The features of xylem tracheary elements in some herbaceous members of the family Convolvulaceae Horan.

Numerous narrow xylem tracheary elements (tracheids and vessels) are present in liana stems, along with a few wide vessels that perform the main water-conducting function. This trait, known as “vessel dimorphism”, has been identified in studies on water-conducting tissue in autotrophic plants, including a large number of perennial climbing plants and a number of annual vines. Information is lacking on the presence of vessel dimorphism in parasitic plants of the lianescent habit. In this study, we performed a structural analysis of stems in the autotrophic herbaceous vines of Convolvulus arvensis L. and Calystegia sepium (L.) R. Br., as well as in the parasitic vines of Cuscuta monogyna Vahl, Cuscuta planiflora Ten., Cuscuta approximata Bab., and Cuscuta campestris Yunck., of the family of Convolvulaceae Horan. The xylem of C. arvensis and C. sepium contains a few wide conductive elements and many narrow ones. This feature is typical of autotrophic climbing plants. Only narrow tracheary elements are present in the xylem of the parasitic vines of the genus of Cuscuta L. (dodders). The total number of the tracheary elements is an order of magnitude less in the dodders than it is in the autotrophic vines. It is possible that the autotrophic ancestor of dodders lost the characteristic feature of the xylem of climbing plants, known as vessel dimorphism, during its transition to the parasitic lifestyle.

The production of auxin by dying cells

In this review, I discuss the possibility that dying cells produce much of the auxin in vascular plants. The natural auxin, indole-3-acetic acid (IAA), is derived from tryptophan by a two-step pathway via indole pyruvic acid. The first enzymes in the pathway, tryptophan aminotransferases, have a low affinity for tryptophan and break it down only when tryptophan levels rise far above normal intracellular concentrations. Such increases occur when tryptophan is released from proteins by hydrolytic enzymes as cells autolyse and die. Many sites of auxin production are in and around dying cells: in differentiating tracheary elements; in root cap cells; in nutritive tissues that break down in developing flowers and seeds; in senescent leaves; and in wounds. Living cells also produce auxin, such as those transformed genetically by the crown gall pathogen. IAA may first have served as an exogenous indicator of the presence of nutrient-rich decomposing organic matter, stimulating the production of rhizoids in bryophytes. As cell death was internalized in bryophytes and in vascular plants, IAA may have taken on a new role as an endogenous hormone.

Differentiation of Tracheary Elements in Sugarcane Suspension Cells Involves Changes in Secondary Wall Deposition and Extensive Transcriptional Reprogramming

Plant lignocellulosic biomass, mostly composed of polysaccharide-rich secondary cell walls (SCWs), provides fermentable sugars that may be used to produce biofuels and biomaterials. However, the complex chemical composition and physical structure of SCWs hinder efficient processing of plant biomass. Understanding the molecular mechanisms underlying SCW deposition is, thus, essential to optimize bioenergy feedstocks. Here, we establish a xylogenic culture as a model system to study SCW deposition in sugarcane; the first of its kind in a C4 grass species. We used auxin and brassinolide to differentiate sugarcane suspension cells into tracheary elements, which showed metaxylem-like reticulate or pitted SCW patterning. The differentiation led to increased lignin levels, mainly caused by S-lignin units, and a rise in p-coumarate, leading to increased p-coumarate:ferulate ratios. RNAseq analysis revealed massive transcriptional reprogramming during differentiation, with upregulation of genes associated with cell wall biogenesis and phenylpropanoid metabolism and downregulation of genes related to cell division and primary metabolism. To better understand the differentiation process, we constructed regulatory networks of transcription factors and SCW-related genes based on co-expression analyses. Accordingly, we found multiple regulatory modules that may underpin SCW deposition in sugarcane. Our results provide important insights and resources to identify biotechnological strategies for sugarcane biomass optimization.

Histone Deacetylase HDT1 is Involved in Stem Vascular Development in Arabidopsis

Histone acetylation and deacetylation play essential roles in eukaryotic gene regulation. HD2 (HD-tuins) proteins were previously identified as plant-specific histone deacetylases. In this study, we investigated the function of the HDT1 gene in the formation of stem vascular tissue in Arabidopsis thaliana. The height and thickness of the inflorescence stems in the hdt1 mutant was lower than that of wild-type plants. Paraffin sections showed that the cell number increased compared to the wild type, while transmission electron microscopy showed that the size of individual tracheary elements and fiber cells significantly decreased in the hdt1 mutant. In addition, the cell wall thickness of tracheary elements and fiber cells increased. We also found that the lignin content in the stem of the hdt1 mutants increased compared to that of the wild type. Transcriptomic data revealed that the expression levels of many biosynthetic genes related to secondary wall components, including cellulose, lignin biosynthesis, and hormone-related genes, were altered, which may lead to the altered phenotype in vascular tissue of the hdt1 mutant. These results suggested that HDT1 is involved in development of the vascular tissue of the stem by affecting cell proliferation and differentiation.

Anatomy of three Onosma species from Turkey

Three Onosma L. species (O. papillosa Riedl, O. rutila Hub-Mor. and O. auriculata Aucher ex DC.) were examined anatomically. All these taxa had secondary root structure and xylem which were composed of sclerenchymatic cells and tracheary elements. O. papillosa has crystals and sclereids in the stem and leaf. Sand crystals are seen in the pith region of O. auriculata. O. papillosa and O. auriculata has bifacial leaf types and O. rutila has equifacial type. Stomata are anisocytic, anomocytic and staurocytic. These species have long and short simple eglandular and glandular trichomes. Setae with glabrous tubercles are present in O. papillosa and O. rutila. O. auriculata has porrect-stellate trichomes. Simple trichomes are unicellular and generally short. They have lignified, ornamental or smooth walls.

Spotting plants’ microfilament morphologies and nanostructures

The tracheary system of plant leaves is composed of a cellulose skeleton with diverse hierarchical structures. It is built of polygonally bent helical microfilaments of cellulose-based nanostructures coated by different layers, which provide them high compression resistance, elasticity, and roughness. Their function includes the transport of water and nutrients from the roots to the leaves. Unveiling details about local interactions of tracheary elements with surrounding material, which varies between plants due to adaptation to different environments, is crucial for understanding ascending fluid transport and for tracheary mechanical strength relevant to potential applications. Here we show that plant tracheary microfilaments, collected from Agapanthus africanus and Ornithogalum thyrsoides leaves, have different surface morphologies, revealed by nematic liquid crystal droplets. This results in diverse interactions among microfilaments and with the environment; the differences translate to diverse mechanical properties of entangled microfilaments and their potential applications. The presented study also introduces routes for accurate characterization of plants’ microfilaments.

New insights into Dutch Elm Disease: cell wall compositional, ecophysiological, vascular and nanomechanical assessments

Comprehensive assessments were made of the chemical profiles of woody cell wall components, and also leaf growth, ecophysiological, vascular and nanomechanical traits for two Dutch elm hybrids 'Groeneveld' and 'Dodoens' which possess contrasting tolerances toward Dutch elm disease. Upon infection with Ophiostoma novo-ulmi ssp. americana × novo-ulmi, medium-molecular weight macromolecules of cellulose were degraded in both hybrids. A loss of crystalline and non-crystalline cellulose regions occurred in parallel. In 'Groeneveld' plants, syringyl-rich lignin provided a far greater degree of protection from cellulose degradation, but only guaiacyl-rich lignin in 'Dodoens' plants was involved in a successful defence against the fungus. Unexpectedly, we found a very high proportion of non-significant differences between the infected and non-infected plants of 'Dodoens', including similarities in leaf growth, leaf gas exchange and leaf midrib vascular traits, as well as in the nanomechanical properties of the cell walls of tracheary elements such as modulus of elasticity, adhesion and energy dissipation. Three years after initial inoculations, except for a few traits such as leaf slenderness, relative chlorophyll content, transpiration rate and sap flow density in branches, we found no evidence of a decrease in leaf trait performances among the infected plants of 'Dodoens', despite the occasional persistence of fungal hyphae in the lumens of leaf midrib tracheary elements.