ECOLOGICAL ADAPTATIONS OF SALT MARSH GRASS,DISTICHLIS SPICATA (GRAMINEAE), AND ENVIRONMENTAL FACTORS AFFECTING ITS GROWTH AND DISTRIBUTION

Salt grass is an important pioneer plant in early stages of succession. The sharp-pointed rhizomes with numerous epidermal silica cells, and the aerenchymatous network of the rhizome, leaf sheath, and roots facilitate development of the plant in heavy clays, shales, and inundated soils. In salt marshes of southern Utah, salt grass contributes to a hummock-building process that favors localized removal of salts by capillary action and evaporation. This process provides a narrow strip of soil that is favorable for the rooting of extended rhizomes. In laboratory experiments, maximum growth for Distichlis spicata, a perennial salt marsh grass, was obtained at 15,000 ppm soluble salts in nutrient solution cultures. Comparable concentrations of salts occurred in soils of the habitat from which plants were taken. Nearly equal concentrations of sodium and potassium were found in the plant tissue where the growth of the plants was optimal; such a ratio was maintained in the plants during most of the growing season. In the field the greatest amount of growth of salt grass takes place when temperatures are cool and soil moisture is quite high during the early spring. During mid-summer as air temperatures rise, crude protein in the plant decreases. During periods of high salt and water stress, morphological and anatomical adaptations of the stomata, salt glands, and trichomes of salt grass are important for survival. Stomata on exposed ridges of vascular bundles, where desiccation is greatest, usually are covered by four epidermal cells. In contrast, stomata found in the grooves between vascular bundles tend to be uncovered. The salt gland is composed of a large basal cell and a cap cell and actively excretes (in a diurnal rhythm) excess sodium, potassium, and chloride ions. A mechanism for salt excretion from this gland is postulated. The silica-containing trichomes on the leaves may play a role in cooling the leaf under conditions of high solar radiation and also serve to protect the plant against attack by herbivores.     

新疆2种盐生补血草营养器官的解剖学研究

采用叶片离析法和石蜡切片法,对生长在新疆盐渍环境中的大叶补血草[Limonium gmelinii(Willd.) Kuntze]和耳叶补血草[Limoniumotolepis(Schrenk) Kuntze]的营养器官解剖学特征进行了观察研究.结果显示,2种补血草属典型泌盐植物,茎和叶片表皮上分布有多细胞组成的盐腺;叶表皮细胞排列紧密,其外切向壁增厚,表皮外还被有厚的角质层;上下表皮都有气孔,气孔与表皮细胞平齐,为不等型气孔;其中大叶补血草为异面叶,而耳叶补血草为等面叶.2种补血草茎中都散生有多轮维管束;大叶补血草根中还有大量通气组织等.研究结果表明,2种补血草的解剖结构表现出与其生境相适应的特征.     

Ozone-induced ethylene release from leaf surfaces

Ozone-induced stress ethylene emissions from the adaxial and abaxial leaf surfaces of four plant species (Glycine max [L.] Merr. cv. Dare, Lycopersicon esculentum Mill cv. Roma VF, Eucalyptus globulus Labill. and Hedera helix L.) were studied to determine if the stress ethylene diffused through the stomata or cuticle. In plants not exposed to ozone, basal ethylene was detected above both the adaxial and abaxial leaf surfaces of all the plant species examined, indicating that some ethylene can diffuse across the leaf cuticle. Ozone induced stress ethylene production in all species examined. Significant ozone-induced ethylene concentrations were detected above both surfaces of amphistomatous soybean (Glycine) and tomato (Lycopersicon) leaves. In contrast, ozone-induced ethylene production was associated only with the leaf surface (abaxial) that contained stomata for hypostomatous blue gum eucalyptus and English ivy (Hedera) leaves; the leaf surface (adaxial) of the eucalyptus and ivy leaves which did not contain stomata did not release significant amounts of stress ethylene. These data indicate that ozone-induced stress ethylene primarily diffuses from the leaf via the stomata.     

北疆荒漠几种盐生(耐盐)植物抗逆附属结构的初步研究

利用石蜡切片、扫描电镜、临时装片等方法,对北疆荒漠的3种藜科植物—灰绿藜、费尔干猪毛菜、蒙古猪毛菜和1种菊科植物—花花柴的表皮附属结构进行了显微和超微观察研究。结果表明:(1)对四种植物的解剖结构观察显示,其叶片都含有角质层;气孔器下陷;茎中含有大量的维管束;多数种的细胞中含有簇状晶体结构;(2)四种植物表皮附属结构研究表明:花花柴表皮具有多细胞组成的盐腺和表皮毛结构;灰绿藜表皮有大量囊泡结构;蒙古猪毛菜叶表皮有短硬毛和乳突状结构;费尔干猪毛菜表皮具大量表皮毛,且表皮毛有节。上述结构和特征反映出不同植物对干旱、盐碱土生境适应的多样性,也为旱生和盐生植物的生理学研究提供了新的实验依据。     

<Emphasis Type="Italic">Virola sebifera</Emphasis> Aubl. (Myristicaceae) leaf chemical composition and implications on leaf-cutter ant foraging choice

Leaf-cutter ant plant material choice is essential for colony maintenance and growth. Plant material is used as a substrate for cultivating symbiotic fungus, and the ants’ preference for particular leaves, tends to be determined by vegetal age-related physicochemical factors. The plant species Virola sebifera Aubl. (Myristicaceae), for example, shows a large number of leaf surface trichomes. Although non-glandular, V. sebifera trichomes may gradually retain an increasing amount of chemical compounds over the lifetime of the leaf. Thus, the present study aims to investigate the role of plant chemical compounds on Atta sexdens rubropilosa preference for V. sebifera leaves of different ages. For this purpose, the chemical composition of trichomes on young and senescent leaves was analyzed, and ants’ preference tested. The chemical compositions differ between V. sebifera young and senescent leaves, with triacontane (C30) predominance in young leaves and tetratriacontane (C34) predominance in senescent leaves. Ants’ preference choice was tested by randomly offering leaves of different ages to A. sexdens rubropilosa workers, following six different treatments: (1) young leaf fragments; (2) young leaf fragments with few trichomes removed; (3) loose trichomes from young leaves; (4) senescent leaf fragments; (5) senescent leaf fragments with few trichomes removed, and (6) loose trichomes from senescent leaves. Ants’ preference was observed for young leaves fragments with a few trichomes removed and also for young leaves loose trichomes. Ants’ preference might be due to specific volatile compounds (GLV) preset in V. sebifera young leaves. Results suggest occurrence of ants’ selectivity resulting from changes on trichomes chemical composition between V. sebifera leaves different age stages.     

Artichoke Leaf Morphology and Surface Features in Different Micropropagation Stages

Artichoke (Cynara scolymus L.) leaf size and shape, glandular and covering trichomes, stomatal density, stomata shape, pore area and epicuticular waxes during micropropagation stages were studied by scanning electron microscopy (SEM) and morphometric analysis with the aim to improve the survival rate after transfer to greenhouse conditions. Leaves from in vitro shoots at the proliferation stage showed a spatular shape, ring-shaped stomata, a large number of glandular trichomes and juvenile covering hairs, but failed to show any epicuticular waxes. Leaves from in vitro plants at the root elongation stage showed a lanceolated elliptic shape with a serrated border, elliptical stomata, decreased pore area percentage, stomatal density, and mature covering trichomes. One week after transfer to ex vitro conditions, epicuticular waxes appeared on the leaf surface and stomata and pore area were smaller as compared to in vitro plants. Artichoke acclimatization may be improved by hormonal stimulation of root development, since useful morphological changes on leaves occurred during root elongation.     

The foliar micromorphology of Solanum pseudocapsicum

Foliar micromorphology of Solanum pseudocapsicum was investigated by electron microscopical examination. The leaves are characterized by anisocytic stomata which are more abundant on the abaxial surfaces. The leaves have short multicellular glandular trichomes sparsely distributed over the entire leaf surfaces. Crystal deposits were also observed on the surfaces above the stomata. Energy dispersive X-ray spectroscopy-SEM showed that Al, K, Na and Si were the major constituents of the crystals analyzed. The presence of glandular trichomes in this plant could be the source of poisonous compounds that are characteristic of this species.     

真红树和半红树植物叶片性状的比较研究

红树植物是一类生长在热带、亚热带海岸潮间带的乔木、灌木或草本植物,根据其分布特征可分为真红树植物植物和半红树植物。为了探究两者对海岸潮间带高盐、高光和缺氧等环境的生态适应策略的异同,该文选取5种真红树植物植物[卤蕨(Acrostichum aureum)、木榄(Bruguiera gymnorrhiza)、老鼠簕(Acanthus ilicifolius)、桐花树(Aegiceras corniculatum)、秋茄(Kandelia candel)]和4种半红树植物[银叶树(Heritiera littoralis)、水黄皮(Pongamia pinnata)、黄槿(Hibiscus tiliaceus)、杨叶肖槿(Thespesia populnea)]为研究对象,对叶片解剖和功能性状进行了对比研究。结果表明:(1)9种红树植物叶片的共同特征表现为均具有角质层、叶肉具有栅栏组织和海绵组织分化、气孔下陷等。(2)不同之处在于真红树植物植物叶片有蜡质层和内皮层、无表皮毛、气孔仅分布在下表皮,而半红树植物的叶片则较少有蜡质层,部分有表皮毛,无内皮层,气孔在上下表皮分布不完全一致。(3)真红树植物植物的气孔密度和比叶面积显著小于半红树植物(P<0.05),而叶片厚度、含水量、比叶重和鲜干重比则显著大于半红树植物(P<0.05)。以上结果说明真红树植物植物的叶片性状使其在维持盐度平衡及贮水保水能力方面强于半红树植物,从而能更好地适应海岸潮间带高盐环境。     

Strategies of leaf water uptake based on anatomical traits

• The ability of leaves to absorb fog water can positively contribute to the water and carbon balance of plants in montane ecosystems, especially in periods of soil water deficit. However, the ecophysiological traits and mechanisms responsible for variations in the speed and total water absorption capacity of leaves are still poorly known.
• This study investigated leaf anatomical attributes of seven species occurring in seasonal tropical high‐altitude ecosystems (rocky outcrop and forest), which could explain differences in leaf water uptake (LWU) capacities. We tested the hypothesis that different sets of anatomical leaf attributes will be more marked in plant individuals living under these contrasting environmental conditions. Anatomical variations will affect the initial rate of water absorption and the total storage capacity, resulting in different strategies for using the water supplied by fog events.
• Water absorption by leaves was inferred indirectly, based on leaf anatomical structure and visual observation of the main access routes (using an apoplastic marker), the diffusion of water through the cuticle, and non‐glandular or glandular trichomes in all species.
• The results suggest that three LWU strategies coexist in the species studied. The different anatomical patterns influenced the speed and maximum LWU capacity. The three LWU strategies can provide different adaptive advantages to adjust to temporal and spatial variations of water availability in these tropical high‐altitude environments.

     

Comparative anatomy of leaves and stems in some species of the South American genus Chrysolaena (Vernonieae,Asteraceae) and taxonomic implications

Vegetative anatomical features are poorly known in the South American genus Chrysolaena. In this study, leaves and stems of six Chrysolaena species were described and compared morphologically and anatomically using diaphanization, microtome serial sectioning and scanning electron microscopy. The species differed in leaf epidermis, type of stomata, shape of anticlinal walls of epidermal cells, trichome density, and presence or absence in stems of small air spaces in the cortical parenchyma and of druse‐shaped oxalate crystals. Furthermore, glandular trichomes and three types of non‐glandular trichomes with different number of basal cells were identified on leaves and stems. Collectively, these features proved instrumental to discriminate among the six studied species, suggesting that leaves and stems of Chrysolaena can represent a source for taxonomically useful characters. We also discuss anatomical features in relation to the environmental conditions in the species’ habitats.     

Heterophylly results in a variety of “spectral signatures” in aquatic plant species

The leaf reflectance spectra (280–887 nm) of two heterophyllous aquatic plant species Polygonum amphibium (L.) and Nuphar luteum (L.) were compared and their relation to physical properties of the leaves examined. In P. amphibium contrasting environmental conditions along water–land gradient affected the majority of anatomical and morphological properties of leaves, but less differences were observed in photosynthetic pigment and total flavonoid contents. Leaf mass per area (LMA), palisade mesophyll, leaf thickness, trichome length and anthocyanin content per dry mass were correlated to the different parts of spectra. In N. luteum natant and submerged leaves differed significantly in all measured parameters. Chlorophyll a, anthocyanin and carotenoid contents per dry mass were related to reflectance in the red region, while leaf thickness, anthocyanin and total flavonoid contents per leaf area were related to reflectance in the near infrared region. Redundancy Analysis (RDA) indicated that in P. amphibium the average length of trichomes and LMA explained 72% and 6% variability of the spectra, whereas in N. luteum anthocyanin content per dry mass, explained 57% variability of the spectra. The comparison of natant leaves of both species showed that they were more similar than different leaf types within the single species.     

Leaf dimorphism in Thuja plicata and Platycladus orientalis (thujoid Cupressaceae s. str., Coniferales): the changes in morphology and anatomy from juvenile needle leaves to mature scale leaves

Thuja plicata and Platycladus orientalis initially produce only bifacial needle leaves. When the first lateral shoots develop, the leaf morphology and anatomy changes dramatically. Subsequently, only greatly reduced, bifacial scale leaves are developed. A new kind of “superimposed bifaciality” occurs with the change from juvenile needle leaves to mature scale leaves. Anatomical dorsiventrality affects not only the individual leaf, but also the complete plagiotropic lateral shoots of Thuja, which have a sun- and shade-exposed side. The upper light-exposed median leaves show adaxial leaf anatomy, contrary to the lower shaded median leaves showing abaxial leaf anatomy. Due to their mixed exposure, the lateral leaves show a lateral differentiation. At vertical lateral shoots of Platycladus, a predominant light-exposed side is absent. Thus, the anatomical dorsiventrality does not affect the complete shoot. Here the morphological abaxial side of a scale leaf becomes functionally and physiologically adaxial by reorientation of the palisade parenchyma and stomata. In juvenile needle leaves, the palisade parenchyma is located adaxial, with the majority of stomata being located abaxial. Conversely, in mature scale leaves, the palisade parenchyma is abaxial and the majority of stomata are adaxial.     

Morpho-anatomical responses ofTrigonella foenum graecum Linn. to induced cadmium and lead stress

Effect of different concentrations of cadmium (0, 5,15, 30, 50 μg/g of soil) and lead (0,25, 50,100,200 μg/g of soil) on morphological and anatomical features ofTrigonella foenum graecum Linn, was studied at pre-flowering, flowering and post flowering stages. Morphological attributes, like number of leaves per plant, total leaf area of the plant and single leaf area, dry mass of stem, root and leaf, length of shoot, root and plant, size of stomata and stomatal pore, and the density of stomata on both epidermises were significantly reduced under metal stress at all the developmental stages. Trichome length on both epidermises increased while their density decreased under metal stress. Under cadmium stress, proportion of pith and vasculature decreased but cortex increased in the stem. Under lead stress, proportion of pith and vasculature increased but cortex decreased in the stem. In the root, proportion of vasculature and pith increased and cortex decreased in response to both cadmium and lead stresses. Dimensions of vessel element and xylem fibre in the wood of stem and root decreased under the cadmium and lead stresses. Decrease in density of vessel element in the stem and root with advancement of age was more pronounced in plants grown under cadmium and lead stresses.     

Explaining differential herbivory in sun and shade: the case of Aristotelia chilensis saplings

Differential herbivory in contrasting environments is commonly explained by differences in plant traits. When several plant traits are considered, separate correlation analyses between herbivory and candidate traits are typically conducted. This makes it difficult to discern which trait best explain the herbivory patterns, or to avoid spurious inferences due to correlated characters. Aristotelia chilensis saplings sustain greater herbivory in shaded environments than in open habitats. We measured alkaloids, phenolics, trichomes, leaf thickness and water content in the same plants sampled for herbivory. We conducted a multiple regression analysis to estimate the relationship between herbivory and each plant trait accounting for the effect of correlated traits, thus identifying which trait(s) better explain(s) the differential herbivory on A. chilensis. We also estimated insect abundance in both light environments. Palatability bioassays tested whether leaf consumption by the main herbivore on A. chilensis was consistent with field herbivory patterns. Overall insect abundance was similar in open and shaded environments. While saplings in open environments had thicker leaves, lower leaf water content, and higher concentration of alkaloids and phenolics, no difference in trichome density was detected. The multiple regression analysis showed that leaf thickness was the only trait significantly associated with herbivory. Thicker leaves received less damage by herbivores. Sawfly larvae consumed more leaf tissue when fed on shade leaves. This result is consistent with field herbivory and, together with results of insect abundance, renders unlikely that the differential herbivory in A. chilensis was due to greater herbivory pressure in open habitats.     

The impact of epicuticular wax on gas-exchange and photoinhibition in Leucadendron lanigerum (Proteaceae)

This study investigated the seasonal modification of wax deposition, and the impact of epicuticular wax on gas-exchange as well as photoinhibition in Leucadendron lanigerum, a species from the Proteaceae family with wax-covered leaf surfaces and the stomata also partially occluded by wax. The results of this study demonstrated that the deposition of epicuticular wax in L. lanigerum is dependent on the age of the leaf as well as the season, and generation and regeneration of wax occur mostly in spring while transformation and also degeneration of wax crystals occur in winter. Epicuticular waxes decreased cuticular water loss, but had little impact on leaf reflectance. The temperature of leaves without wax was lower than that of wax-covered leaves, indicating that the rate of transpiration impacted more on leaf temperature than reflectance of light in the PAR range in L. lanigerum. The wax coverage at the entrance of stomata in L. lanigerum increased resistance to gas diffusion and as a consequence decreased stomatal conductance, transpiration and photosynthesis. Also, the results indicated that epicuticular waxes do help prevent photodamage in L. lanigerum, and so this property could benefit plants living in arid environments with high solar radiation.     

Automatic measurement of stomatal density from microphotographs

Key message

An automated process using a cascade classifier allowed the rapid assessment of the density and distribution of stomata on microphotographs from leaves of two oak species.

Abstract

Stomatal density is the number of stomata per unit area, an intensively studied trait, involved in the control of CO₂ and H₂O exchange between leaf and atmosphere. This trait is usually estimated by counting manually each stoma on a given surface (e.g., a microphotograph), usually repeating the procedure with images from different parts of the leaf. To improve this procedure, we tested the performance of a cascade classifier to automatically detect stomata on microphotographs from two oak species: Quercus afares Pomel and Quercus suber L. The two species are phylogenetically close with similar stomatal morphology, which allowed testing the reuse of the cascade classifier on stomata with similar shape. The results showed that a cascade classifier trained on only 100 sample views of stomata from Q. afares was able to rapidly detect stomata in Q. afares as well as in Q. suber with a very low number of false positives (5 %/1.9 %) and a small number of undetected stomata (14.8 %/0.74 %), when partial stomata near the edge of the microphotographs were ignored. The remaining undetected stomata were due to obstacles such as trichomes. As an example of further applications, we used the positions detected by the cascade classifier to assess the spatial distribution of stomata and group them on the leaf surface. To our knowledge this is the first time that a cascade classifier has been applied to plant microphotographs, and we were able to show that it can dramatically decrease the time needed to estimate stomatal density and spatial distribution.     

Marginal and laminar hydathode-like structures in the leaves of the desiccation-tolerant angiosperm Myrothamnus flabellifolius Welw.

The fan-shaped leaves of the resurrection plant Myrothamnus flabellifolius Welw. fold during episodes of drought and consequent desiccation of the tissue. The leaf teeth of M. flabellifolius have several features characteristic of hydathodes. Tracheary elements from the three vein endings that converge in each leaf tooth subtend and extend into a cluster of cells significantly smaller than those of the adjacent mesophyll. The stomata overlying this putative epithem are larger than the other stomata on the leaf surface. Crystal violet is absorbed via these stomata in non-transpiring leaves, suggesting that they are water pores. Two to four such water pores occur per hydathode and are readily distinguished in desiccated leaves. Laminar hydathodes apparently also occur in the leaves of M. flabellifolius. Branched vein endings that terminate in short, wide tracheary elements subtend the outer edges of the abaxial leaf ridge, which otherwise lack stomata, and coincide with regions of crystal violet uptake. Guttation could not be induced in M. flabellifolius. However, desiccated leaves readily absorb liquid water through the leaf surface. The use of Calcafluor White to trace the pathway of apoplastic water movement suggests a role for both types of hydathode in foliar water uptake during rehydration while the accumulation of Sulphorhodamine G (indicating solute retrieval from the apoplast) in the epithem of transpiring plants suggests the hydathodes may be a pathway of water loss in the desiccating leaf.     

Leaf plasticity in peanut (Arachis hypogaea L.) in response to heavy metal stress

Phenotypic plasticity in morphological, anatomical and physiological traits of peanut (Arachis hypogaea L.) leaves was tested at four different concentrations of Cd, Cu and Zn under greenhouse conditions. Among 18 characteristics tested, nine were found to be the most sensitive and demonstrate the greatest phenotypic plasticity. These were: the leaf area (LA), the leaf mass per area (LMA), chlorophyll a concentration (Chl a), chlorophyll b concentration (Chl b), total chlorophyll concentration (Chl t), the effective quantum yield of photosystem II (ΦPS II), stomatal density of upper epidermis (SDU), palisade thickness (PT), and palisade to spongy thickness ratio (P/S). The plasticity of chlorophyll concentration and fluorescence parameters may be maladaptive and reflects metal toxicity to leaves, whereas the anatomical plasticity is adaptive, indicative of a tradeoff between the physiological and anatomic plasticity. The anatomical plasticity resulted in a xerophyte feature of leaves (i.e. small leaflets, thick lamina, upper epidermis, palisade mesophyll, as well as abundant and small stomata), which enhanced the capacity to resist drought caused by heavy metals via a decrease in root growth.     

珍稀植物扇脉杓兰营养器官的解剖学研究

采用石蜡切片技术对扇脉杓兰营养器官的解剖结构进行了研究。结果表明：根状茎的薄壁细胞中含丰富的淀粉粒,维管柱中分布着排列紧凑的周木维管束;根的皮层发达,有的皮层细胞中存在真菌菌丝团,木质部与韧皮部呈辐射状相间排列,根和根状茎的内皮层细胞都形成马蹄形加厚结构。茎的表面分布气孔,皮层面积较小,皮层内部的基本组织发达,外韧维管束散生分布其中,茎和叶上都附有非腺性毛;叶为等面叶,叶肉细胞排列疏松,气孔主要分布于远轴面,略外凸,保卫细胞中含有叶绿体,叶缘处的叶肉组织中含有气腔结构。扇脉杓兰营养器官的这些特征与其荫蔽湿润的生境是相适应的。     

Internal water balance of barley under soil moisture stress

Leaf water potential, leaf relative water content, and relative transpiration of barley were determined daily under greenhouse conditions at 3 growth stages: tillering to boot, boot to heading, and heading to maturity. The leaf moisture characteristic curve (relative water content versus leaf water potential) was the same for leaves of the same age growing in the same environment for the first 2 stages of growth, but shifted at the heading to maturity stage to higher leaf relative water content for a given leaf water potential. Growth chamber experiments showed that the leaf moisture characteristic curve was not the same for plants growing in different environments.

Relative transpiration data indicated that barley stomates closed at a water potential of about −22 bars at the 3 stages studied.

The water potential was measured for all the leaves on barley to determine the variation of water potential with leaf position. Leaf water potential increased basipetally with plant leaf position. In soil with a moisture content near field capacity a difference of about 16.5 bars was observed between the top and bottom leaves on the same plant, while in soil with a moisture content near the permanent wilting point the difference was only 5.6 bars between the same leaf positions.