Subepidermal Cell Layers Research Articles

Speciation and distribution of chromium (III) in rice root tip and mature zone: The significant impact of root exudation and iron plaque on chromium bioavailability

Evidence on the contribution of root regions with varied maturity levels in iron plaque (IP) formation and root exudation of metabolites and their consequences for uptake and bioavailability of chromium (Cr) remains unknown. Therefore, we applied combined nanoscale secondary ion mass spectrometry (NanoSIMS) and synchrotron-based techniques, micro-X-ray fluorescence (µ-XRF) and micro-X-ray absorption near-edge structure (µ-XANES) to examine the speciation and localisation of Cr and the distribution of (micro-) nutrients in rice root tip and mature region. µ-XRF mapping revealed that the distribution of Cr and (micro-) nutrients varied between root regions. Cr K-edge XANES analysis at Cr hotspots attributed the dominant speciation of Cr in outer (epidermal and sub-epidermal) cell layers of the root tips and mature root to Cr(III)-FA (fulvic acid-like anions) (58–64%) and Cr(III)-Fh (amorphous ferrihydrite) (83–87%) complexes, respectively. The co-occurrence of a high proportion of Cr(III)-FA species and strong co-location signals of 52Cr16O and 13C14N in the mature root epidermis relative to the sub-epidermis indicated an association of Cr with active root surfaces, where the dissolution of IP and release of their associated Cr are likely subject to the mediation of organic anions. The results of NanoSIMS (poor 52Cr16O and 13C14N signals), dissolution (no IP dissolution) and µ-XANES (64% in sub-epidermis >58% in the epidermis for Cr(III)-FA species) analyses of root tips may be indicative of the possible re-uptake of Cr by this region. The results of this research work highlight the significance of IP and organic anions in rice root systems on the bioavailability and dynamics of heavy metals (e.g. Cr).

A cellular expression map of epidermal and subepidermal cell layer-enriched transcription factor genes integrated with the regulatory network in Arabidopsis shoot apical meristem.

Transcriptional control of gene expression is an exquisitely regulated process in both animals and plants. Transcription factors (TFs) and the regulatory networks that drive the expression of TF genes in epidermal and subepidermal cell layers in Arabidopsis are unexplored. Here, we identified 65 TF genes enriched in the epidermal and subepidermal cell layers of the shoot apical meristem (SAM). To determine the cell type specificity in different stages of Arabidopsis development, we made YFP based transcriptional fusion constructs by taking a 3‐kb upstream noncoding region above the translation start site. Here, we report that for ~52% (22/42) TF genes, we detected transcription activity. TF genes derived from epidermis show uniform expression in early embryo development; however, in the late globular stage, their transcription activity is suppressed in the inner cell layers. Expression patterns linked to subepidermal cell layer identity were apparent in the postembryonic development. Potential upstream regulators that could modulate the activity of epidermal and subepidermal cell layer‐enriched TF genes were identified using enhanced yeast‐one‐hybrid (eY1H) assay and validated. This study describes the activation of TF genes in epidermal and subepidermal cell layers in embryonic and postembryonic development of Arabidopsis shoot apex.

In planta particle bombardment (iPB): A new method for plant transformation and genome editing.

Transformation is a key step in modern breeding technology that involves genome editing. The requirement for in vitro tissue culture and regeneration hampers application of this technology to commercially important varieties of many crop species. To overcome this problem, we developed a simple and reproducible in planta transformation method in wheat (Tritticum aestivum L.). Our in planta particle bombardment (iPB) method utilizes the shoot apical meristem (SAM) as a target tissue. The SAM contains a subepidermal cell layer termed L2, from which germ cells later develop during floral organogenesis. The iPB method can also be used for genome editing through transient CRISPR/Cas9 expression or direct delivery of the CRISPR/Cas9 ribonucleoprotein. In this review, we describe the iPB technology and provide an overview of its current and future applications in plant transformation and genome editing.

Anatomical features related with pollination of Neottia ovata (L.) Bluff & Fingerh. (Orchidaceae)

The survey of anatomical features of Neottia ovata confirmed that the lip base and the groove function as a nectary. The secretory tissue was present in buds about 1,3 mm width. The sweet scent comes from the aromatic constituents of the nectar and also is released by the lip lobes and margins of all tepals. Additionally, the stomata present on the keels on the abaxial surface of sepals and large substomatal cavities may be connected with fragrance emission. The secretory function was not observed on the stem trichomes. The groove is formed by a single-layered epidermis, few layers of subepidermal cells and underlying parenchyma. The abundant starch grains present in buds, absent in sepals and lip epidermis in larger buds and almost absent in open flowers (visible in plastids in TEM) suggest gradual reduction during floral development and nectar secretion. The nectar was gathered under the cuticle, which was visible in the groove and lip base. The main mode of nectar release is by diffusion through micro-channels. The presence of irregular plasmalemma, dictyosomes, and profiles of ER could also indicate the granulocrine mode of secretion. The vesicles originated from ER or dictyosomes are fused with irregular plasmalemma. The irregular plasmalemma with invaginations (observed in groove) and cell wall protuberances (observed at the lip base) along the outer periclinal wall may function as highly specialized cells - transfer cells. Numerous idioblasts, visible in all tepals and in the staminodium, attract pollinators. In the anther, the endothecial cell thickenings were composed of numerous complete rings or helical segments in a closely spaced parallel arrangement (type I), providing the mechanical forces for anther dehiscence and opening and release of pollen grains.

A detailed description of morphological and anatomical characters of olive (Olea europaea) fruits in relation to phenological growth stages

This paper describes both morphological and anatomical changes of olive (Olea europaea) fruits of “Nevadillo” variety, growing under rainfed conditions, in relation to the phenological stages of fruit formation and development described by the Biologische, Bundesantalt, Bundessortenamt and Chemische Industrie (BBCH) scale. Mesocarp transverse area (TA m), total number of cells and TA per cell were measured in mesocarp equatorial transverse sections of the fruits. Changes in cell dimensions and shape along the mesocarp radial longitudinal section and endocarp sclerification were also analysed. The pattern of fruit growth showed linear increases in TA m, coupled with the whole fruit TA (TA f) increases throughout its whole developmental period. This observation disagrees with the classical growth model which suggested that the growth of a drupe adjusts to a double sigmoid curve. A strong correlation between TA m and TA f and a weak correlation between endocarp TA and TA f were observed. The tissue organisation in the cross‐sectional area of the fruit agrees with previous histological descriptions. Cell organisation in the longitudinal radial plane of the olive fruit was established for the first time: a single‐layered epidermis; a hypodermis: first four layers of subepidermal parenchyma cells; an outer mesocarp: from the layer 5 to layer 24 to 27 and an internal mesocarp: following layers of parenchyma cells up to the vascular bundles. Until now, comparative anatomical studies on olive fruit have been carried out only in the cross section, that is, in two dimensions. The anatomy of longitudinal section described here, together with the cell organisation in the transverse plane, will allow designing a tridimensional model of the fruit anatomy. This model will be useful to interpret the cell processes (division and expansion) involved in fruit growth, morphogenesis and oil storage, and to explore how climate and agricultural management practices could impact on olive fruit development on “Nevadillo” and other cultivars under different growing conditions (e.g., water status and temperature variations).

Biolistic-delivery-based transient CRISPR/Cas9 expression enables in planta genome editing in wheat

The current application of genome editing to crop plants is limited to cultivars that are amenable to in vitro culture and regeneration. Here, we report an in planta genome-editing which does not require callus culture and regeneration. Shoot apical meristems (SAMs) contain a subepidermal cell layer, L2, from which germ cells later develop during floral organogenesis. The biolistic delivery of gold particles coated with plasmids expressing CRISPR/Cas9 components designed to target TaGASR7 were bombarded into SAM-exposed embryos of imbibed seeds. Bombarded embryos showing transient GFP expression within SAM were selected and grown into adult plants. Mutations in the target gene were assessed in fifth-leaf tissue by cleaved amplified polymorphic sequence analysis. Eleven (5.2%) of the 210 bombarded plants carried mutant alleles, and the mutations of three (1.4%) of these were inherited in the next generation. Genotype analysis of T1 plants identified plants homozygous for the three homeologous genes, which were all derived from one T0 plant. These plants showed no detectable integration of the Cas9 and guide RNA genes, indicating that transient expression of CRISPR/Cas9 introduced the mutations. Together, our current method can be used to achieve in planta genome editing in wheat using CRISPR/Cas9 and suggests possible applications to other recalcitrant plant species and variations.

Localization of phenolic compounds in the fruits of Silybum marianum characterized by different silymarin chemotype and altered colour

Silybum marianum (L.) Gaertn (Asteraceae) is a valuable medicinal plant utilized for silymarin production. However, only fragmentary and contradictory information about silymarin localization within S. marianum fruit are available. In this work, a twofold research approach was adopted in order to investigate the distribution and quantification of silymarin and of other phenolic compounds within the different fruit regions (pericarp, seed integument, cotyledon). Two S. marianum wild accessions with contrasting silymarin chemotype (A and B) and a mutant line (C) with an altered fruit colour were analysed. Fruits of Cynara cardunculus were studied as a reference.Firstly, the fruit morpho-anatomy was reviewed by means of light microscopy digital imaging and, secondly, a comprehensive histolocalization of the different classes of polyphenols within the fruit was carried out. The experimental evidences confirmed that silymarin, and its precursor taxifolin, are only accumulated in the seed integuments. The dark colour of fully-ripened fruits is due to the accumulation of condensed tannins in the pericarp subepidermal cell layer. On the contrary, the studied mutant line shows reduced condensed tannin content that probably result from impairment at the level of flavonoid biosynthetic pathway.Condensed tannins content is comparatively low in S. marianum fruits and very low in the identified mutant line. This could represent an advantage for the possible employment of S. marianum fruits and of silymarin extraction by-products in the feed and food sector.

Minimum requirements for changing and maintaining endodermis cell identity in the Arabidopsis root.

Changes in gene regulation during differentiation are governed by networks of transcription factors. The Arabidopsis root endodermis is a tractable model to address how transcription factors contribute to differentiation. We used a bottom-up approach to understand the extent to which transcription factors required for endodermis differentiation can confer endodermis identity to a non-native cell-type. Our results show the transcription factors SHORTROOT and MYB36 alone have limited ability to induce ectopic endodermal features in the absence of additional cues. The stele-derived signaling peptide CIF2 stabilizes SHORTROOT-induced endodermis identity acquisition. The outcome is a partially impermeable barrier deposited in the sub-epidermal cell layer, which has a transcriptional signature similar to the endodermis. These results demonstrate other root cell-types can be forced to differentiate into endodermis and highlights a previously unappreciated role for receptor-kinase signaling in maintaining endodermis identity.

Bulb tunic anatomy and its taxonomic implication in Allium L. (Amaryllidaceae: Allioideae)

Allium is taxonomically a difficult genus with blurred taxonomic borders at all taxonomic ranks. In this research, anatomy and morphology of bulb tunics in 42 species of the genus representing its 16 currently recognized sections and 6 subgenera (Allium, Cepa, Reticulatobulbosa, Amerallium, Polyprason and Melanocrommyum) were investigated. Our results indicated the following characters to be most informative at sectional and subgeneric levels: features of calcium oxalate crystals and subepidermal cell layer of the outermost bulb tunic, type of tracheids, and bulbils presence. Three main types of crystals, i.e. prismatic, sand and druses, were fairly common among the investigated species except for the members of A. sect. Acanthoprason (A. subg. Melanocrommyum) that often lack crystals. The subepidermal layers of outer tunics were mostly composed of hexagonal, rectangular, or elongated cells but A. paradoxum (A. subg. Amerallium, sect. Briseis) showed the pentagonal type and A. longisepalum (A. subg. Amerallium, sect. Molium) the elliptic type of subepidermal cells. The members of A. sub. Melanocrommyum showed various types of tunic cells and crystals.

Developmental patterning of sub-epidermal cells in the outer integument of Arabidopsis seeds.

The seed, the reproductive unit of angiosperms, is generally protected by the seed coat. The seed coat is made of one or two integuments, each comprising two epidermal cells layers and, in some cases, extra sub-epidermal cell layers. The thickness of the seed-coat affects several aspects of seed biology such as dormancy, germination and mortality. In Arabidopsis, the inner integument displays one or two sub-epidermal cell layers that originate from periclinal cell divisions of the innermost epidermal cell layer. By contrast, the outer integument was considered to be two-cell layered. Here, we show that sub-epidermal chalazal cells grow in between the epidermal outer integument cell layers to create an incomplete three-cell layered outer integument. We found that the MADS box transcription factor TRANSPARENT TESTA 16 represses growth of the chalaza and formation of sub-epidermal outer integument cells. Finally, we demonstrate that sub-epidermal cells of the outer and inner integument respond differently to the repressive mechanism mediated by FERTILIZATION INDEPENDENT SEED Polycomb group proteins and to fertilization signals. Our data suggest that integument cell origin rather than sub-epidermal cell position underlies different responses to fertilization.

Growth of the Arabidopsis sub-epidermal integument cell layers might require an endosperm signal

ABSTRACTThe seed, the reproductive unit of angiosperms, is physically protected by the seed coat. The seed coat develops from the ovule integuments after fertilization. The Arabidopsis ovule integuments are made of 5–6 cell layers of epidermal and sub-epidermal origin. The growth of the epidermal integument cell layers responds to an endosperm signal mediated by the AGAMOUS-LIKE 62 MADS box transcription factor with limited embryo contribution. By contrast, the sub-epidermal integument cell layers require the embryo to expand whereas the role of the endosperm is still unclear. Here, we analyzed the development of the sub-epidermal integument cell layers in agl62 mutant seeds, which undergo premature endosperm cellularization and arrest. Our data suggest that embryo and endosperm are both necessary to trigger the expansion of the sub-epidermal integument cell layers.

Cell layer-specific patterns of cell division and cell expansion during fruit set and fruit growth in tomato pericarp.

In angiosperms, the ovary wall resumes growth after pollination through a balanced combination of cell division and cell expansion. The quantitative pattern of these events remains poorly known in fleshy fruits such as tomato (Solanum spp.), in which dramatic growth of the pericarp occurs together with endoreduplication. Here, this pattern is reported at the level of each of the cell layers or groups of cell layers composing the pericarp, except for vascular bundles. Overall, cell division and cell expansion occurred at similar rates for 9 days post anthesis (DPA), with very specific patterns according to the layers. Subsequently, only cell expansion continued for up to 3-4 more weeks. New cell layers in the pericarp originated from periclinal cell divisions in the two sub-epidermal cell layers. The shortest doubling times for cell number and for cell volume were both detected early, at 4 DPA, in epicarp and mesocarp respectively, and were both found to be close to 14 h. Endoreduplication started before anthesis in pericarp and was stimulated at fruit set. It is proposed that cell division, endoreduplication, and cell expansion are triggered simultaneously in specific cell layers by the same signals issuing from pollination and fertilization, which contribute to the fastest relative fruit growth early after fruit set.

Developmental patterning of the sub-epidermal integument cell layer in Arabidopsis seeds.

Angiosperm seed development is a paradigm of tissue cross-talk. Proper seed formation requires spatial and temporal coordination of the fertilization products – embryo and endosperm – and the surrounding seed coat maternal tissue. In early Arabidopsis seed development, all seed integuments were thought to respond homogenously to endosperm growth. Here, we show that the sub-epidermal integument cell layer has a unique developmental program. We characterized the cell patterning of the sub-epidermal integument cell layer, which initiates a previously uncharacterized extra cell layer, and identified TRANSPARENT TESTA 16 and SEEDSTICK MADS box transcription factors as master regulators of its polar development and cell architecture. Our data indicate that the differentiation of the sub-epidermal integument cell layer is insensitive to endosperm growth alone and to the repressive mechanism established by FERTILIZATION INDEPENDENT ENDOSPERM and MULTICOPY SUPPRESSOR OF IRA1 Polycomb group proteins. This work demonstrates the different responses of epidermal and sub-epidermal integument cell layers to fertilization.

Metabolic Profile and Root Development of Hypericum perforatum L. In vitro Roots under Stress Conditions Due to Chitosan Treatment and Culture Time

The responses of Hypericum perforatum root cultures to chitosan elicitation had been investigated through 1H-NMR-based metabolomics associated with morpho-anatomical analyses. The root metabolome was influenced by two factors, i.e., time of culture (associated with biomass growth and related “overcrowding stress”) and chitosan elicitation. ANOVA simultaneous component analysis (ASCA) modeling showed that these factors act independently. In response to the increase of biomass density over time, a decrease in the synthesis of isoleucine, valine, pyruvate, methylamine, etanolamine, trigonelline, glutamine and fatty acids, and an increase in the synthesis of phenolic compounds, such as xanthones, epicatechin, gallic, and shikimic acid were observed. Among the xanthones, brasilixanthone B has been identified for the first time in chitosan-elicited root cultures of H. perforatum. Chitosan treatment associated to a slowdown of root biomass growth caused an increase in DMAPP and a decrease in stigmasterol, shikimic acid, and tryptophan levels. The histological analysis of chitosan-treated roots revealed a marked swelling of the root apex, mainly due to the hypertrophy of the first two sub-epidermal cell layers. In addition, periclinal divisions in hypertrophic cortical cells, resulting in an increase of cortical layers, were frequently observed. Most of the metabolic variations as well as the morpho-anatomical alterations occurred within 72 h from the elicitation, suggesting an early response of H. perforatum roots to chitosan elicitation. The obtained results improve the knowledge of the root responses to biotic stress and provide useful information to optimize the biotechnological production of plant compounds of industrial interest.

Anatomy and ultrastructure of osmophores of Cymbidium tracyanum Rolfe (Orchidaceae)

The intense smell secreted by flowers of <i>Cymbidium tracyanum</i> Rolfe (<i>Orchidaceae</i>) derives from osmophores situated on the axipetal surface, mainly at the petals' base and the margin of labellum. The epiderm in those places created vesicular or somewhat elongated glandular cells, particularly on the labellum. In the production of smell 2-3 layers of subepidermal cells also take part. Submicroscopic examinations showed that those cells were characterized by the presence of a big nucleus. There were also numerous granules of starch and plastoglobules in plastids, a great amount of mitochondria and smooth-surfaced endoplasmic reticula. The traces of secretion products are visible on the surface of glandular cells. The above mentioned features are typical for osmophore cells.

Erythronium dens-canis L. (Liliaceae): An unusual case of change of leaf mottling

Erythronium dens-canis is an early-flowering understory lily of southern Europe with two leaves and a single flower, although a number of plants have only one leaf and do not flower. The leaves are mottled with silvery flecks and brown patches, that gradually vanish turning to a lively green color. The nature and function of this striking variegation pattern were investigated in differently colored leaf parts following the springtime color change. Tissue organization was examined by light and electron microscopy; photosynthetic pigments were analyzed by spectrophotometry and HPLC; chlorophyll fluorescence parameters were evaluated by MINI-PAM. The results showed that brown patches originated in vacuolar anthocyanins in the subepidermal cell layer while air spaces between the upper epidermis and underlying chlorenchyma resulted in silvery flecks. The two leaf areas did not differ in photosynthetic pigments, chloroplast organization and photosynthetic parameters (Fv/Fm, NPQ, rETR). Greening of brown patches due to anthocyanin resorption was faster in non-flowering plants than in flowering ones, occurring only when young fruits were developing. Anthocyanin disappearance did not change the structural-functional features of photosynthetic tissues. As a whole the results suggest that the anthocyanin pigmentation of E. dens-canis leaves does not affect the photosynthetic light use and has no photoprotective function. It is proposed that the complex leaf color pattern may act as a camouflage to escape herbivores, while the reflective silvery spots may have a role in attracting pollinators of this early-flowering species.

Differential aluminum resistance in Brachiaria species

Brachiaria are increasingly cropped in the tropics because these species combine good fodder quality and yield with high resistance to aluminum (Al) toxicity, an important stress factor in acidic soils. The mechanisms for the extraordinarily high resistance to Al toxicity in Brachiaria decumbens remain unclear. It has been suggested that the presence of a multiseriate exodermis might contribute to efficient Al exclusion in B. decumbens. However, no data concerning the root structure of less Al-resistant Brachiaria species have been reported. The aim of the present study was determine whether the exodermis is a distinctive feature of Al hyper-resistant B. decumbens compared with Brachiaria species with lower Al resistance. B. decumbens, B. brizantha, and B. ruziziensis were grown in nutrient solution without (control) or with 200μM Al (32μM Al3+ activity) for 96h. Differences in the Al resistance were assessed using various indicators: Al-induced inhibition of root elongation, membrane damage, and the maintenance of nutrient homeostasis. Transversal root sections were examined using fluorescence microscopy to reveal the presence of an exodermis through auto-fluorescence. Aluminum resistance decreased in the order B. decumbens>B. brizantha>B. ruziziensis. Both the hyper-resistant B. decumbens and the moderately resistant B. brizantha were more efficient in Al-exclusion than the sensitive B. ruziziensis. Apoplastic barriers, in the form of a multiseriate exodermis, were constitutively present in B. decumbens, but not in Al-sensitive B. ruziziensis. Under control conditions, B. brizantha exhibited slightly auto-fluorescent epidermal cell walls, while under Al exposure auto-fluorescent deposits were observed in the intercellular spaces between the epidermal and sub-epidermal cell layers. The results provide circumstantial evidence of a role for apoplastic barriers in the Al resistance of B. decumbens and, to a lesser extent, in B. brizantha. Nonetheless, additional research is required to determine a causal relationship between the exodermal barrier and Al resistance.

Quantitative Analysis of Cell Organization in the External Region of the Olive Fruit

Definitions of the cells that constitute the exocarp or exterior tissue of fleshy fruits are often vague, sometimes providing contradictory descriptions of the epidermis plus none or varying numbers of underlying cell layers for the same species. This study uses a morphometric approach to investigate how cell dimensions, cell number, and their relation with genetically based fruit size differences can contribute to a characterization of tissue organization in the external fruit region, using the olive drupe as an example. We determined cell area, radial and tangential widths, and cell number in the epidermis and 20 subepidermal cell layers of mature fruits of four olive cultivars that range in fruit size. Variation of these measurements among cell layers and the implied cellular contributions to fruit expansion revealed two different subepidermal regions, but with constant widths and layer numbers for all cultivars: (1) the first four cell layers (1–4), which have similar behavior to the epidermis; and (2) the following five cell layers (5–9), which are more similar to the mesocarp. The results provide new insights about cell patterns in the external region of the olive fruit and suggest that layers 1–4 together with the epidermis may act as a multiseriate exocarp and layers 5–9 may act as an outer mesocarp.

복숭아 '진미'의 외과피 발달과 미세균열

본 연구는 복숭아 '진미'의 미세균열 발생원인을 구명하기 위하여 시기별로 외과피 조직의 발달양상을 관찰하였으며, 수확기에는 '가납암백도', '천중도백도', '유명'과 외과피 조직의 차이를 비교하였다. 미세균열 발생은 '진미'에서 59.1%로 가장 높았고, '가납암백도' 30.6%, '천중도백도' 21.5%, '유명' 6.4%의 순이었다. '진미'는 만개 후 69일부터 외표피 바로 아래에서 공동화 현상이 쉽게 관찰되었으며, 생육이 진전될수록 공동화 현상이 확대되었다. 또한 수확기에 '진미' 품종은 외과피 층의 수가 다른 품종들에 비하여 적었으며, '천중도백도'와 '유명'에 비하여 외과피층의 두께가 얇고, 아표피 세포들의 크기가 작으며, 모양이 납작하였다. 따라서 복숭아 '진미'의 미세균열은 다른 품종에 비해서 외표피층의 발달 불량과 외과피 바로 아래 부분의 공동화 현상 발달에 기인한 것으로 판단되었다. This study was conducted to elucidate the cause of micro-cracking in the exocarp of 'Jinmi' peach (Prunus persica). through the microscopic observation of fruit skin development in 4 varieties such as 'Jinmi', 'Kanoiwa Hakuto', 'Kawanakajima Hakuto', and 'Yumyeong'. Micro-cracking was noted in 59.1% of 'Jinmi', 30.6% of 'Kanoiwa Hakuto', 21.5% 'Kawanakajima Hakuto' and 6.4% of 'Yumyeong', respectively. The development of intercellular spaces, which increased rapidly with the fruit development, was easily observed at 69 days after full bloom. Histological studies revealed that the number of outer epiderm cell layers of 'Jinmi' was smaller than that of the other three cultivars, and thinner than the 'Kawanakajima Hakuto' and 'Yumyeong'. Moreover, 'Jinmi' exhibited smaller and flatter shapes in the sub-epidermal cell layer than those of the 'Kawanakajima Hakuto' and 'Yumyeong' at harvest season. Therefore, these results suggest that micro-cracking of 'Jinmi' fruit skin was due to poor-developed outer epidermis and well-developed intercellular spaces just under exocarp as compared with other varieties.

Anatomy and Lignin Characterisation of Twigs in the Chaparral Shrub Rhamnus Californica

Characterisation of anatomical properties and analysis of lignin content and monomer composition were performed on twigs of the shrub Rhamnus californica L. in order to highlight their role in the adaptive strategies of this species in Mediterranean-type ecosystems. Our results showed that R. californica twigs develop a thick cuticle accompanied by several layers of subepidermal cells with suberised walls aiming to save water. The xylem is characterised by anatomical and chemical traits ensuring safety of water transport and preventing permanent damage through the enhancement of mechanical strength, also favoured by the lignification of pith cell walls. Moreover, the accumulation of phenolic compounds in the cortical cylinder is a strategy to protect against herbivory and to screen against high levels of radiation. Our overall analysis suggests that R. californica has evolved a strategy of shoot development that allows it to cope with the multiple environmental stresses found in Mediterraneantype ecosystems, among which summer drought and grazing play a major role especially for the survival of seedlings and young plants.