Distribution of cell-wall polysaccharides and proteins during growth of the hemp hypocotyl

Bouncing back stronger: Diversity, structure, and molecular regulation of gelatinous fiber development

Gelatinous fibers (G-fibers) are specialized contractile cells found in a diversity of vascular plant tissues, where they provide mechanical support and/or facilitate plant mobility. G-fibers are distinct from typical fibers by the presence of an innermost thickened G-layer, comprised mainly of axially oriented cellulose microfibrils. Despite the disparate developmental origins-tension wood fibers from the vascular cambium or primary phloem fibers from the procambium-G-fiber development, composition, and molecular signatures are remarkably similar; however, important distinctions do exist. Here, we synthesize current knowledge of the phylogenetic diversity, compositional makeup, and the molecular profiles that characterize G-fiber development and highlight open questions for future investigation.

Immunohistochemical analyses on two distinct internodes of stinging nettle show different distribution of polysaccharides and proteins in the cell walls of bast fibers

Stinging nettle is a perennial herbaceous species holding value as a multi-purpose plant. Indeed, its leaves and roots are phytofactories providing functional ingredients of medicinal interest and its stems produce silky and resistant extraxylary fibers (a.k.a. bast fibers) valued in the biocomposite sector. Similarly to what is reported in other fiber crops, the stem of nettle contains both lignified and hypolignified fibers in the core and cortex, respectively, and it is therefore a useful model for cell wall research. Indeed, data on nettle stem tissues can be compared to those obtained in other models, such as hemp and flax, to support hypotheses on the differentiation and development of bast fibers. The suitability of the nettle stem as model for cell wall-related research was already validated using a transcriptomics and biochemical approach focused on internodes at different developmental stages sampled at the top, middle, and bottom of the stem. We here sought to complement and enrich these data by providing immunohistochemical and ultrastructural details on young and older stem internodes. Antibodies recognizing non-cellulosic polysaccharides (galactans, arabinans, rhamnogalacturonans) and arabinogalactan proteins were here investigated with the goal of understanding whether their distribution changes in the stem tissues in relation to the bast fiber and vascular tissue development. The results obtained indicate that the occurrence and distribution of cell wall polysaccharides and proteins differ between young and older internodes and that these changes are particularly evident in the bast fibers.

Transcriptomic Changes in Internode Explants of Stinging Nettle during Callogenesis

Callogenesis, the process during which explants derived from differentiated plant tissues are subjected to a trans-differentiation step characterized by the proliferation of a mass of cells, is fundamental to indirect organogenesis and the establishment of cell suspension cultures. Therefore, understanding how callogenesis takes place is helpful to plant tissue culture, as well as to plant biotechnology and bioprocess engineering. The common herbaceous plant stinging nettle (Urtica dioica L.) is a species producing cellulosic fibres (the bast fibres) and a whole array of phytochemicals for pharmacological, nutraceutical and cosmeceutical use. Thus, it is of interest as a potential multi-purpose plant. In this study, callogenesis in internode explants of a nettle fibre clone (clone 13) was studied using RNA-Seq to understand which gene ontologies predominate at different time points. Callogenesis was induced with the plant growth regulators α-napthaleneacetic acid (NAA) and 6-benzyl aminopurine (BAP) after having determined their optimal concentrations. The process was studied over a period of 34 days, a time point at which a well-visible callus mass developed on the explants. The bioinformatic analysis of the transcriptomic dataset revealed specific gene ontologies characterizing each of the four time points investigated (0, 1, 10 and 34 days). The results show that, while the advanced stage of callogenesis is characterized by the iron deficiency response triggered by the high levels of reactive oxygen species accumulated by the proliferating cell mass, the intermediate and early phases are dominated by ontologies related to the immune response and cell wall loosening, respectively.

Olive Varieties under UV-B Stress Show Distinct Responses in Terms of Antioxidant Machinery and Isoform/Activity of RubisCO

In recent decades, atmospheric pollution led to a progressive reduction of the ozone layer with a consequent increase in UV-B radiation. Despite the high adaptation of olive trees to the Mediterranean environment, the progressive increase of UV-B radiation is a risk factor for olive tree cultivation. It is therefore necessary to understand how high levels of UV-B radiation affect olive plants and to identify olive varieties which are better adapted. In this study we analyzed two Italian olive varieties subjected to chronic UV-B stress. We focused on the effects of UV-B radiation on RubisCO, in terms of quantity, enzymatic activity and isoform composition. In addition, we also analyzed changes in the activity of antioxidant enzymes (SOD, CAT, GPox) to get a comprehensive picture of the antioxidant system. We also evaluated the effects of UV-B on the enzyme sucrose synthase. The overall damage at biochemical level was also assessed by analyzing changes in Hsp70, a protein triggered under stress conditions. The results of this work indicate that the varieties (Giarraffa and Olivastra Seggianese) differ significantly in the use of specific antioxidant defense systems, as well as in the activity and isoform composition of RubisCO. Combined with a different use of sucrose synthase, the overall picture shows that Giarraffa optimized the use of GPox and opted for a targeted choice of RubisCO isoforms, in addition to managing the content of sucrose synthase, thereby saving energy during critical stress points.

Cell Wall Layer Induced in Xylem Fibers of Flax Upon Gravistimulation Is Similar to Constitutively Formed Cell Walls of Bast Fibers

In the fibers of many plant species after the formation of secondary cell walls, cellulose-enriched cell wall layers (often named G-layers or tertiary cell walls) are deposited which are important in many physiological situations. Flax (Linum usitatissimum L.) phloem fibers constitutively develop tertiary cell walls during normal plant growth. During the gravitropic response after plant inclination, the deposition of a cellulose-enriched cell wall layer is induced in xylem fibers on one side of the stem, providing a system similar to that of tension wood in angiosperm trees. Atomic force microscopy (AFM), immunochemistry, and transcriptomic analyses demonstrated that the G-layer induced in flax xylem fibers was similar to the constitutively formed tertiary cell wall of bast (phloem) fibers but different from the secondary cell wall. The tertiary cell walls, independent of tissue of origin and inducibility, were twice as stiff as the secondary cell walls. In the gravitropic response, the tertiary cell wall deposition rate in xylem was higher than that of the secondary cell wall. Rhamnogalacturonan I (RG-I) with galactan side chains was a prominent component in cellulose-rich layers of both phloem and xylem flax fibers. Transcriptomic events underlying G-layer deposition in phloem and xylem fibers had much in common. At the induction of tertiary cell wall deposition, several genes for rhamnosyltransferases of the GT106 family were activated in xylem samples. The same genes were expressed in the isolated phloem fibers depositing the tertiary cell wall. The comparison of transcriptomes in fibers with both inducible and constitutive tertiary cell wall deposition and xylem tissues that formed the secondary cell walls is an effective system that revealed important molecular players involved in the formation of cellulose-enriched cell walls.

Physico-chemical properties and toxicological effects on plant and algal models of carbon nanosheets from a nettle fibre clone

Carbon nanosheets are two-dimensional nanostructured materials that have applications as energy storage devices, electrochemical sensors, sample supports, filtration membranes, thanks to their high porosity and surface area. Here, for the first time, carbon nanosheets have been prepared from the stems and leaves of a nettle fibre clone, by using a cheap and straight-forward procedure that can be easily scaled up. The nanomaterial shows interesting physical parameters, namely interconnectivity of pores, graphitization, surface area and pore width. These characteristics are similar to those described for the nanomaterials obtained from other fibre crops. However, the advantage of nettle over other plants is its fast growth and easy propagation of homogeneous material using stem cuttings. This last aspect guarantees homogeneity of the starting raw material, a feature that is sought-after to get a nanomaterial with homogeneous and reproducible properties. To evaluate the potential toxic effects if released in the environment, an assessment of the impact on plant reproduction performance and microalgal growth has been carried out by using tobacco pollen cells and the green microalga Pseudokirchneriella subcapitata. No inhibitory effects on pollen germination are recorded, while algal growth inhibition is observed at higher concentrations of leaf carbon nanosheets with lower graphitization degree.

Chronic heat stress affects the photosynthetic apparatus of Solanum lycopersicum L. cv Micro-Tom

Tomato (Solanum lycopersicum L.) is one of the most widely cultivated crops in the world. Tomato is a plant model and the relationship between yield and biotic/abiotic stress has attracted increasing scientific interest. Tomato cultivation under sub-optimal conditions usually negatively impacts growth and development; in particular, heat stress affects several cellular and metabolic processes, such as respiration and photosynthesis. In this work, we studied the effects of chronic heat stress on various cytological and biochemical aspects using the Micro-Tom cultivar as a model. Photosynthetic efficiency decreased during heat stress while levels of post-photosynthetic sugars (sucrose, fructose, glucose and glucose 6-phosphate) oscillated during stress. Similarly, photosynthetic pigments (lutein, chlorophyll a, chlorophyll b and β-carotene) showed an oscillating downward trend with partial recovery during the stress-free phase. The energetic capacity of leaves (e.g. ATP and ADP) was altered, as well as the reactive oxygen species (ROS) profile; the latter increased during stress. Important effects were also found on the accumulation of Rubisco isoforms, which decreased in number. Heat stress also resulted in a decreased accumulation of lipids (oleic and linoleic acid). Photosynthetically alterations were accompanied by cytological changes in leaf structure, particularly in the number of lipid bodies and starch granules. Prolonged heat stress progressively compromised the photosynthetic efficiency of tomato leaves. The present study reports multi-approach information on metabolic and photosynthetic injuries and responses of tomato plants to chronic heat stress, highlighting the plant's ability to adapt to stress.

Plant Fibers and Phenolics: A Review on Their Synthesis, Analysis and Combined Use for Biomaterials with New Properties

Devising environmental-friendly processes in biotechnology is a priority in the current economic scenario. We are witnessing a constant and steady push towards finding sustainable solutions to societal challenges by promoting innovation-driven activities minimizing the environmental impact and valorizing natural resources. In bioeconomy, plants are among the most important renewable sources of both fibers (woody and cellulosic) and phytochemicals, which find applications in many industrial sectors, spanning from the textile, to the biocomposite, medical, nutraceutical, and pharma sectors. Given the key role of plants as natural sources of (macro)molecules, we here provide a compendium on the use of plant fibers functionalized/impregnated with phytochemicals (in particular phenolic extracts). The goal is to review the various applications of natural fibers functionalized with plant phenolics and to valorize those plants that are source of both fibers and phytochemicals.