

Research was carried out with the objective of investigating the mineral composition and Si accumulation in tissues of young cuttings of blueberry (Vaccinum corymbosus L. cv. Bluecrop). Blueberry cuttings were irrigated every day for 1 hour (140 ml per pot) with river water containing 0.66 to 1.0 mol m^–3 SiO₂, and after 7 months of growth their mineral composition and silicon distribution were investigated by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The mean contents of N, K, Mg, Cu and Zn in young leaves were the same as those in old ones. On the other hand, the mean contents of P, Ca, Si, Fe and Mn in old leaves were higher than those in young leaves. Although Si is not known to be an essential element for growth of blueberries, it was the element that accumulated the most in leaves, with a mean content of 32.0 and 60.0 mg g^–1 dry weight in young and old leaves, respectively. The mean Si content in young leaves was 3.1, 56.7, 4.8, 4.9 and 85 times higher than the mean contents of N, P, K, Ca and Mg, respectively, and was 5.4, 60.0, 8.8, 6.8 and 100 times higher than in old leaves. Scanning electron microscopy and energy-dispersive X-ray spectroscopy analysis of dry ash samples showed that Si accumulated in many parts of the leaves, forming phytoliths in the upper epidermis, including some parts of the palisade mesophyll, in the lower epidermis around the stomata, including guard cells, and in some parts of the spongy mesophyll, and in the veins. There were also silica bodies of unknown origin on the upper epidermis.     

Soybean genotypic difference in growth, nutrient accumulation and ultrastructure in response to manganese and iron supply in solution culture

* BACKGROUND AND AIMS: The objective of this research was to characterize the physiology and cell ultrastructure of two soybean genotypes subjected to nutrient solutions with increasing concentrations of manganese (Mn) at two contrasting iron (Fe) concentrations. Genotypes 'PI227557' and 'Biloxi' were selected based on their distinctly different capacities to accumulate Mn and Fe. * METHODS: Bradyrhizobium-inoculated plants were grown in hydroponic cultures in a greenhouse. Nutrient solutions were supplied with Mn concentrations ranging from 0.3 to 90 microm, at either 5 or 150 microm Fe as FeEDTA. * KEY RESULTS: For both genotypes and at both Fe concentrations, Mn concentrations from 6.6 to 50 microm did not affect shoot, root and nodule mass, or leaf and nodule ureide concentration. Mn concentrations of 70 and 90 microm did not result in visible toxicity symptoms, but hindered growth and nodulation of 'Biloxi'. An Mn concentration of 0.3 microm was, however, deleterious to growth and nodulation for both genotypes, and caused an accumulation of ureides in leaves and major alterations in the ultrastructure of chloroplasts, nuclei and mitochondria, regardless of the Fe concentration. In 'PI227557', there was also a proliferation of Golgi apparatus and endoplasmic reticulum in the cytoplasm of leaf cells, and nodules showed disrupted symbiosomes lacking poly-beta-hydroxybutirate grains concomitantly with a proliferation of endoplasmic reticulum as well as arrested bacterial division. At 15 microm Fe, ferritin-like crystals were formed in the lumen of chloroplasts of 'PI227557' plants. For both genotypes, there was an antagonism between the Fe and Mn concentrations in leaves, the higher values of both microelements being detected in 'PI227557'. The absence of any detectable relationship between Fe or Mn and zinc, phosphorus and copper concentrations in leaves ruled out those micronutrients as relevant for Mn and Fe nutrition in soybeans. * CONCLUSIONS: The results confirmed the greater capacity of 'PI227557' for Mn and Fe accumulation than 'Biloxi' for most nutrient treatments. Hence, 'PI227557' may be a very useful genetic resource both in developing soybean cultivars for growth on low nutrient soils and in physiological studies to understand differing approaches to nutrient accumulation in plants.     

Leaf anatomy and ultrastructure of the Crassulacean-acid-metabolism plant Kalanchoe daigremontiana

Light-microscopic analysis of leaf clearings of the obligate Crassulacean-acid-metabolism (CAM) species Kalanchoe daigremontiana Hamet et Perr. has shown the existence of unusual and highly irregular venation patterns. Fifth-order veins exhibit a three-dimensional random orientation with respect to the mesophyll. Minor veins were often observed crossing over or under each other and over and under major veins in the mesophyll. Paraffin sections of mature leaves show tannin cells scattered throughout the mesophyll rather evenly spaced, and a distinct layer of tannin cells below the abaxial epidermis. Scanning electron microscopy showed that bundle-sheath cells are distinct from the surrounding mesophyll in veins of all orders. Transmission electron microscopy demonstrated developing sieve-tube elements in expanded leaves. Cytosolic vesicles produced by dictyosomes undergo a diurnal variation in number and were often observed in association with the chloroplasts. These vesicles are an interesting feature of cell ultrastructure of CAM cells and may serve a regulatory role in the diurnal malic-acid fluctuations in this species.Abbreviations CAM Crassulacean acid metabolism - SEM scanning-electron microscopy - TEM transmission-electron microscopy     

Effect of Meloidogyne incognita on Plant Nutrient Concentration and Its Influence on the Physiology of Beans

Phaseolus vulgaris plants, 3, 8, 11, and 13 days old, were inoculated with 0, 2,000, 4,000, or 8,000 second-stage Meloidogyne incognita larvae and maintained under controlled conditions. The photosynthetic rate and the shoot and root concentration of K, Ca, Mn, Fe, Cu, and Zn were determined by destructive assay at 1-27-day intervals and by nondestructive assay of leaves, stems, and roots at 27 or 28 days after inoculation. In the destructive assay, the concentration of the elements in the plant tissues did not change until 1 week after inoculation. Thereafter, the trend was mostly decreasing for shoot K and Fe and increasing in the root, whereas Ca had the opposite trend in the shoots. Manganese, Cu, and Fe showed variable trends. Generally, the concentration of K and Mn increased, whereas Ca and Fe decreased, with duration of infection in all treatments. Zinc and Cu decreased in the highest nematode treatments. The overall elemental content generally decreased with level of infection from 1 week after inoculation. Photosynthetic rate based on shoot K concentration significantly decreased with level of infection. In most of the nondestructive assays, the concentrations of shoot K, Zn, and Mn decreased, whereas Ca increased with increasing nematode treatment. One of the first effects of the nematode on host physiology appears to be a change in concentration of nutrient elements in the host plant.     

Cesium-insensitive mutants of Arabidopsis thaliana

The molecular analysis of solute transport across the plasma membrane in animals and microorganisms has been aided by the analysis of well-defined transport mutants. To obtain mutant plants with genetic defects in cation transport, the inhibitory effect of monovalent cations (Li⁺, Na⁺, Rb⁺, and Cs⁺) on Arabidopsis thaliana seed germination was tested. Cesium was unique in that at low concentration it strongly inhibited seedling development. In this report it is demonstrated that cesium is a competitive inhibitor for potassium transport in A. thaliana and its toxicity is closely tied to the level of potassium supplied. Conditions were obtained to maximize the cesium-sensitivity for seed germination in a large population, and selection for resistance using M₂ seeds derived from ethyl methane sulfonate (EMS)-treated plants yielded several dozen resistant plants. Seeds derived from these plants yielded cesium-insensitive mutant lines with heritable changes in energy-dependent potassium uptake. In progeny from a backcross to wild-type plants, at least one of the lines showed the segregation ratio expected for a single-gene recessive mutation and an RFLP analysis mapped the mutant locus to the top of chromosome 4.     

岷江上游干旱河谷海拔梯度上白刺花叶片生态解剖特征研究

对岷江上游干旱河谷海拔梯度上（1 650～1 950 m）白刺花(Sophora davidii)叶片进行生态解剖学研究.观测指标包括叶片形态特征（叶长宽比、叶面积、叶片厚度）、解剖结构（表皮厚度、栅栏组织厚度(P)、海绵组织厚度(S)、P/S比值、表皮角质膜厚度）及叶表皮特征（气孔器密度和面积、表皮细胞密度和面积、表皮毛密度和长度）.结果表明,白刺花叶片面积为0.144～0.208 cm²,叶总厚度为171.58～195.83 μm;叶肉组织分化明显,栅栏组织厚度与海绵组织厚度分别为69.83～82.42和62.00～ 80.67 μm,P/S的比值为1.14～1.01,上下表皮厚度分别为14.03～15.33和13.88～16.17 μm,上下角质膜厚度分别为2.66～4.56和2.76～2.02 μm;气孔密度为13.71～15.02个·mm^-2,其面积为249.86～280.43 μm²;表皮细胞密度为160.54～178.43个·mm^-2,其面积为557.43～626.85 μm²;表皮毛长度为186.51～260.99 μm,其密度为18.29～32.27个·mm^-2.随海拔升高叶面积、叶厚度、栅栏组织和海绵组织的厚度、气孔器面积、表皮细胞面积以及表皮毛密度呈增加趋势,而角质膜厚度、表皮细胞密度和表皮毛长度则呈减小趋势;叶长宽比、P/S的比值、表皮厚度与气孔器密度无明显差异.     

铯进入红细胞的NMR研究

在生理及生化研究中铯离子的行为受到极大的关注,因为可由它来阐述碱金属离子输运及酶活性等一些基本功能。当所研究的体系中没有K~+时,Cs离子有类似K~+的功能,它能激活Na/K ATPase。Cs进入细胞的速率及激活Na/K ATPase所要求的浓度与被研究系统的条件密切有关。本文用核磁共振谱方法测定红细胞内外的Cs~+及Cs~+进入细胞的速率。结果表明Cs-133的核磁共振谱是研究生物体系离子的分布及输运的极好工具。     

Intercellular Compartmentation of Ions in Barley Leaves in Relation to Potassium Nutrition and Salinity

X-ray microanalysis was used to determine the distributionsof several nutrient elements between vacuoles of epidermal andmesophyll cells in barley leaves and these distributions wererelated to shoot nutrient concentrations. Under the growth conditionsused, P was found only in mesophyll vacuoles, never in the epidermis.In contrast, Cl and Ca were located almost exclusively in theepidermis while K and Na were more evenly distributed betweenthe two cell types. The compartmentation of Ca and Cl in theepidermis was maintained over a wide range of tissue concentrationsof these ions. In particular, Cl was excluded from the mesophyllof salt-grown barley until the tissue concentration reachedabout 170 mol m^–3 and then it appeared in the vacuolesof these cells, but only at low concentrations. In contrast,Na was not excluded from the mesophyll of salt-grown or K-deficientbarley and there was evidence that this ion was preferentiallyaccumulated in the mesophyll. Nutrients were evenly distributedbetween the adaxial and abaxial epidermal layers, except K.which was at slightly higher concentrations in the adaxial epidermis.There was considerable variation in the concentrations of ionsin adjacent epidermal cells. The results indicate that intercellularcompartmentation of nutrients occurs in barley leaves and therole of this phenomenon in responses to nutrient deficienciesand salinity is discussed Key words: Compartmentation, barley, salinity, ions, potassium nutrition     

Technical advance: reduction of Fe(III)-chelates by mesophyll leaf disks of sugar beet. Multi-component origin and effects of Fe deficiency

The characteristics of the Fe(III)-chelate reductase activity have been investigated in mesophyll disks of Fe-sufficient and Fe-deficient sugar beet leaves. The Fe(III)-chelate reductase activity of mesophyll disks was light dependent and increased markedly when the epidermis was removed. Iron(III)-citrate was photo-reduced directly by light in the absence of plant tissue. Total reductase activity was the sum of enzymatic mesophyll reduction, enzymatic reduction carried out by organelles exposed at the disk edge and reduction caused by the release of substances both by exposed mesophyll cells and at the disk edge. Compounds excreted were shown by HPLC to include organic anions, mainly oxalate, citrate and malate. When expressed on a leaf surface basis, Fe deficiency decreased the total mesophyll Fe(III)-chelate reductase activity. However, Fe-sufficient disks reduced less Fe than the Fe-deficient ones when expressed on a chlorophyll basis. The optimal pH values for Fe(III) reduction were always in the range 6.0-6.7. In control leaves Fe(III)-citrate and Fe(III)-malate were the substrates that led to the highest Fe reduction rates. In Fe-deficient leaves Fe(III)-malate led to the highest Fe reduction rates, followed by Fe(III)-EDTA and then Fe(III)-citrate. K:(m) values for the total reductase activity, enzymatic mesophyll reduction and enzymatic reduction carried out by organelles at the disk edge were obtained.     

Long duration responses in squid giant axons injected with 134cesium sulfate solutions

Giant axons from the squid were injected with 1.5 M cesium sulfate solutions containing the radioactive isotopes 42K and 134Cs. These axons, when stimulated, gave characteristic long duration action potentials lasting between 5 and 45 msec. The effluxes of 42K and 134Cs were measured both under resting conditions and during periods of repetitive stimulation. During the lengthened responses there were considerable increases in potassium efflux but only small increases in cesium efflux. The selectivity of the delayed rectification process was about 9 times greater for potassium ions than for cesium ions. The data suggest that internal cesium ions inhibit the outward potassium movement occurring during an action potential. The extra potassium effluxes taking place during excitation appear to be reduced in the presence of cesium ions to values between 7 and 22% of those expected in the absence of cesium inhibition.     

Extracellular Ca2+ ameliorates NaCl-induced K+ loss from Arabidopsis root and leaf cells by controlling plasma membrane K+ -permeable channels

Calcium can ameliorate Na+ toxicity in plants by decreasing Na+ influx through nonselective cation channels. Here, we show that elevated external [Ca2+] also inhibits Na+ -induced K+ efflux through outwardly directed, K+ -permeable channels. Noninvasive ion flux measuring and patch-clamp techniques were used to characterize K+ fluxes from Arabidopsis (Arabidopsis thaliana) root mature epidermis and leaf mesophyll under various Ca2+ to Na+ ratios. NaCl-induced K+ efflux was not related to the osmotic component of the salt stress, was inhibited by the K+ channel blocker TEA+, was not mediated by inwardly directed K+ channels (tested in the akt1 mutant), and resulted in a significant decrease in cytosolic K+ content. NaCl-induced K+ efflux was partially inhibited by 1 mm Ca2+ and fully prevented by 10 mm Ca2+. This ameliorative effect was at least partially attributed to a less dramatic NaCl-induced membrane depolarization under high Ca2+ conditions. Patch-clamp experiments (whole-cell mode) have demonstrated that two populations of Ca2+ -sensitive K+ efflux channels exist in protoplasts isolated from the mature epidermis of Arabidopsis root and leaf mesophyll cells. The instantaneously activating K+ efflux channels showed weak voltage dependence and insensitivity to external and internal Na+. Another population of K+ efflux channels was slowly activating, steeply rectifying, and highly sensitive to Na+. K+ efflux channels in roots and leaves showed different Ca2+ and Na+ sensitivities, suggesting that these organs may employ different strategies to withstand salinity. Our results suggest an additional mechanism of Ca2+ action on salt toxicity in plants: the amelioration of K+ loss from the cell by regulating (both directly and indirectly) K+ efflux channels.     

VARIATIONS IN ANATOMY,ASSOCIATIONS, AND ORIGINS OF KRANZ TISSUE

Although the unique tissue required for C₄ photosynthesis in nonsucculent plants is often described as being modified leaf parenchyma sheath, which is positioned meaningfully between the mesophyll externally and the vascular tissues internally, the actual range of locations and known associations make that concept untenable. In origin the Kranz tissue develops from procambium as well as ground parenchyma. It is found in stems as well as leaves. In position Kranz tissue can lie in the parenchyma sheath, in the mestome sheath, isolated in the mesophyll, peripherally in some thick leaves, or within the veins. It can be associated with mesophyll only, mesophyll and colorless parenchyma, mesophyll and sclerenchyma, other Kranz tissue and vascular tissues, mesophyll and mestome sheath, mesophyll and phloem, mesophyll and xylem, epidermis, and, finally, mestome sheath and xylem and phloem. The use of the term Kranz is expounded.     

Integration of XAS techniques and genetic methodologies to explore Cs-tolerance in Arabidopsis

We have characterised genetically and phenotypically a T-DNA insertion mutant line of A. thaliana (L.) Heynh. selected for Cs resistance when germinating and growing on Cs concentrations up to 600microM, lethal for the wild type. Measures of concentration and localisation of Cs, K, and Ca have been conducted on plants grown in vivo also utilising synchrotron light-based techniques as micro-SRXF (synchrotron radiation induced X-ray micro-fluorescence) and micro-XANES (micro X-ray absorption near edge structure) spectroscopy. We report here an attempt to apply micro-XANES to investigate Cs speciation and to measure the Cs content of living plants. The results obtained with micro-SRXF and micro-XANES spectroscopy complemented the genetic and physiological analyses: a comparison between wild type and mutant plants led to the conclusion that in our case a single gene mutation impairs Cs uptake and translocation, K and Ca homeostasis and plant biomass production.     

Cesium Toxicity Alters MicroRNA Processing and AGO1 Expressions in Arabidopsis thaliana

MicroRNAs (miRNAs) are short RNA fragments that play important roles in controlled gene silencing, thus regulating many biological processes in plants. Recent studies have indicated that plants modulate miRNAs to sustain their survival in response to a variety of environmental stimuli, such as biotic stresses, cold, drought, nutritional starvation, and toxic heavy metals. Cesium and radio-cesium contaminations have arisen as serious problems that both impede plant growth and enter the food chain through contaminated plants. Many studies have been performed to define plant responses against cesium intoxication. However, the complete profile of miRNAs in plants during cesium intoxication has not been established. Here we show the differential expression of the miRNAs that are mostly down-regulated during cesium intoxication. Furthermore, we found that cesium toxicity disrupts both the processing of pri-miRNAs and AGONOUTE 1 (AGO1)-mediated gene silencing. AGO 1 seems to be especially destabilized by cesium toxicity, possibly through a proteolytic regulatory pathway. Our study presents a comprehensive profile of cesium-responsive miRNAs, which is distinct from that of potassium, and suggests two possible mechanisms underlying the cesium toxicity on miRNA metabolism.     

虉草营养器官解剖结构与抗旱耐涝性及利用之间的关系

为了从显微结构上进一步探讨虉草(Phalaris arundinacea L.)的抗旱耐涝性及与利用的关系,于2011年采用常规石蜡切片技术,对其根、茎叶3种营养器官进行解剖观察。结果表明,虉草根的结构自外而内依次为表皮、皮层、维管束鞘、初生韧皮部和初生木质部;茎由表皮、基本组织和维管束构成;叶片内部结构可分为表皮、叶肉和叶脉3部分。根皮层大的细胞间隙和气腔,初生木质部的后生大导管和茎基本组织解体形成的髓腔都是虉草良好的通气组织,是其耐水淹的主要显微特征。茎、叶片角质化的表皮和叶表皮所含的丰富泡状细胞组是虉草具有抗旱性的主要解剖结构特征。叶肉细胞排列紧密且只有少量气孔分布于叶片下表皮,这样的结构可减少蒸腾;叶肉细胞富含叶绿体,增强光合作用,获得更多的同化产物,确保了植株在干旱条件下也有足够的光合产物来维持正常的生理活动。茎、叶维管束部分大量的木纤维起到支撑作用。虉草根的皮层和维管柱部分、茎的基本组织和维管束部分、叶的叶脉部分都含有大面积的厚壁细胞,厚壁细胞中含有丰富的粗纤维和木质素。丰富的粗纤维、木质素等成分则是虉草能成为新能源燃料植物的必备条件。