Although angiosperm plants generally react to immunity elicitors like chitin or chitosan by the cell wall callose deposition, this response in particular cell types, especially upon chitosan treatment, is not fully understood. Here we show that the growing root hairs (RHs) of Arabidopsis can respond to a mild (0.001%) chitosan treatment by the callose deposition and by a deceleration of the RH growth. We demonstrate that the glucan synthase-like 5/PMR4 is vital for chitosan-induced callose deposition but not for RH growth inhibition. Upon the higher chitosan concentration (0.01%) treatment, RHs do not deposit callose, while growth inhibition is prominent. To understand the molecular and cellular mechanisms underpinning the responses to two chitosan treatments, we analysed early Ca2+ and defence-related signalling, gene expression, cell wall and RH cellular endomembrane modifications. Chitosan-induced callose deposition is also present in the several other plant species, including functionally analogous and evolutionarily only distantly related RH-like structures such as rhizoids of bryophytes. Our results point to the RH callose deposition as a conserved strategy of soil-anchoring plant cells to cope with mild biotic stress. However, high chitosan concentration prominently disturbs RH intracellular dynamics, tip-localised endomembrane compartments, growth and viability, precluding callose deposition.

• Klíčová slova
• arabidopsis, cell wall, defence, gene expression, signalling,
• MeSH
• Arabidopsis * růst a vývoj   účinky léků   metabolismus   fyziologie   MeSH
• buněčná membrána metabolismus   MeSH
• buněčná stěna * metabolismus   MeSH
• chitosan * farmakologie   MeSH
• glukany * metabolismus   MeSH
• glukosyltransferasy metabolismus   MeSH
• kořeny rostlin * růst a vývoj   metabolismus   účinky léků   MeSH
• proteiny huseníčku * metabolismus   genetika   MeSH
• regulace genové exprese u rostlin účinky léků   MeSH
• vápník metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• callose MeSH Prohlížeč
• chitosan * MeSH
• glukany * MeSH
• glukosyltransferasy MeSH
• proteiny huseníčku * MeSH
• vápník MeSH

Fluorescent selective probes for reactive oxygen species (ROS) detection in living cells are versatile tools for the documentation of ROS production in plant developmental or stress reactions. We employed high-resolution live-cell imaging and semiquantitative analysis of Arabidopsis (Arabidopsis thaliana) stained with CM-H2DCFDA, CellROX Deep Red, and Amplex Red for functional characterization of the spatiotemporal mode of ROS production, delivery, and utilization during root hair formation. Cell viability marker fluorescein diacetate served as a positive control for dye loading and undisturbed root hair tip growth after staining. Using a colocalization analysis with subcellular molecular markers and two root hair mutants with similar phenotypes of nonelongating root hairs, but with contrasting reasons for this impairment, we found that: (i) CM-H2DCFDA is a sensitive probe for ROS generation in the cytoplasm, (ii) CellROX Deep Red labels ROS in mitochondria, (iii) Amplex Red labels apoplastic ROS and mitochondria and shows high selectivity to root hairs, (iv) the root hair defective 2-1 (rhd2-1) mutant with nonfunctional NADPH oxidase RESPIRATORY BURST OXIDASE HOMOLOG PROTEIN C/ROOT HAIR-DEFECTIVE 2 (AtRBOHC/RHD2) has a low level of CM-H2DCFDA-reactive ROS in cytoplasm and lacks Amplex Red-reactive ROS in apoplast, and (v) the ACTIN2-deficient deformed root hairs1-3 (der1-3) mutant is not altered in these aspects. The sensitivity of CellROX Deep Red was documented by discrimination between larger ROS-containing mitochondria and small, yet ROS-free premature mitochondria in the growing tip of root hairs. We characterized spatial changes in ROS production and compartmentalization induced by external ROS modulators, ethylene precursor 1-aminocyclopropane-1-carboxylic acid, and ionophore valinomycin. This dynamic and high-resolution study of ROS production and utilization opens opportunities for precise speciation of particular ROS involved in root hair formation.

• MeSH
• Arabidopsis * metabolismus   MeSH
• fenotyp MeSH
• kořeny rostlin metabolismus   MeSH
• proteiny huseníčku * genetika   metabolismus   MeSH
• reaktivní formy kyslíku metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• 2',7'-dichlorodihydrofluorescein diacetate MeSH Prohlížeč
• proteiny huseníčku * MeSH
• reaktivní formy kyslíku MeSH

Primary root growth is required by the plant to anchor in the soil and reach out for nutrients and water, while dealing with obstacles. Efficient root elongation and bending depends upon the coordinated action of environmental sensing, signal transduction, and growth responses. The actin cytoskeleton is a highly plastic network that constitutes a point of integration for environmental stimuli and hormonal pathways. In this review, we present a detailed compilation highlighting the importance of the actin cytoskeleton during primary root growth and we describe how actin-binding proteins, plant hormones, and actin-disrupting drugs affect root growth and root actin. We also discuss the feedback loop between actin and root responses to light and gravity. Actin affects cell division and elongation through the control of its own organization. We remark upon the importance of longitudinally oriented actin bundles as a hallmark of cell elongation as well as the role of the actin cytoskeleton in protein trafficking and vacuolar reshaping during this process. The actin network is shaped by a plethora of actin-binding proteins; however, there is still a large gap in connecting the molecular function of these proteins with their developmental effects. Here, we summarize their function and known effects on primary root growth with a focus on their high level of specialization. Light and gravity are key factors that help us understand root growth directionality. The response of the root to gravity relies on hormonal, particularly auxin, homeostasis, and the actin cytoskeleton. Actin is necessary for the perception of the gravity stimulus via the repositioning of sedimenting statoliths, but it is also involved in mediating the growth response via the trafficking of auxin transporters and cell elongation. Furthermore, auxin and auxin analogs can affect the composition of the actin network, indicating a potential feedback loop. Light, in its turn, affects actin organization and hence, root growth, although its precise role remains largely unknown. Recently, fundamental studies with the latest techniques have given us more in-depth knowledge of the role and organization of actin in the coordination of root growth; however, there remains a lot to discover, especially in how actin organization helps cell shaping, and therefore root growth.

• Klíčová slova
• actin, actin-binding protein, auxin, cell elongation, gravitropism, light, root growth,
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH

Single-point mutation in the ACTIN2 gene of the der1-3 mutant revealed that ACTIN2 is an essential actin isovariant required for root hair tip growth, and leads to shorter, thinner and more randomly oriented actin filaments in comparison to the wild-type C24 genotype. The actin cytoskeleton has been linked to plant defense against oxidative stress, but it is not clear how altered structural organization and dynamics of actin filaments may help plants to cope with oxidative stress. In this study, we characterized root growth, plant biomass, actin organization and antioxidant activity of the der1-3 mutant under oxidative stress induced by paraquat and H2O2. Under these conditions, plant growth was better in the der1-3 mutant, while the actin cytoskeleton in the der1-3 carrying pro35S::GFP:FABD2 construct showed a lower bundling rate and higher dynamicity. Biochemical analyses documented a lower degree of lipid peroxidation, and an elevated capacity to decompose superoxide and hydrogen peroxide. These results support the view that the der1-3 mutant is more resistant to oxidative stress. We propose that alterations in the actin cytoskeleton, increased sensitivity of ACTIN to reducing agent dithiothreitol (DTT), along with the increased capacity to decompose reactive oxygen species encourage the enhanced tolerance of this mutant against oxidative stress.

• Klíčová slova
• ACTIN2, Arabidopsis, actin cytoskeleton, antioxidant capacity, der1–3 mutant, lipid peroxidation, oxidative stress, root hairs, single amino acid exchange,
• MeSH
• aktiny * genetika   metabolismus   MeSH
• Arabidopsis * genetika   metabolismus   MeSH
• kořeny rostlin * genetika   metabolismus   MeSH
• missense mutace * MeSH
• oxidační stres genetika   MeSH
• proteiny huseníčku * genetika   metabolismus   MeSH
• substituce aminokyselin MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• ACT2 protein, Arabidopsis MeSH Prohlížeč
• aktiny * MeSH
• proteiny huseníčku * MeSH