Compartmental nitrate concentrations in barley root cells measured with nitrate-selective microelectrodes and by single-cell sap sampling

Nitrate-selective microelectrodes were used to measure intracellular nitrate concentrations (as activities) in epidermal and cortical cells of roots of 5-d-old barley (Hordeum vulgare L.) seedlings grown in nutrient solution containing 10 mol · m^–3 nitrate. Measurements in each cell type grouped into two populations with mean (±SE) values of 5.4 ± 0.5 mol · m^–3 (n=19) and 41.8 ± 2.6 mol · m^–3 (n = 35) in epidermal cells, and 3.2 ± 1.2 mol · m^–3 (n = 4) and 72.8 ± 8.4 mol · m^–3 (n = 13) in cortical cells. These could represent the cytoplasmic and vacuolar nitrate concentrations, respectively, in each cell type. To test this hypothesis, a single-cell sampling procedure was used to withdraw a vacuolar sap sample from individual epidermal and cortical cells. Measurement of the nitrate concentration in these samples by a fluorometric nitrate-reductase assay confirmed a mean vacuolar nitrate concentration of 52.6 ± 5.3 mol · m^–3 (n = 10) in epidermal cells and 101.2 ± 4.8 mol · m^–3 (n = 44) in cortical cells. The nitrate-reductase assay gave only a single population of measurements in each cell type, supporting the hypothesis that the higher of the two populations of electrode measurements in each cell type are vacuolar in origin. Differences in the absolute values obtained by these methods are probably related to the fact that the nitrate electrodes were calibrated against nitrate activity but the enzymic assay against concentration. Furthermore, a 28-h time course for the accumulation of nitrate measured with electrodes in epidermal cells showed the apparent cytoplasmic measurements remained constant at 5.0 ± 0.7 mol · m^–3, while the vacuole accumulated nitrate to 30–50 mol · m^–3. The implications of the data for mechanisms of nitrate transport at the plasma membrane and tonoplast are discussed.Symbol _n ² Chi-squared with n degrees of freedom R.-G.Z. was awarded a Sino-British Friendship Scholarship sponsored by the British Council and H.-W.K. was supported by an AFRC Linked Research Grant to A.D.T for collaboration with R.A.L. We wish to thank Dr. K. Goulding for advice on ion chromatography, Dr. K. Moore for assistance with statistical analysis and Dr. J.H. Williams for advice on the microsample analysis.     

Flow cytometric evidence for endopolyploidization in cabbage (Brassica oleracea L.) flowers

Flow cytometric analysis of the nuclear DNA contents of somatic tissues from flowers of cabbage (Brassica oleracea L.) revealed extensive endoreduplication, resulting in tissues that contain cells with multiple ploidy levels (also called ’endopolyploidy’). Multiples of the haploid nuclear genome complement (1C) corresponding to 2C, 4C, 8C, 16C, 32C and 64C were observed in mature flowers. The distribution of cells with the differerent ploidy levels is tissue-specific and is characteristic of the stage of development. Nuclei of young flower buds exclusively gave 2C and 4C peaks, indicating that the tissues maintained diploid level. Endoreduplication was consistently detected during flower development. Endopolyploidy is probably common in differentiation of cabbage plants. Implications of this original feature are discussed. Received: 28 August 2000 / Revision accepted: 20 December 2000     

Composition of organic matter in sediments facing a river estuary (Tyrrhenian Sea): relationships with bacteria and microphytobenthic biomass

The relationships between the biochemical composition of sediment organic matter and bacteria and microphytobenthic biomass distribution, were investigated along the coast of Northern Tuscany (Tyrrhenian Sea). Organic matter appeared to be of highly refractory composition. Among the three main biochemical classes, proteins were the major component (0.96 mg g^-1 sediment d.w.) followed by total carbohydrates (0.81 mg g^-1 sediment d.w.) and lipids (8.1 µg g^-1 sediment d.w.). Bacterial number in surface sediments (0–2 cm) ranged from 1.7 to 24.5 × 10⁸ cells g^-1 of sediment dry weight showing a strong decrease with sediment depth. In surface sediments, significant correlations were found between bacterial biomass and protein concentration. Bacterial activity (measured by the frequency of dividing cells) was significantly related to lipid concentration. Bacterial and microphytobenthic biomass accounted for 3.1 and 18.1% respectively of the sediment organic carbon. In surface sediments bacterial lipids accounted, on average, for 27 % of total lipids, whereas bacterial proteins and carbohydrates accounted for 2.5 and 0.5% of total proteins and carbohydrates, respectively.The benthic degradation process indicated that lipids were a highly degradable compound (about 35% in the top 10 cm). Carbohydrate decreased for 25.6% in the top 10 cm, whereas proteins increased with depth, thus indicating that this compound may resist to diagenetic decomposition.These data suggest that specific organic compounds need to be measured rather than bulk carbon and nitrogen measurements in order to relate microbial biomass to the quality of organic matter.     

外源ABA、NO和H2O2对葱莲花瓣及叶片表皮气孔开闭的影响

以葱莲（Zephyranthes candida）为材料,研究不同浓度外源脱落酸、硝普钠（sodium nitroprusside,SNP）及过氧化氢对花瓣和叶片表皮气孔开闭的影响,以期为三者在切花保鲜中的应用提供新的依据。实验结果表明,10～1000μmol/L脱落酸和硝普钠均能不同程度地引起花瓣和叶片表皮气孔关闭,且花瓣气孔较叶片气孔有更高的敏感性。过氧化氢对叶片表皮气孔开闭的影响大于对花瓣气孔的影响,花瓣表皮的气孔孔径仅在1000μmol/L处理时变化显著。这说明在外源信号物质延缓切花衰老的过程中,花瓣表皮气孔的运动也可能起到了一定的作用。适当外源信号物质处理能诱导花瓣表皮气孔关闭,从而使花瓣的蒸腾作用减小,维持植物体内水势,延缓切花衰老。     

Genetic variation in leaf pigment,optical and photosynthetic function among diverse phenotypes of <Emphasis Type="Italic">Metrosideros polymorpha</Emphasis> grown in a common garden

Coordinated variation has been reported for leaf structure, composition and function, across and within species, and theoretically should occur across populations of a species that span an extensive environmental range. We focused on Hawaiian keystone tree species Metrosideros polymorpha, specifically, 13-year old trees grown (2–4 m tall) in a common garden (approximately 1 ha field with 2–3 m between trees) from seeds collected from 14 populations along an altitude–soil age gradient. We determined the genetic component of relationships among specific leaf area (SLA), the concentrations of nitrogen (N) and pigments (chlorophylls, carotenoids, and anthocyanins), and photosynthetic light-use efficiency. These traits showed strong ecotypic variation; SLA declined 35% with increasing source elevation, and area-based concentrations of N, Chl a + b and Car increased by 50, 109 and 96%, respectively. Concentrations expressed on a mass basis were not well related to source elevation. Pigment ratios expressed covariation that suggested an increased capacity for light harvesting at higher source elevation; Chl/N and Car/Chl increased with source elevation, whereas Chl a/b declined; Chl a/b was higher for populations on younger soil, suggesting optimization for low N supply. Parallel trends were found for the photosynthetic reactions; light-saturated quantum yield of photosystem II (Φ _PSII) and electron transport rate (ETR) increased with source elevation. Correlations of the concentrations of photosynthetic pigments, pigment ratios, and photosynthetic function across the ecotypes indicated a stoichiometric coordination of the components of the light-harvesting antennae and reaction centers. The constellation of coordinated morphological, biochemical and physiological properties was expressed in the leaf reflectance and transmittance properties in the visible and near-infrared wavelength region (400–950 nm), providing an integrated metric of leaf status among and between plant phenotypes.     

植物LEAFY同源基因的研究进展

本文就近10年来LEAFY(简写为LFY)同源基因的研究进展做了综合分析.通过对19种植物中已分离到的LFY同源基因的序列比较分析发现:LFY同源基因编码区核苷酸和氨基酸序列同源性都较高;在双子叶植物基因组中,拷贝数却有所不同.该基因的表达特性显示其在不同植物中表达的时间和空间有所差异.根据已知序列推导的氨基酸序列构建的系统进化树表明,单子叶植物与裸子植物的亲缘关系近于双子叶与裸子植物的亲缘关系.上述研究资料为植物成花机理研究提供了重要参考,且在研究植物系统进化方面也具有重要的意义.     

Separation and quantification of pigments from natural phototrophic microbial populations

Abstract A simple high-performance liquid chromatography (HPLC) method is described for the rapid (approx. 20 min) simultaneous separation and identification of the major chlorophylls and carotenoids from phytoplankton cells and phototrophic sulfur bacteria. Lyophilized samples were extracted with acetone in the dark at room temperature. Pigments were eluted from a silica column with a hexane-acetone mixture (80: 20, v/v). About 20 algal and bacterial chlorophyll and carotenoid pigments could be separated in one run. The method allowed for the detection of trace amounts of major carotenoids (> approx. 6 ng · 1⁻¹) and of chlorophylls and pheophytins (> approx. 200 ng · 1⁻¹) in natural samples. The method has been applied to samples from the metalimnion of Lake Vechten (The Netherlands) and has proved very useful in estimating algal and bacterial pigments simultaneously with respect to depth distribution and biomass changes of the microbial populations.     

A novel method to investigate the pollen diets of hoverflies

A novel method to investigate the pollen diets of hoverflies is described. The method dispenses with the need for dissection skills or the use of hazardous chemicals thus making it particularly useful for school, college or undergraduate projects and for amateurs. It utilises the properties of the indigestible pollen coat, or exine, which enables pollen to pass through the gut of a hoverfly intact and remain identifiable, even when defaecated. Importantly it does not require the harvesting of insects making it particularly useful for work with rare species. The method was used to investigate the pollen diet of marmalade flies (Episyrphus balteatus) caught in a meadow but it could also be used to investigate many other aspects of syrphid ecology.     

Effect of UV Irradiance on Utilization of Inorganic Nitrogen by the Antarctic Diatom Odontella weissflogii (Janisch) Grunow

Abstract: The impact of UV-B irradiation on unialgal cultures of the temperate marine diatom Odontella sinensis and of the Antarctic Odontella weissflogii was tested under controlled laboratory conditions. Uptake rates of inorganic nitrogen by Odontella sinensis were more affected by UV-B radiation than those of Odontella weissflogii. Utilization of ¹⁵N-ammonium was reduced after 3 h of UV-B exposure. Values of K_m from several marine phytoplankton species were estimated from algae not exposed to UV-B and from those after 3 h of UV-B radiation. Calculation of Lineweaver-Burk plot showed, under UV-B stress, a noncompetitive inhibition for ¹⁵NH⁺₄ uptake and a competitive inhibitory effect for ¹⁵NO^?₃ by Odontella weissflogii. The damage to ¹⁵NH⁺₄ uptake by UV-B was more pronounced under red than blue light; a contradictory result was obtained for ¹⁵NO^?₃ utilization by Odontella weissflogii. Reduction of the pigments by UV-B under white light was dependent on the exposure time; a strong depression of the contents of chlorophyllide a, chlorophyll c, diatoxanthin and the fucoxanthins was found. Contents of the chlorophylls are markedly affected by UV-B under red light whereas the chlorophyll a concentration is enhanced in blue and green light. UV-B exposure in conjunction with blue and green light led to a reduction of the protein content and an increase in the amino acid contents. The pattern of pool sizes of free amino acids varied after UV-B exposure. UV-A irradiance had no effect. The possible targets of UV-B irradiation on the uptake system of inorganic nitrogen are discussed in detail. Adaptation to the environmental conditions, e.g. via synthesis of UV stress proteins or mycosporine-like amino acids, were also considered.