Responses of Trapa natans L. floating laminae to high concentrations of manganese

Summary. The present study focuses on the responses of floating laminae of the Mn-tolerant hydrophyte Trapa natans L. to 1 mM Mn and their ability to accumulate the metal. Studies were carried out first on young floating laminae belonging to the second verticil of 30-day-old plants which originated from fruits that had been maintained in a 1 mM Mn-treated environment and again on the young floating laminae after 10 days of further treatment with 1 mM Mn. Mn storing was observed from the first days after germination, but only 10-day-treated laminae showed the capability to hyperaccumulate the element inside specialised cells (>20000 μg/g [dry weight]). Electron microscopy and the Folin–Ciocalteu reaction for phenolics revealed deposits of chelated material inside vacuoles of the first palisade layer and of idioblasts in the spongy tissue. X-ray microanalysis indicated that the deposits were Mn chelated with phenolic compounds. Numerous trichomes were observed at the lower epidermis of 10-day-treated laminae. They were rich in phenolics and characterised by Mn concretions at their base. As they are associated with a high concentration of the metal in culture water and sediments, trichomes may constitute a morphological differentiation for the secretion of Mn-chelating molecules into the culture water, as a probable “avoidance” mechanism. Finally, monitoring of the photosynthetic apparatus showed that photosynthetic function was not impaired, though differences in development occurred. Correspondence and reprints: Department of Natural and Cultural Resources, University of Ferrara, Corso Ercole I d’Este 32, 44100 Ferrara, Italy.     

Morpho-physiological and biochemical responses in the floating lamina of Trapa natans exposed to molybdenum

The response to molybdenum (Mo) was studied in the metal-tolerant hydrophyte Trapa natans L. Previously, it was shown that the plant accumulates Mn in the floating lamina by means of phenolic compounds and responded with acclimation responses of the chloroplast. Since the involvement of phenolics has been proposed also in Mo resistance, we tested the response of T. natans to increasing doses (5, 50, 150, 600 µM) of Mo using the photosynthetic apparatus as an indicator of cellular stress. Only 5 μM Mo did not cause evident modifications with respect to controls. Conversely, 50 to 600 μM Mo induced progressively marked alterations of the lamina morphology. The chloroplast ultrastructure showed disorganisation of the thylakoid system, and correspondingly, the photosynthetic pigment pattern was altered with a fall-down in photosynthesis. Microspectrofluorimetry indicated alterations of photosystem II, with differences among the three cell layers (first and second palisade and spongy tissues). While the highest dose caused plant death, 50 and 150 μM Mo-treated plants underwent partial recovery, and the plant survived up to the end of the vegetative season. However, reproduction was unsuccessful. Mo treatment did not induce increase in total phenolics, but only in anthocyanin. In contrast to Mn, detoxification of Mo by chelation inside vacuoles, possibly by anthocyanins, is suggested to be an insufficient mechanism to reduce Mo toxicity, which probably includes an impairment of nitrogen metabolism. However, the metal was accumulated in the lamina. On the whole, T. natans showed limited capabilities to survive Mo excess as compared with Mn.     

遮荫对金莲花光合特性和叶片解剖特征的影响

以金莲花为材料,系统研究了不同遮荫处理(全光照、40%、60%和80%遮荫)对金莲花叶片光合特性和叶解剖结构的影响,为金莲花引种驯化和抚育管理提供理论依据。结果表明:全光照下金莲花叶净光合速率有明显光合"午休"现象,遮荫处理下"午休"现象不明显。其中,40%遮荫处理显著促进了金莲花叶片净光合速率,80%遮荫处理则起抑制作用;40%和60%遮荫处理促进金莲花叶蒸腾速率和气孔导度的提高,降低了蒸汽压亏缺,有利于光合作用的进行;80%遮荫处理下胞间CO2浓度提高,气孔限制值和蒸汽压亏缺均显著高于其它处理,抑制了金莲花叶蒸腾作用和光合作用;遮荫处理降低了金莲花叶光补偿点和暗呼吸速率,40%和60%遮荫处理下表观量子效率和最大净光合速率提高,说明金莲花有一定耐荫性;金莲花叶光合特性与解剖结构关系密切。遮荫降低了金莲花叶气孔密度和气孔指数,但气孔纵轴长和横轴长显著高于对照。40%和60%遮荫处理下,单叶气孔数量没有明显变化;遮荫下金莲花叶片增厚。栅栏组织厚度和细胞层数减少,栅栏细胞宽度加大,且第二层栅栏细胞有向海绵组织过度的趋势。海绵组织厚度增加,栅栏组织/海绵组织比值减小。随遮荫度增高,栅栏组织和海绵组织细胞间隙增大。该结构有利于提高对光能的利用效率;遮荫处理促进维管束的发育,维管束数量增加,木质部、韧皮部分化明显,其中中脉导管直径和导管数目增加,有利于蒸腾作用和光合作用的进行。     

Photosystem II organisation in chloroplasts of <Emphasis Type="Italic">Arum italicum</Emphasis> leaf depends on tissue location

The growth of plants under stable light quality induces long-term acclimation responses of the photosynthetic apparatus. Light can even cause variations depending on the tissue location, as in Arum italicum leaf, where chloroplasts are developed in the lamina and in the entire thickness of the petiole. We addressed the question whether differences in plastids can be characterised in terms of protein–protein interactions in the thylakoid membranes. Thylakoid assembly was studied in the palisade and spongy tissue of the lamina and in the outer parenchyma and inner aerenchyma of the petiole of the mature winter leaf of Arum italicum. The chlorophyll–protein complexes were analysed by means of blue-native-PAGE and fluorescence emission spectra. The petiole chloroplasts differ from those in the lamina in thylakoid composition: (1) reaction centres are scarce, especially photosystem (PS) I in the inner aerenchyma; (2) light-harvesting complex (LHC) II is abundant, (3) the relative amount of LHCII trimers increases, but this is not accompanied by increased levels of PSII–LHCII supercomplexes. Nevertheless, the intrinsic PSII functionality is comparable in all tissues. In Arum italicum leaf, the gradient in thylakoid organisation, which occurs from the palisade tissue to the inner aerenchyma of the petiole, is typical for photosynthetic acclimation to low-light intensity with a high enrichment of far-red light. The results obtained demonstrate a high plasticity of chloroplasts even in an individual plant. The mutual interaction of thylakoid protein complexes is discussed in relation to the photosynthetic efficiency of the leaf parts and to the ecodevelopmental role of light.     

不同倍性大青杨的光合特性及叶片解剖结构比较

通过对二年生二倍体、三倍体和四倍体大青杨叶片结构和光合特性的研究,探讨不同倍性大青杨生长性状差异的原因。结果表明：不同倍性大青杨的净光合速率（Pn）、光饱和点（LSP）、光补偿点（LCP）等光合指标差异显著。三倍体的最大净光合速率（Pmax）高出二倍体21%。叶片厚度、表皮细胞厚度、栅栏组织厚度、栅栏组织与海绵组织厚度的比值,都是三倍体和四倍体大青杨比二倍体高,且均呈现增加的趋势。其中,四倍体大青杨表皮细胞最厚,上下表皮分别高出二倍体64%和17%。三倍体大青杨的栅栏组织厚度及栅栏组织与海绵组织厚度的比值最大,比值高出二倍体50%。通过叶片光合特性和解剖结构比较证明,三倍体和四倍体大青杨对光的适应性和光合作用能力强于二倍体。     

Comparative ultrastructural properties of pallisade tissue and spongy tissue chloroplasts from normal and mutant leaves of Pisum sativum L.*

Abstract. The ultrastructure of chloroplasts from palisade and spongy tissue was studied in order to analyse the adaptation of chloroplasts to the light gradient within the bifacial leaves of pea. Chloroplasts of two nuclear gene mutants of Pisum sativum (chlorotica-29 and chlorophyll b-less 130A), grown under normal light conditions, were compared with the wild type (WT) garden-pea cv. ‘Dippes Gelbe Viktoria’. The differentiation of the thylakoid membrane system of plastids from normal pea leaves exhibited nearly the same degree of grana formation in palisade and in spongy tissue. Using morphometrical measurements, only a slight increase in grana stacking capacity was found in chloroplasts of spongy tissue. In contrast, chloroplasts of mutant leaves differed in grana development in palisade and spongy tissue, respectively. Their thylakoid systems appeared to be disorganized and not developed as much as in chloroplasts from normal pea leaves. Grana contained fewer lamellae per granum, the number of grana per chloroplast section was reduced and the length of appressed thylakoid regions was decreased. Nevertheless, chloroplasts of the mutants were always differentiated into grana and stroma thylakoids. The structural changes observed and the reduction of the total chlorophyll content correlated with alterations in the polypeptide composition of thylakoid membrane preparations from mutant chloroplasts. In sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE), polypeptide bands with a relative molecular mass of 27 and 26 kilodalton (kD) were markedly reduced in mutant chloroplasts. These two polypeptides represented the major apoproteins of the light harvesting chlorophyll a/b complex from photosystem II (LHC-II) as inferred from a comparison with the electrophoretic mobility of polypeptides isolated from the LHC-II.     

In vivo localization of manganese in the hyperaccumulator Gossia bidwillii (Benth.) N. Snow & Guymer (Myrtaceae) by cryo-SEM/EDAX

Gossia bidwillii (Myrtaceae) is a manganese (Mn)-hyperaccumulating tree native to subtropical eastern Australia. It typically contains foliar Mn levels in excess of 1% dry weight. However, in G. bidwillii and other Mn-hyperaccumulating species, the cellular and subcellular localization of Mn has not been measured. Quantitative in vivo cryo-scanning electron microscopy (SEM)/energy dispersive X-ray analysis (EDAX) was used to localize Mn and other elements in tissue collected from mature trees growing in a natural population. Cryo-SEM showed that the leaf mesophyll is differentiated as a double-layer palisade mesophyll above spongy mesophyll. Transmission electron microscopy (TEM) revealed that the palisade and epidermal cells are highly vacuolated. EDAX data were used to estimate in situ vacuolar Mn concentrations of all cell types in fresh cryo-fixed leaf tissues. The highest average vacuolar Mn concentration of over 500 mM was found in the upper-layer palisade mesophyll, while the lowest concentration of around 100 mM was found in the spongy mesophyll. Qualitative in vivo cryo-SEM/EDAX was employed to further investigate the spatial distribution of Mn in fresh leaf tissues and young bark tissue, which was also found to have a high Mn concentration. It is concluded that Mn distribution in G. bidwillii is quantitatively different to metal distribution in other hyperaccumulating species where the highest localized concentrations of these elements occur in non-photosynthmetic tissues such as epidermal cells and associated dermal structures including trichomes and leaf hairs.     

白蜡虫7种寄主植物叶片解剖结构与寄主选择性的关系

用石蜡切片法在显微镜下观察白蜡虫[Ericerus pela(Chavannes)]7种寄主植物叶的解剖结构。结果表明,寄主植物的叶脉、表皮、栅栏组织、海绵组织、维管束解剖结构及数量性状特征在属、种间存在显著差异。7种寄主植物中,华南小蜡(Ligustrum calleryanum Decne.)和白蜡树(Fraxinus chinensis Roxb.)表皮被毛,华南小蜡表皮毛浓密,白蜡树表皮毛稀疏,其它寄主植物表皮无毛;女贞树(Ligustrum lucidum Ait.)栅栏组织、海绵组织和叶脉的厚度最厚、维管束直径最大,其它寄主植物相对较小。因此,叶片表面光滑、叶脉发达、叶片肥厚是白蜡虫优良寄主植物的重要解剖学特征。7种寄主植物中脉和侧脉发达,近轴面凹陷,远轴面突起,肉脉包埋在叶肉中,推测叶脉突起和凹槽可能是白蜡虫固定位点选择的关键线索。     

Leaf responses to iron nutrition and low cadmium in peanut: anatomical properties in relation to gas exchange

Aims

This study evaluated how iron nutrition affect leaf anatomical and photosynthetic responses to low cadmium and its accumulation in peanut plants.

Methods

Seedlings were treated with Cd (0 and 0.2 μM CdCl₂) and Fe (0, 10, 25, 50 or 100 μM EDTA-Na₂Fe) in hydroponic culture.

Results

Cadmium accumulation is highest in Fe-deficient plants, and dramatically decreased with increasing Fe supply. The biomass, gas exchange, and reflectance indices were highest at 25 μM Fe²⁺ treatments, indicating the concentration is favorable for the growth of peanut plants. Both Fe deficiency and Cd exposure impair photosynthesis and reduce reflectance indices. However, they show different effects on leaf anatomical traits. Fe deficiency induces more and smaller stomata in the leaf surface, but does not affect the inner structure. Low Cd results in a thicker lamina with smaller stomata, thicker palisade and spongy tissues, and lower palisade to spongy thickness ratio. The stomatal length and length/width ratio in the upper epidermis, spongy tissue thickness, and palisade to spongy thickness ratio were closely correlated with net photosynthetic rate, stomatal conductance, and transpiration rate.

Conclusions

Cd accumulation rather than Fe deficiency alters leaf anatomy that may increase water use efficiency but inhibit photosynthesis.     

山茶属五种植物叶片解剖特征及与光合生理相关性研究

利用扫描电子显微镜观察山茶属（ＣａｍｅｌｌｉａＬｉｎｎ．）五种植物叶片解剖特征,并与光合生理相关性进行分析。实验选择的五种植物均为Ｃ３植物,其中小黄花茶（ＣａｍｅｌｌｉａｌｕｔｅｏｆｌｏｒａＹ．Ｋ．Ｌｉ）和四球茶（Ｃ．ｔａｃｈａｎｇｅｎｓｉｓＦ．Ｃ．Ｚｈａｎｇ）为阴性植物．叶绿素含量较高;咸宁短柱茶（Ｃ．ｓａｌｕｅｎｅｎｓｉｓＳｔａｐｆ．ｅｘＢｅａｎ．）为偏阴性植物,叶绿素含量较低;美丽红山茶（Ｃ．ｄｅｌｉｃａｔａＹ．Ｋ．Ｌｉ）和狭叶瘤果茶（Ｃ．ｎｅｒｉｉｆｏｌｉａＣｈａｎｇ）则属于半阴性植物。它们的光合生理指标值差异取决于叶片解剖特征的差异;与光补偿点,光饱和点,净光合速率（Ｐｎ）,光呼吸速率（Ｐｒ）,暗呼吸速率（Ｄｒ）相关性最密切的解剖指标是栅栏组织厚度、栅栏组织中的细胞层数、栅栏细胞内的叶绿体数,栅栏组织厚与叶厚的比值、与栅栏细胞粗度的比值、与海绵组织厚度的比值．叶片上表皮厚、上表皮角质层厚及下表皮气孔密度亦与上述光合生理指标呈弱正相关,叶片大小、气孔器大小及气孔口长则与上述光合生理指标呈弱负相关;下表皮厚、海绵组织厚度及栅栏细胞内叶绿体大小与各项光合生理指标几乎无关。该五种植物的叶片解剖和光合生理特     

Manganese accumulation in the leaf mesophyll of four tree species: a PIXE/EDAX localization study

Little is known about the spatial distribution of excess manganese (Mn) in the leaves of tolerant plants. Recently, the first such study of a Mn hyperaccumulator showed that the highest localized Mn concentrations occur in the photosynthetic tissue. This is in contrast to reports based on localization of foliar accumulation of other heavy metals. Here, four tree species, Gossia bidwillii, Virotia neurophylla, Macadamia integrifolia and Macadamia tetraphylla, which hyperaccumulate or strongly accumulate Mn, were studied. Cross-sectional foliar Mn localization was carried out in situ using proton-induced X-ray emission/energy dispersive X-ray analysis (PIXE/EDAX). All four species contained photosynthetic tissues with multiple palisade layers. These were shown to be the primary sequestration sites for Mn. Mn was not detected in the epidermal tissues. The findings of this study demonstrate a concurrence of three traits in four tree species, that is, accumulation of excess Mn in the leaves, its primary sequestration in the photosynthetic tissues, and multiple-layer palisade mesophyll.     

A New Model for Leaf Photosynthesis Incorporating the Gradients of Light Environment and of Photosynthetic Properties of Chloroplasts within a Leaf

A leaf photosynthesis model was constructed based upon the notionthat the leaf photosynthesis is a summation of photosynthesisof each chloroplast under in situ micro-environmental conditions.Intra-leaf light environment was calculated using the valuesof transmittance and reflectance of leaf tissues reported previously.Simulations of light response curves of whole leaf photosynthesiswere carried out for the model leaves with different patternsof gradients in light environment and/or in photosynthetic activities.The results indicate that the higher absorption coefficientof chlorophyll in spongy tissue than in palisade tissue andintra-leaf vertical gradient in photosynthetic activity of thechloroplasts as reported for real dorsiventral leaves are bothadvantageous to the productivity of the leaf because these propertiesraise the efficiency of the light utilization. Intra-leaf light environment, leaf photosynthesis, light utilization, palisade tissue, photosynthetic productivity, spongy tissue     

不同类型土壤栽培对苦丁茶树叶片生长和光合特性的影响

研究苦丁茶树叶片生长与光合特性对不同类型土壤栽培的响应特征,确定最适苦丁茶栽培的土壤类型,可为高产优质化的苦丁茶种植业及其规模化生产基地的建立提供科学依据。通过土壤栽培实验研究了不同类型的土壤对苦丁茶树叶片生长、叶片解剖结构、叶绿素含量和光合特性的影响。结果表明:石灰岩土壤栽培条件下,苦丁茶叶长和叶面积比其他6种土壤栽培下的显著提高了34%—57%和43%—68%,叶绿素总量显著增加9%—33%,叶片、上下表皮、海绵组织和栅栏组织的厚度均显著高于其他6种土壤栽培。不同类型土壤栽培下苦丁茶净光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)和饱和蒸气压亏缺(Vpdl)的日变化趋势均呈单峰型,日均Pn和Tr值大小依次为:石灰岩石英砂岩玄武岩长石石英砂岩第四纪红色黏土变余砂岩煤系砂页岩,其中石灰岩土壤栽培下的日均Pn值相比其他6种土壤下的显著提高了13%—45%,且叶片最大净光合速率、表观量子效率、暗呼吸速率、光补偿点(LCP)和光饱和点(LSP)也最大,而煤系砂页岩栽培时最低,其LSP和LCP较石灰岩栽培的分别显著下降了40%和46%。综上,在7种类型的土壤中,石灰岩土壤栽培最有利于苦丁茶树叶片的生长发育、并促进叶绿素的合成和加强对光能的吸收利用,最终提高其叶片光合能力,其次为玄武岩土壤,而煤系砂页岩土壤是最不利于苦丁茶树叶片生长发育和光合作用。建议在苦丁茶种植业的发展和规模化生产基地建立时因选择由石灰岩性母岩发育的土壤进行栽培,从而提高苦丁茶的产量和品质。     

烤烟鲜叶组织结构、近红外反射率及其影响因素的研究

对烤烟品种‘中烟101’进行了叶片近红外反射率测定、组织结构解剖观察以及两者关系分析,并研究了成熟度、叶位、施氮量因素对它们的影响。结果表明：随施氮量增加、叶位上升、成熟度降低,叶片厚度、栅栏组织厚度、海绵组织厚度、组织比、比叶重均呈上升趋势,鲜烟叶近红外（800nm）反射增加;叶片厚度、栅栏组织厚度、海绵组织厚度、组织比与近红外反射率之间均呈显著正相关关系;叶片厚度能较好地预测近红外反射率,预测方程决定系数为0．871^＊＊（P〈0．001）。     

不同光合特性大豆叶的比较解剖研究

本研究选取不同光合速率的品种‘黑农 2 6’(高产低光效 )、‘黑农 40’、‘黑农 41’(高产高光效 )为材料 ,于大豆开花后的不同生育时期 ,对大豆的功能叶片、叶柄解剖学进行了研究。结果表明 :(1 )不同类型大豆的叶肉结构有明显区别。叶片厚度依次为‘黑农 40’ >‘黑农 41’ >‘黑农 2 6’。各期的基本趋势是一致的。栅栏组织的厚度和层数与叶片的厚度趋势一致。 (2 )各品种栅栏组织中的叶绿体数目均多于海绵组织 ,且高光效类型多于低光效类型。局部观察不同品种间 ,叶绿体内的基粒和间质片层结构高光效的也明显优于低光效的品种。 (3 )气孔包含数量和大小两个因素 ,气孔大小基本一致 ,下表皮数量 >上表皮 ,高光效类型 >低光效类型。 (4)各品种主脉维管束中木质部的导管数目依次为‘黑农 41’ >‘黑农 40’ >‘黑农 2 6’。     

The paraveinal mesophyll of soybean leaves in relation to assimilate transfer and compartmentation

Nitrogen and carbohydrate assimilates were temporally and spatially compartmented among various cell types in soybean (Glycine max L., Merr.) leaves during seed filling. The paraveinal mesophyll (PVM), a unique cell layer found in soybean, was demonstrated to function in the synthesis, compartmentation and remobilization of nitrogen reserves prior to and during the seed-filling stages. At anthesis, the PVM vacuoles contain substantial protein which completely disappears by two weeks into the seed filling. Distinct changes in the PVM cytoplasm, tonoplast and organelles were correlated with the presence or absence of the vacuolar material. Microautoradiography following the accumulation of several radiolabeled sugars and amino acids demonstrated the glycoprotein nature of the vacuolar material. Incorporation of methionine, leucine, glucose, and glucosamine resulted in heavy labelling of the PVM vacuole, in contrast to galactose, proline, and mannose which resulted in a much reduced labelling pattern. In addition, starch is unequally compartmented and degraded among the various leaf cells during seed filling. At the end of the photoperiod at the flowering stage, the highest starch accumulation was in the second palisade layer followed by the spongy mesophyll and the first (uppermost) palisade layer. Starch in the first palisade layer was completely degraded during the dark whereas the starch in the second palisade and spongy mesophyll was not remobilized to any appreciable extent. By mid-podfilling (approximately five weeks postanthesis) starch was absent in the first palisade layer at the end of the photoperiod while the second palisade and spongy mesophyll layers contained substantial starch. Starch was remobilized from these latter cells during the remainder of seed filling when current photosynthetic production is low. Structural changes associated with cell senescence first appear in the upper palisade layer and then progress (excluding the PVM) to the second palisade and spongy mesophyll layer. The PVM and phloem appear to retain their structural integrity into the leaf yellowing stage. Reducing sink capacity by pod removal resulted in a continued accumulation of vacuolar protein, an increase in cytoplasmic volume, and fragmentation of the vacuole in the PVM. Pod removal also resulted in an increased amount of accumulated starch (which did not turn over) in all mesophyll layers, and an increase in cell size and cell-wall thickness.     

不同光合特性大豆叶的比较解剖研究

本研究选取不同光合速率的品种‘黑农26’（高产低光效）、‘黑农40’、‘黑农41’（高产高光效）为材料,于大豆开花后的不同生育时期,对大豆的功能叶片、叶柄解剖学进行了研究。结果表明：（1）不同类型大豆的叶肉结构有明显区别。叶片厚度依次为‘黑农40’>‘黑农41’>‘黑农26’。各期的基本趋势是一致的。栅栏组织的厚度和层数与叶片的厚度趋势一致。（2）各品种栅栏组织中的叶绿体数目均多于海绵组织,且高光效类型多于低光效类型。局部观察不 同品种间,叶绿体内的基粒和间质片层结构高光效的也明显优于低光效的品种。（3）气孔包含数量和大小两个因素,气孔大小基本一致,下表皮数量>上表皮,高光效类型>低光效类型。（4）各品种主脉维管束中木质部的导管数目依次为‘黑农41’>‘黑农40’>‘黑农26’。     

The complete chloroplast genome of the chlorarachniophyte Bigelowiella natans: evidence for independent origins of chlorarachniophyte and euglenid secondary endosymbionts

Chlorarachniophytes are amoeboflagellate cercozoans that acquired a plastid by secondary endosymbiosis. Chlorarachniophytes are the last major group of algae for which there is no completely sequenced plastid genome. Here we describe the 69.2-kbp chloroplast genome of the model chlorarachniophyte Bigelowiella natans. The genome is highly reduced in size compared with plastids of other photosynthetic algae and is closer in size to genomes of several nonphotosynthetic plastids. Unlike nonphotosynthetic plastids, however, the B. natans chloroplast genome has not sustained a massive loss of genes, and it retains nearly all of the functional photosynthesis-related genes represented in the genomes of other green algae. Instead, the genome is highly compacted and gene dense. The genes are organized with a strong strand bias, and several unusual rearrangements and inversions also characterize the genome; notably, an inversion in the small-subunit rRNA gene, a translocation of 3 genes in the major ribosomal protein operon, and the fragmentation of the cluster encoding the large photosystem proteins PsaA and PsaB. The chloroplast endosymbiont is known to be a green alga, but its evolutionary origin and relationship to other primary and secondary green plastids has been much debated. A recent hypothesis proposes that the endosymbionts of chlorarachniophytes and euglenids share a common origin (the Cabozoa hypothesis). We inferred phylogenies using individual and concatenated gene sequences for all genes in the genome. Concatenated gene phylogenies show a relationship between the B. natans plastid and the ulvophyte-trebouxiophyte-chlorophyte clade of green algae to the exclusion of Euglena. The B. natans plastid is thus not closely related to that of Euglena, which suggests that plastids originated independently in these 2 groups and the Cabozoa hypothesis is false.     

太白山5种杜鹃属植物叶片光合特性及解剖结构的生态适应性研究

对分布于太白山海拔2 000～3 700 m的5种杜鹃属植物的叶片光合特性和形态解剖结构进行了研究.结果显示:头花杜鹃分布于高山灌丛,光饱和点、光补偿点高,强光适应性好,耐荫性差;爬枇杷分布于3 000～3 400 m的太白红杉林下,光饱和点较低,光补偿点最高,利用强光能力较弱,生态幅较窄;金背杜鹃、药枇杷、秀雅杜鹃分布于2 000～3 200 m的红桦、牛皮桦林下,光补偿点低,耐荫性强,生态幅宽.在形态结构上,5种杜鹃的栅海组织比均远小于1,属耐荫植物.头花杜鹃叶表密被鳞片,栅栏组织发达,通气组织发达;爬枇杷栅栏组织发达,排列紧密;金背杜鹃叶下表皮密被毛,气孔密度最高,海绵组织排列疏松;秀雅杜鹃叶上下表皮密被鳞片;药枇杷的栅栏组织厚度最小,栅海组织比最低.研究表明,5种杜鹃属植物叶片结构特征的形成是对生境条件长期适应的结果.     

Photosynthetic Characteristics of the Palisade Mesophyll and Spongy Mesophyll in the CAM/C4 Intermediate Plant,Peperomia camptotricha*

Several photosynthetic parameters were examined in the different tissue layers of leaves from the recently characterized crassulacean acid metabolism/C₄ intermediate plant, Peperomia camptotricha (Nishio and Ting, 1987). Light appears to control the development of certain photosynthetic characteristics within the tissue layers, while factors other than light seem to dictate others. Analysis of the chlorophyll content (including P700) and chlorophyll-proteins indicated that more light harvesting chlorophylls were associated with reaction centers in the tissues that were shaded by overlying tissue. Electron transport activity and chlorophyll-protein analysis indicated that the ratio of photosystem I to photosystem II in the spongy mesophyll (the abaxial tissue type and hence most shaded) was elevated relative to the overlying chlorophyll-rich median palisade mesophyll. The elevated photosystem I relative to photosystem II in the spongy mesophyll of Peperomia camptotricha may be related to C₄ metabolism and an increased requirement for ATP.