Palisade Cell Layers Research Articles

Three-dimensional patterns of cell division and expansion throughout the development of Arabidopsis thaliana leaves.

Variations in size and shape of multicellular organs depend on spatio-temporal regulation of cell division and expansion. Here, cell division and expansion rates were quantified relative to the three spatial axes in the first leaf pair of Arabidopsis thaliana. The results show striking differences in expansion rates: the expansion rate in the petiole is higher than in the leaf blade; expansion rates in the lateral direction are higher than longitudinal rates between 5 and 10 days after stratification, but become equal at later stages of leaf blade development; and anticlinal expansion co-occurs with, but is an order of magnitude slower than periclinal expansion. Anticlinal expansion rates also differed greatly between tissues: the highest rates occurred in the spongy mesophyll and the lowest in the epidermis. Cell division rates were higher and continued for longer in the epidermis compared with the palisade mesophyll, causing a larger increase of palisade than epidermal cell area over the course of leaf development. The cellular dynamics underlying the effect of shading on petiole length and leaf thickness were then investigated. Low light reduced leaf expansion rates, which was partly compensated by increased duration of the growth phase. Inversely, shading enhanced expansion rates in the petiole, so that the blade to petiole ratio was reduced by 50%. Low light reduced leaf thickness by inhibiting anticlinal cell expansion rates. This effect on cell expansion was preceded by an effect on cell division, leading to one less layer of palisade cells. The two effects could be uncoupled by shifting plants to contrasting light conditions immediately after germination. This extended kinematic analysis maps the spatial and temporal heterogeneity of cell division and expansion, providing a framework for further research to understand the molecular regulatory mechanisms involved.

The role of the testa during development and in establishment of dormancy of the legume seed.

Timing of seed germination is one of the key steps in plant life cycles. It determines the beginning of plant growth in natural or agricultural ecosystems. In the wild, many seeds exhibit dormancy and will only germinate after exposure to certain environmental conditions. In contrast, crop seeds germinate as soon as they are imbibed usually at planting time. These domestication-triggered changes represent adaptations to cultivation and human harvesting. Germination is one of the common sets of traits recorded in different crops and termed the “domestication syndrome.” Moreover, legume seed imbibition has a crucial role in cooking properties. Different seed dormancy classes exist among plant species. Physical dormancy (often called hardseededness), as found in legumes, involves the development of a water-impermeable seed coat, caused by the presence of phenolics- and suberin-impregnated layers of palisade cells. The dormancy release mechanism primarily involves seed responses to temperature changes in the habitat, resulting in testa permeability to water. The underlying genetic controls in legumes have not been identified yet. However, positive correlation was shown between phenolics content (e.g., pigmentation), the requirement for oxidation and the activity of catechol oxidase in relation to pea seed dormancy, while epicatechin levels showed a significant positive correlation with soybean hardseededness. myeloblastosis family of transcription factors, WD40 proteins and enzymes of the anthocyanin biosynthesis pathway were involved in seed testa color in soybean, pea and Medicago, but were not tested directly in relation to seed dormancy. These phenolic compounds play important roles in defense against pathogens, as well as affecting the nutritional quality of products, and because of their health benefits, they are of industrial and medicinal interest. In this review, we discuss the role of the testa in mediating legume seed germination, with a focus on structural and chemical aspects.

Leaf anatomical and photosynthetic acclimation to cool temperature and high light in two winter versus two summer annuals

Acclimation of foliar features to cool temperature and high light was characterized in winter (Spinacia oleracea L. cv. Giant Nobel; Arabidopsis thaliana (L.) Heynhold Col-0 and ecotypes from Sweden and Italy) versus summer (Helianthus annuus L. cv. Soraya; Cucurbita pepo L. cv. Italian Zucchini Romanesco) annuals. Significant relationships existed among leaf dry mass per area, photosynthesis, leaf thickness and palisade mesophyll thickness. While the acclimatory response of the summer annuals to cool temperature and/or high light levels was limited, the winter annuals increased the number of palisade cell layers, ranging from two layers under moderate light and warm temperature to between four and five layers under cool temperature and high light. A significant relationship was also found between palisade tissue thickness and either cross-sectional area or number of phloem cells (each normalized by vein density) in minor veins among all four species and growth regimes. The two winter annuals, but not the summer annuals, thus exhibited acclimatory adjustments of minor vein phloem to cool temperature and/or high light, with more numerous and larger phloem cells and a higher maximal photosynthesis rate. The upregulation of photosynthesis in winter annuals in response to low growth temperature may thus depend on not only (1) a greater volume of photosynthesizing palisade tissue but also (2) leaf veins containing additional phloem cells and presumably capable of exporting a greater volume of sugars from the leaves to the rest of the plant.

Anatomical structure of leaf sectors with different resistance to powdery mildew (Erisiphe cruciferarum Opiz ex. L. Junell) in winter rapeseed chimera

The subject of the study was a sectorial chimera of dihaploid winter rapeseed, obtained with the help of gamma ray treatment (30 Gy) during shoot cloning in vitro. One sector of the plant was infected by <i>Erisiphe cruciferarum</i> Opiz ex. L. Junell and the other one was resistant. The anatomical structure of a leaf, divided into the two sectors along the midrib, was studied. The infected part of the leaf blade was thinner and built of a smaller number of palisade and spongy mesophyll cell layers. The size of cells in this sector, both in the epidermis and in the mesophyll, as well as the size of nuclei, chloroplasts and intercellular spaces were bigger than those in the resistant portion. On the other hand, the stomata in the infected segment were smaller but their number was higher than that in the healthy part. The study made it possible to analyse the relation between the anatomical structure of the host plant and the pathogen.

Localisation of Storage Reserves in Developing Seeds of Pongamia pinnata (L.) Pierre, a Potential Agroforestry Tree

AbstractPongamia pinnata is an important oil yielding perennial tree species. The aim of the present study was to document the histological and ultrastructural change that is occurring during pongamia seed development. The seeds were sampled at five stages of development at intervals of 3 weeks starting from 30 weeks after flowering up to 42 weeks. The seed development was followed microscopically using toluidine blue staining. The seed coat was made up of an external layer of palisade cells, an internal layer of hourglass cells followed by a parenchymatous cell layer and aleurone cell layer. The seed reserve compounds such as polysaccharides, proteins and starch showed distinct histochemical characterisation. Lignin was mainly found in the seed coat cell layers, while polysaccharides, proteins and starch granules in the cotyledon cells. The ultrastructural studies showed marked cellular changes during the seed development. The cell size varied from 9.4 to 78 μm during the seed development. The number of oil bodies per cell ranged from 200 to 300 at 42 weeks after flowering. Protein storage vacuoles were observed during the later stages of seed development. The plastids contained electron‐dense starch granules. The seeds harvested after 42 weeks after flowering had maximum physiological maturity with high oil content and other seed reserve materials. This basic knowledge on pongamia seed development could invariably be used for further understanding of biochemical changes that might be involved in the biosynthetic pathway of oil.

Identification and characterization of ten new water gaps in seeds and fruits with physical dormancy and classification of water-gap complexes

Physical dormancy (PY) occurs in seeds or fruits of 18 angiosperm families and is caused by a water-impermeable palisade cell layer(s) in seed or fruit coats. Prior to germination, the seed or fruit coat of species with PY must become permeable in order to imbibe water. Breaking of PY involves formation of a small opening(s) (water gap) in a morpho-anatomically specialized area in seeds or fruits known as the water-gap complex. Twelve different water-gap regions in seven families have previously been characterized. However, the water-gap regions had not been characterized in Cucurbitaceae; clade Cladrastis of Fabaceae; subfamilies Bombacoideae, Brownlowioideae and Bythnerioideae of Malvaceae; Nelumbonaceae; subfamily Sapindoideae of Sapindaceae; Rhamnaceae; or Surianaceae. The primary aims of this study were to identify and describe the water gaps of these taxa and to classify all the known water-gap regions based on their morpho-anatomical features. Physical dormancy in 15 species was broken by exposing seeds or fruits to wet or dry heat under laboratory conditions. Water-gap regions of fruits and seeds were identified and characterized by use of microtome sectioning, light microscopy, scanning electron microscopy, dye tracking and blocking experiments. Ten new water-gap regions were identified in seven different families, and two previously hypothesized regions were confirmed. Water-gap complexes consist of (1) an opening that forms after PY is broken; (2) a specialized structure that occludes the gap; and (3) associated specialized tissues. In some species, more than one opening is involved in the initial imbibition of water. Based on morpho-anatomical features, three basic water-gap complexes (Types-I, -II and -III) were identified in species with PY in 16 families. Depending on the number of openings involved in initial imbibition, the water-gap complexes were sub-divided into simple and compound. The proposed classification system enables understanding of the relationships between the water-gap complexes of taxonomically unrelated species with PY.

Pararaucaria carriisp. nov., Anatomically Preserved Evidence for the Conifer Family Cheirolepidiaceae in the Northern Hemisphere

A cylindrical permineralized conifer seed cone has been identified from the Officer Member of the Trowbridge Formation, near Izee, in east-central Oregon. The cone is preserved in a Middle Jurassic (Callovian) marine calcium carbonate concretion, associated with araucarian seed cones, conifer twigs and wood, cycad seeds, fern rachides, and lycopodialean remains and was prepared by the cellulose acetate peel technique. The specimen is abraded, 2.8 cm long and 1.3 cm wide, and consists of a cone axis with helically arranged bract/scale complexes, with a large ovuliferous scale and a broad, flattened bract. The bract/scale trace arises as a cylindrical unit from the cone axis, in which the bract and scale traces are separated by ground tissue. The traces separate immediately in the cortex to form a crescent-shaped bract trace and a horseshoe-shaped scale trace with associated sclerenchyma bands that form two triangular bundles toward the distal end of the scale. Ovuliferous scale tissue covers one inverted seed per scale, forming a pocket that contains the seed. Seeds are attached at the chalaza to the inside of the pocket. Seed integuments have an outer epidermis of isodiametric cells with dark contents; one or two layers of palisade cells, occasionally appearing in I-beam configuration; and several inner layers of randomly arranged cells. The nucellus is adnate to the integument, to near the apex, where it forms a cellular mound of tissue. Cylindrical cones with helically arranged bract/scale complexes, bract and scale free to the base, one seed per scale enclosed in a pocket, and triangular sclerenchyma bands are characteristic of the genus Pararaucaria, which recently has been placed in the extinct conifer family Cheirolepidiaceae. This third species extends the known range of Pararaucaria from the Southern Hemisphere to the Northern Hemisphere and emphasizes that the association of araucarian and pararaucarian conifers extended over a wide geographic area during the Jurassic.

TISSUE CULTURE, ANATOMICAL AND MORPHOLOGICAL STUDIES OF TRIPHASIA TRIFOLIA (BURM. F.) P. WILSON

Comparative anatomical studies were carried out on in vivo plants of Triphasia trifolia (Burm. f.) P. Wilson and in vitro plantlets of the same age. To get the in vitro plantlets, explants were cultured on MS (Murashige and Skoog) media supplemented with different concentrations and combinations of hormones. The explant sources of Triphasia trifolia (Burm. f.) P. Wilson were obtained from cotyledons, leaves, stems, roots and shoot tips that were placed under conditions of 16 hours light and 8 hours dark. The optimum media for regeneration was MS supplemented with 1.0 mg/L BAP and 1.0 mg/L NAA. Cotyledon explants were found to be the most responsive. Regeneration of complete plantlets was achieved from cotyledon explants after about 4 months in culture. Sectioning was done to study the characteristics of the respective vascular bundles, shape of cells, palisade cell layers, presence of oil glands, druse and cuticle layers. Vascular bundles of in vivo leaves were extremely well developed compared to those in in vitro leaves. The vascular bundle of the in vivo leaf showed well developed xylem. However, the xylem and phloem cells of the in vitro leaf were very poorly developed which is one of the features of in vitro plants. Scanning electron microscope (SEM) studies were also carried out on the in vivo and in vitro plantlets to observe differences on the leaf surface.

Identification and analysis of an outer-seed-coat-specific promoter from Arabidopsis thaliana

Differentiation of the Arabidopsis thaliana (Arabidopsis) seed coat epidermal cells involves pronounced changes highlighted by the synthesis and secretion of copious amounts of dispensable, pectinaceous mucilage followed by a thick cellulosic secondary cell wall. This cell type, therefore, represents an excellent molecular-genetic model to study the biosynthesis and modification of cell wall components, particularly pectin. To support such research, we sought to identify a promoter that drives expression specifically in the Arabidopsis seed coat epidermis. Arabidopsis seed coat microarray data was analysed for genes expressed in the wild type seed coat but not the seed coat of the apetala2 mutant where the epidermal cells fail to differentiate. Of 14 candidate genes, 9 showed a seed-specific expression pattern by reverse transcriptase-PCR. Transcriptional regulatory region-β-glucuronidase (GUS) reporter gene fusions introduced into Arabidopsis identified one promoter, that of the DIRIGENT PROTEIN1 (DP1) gene, as seed coat specific. The specificity of the expression was confirmed using a second reporter gene, Citrine YFP. Expression of both reporter genes was limited to the epidermal and palisade cell layers of the seed coat. Quantitative PCR data using wild type seed coat RNA suggested that the promoter is particularly active at 7 days post anthesis. The DP1 promoter was able to direct transcription of GUS in a similar pattern in the Brassica napus seed coat. Thus, in addition to its application in studying the plant cell wall, this promoter will provide an experimental tool for expressing high-valued recombinant proteins as well as modifying seed coat traits in economically important crops.

Low temperature acclimation of photosynthetic capacity and leaf morphology in the context of phloem loading type

Carbon export from leaf mesophyll to sugar-transporting phloem occurs via either an apoplastic (across the cell membrane) or symplastic (through plasmodesmatal cell wall openings) pathway. Herbaceous apoplastic loaders generally exhibit an up-regulation of photosynthetic capacity in response to growth at lower temperature. However, acclimation of photosynthesis to temperature by symplastically loading species, whose geographic distribution is particularly strong in tropical and subtropical areas, has not been characterized. Photosynthetic and leaf anatomical acclimation to lower temperature was explored in two symplastic (Verbascum phoeniceum, Cucurbita pepo) and two apoplastic (Helianthus annuus, Spinacia oleracea) loaders, representing summer- and winter-active life histories for each loading type. Regardless of phloem loading type, the two summer-active species, C. pepo and H. annuus, exhibited neither foliar anatomical nor photosynthetic acclimation when grown under low temperature compared to moderate temperature. In contrast, and again irrespective of phloem loading type, the two winter-active mesophytes, V. phoeniceum and S. oleracea, exhibited both a greater number of palisade cell layers (and thus thicker leaves) and significantly higher maximal capacities of photosynthetic electron transport, as well as, in the case of V. phoeniceum, a greater foliar vein density in response to cool temperatures compared to growth at moderate temperature. It is therefore noteworthy that symplastic phloem loading per se does not prevent acclimation of intrinsic photosynthetic capacity to cooler growth temperatures. Given the vagaries of weather and climate, understanding the basis of plant acclimation to, and tolerance of, low temperature is critical to maintaining and increasing plant productivity for food, fuel, and fiber to meet the growing demands of a burgeoning human population.

Histo-anatomical Study of Anisochilus carnosus (L.f.) Wall: An Indian Habitant

Indian habitant Anisochilus carnosus (L.f.) wall is an annual shrub found in the high altitude regions. The plant has been of interest to researchers due to its potency towards various pathological conditions. Pharmacognostical, physicochemical and phytochemical evaluation of the leaves of A. carnosus was carried out to determine its qualitative and quantitative standards. Histological parameters revealed the dorsiventral nature of the leaf shows upper and lower epidermis with numerous multicellular covering and collapsed trichomes. A layer of palisade cells, spongy parenchyma embedded with few vascular strands and yellow color oil cells. Midrib showed the presence of patches of collenchyma, abundant trichomes identical to that of lamina and prominent bicollateral vascular bundles. Physico chemical parameters were determined and found to be total ash 89.02%, acid-insoluble ash 1.39% and water-soluble ash were 73.3% w/w of dried powder. The extractive values were found to be 6.19% w/w and 7.17% w/w for water and ethanol, respectively. The moisture content of the sample was found to be 15.89% w/w and foaming index was found to be 212.76. Phytochemical screening confirmed the presence of glycosides, saponins, tannins, phytosterols and volatile oil. Histological, physico-chemical and phytochemical evaluations carried out help to lay down the standards to the identification and authentication of this valuable crude drug.

Anatomical Structure and Histochemical Localization of the Leaf of Prinsepia uniflora Batal

The methods of anatomy and histochemistry were used to research the anatomical structure and histochemical localization of flavonoids,alkaloids and polysaccharides of the leaf of Prinsepia uniflora Batal.The results showed that the structure of the leaf of P.uniflora Batal was as follows: the upper epidermis cell with relative thick horny layer,the stomata existed in lower epidermis,the density of the stomata was 278mm-2.The upper side included 2 to 3 layers of palisade tissue cells,with a lot of crystals;the main vein of leaves had well developed xylem,with a number of radial arranged vessels.The characteristics mentioned above showed that P.uniflora Batal adapted well to the environment.The histochemical localization showed that: the total flavonoids mainly accumulated in the palisade tissue and collenchyma,alkaloids were poor existed in the leaf,polysaccharides were generally distributed in mesophyll of P.uniflora Batal.

Características físicas e estrutura de sementes e morfologia de plântulas de Flemingia macrophylla (Willd.) Alston

A Flemingia macrophylla (Willd.) Alston tem sido introduzida em diferentes sistemas de produção em razão de sua versatilidade de cultivo. Objetivou-se com este trabalho avaliar a estrutura e características físicas da semente e a morfologia de plântulas de Flemingia macrophylla (Willd.) Alston. Amostras de três lotes de sementes colhidos em 2007, 2008 e 2009 foram avaliadas em relação ao tamanho, grau de umidade, massa de mil sementes, massa do hectolitro e número de sementes por grama. O delineamento experimental utilizado foi inteiramente casualizado, com três lotes e oito repetições. Em outro ensaio, as sementes foram seccionadas para a observação e descrição da anatomia do tegumento, tecido de reserva e do embrião. As estruturas de plântulas foram avaliadas e registradas durante o seu desenvolvimento. As sementes de flemingia são globulares e esféricas, o tegumento apresenta coloração preta e marron. O grau de umidade das sementes variou entre 9,5 e 12,1%, a massa de mil sementes variou de 18,11 a 19,28 g, o peso hectolitro de 72,23 a 74,39 kg e o número de sementes por grama de 52 a 55. A estrutura do tegumento é formada por camada de células paliçádicas, característica da família Fabaceae. A germinação é do tipo hipógea.

Phytochemical and pharmacognostic studies of the leaf and stem-bark of Anthocleista vogelii (Planch)

The phytochemical screening of the powdered leaves and the stem bark of Anthocleista vogelii revealed the presence of carbohydrates, saponins, flavonoids, terpenes, sterols and phenols. Alkaloid was present in the leaves only. Moisture content, total ash value, acid-insoluble ash, water-soluble ash values and extractive values were also determined. Thin layer chromatography (TLC) analyses revealed seven spots for the leaf while the stem-bark revealed three spots using normal phase plates. The microscopic analysis of the upper and lower surfaces of the leaf revealed the presence of polygonal epidermal cells. The stomata distribution in the upper surface of the epidermis is more than that of the lower surface. The transverse section of the leaf indicated the presence of two layers of palisade cells, peculiar lignified astrosclereids scattered in the mesophyll. The transverse section of the stem bark showed diagnostic features such as the presence of astrosclereids, brachysclereids, macrosclereids, 3 or 4 layers of cork cells and medullary rays. The chemo microscopic analysis of the leaf and stem bark revealed the presence of lignin, cutin and oil globules. The result of this study revealed the chemical constituents and pharmacognostic profile of the plant. These are required in the preparation of a monograph in the plant. Key words: Anthocleista vogelli, pharmacognosy, medicinal plants.

Effects of elevated CO<sub>2</sub> applied to potato roots on the anatomy and ultrastructure of leaves

The root system of potato (Solanum tuberosum L. cv. Favorita) plants was treated with different O2 and CO2 concentrations for 35 d in aeroponic culture. Under 21 or 5 % O2 in the root zones, the thickness of leaves and palisade parenchyma significantly increased at 3 600 μmol(CO2) mol−1 in the root zone, compared with CO2 concentration 380 μmol mol−1 or low CO2 concentration (100 μmol mol−1). In addition, smaller cells of palisade tissue, more intercellular air spaces and partially two layers of palisade cells were observed in the leaves with root-zone CO2 enrichment. Furthermore, there was a significant increase in the size of chloroplasts and starch grains, and the number of starch grains per chloroplast due to elevated CO2 only under 21 % O2. In addition, a significant decline in the thickness of grana and the number of lamellas, but no significant differences in the number of grana per chloroplast were observed under elevated CO2 concentration. The accumulation of starch grains in the chloroplast under elevated CO2 concentration could change the arrangement of grana thylakoids and consequently inhibited the absorption of sun radiation and photosynthesis of potato plants.

Variegation in Arum italicum leaves. A structural–functional study

The presence of pale-green flecks on leaves (speckling) is a frequent character among herbaceous species from shady places and is usually due to local loosening of palisade tissue (air space type of variegation). In the winter-green Arum italicum L. (Araceae), dark-green areas of variegated leaf blades are ca. 400 μm thick with a chlorophyll content of 1080 mg m⁻² and a palisade parenchyma consisting of a double layer of oblong cells. Pale-green areas are 25% thinner, have 26% less chlorophyll and contain a single, loose layer of short palisade cells. Full-green leaves generally present only one compact layer of cylindrical palisade cells and the same pigment content as dark-green sectors, but the leaf blade is 13% thinner. A spongy parenchyma with extensive air space is present in all leaf types. Green cells of all tissues have normal chloroplasts. Assays of photosynthetic activities by chlorophyll fluorescence imaging and O₂ exchange measurements showed that variegated pale-green and dark-green sectors as well as full-green leaves have comparable photosynthetic activities on a leaf area basis at saturating illumination. However, full-green leaves require a higher saturating light with respect to variegated sectors, and pale-green sectors support relatively higher photosynthesis rates on a chlorophyll basis. We conclude that i) variegation in this species depends on number and organization of palisade cell layers and can be defined as a "variable palisade" type, and ii) the variegated habit has no limiting effects on the photosynthetic energy budget of A. italicum, consistent with the presence of variegated plants side by side to full-green ones in natural populations.

Pharmacognostical and Preliminary Phytochemical Evaluation of Clitoria ternatea leaves

Clitoria ternatea L. (Family: Fabaceae) a perennial twing herb, steams are terete, more or less pubescent. Root is bitter in taste used to cure sever bronchitis, asthma. In Kokan root juice s given in cold milk to remove the phlegm in chronic bronchitis. C. ternatea have reported number of pharmacological activities such as nootropic, anxiolytic, anticonvulsant, sedative, antipyretic, anti-inflammatory and analgesic. In present study pharmacognostic investigation of leaves was carried out by using morphological, microscopic and physicochemical parameters. It was found that leaves are odd pinnately compound, with obovate in shape, entire margin, Emarginate tip and symmetrical base, green in color, bitter in taste, with characteristic odor. Microscopic study reveals that presence of Upper and lower epidermis consists of single layer of cells covered with thick cuticle. Covering trichomes are present on both the surfaces. The upper and lower epidermis is followed collenchymatous cells. The upper epidermis consists of polygonal tabular cells, followed by layer of palisade cells, lignified xylem and paracytic stomata. The powder is green in colour and contains paracytic stomata, covering trichomes, fibres, wavy epidermal cells, covering trichomes and presewnce of starch grain in epidermal cell Physicochemical parameter observed that 13.2 ± 3.49 total ash, 4.8 ± 2.16 acid insoluble ash and 5.3 ± 0.08 water soluble ash. The moisture content found to be 12.5±2.57. Water soluble and alcohol soluble extractive value found to be 25.2 and 18.4 respectively.

Transcriptome analysis of secondary-wall-enriched seed coat tissues of canola (Brassica napus L.)

The seed coat of Brassica napus (canola, oilseed rape) is derived from ovule integuments and contains a layer of palisade cells, which have thick secondary walls. Because cellulosic walls and other indigestible components of the seed coat contribute negatively to the value of oilseeds, efforts are underway to alter seed development. To facilitate these efforts, and to better understand the biology of seed coats, we used a 90,000 element microarray to identify genes whose transcripts were expressed in developing seed coats of B. napus. After dissecting seed coats into three layers, and comparing transcript expression in the middle fraction (which contained the palisade-enriched tissue and bulk of inner integument) to transcript expression in developing hypocotyls, we identified 674 genes whose transcripts were more abundant in the middle fraction of the seed coat. Among these were well-characterized markers of seed coat identity and many genes associated with metabolism of cell wall polysaccharides, flavonoids and various cell wall proteins and transcription factors. Conversely, we identified 1,203 genes whose transcripts were more abundant in the hypocotyl tissue as compared to seed coat, including xylem-specific markers, such as XCP1 and XCP2. We validated 21 of the differentially expressed transcripts using quantitative RT-PCR. The results define a set of transcripts that are highly enriched in the developing seed coat of B. napus.

The microclimate under coloured hailnets affects leaf and fruit temperature, leaf anatomy, vegetative and reproductive growth as well as fruit colouration in apple

The purpose of this study was to investigate supposedly positive biological effects of coloured hailnets on microclimate, including photosynthetically active radiation (PAR), UV‐B, air, soil, fruit and leaf temperature as well as humidity, which in turn may affect leaf anatomy, tree growth and fruit quality; apple was chosen as a model crop at Klein‐Altendorf near Bonn, Germany; adjacent uncovered trees served as control.Red and green hailnets transmitted 3–6% more red or green light, without alteration of the red:far red (R–666 nm:FR–730 nm) ratio (0.99–1.01:1) and hence without affecting the phytochrome system. The microclimate was changed with a reduction by 12–23% in PAR and, to a larger extent, by 20–28% in UV, viz. shading. Light measurements at a 45° angle, to mimic the fruit or leaf position, showed that PAR was 90–210 µmol m−2 s−1 larger outside on a sunny summer day than under the white or red‐white and 150–340 µmol m−2 s−1 larger than under red‐black and green‐black hailnets.Air temperature and relative humidity under coloured hailnets decreased by ca. 1.3°C and by ca 2% rh (cloudy) to 5% rh (sunny day), respectively, compared with outside; leaf temperature was decreased by up to 3°C and fruit temperature by up to 6°C. Soil temperatures at 5 cm depth were 0.5–1°C colder under red‐black and green‐black hailnets, but up to 0.9°C warmer under white and red‐white hailnets compared with the uncovered control outside.Alternate bearing had a larger impact on vegetative growth in the affected year than the coloured hailnets; annual trunk diameter increments in cv. ‘Fuji’, i.e. the variety susceptible to alternate bearing, showed a larger variation than cv. ‘Pinova’ without alternate bearing. Reproductive growth, viz. return bloom and leaf anatomy were impaired by the coloured hailnets. Apple trees under dark hailnets developed thinner leaves with a thinner epidermis and fewer layers of palisade cells. These leaves were 3.5°C (dark hailnets) and 2.5°C (white hailnets) cooler than outside on a sunny day compared with ca. 1.5°C (dark hailnets) and 0.85°C (white hailnets) on a cloudy day. Transpirational cooling of cv. ‘Fuji’ leaves was 0.3–0.6°C outside and 1.4–1.6°C under the green‐black hailnet on sunny days compared to <0.1°C on cloudy days. As a practical application, apple fruit colouration was dependent on light (PAR and UV‐B) transmission of the respective hailnet colour.

The volumetric component of individual leaf expansion: Taking into account sub-epidermal tissues in the description of leaf expansion over time

Most leaf development studies at the cell and organ levels have been limited to the leaf surface, with data referring to the leaf surface area and to the number and surface area of epidermal cells. However, leaf sub-epidermal tissues, the palisade and spongy mesophyll, contain the main actors in photosynthesis. The number and thickness of palisade cell layers and the volume occupied by spongy mesophyll (cells and intercellular spaces) affect the accumulation of photosynthates and, as such, whole plant growth. Studies into the leaf phenotype of growth-affected Arabidopsis thaliana mutants have revealed a higher variability in leaf thickness than in leaf surface area. In general, there is no correlation between these two variables, which means that to describe a leaf phenotype, leaf volume has to be taken into account. A method has been developed for high-resolution imaging of leaves in three dimensions usingmultiphoton laser scanning microscopy, and for the analysis of images, providing data on volumes and volumetric proportions of cells and tissues and cell density. The method has been used in the study of A. thaliana leaf expansion from emergence to the onset of senescence for leaves located at different nodal positions in the rosette, completing our knowledge of individual leaf development processes with their volumetric component. The method will further be applied in the study of leaf plasticity in response to the environment for both A. thaliana and apple tree, a model and an agronomic species, respectively. (Texte integral)