Meristematic Region Research Articles

Developmental Nuclear Localization and Quantification of GFP-Tagged EB1c in Arabidopsis Root Using Light-Sheet Microscopy.

The development of the root apex is determined by progress of cells from the meristematic region to the successive post-mitotic developmental zones for transition, cell elongation and final cell differentiation. We addressed root development, tissue architecture and root developmental zonation by means of light-sheet microscopic imaging of Arabidopsis thaliana seedlings expressing END BINDING protein 1c (EB1c) fused to green fluorescent protein (GFP) under control of native EB1c promoter. Unlike the other two members of the EB1 family, plant-specific EB1c shows prominent nuclear localization in non-dividing cells in all developmental zones of the root apex. The nuclear localization of EB1c was previously mentioned solely in meristematic cells, but not further addressed. With the help of advanced light-sheet microscopy, we report quantitative evaluations of developmentally-regulated nuclear levels of the EB1c protein tagged with GFP relatively to the nuclear size in diverse root tissues (epidermis, cortex, and endodermis) and root developmental zones (meristem, transition, and elongation zones). Our results demonstrate a high potential of light-sheet microscopy for 4D live imaging of fluorescently-labeled nuclei in complex samples such as developing roots, showing capacity to quantify parameters at deeper cell layers (e.g., endodermis) with minimal aberrations. The data presented herein further signify the unique role of developmental cell reprogramming in the transition from cell proliferation to cell differentiation in developing root apex.

NO FLOWERING IN SHORT DAY (NFL) is a bHLH transcription factor that promotes flowering specifically under short-day conditions in Arabidopsis.

Flowering in plants is a dynamic and synchronized process where various cues including age, day length, temperature and endogenous hormones fine-tune the timing of flowering for reproductive success. Arabidopsis thaliana is a facultative long day (LD) plant where LD photoperiod promotes flowering. Arabidopsis still flowers under short-day (SD) conditions, albeit much later than in LD conditions. Although factors regulating the inductive LD pathway have been extensively investigated, the non-inductive SD pathway is much less understood. Here, we identified a key basic helix-loop-helix transcription factor called NFL (NO FLOWERING IN SHORT DAY) that is essential to induce flowering specifically under SD conditions in Arabidopsis. nfl mutants do not flower under SD conditions, but flower similar to the wild type under LD conditions. The no-flowering phenotype in SD is rescued either by exogenous application of gibberellin (GA) or by introducing della quadruple mutants in the nfl background, suggesting that NFL acts upstream of GA to promote flowering. NFL is expressed at the meristematic regions and NFL is localized to the nucleus. Quantitative RT-PCR assays using apical tissues showed that GA biosynthetic genes are downregulated and the GA catabolic and receptor genes are upregulated in the nfl mutant compared with the wild type, consistent with the perturbation of the endogenous GA biosynthetic and catabolic intermediates in the mutant. Taken together, these data suggest that NFL is a key transcription factor necessary for promotion of flowering under non-inductive SD conditions through the GA signaling pathway.

EGTA, a calcium chelator, affects cell cycle and increases DNA methylation in root tips of Triticum aestivum L.

In this study, when germinated <em>Triticum aestivum</em> L. seeds were treated with 0, 2, 4 and 6 mM ethyl glycol tetraacetic acid (EGTA), root growth was suppressed and the mitotic index decreased. These inhibitory effects were positively correlated with EGTA concentration. RT-PCR analysis revealed that the expression of several gene markers related to the G1/S transition of the cell cycle were significantly downregulated. Confocal microscopy of Fluo-3/AM-stained roots showed chelation of nearly all of the Ca<sup>2+</sup> within the root meristematic regions. Both random amplified polymorphic DNA (RAPD) and coupled restriction enzyme digestion-random amplification (CRED-RA) techniques showed significant increases in the levels of genomic DNA polymorphisms and degree of DNA methylation. The study provides information concerning the impact of Ca<sup>2+</sup> chelator, EGTA, on the growth, expression of cell cycle transition marker genes, and changes in DNA structure and methylation in the wheat roots.

Fibonacci spirals in a brown alga [Sargassum muticum (Yendo) Fensholt] and in a land plant [Arabidopsis thaliana (L.) Heynh.]: a case of morphogenetic convergence

In this article, the morphology of a brown alga is revisited and compared to the phyllotaxis of land plants. The alga, <em>Sargassum muticum</em> (Yendo) Fensholt has a highly organized thallus with a stipe, the stem-like main axis, and hierarchically organized lateral branches of successive orders. Around each of these axes, the lateral organs: blades, side-branches, and receptacles grow in a spiral disposition. As in land plants, this organization is related to an apical mode of growth. Measurements performed along the mature differentiated axes as well as in their meristematic regions confirm the similarity of the large-scale organization of this brown alga with that of the land plants. In particular, the divergence angle between successive elements has similar values and it results from the existence around the meristem of parastichies having the same Fibonacci ordering. This is remarkable in view of the fact that brown algae (Phaeophyceae) and land plants (Embryophyta) are two clades that diverged approximately 1800 million years ago when they were both unicellular organisms. We argue that the observed similarity results from a morphogenetic convergence. This is in strong support of the genericity and robustness of self-organization models in which similar structures, here Fibonacci related spirals, can be obtained in various situations in which the genetic and physiological implementation of development can be of a different nature.

Antioxidant defences of Norway spruce bark against bark beetles and its associated blue-stain fungus

Abstract Bark beetles and their fungal associates are integral parts of forest ecosystems, the European spruce bark beetle (Ips typographus Linnaeus, 1758) and the associated pathogenic blue stain fungus Ceratocystis polonica (SIEM.) C. MOREAU, are the most devastating pests regarding Norway spruce [Picea abies (L.) H. KARST.]. Bark beetles commonly inhabit weakened and felled trees as well as vital trees. They cause physiological disorders in trees by destroying a phloem and cambium or interrupt the transpiration -ow in the xylem. Conifers have a wide range of effective defence mechanisms that are based on the inner bark anatomy and physiological state of the tree. The basic function of bark defences is to protect the nutrient-and energy-rich phloem, the vital meristematic region of the vascular cambium, and the transpiration -ow in the sapwood. The main area of defence mechanisms is secondary phloem, which is physically and chemically protected by polyphenolic parenchyma (PP) cells, sclerenchyma, calcium oxalate crystals and resin ducts. Conifer trunk pest resistance includes constitutive, inducible defences and acquired resistance. Both constitutive and inducible defences may deter beetle invasion, impede fungal growth and close entrance wounds. During a successful attack, systemic acquired resistance (SAR) becomes effective and represents a third defence strategy. It gradually develops throughout the plant and provides a systemic change within the whole tree’s metabolism, which is maintained over a longer period of time. The broad range of defence mechanisms that contribute to the activation and utilisation of SAR, includes antioxidants and antioxidant enzymes, which are generally linked to the actions of reactive oxygen species (ROS). The presented review discusses the current knowledge on the antioxidant defence strategies of spruce inner bark against the bark beetle (Ips typographus) and associated blue stain fungus (Ceratocystis polonica).

Core cell cycle regulatory genes in rice and their expression profiles across the growth zone of the leaf.

Rice (Oryza sativa L.) as a model and crop plant with a sequenced genome offers an outstanding experimental system for discovering and functionally analyzing the major cell cycle control elements in a cereal species. In this study, we identified the core cell cycle genes in the rice genome through a hidden Markov model search and multiple alignments supported with the use of short protein sequence probes. In total we present 55 rice putative cell cycle genes with locus identity, chromosomal location, approximate chromosome position and EST accession number. These cell cycle genes include nine cyclin dependent-kinase (CDK) genes, 27 cyclin genes, one CKS gene, two RBR genes, nine E2F/DP/DEL genes, six KRP genes, and one WEE gene. We also provide characteristic protein sequence signatures encoded by CDK and cyclin gene variants. Promoter analysis by the FootPrinter program discovered several motifs in the regulatory region of the core cell cycle genes. As a first step towards functional characterization we performed transcript analysis by RT-PCR to determine gene specific variation in transcript levels along the rice leaves. The meristematic zone of the leaves where cells are actively dividing was identified based on kinematic analysis and flow cytometry. As expected, expression of the majority of cell cycle genes was exclusively associated with the meristematic region. However genes such as different D-type cyclins, DEL1, KRP1/3, and RBR2 were also expressed in leaf segments representing the transition zone in which cells start differentiation.

Bald kelp: natural and harvesting-induced frond loss in the South African kelp Ecklonia maxima

Ecklonia maxima dominates kelp beds on the west coast of southern Africa, and is commercially and ecologically valuable. Some plants lose all their secondary blades (fronds), leaving only the gas-filled bulb and short primary blade at the top of the stipe. These ‘bald’ kelps may persist for months or longer, occupying substratum space but contributing little to productivity. We investigated natural causes of balding in five kelp beds in False Bay, South Africa, and the effect of simulated commercial frond-harvesting on loss of fronds. Densities of sporophytes with and without fronds were measured at the water surface during low tides. Generalised linear modelling analysis showed a significant relationship between balding and site (whether sheltered from or exposed to swell/wind), position in the kelp bed (shoreward or seaward) and total E. maxima density. We conclude that balding is caused mainly by drying of meristematic basal regions of fronds during emersion of kelp heads at low tide. After partial harvesting of fronds, kelp heads floated higher out of the water, but after 95 days frond loss was significantly higher only when fronds were cut too close to the primary blade, possibly because of damage to meristematic tissue. Nevertheless, increased emersion that results from frond-harvesting may increase desiccation and blade loss and we suggest caution in setting harvest limits for this kelp.

WEREWOLF and ENHANCER of GLABRA3 are interdependent regulators of the spatial expression pattern of GLABRA2 in Arabidopsis

In multicellular organisms, cell fates are specified through differential regulation of transcription. Epidermal cell fates in the Arabidopsis thaliana root are precisely specified by several transcription factors, with the GLABRA2 (GL2) homeodomain protein acting at the farthest downstream in this process. To better understand the regulation of GL2 expression, we ectopically expressed WEREWOLF (WER) and ENHANCER OF GLABRA3 (EGL3) in various tissues and examined GL2 expression. Here we show that WER expressed ubiquitously in the root induced GL2 expression only in the root epidermis, whereas co-expression of WER and EGL3 induced GL2 expression in the corresponding tissues. We also found that GL3 accumulated in the nucleus at the early meristematic region and EGL3 accumulated later in the nucleus of epidermal cells. We further found that ectopic expression of WER and EGL3 in ground tissues inhibited GL2 expression in the epidermis. Our results suggest that the co-expression of WER and EGL3 is sufficient for driving GL2 and CPC expression.

Morphological effects at radicle level by direct contact of invasive Acacia dealbata Link

Seeds of Lactuca sativa L. (model plant) and Quillaja saponaria Mol. (native tree) were subjected to germination in direct contact with leaves, pods and seeds from invasive Acacia dealbata Link. (Fabaceae) to reveal whether morphological changes occur at radicle level. Bioassays were carried out with plant material deposited underneath A. dealbatás canopy under natural conditions at Mediterranean ecosystem in South America. Segments of radicle tip, cell elongation zone and root hair zone were analyzed under scanning electron microscopy. The three plant parts from A. dealbata inhibited the formation of root hairs and altered the rhizodermis (deformation and tissue destruction) of the two recipient species. In the case of Q. saponaria, an increase in thickness in the cell elongation zone was observed and internal tissues up to the vascular cylinder in the root hair zone were intensely damaged. The root cap and meristematic region suffered structural changes and damage resulting from the contact with leaves and pods. All morphological effects have been attributed to the impact caused at root level by potential allelochemicals released by different tested plant materials of A. dealbata. These results suggest that the morphological changes and damage produced by A. dealbata at the radicle level may pose a threat to the growth and survival of the recipient species.

NO3 −/NH4 + ratios affect plant growth, chlorophyll content, respiration rate, and morphological structure in Malus hupehensis seedlings

Malus hupehensis (Pamp.) Rehd. is a widely cultivated rootstock in China. We studied the effect of three NO3 −/NH4 + ratios (100/0, 50/50, and 0/100, molar basis) at total nitrogen (N) concentration of 8 mmoL L−1 in a nutrient solution on M. hupehensis seedlings. Plant biomass, NO3 − and NH4 +concentration, chlorophyll content, respiratory rate, and cellular structure were investigated. M. hupehensis seedlings at the NO3 −/NH4 + ratio of 50/50 had the highest level of fresh weight, dry weight, shoot length, and chlorophyll (a, b, and a + b) content, but the lowest respiration rate in the leaves and roots. In addition, thickness and numbers of palisade and spongy tissue cells of the leaves were greater with this treatment than with other treatments. At the NO3 −/NH4 + ratio of 100/0, the leaves and roots had higher NO3 − concentration and lower NH4 + concentration. However, the opposite trend occurred at the NO3 −/NH4 + ratio of 0/100. Chlorophyll (a, b, and a + b) content was lowest at the NO3 −/NH4 + ratio of 100/0 than at the other ratios. At the NO3 −/NH4 + ratio of 0/100, oxygen (O2) consumption increased in the leaves and roots, and irregular epidermis and cortex cells were observed in the root apical meristematic and mature region. Our results indicated that the NO3 −/NH4 + ratio at 50/50 was suitable for growth of M. hupehensis seedling to achieve the highest biomass production and efficiency.

Repression of AS2 by WOX family transcription factors is required for leaf development in Medicago and Arabidopsis

WOX transcription factors are key regulators of meristematic activity in plants. The Medicago WOX gene, STF, functions in maintenance of leaf marginal meristem, analogous to the function of WUS in the shoot apical meristem. Both STF and WUS directly repress AS2 expression in their respective domains. Ectopic expression of AS2 with WUS promoter leads to a narrow leaf phenotype and other phenotypes similar to the wus mutant. We also found that a wox1 prs wus triple mutant produces much narrower leaf blades than the wox1 prs double mutant, indicating that WUS genetically interacts with WOX1 and PRS in Arabidopsis leaf blade development. Our data points to a general requirement for AS2 repression in meristematic regions to allow cell proliferation.

In Vivo Cytogenotoxicity of Electronic Waste Leachate from Iloabuchi Electronic Market, Diobu, Rivers State, Nigeria on Allium Cepa

The human and environmental impact of electronic waste is increasing due to its careless disposal. Cytogenotoxicity of electronic waste from Iloabuchi electronic market, Diobu, Rivers State was investigated using the Allium cepa bioassay comprised of the root elongation and chromosome aberration tests. Leachate samples of e-waste analysed were above maximum permissible limits. Toxicity to root growth of A. cepa was evaluated at concentrations of 5%, 10%, 25%, 50%, and 100% showed root growth inhibition at all concentrations of the samples compared to the control and root growth inhibition was concentration dependent. An effective concentration (EC50) at which root growth amounted to 50 % of control for the sample was 37.5%. Various morphological defects of the onion roots were observed including short, crochet roots, C-tumor roots and severe toxic effects where no growth was observed. In the in vivo genotoxity assay, all samples lowered the frequency of mitotic cells in the meristematic region of the roots at statistically significant levels (P < 0.05) compared to the control and mitotic inhibition was also concentration dependent. There was significant induction of aberrations at all concentrations tested compared to control. The high metal content of the e-waste leachate may be responsible for observed cytotoxicity in A. cepa roots cells.

Auxin Produced by the Indole-3-Pyruvic Acid Pathway Regulates Development and Gemmae Dormancy in the Liverwort Marchantia polymorpha.

The plant hormone auxin (indole-3-acetic acid [IAA]) has previously been suggested to regulate diverse forms of dormancy in both seed plants and liverworts. Here, we use loss- and gain-of-function alleles for auxin synthesis- and signaling-related genes, as well as pharmacological approaches, to study how auxin regulates development and dormancy in the gametophyte generation of the liverwort Marchantia polymorpha. We found that M. polymorpha possess the smallest known toolkit for the indole-3-pyruvic acid (IPyA) pathway in any land plant and that this auxin synthesis pathway mainly is active in meristematic regions of the thallus. Previously a Trp-independent auxin synthesis pathway has been suggested to produce a majority of IAA in bryophytes. Our results indicate that the Trp-dependent IPyA pathway produces IAA that is essential for proper development of the gametophyte thallus of M. polymorpha. Furthermore, we show that dormancy of gemmae is positively regulated by auxin synthesized by the IPyA pathway in the apex of the thallus. Our results indicate that auxin synthesis, transport, and signaling, in addition to its role in growth and development, have a critical role in regulation of gemmae dormancy in M. polymorpha.

Influence of oxygen deficiency and the role of specific amino acids in cryopreservation of garlic shoot tips.

BackgroundGarlic has lost its ability to form seeds in the course of its domestication. Therefore, the germplasm storage via cryopreservation is increasingly applied. The progression of the various steps within the cryopreservation procedure is accompanied by declining survival rates of the explants. Much of the recent work on cryo-stress has been focussed on osmotic and cold stress components. However, two decades after invention of garlic cryopreservation, the function of metabolites and oxygen in and around the cryopreserved tissues is still largely obscure.MethodsIn this study, hypoxia was characterized in cryopreservation of garlic with oxygen sensors and amino acid metabolism. Furthermore, malondialdehyde, soluble sugars and ammonium were quantified to demonstrate the influence of cryo-stress in declining survival rates.ResultsTo better understand the possible reasons for a reduction in the survival rate at the subsequent steps of cryopreservation, the concentration of amino acids, ammonium, γ-aminobutyric acid (GABA), soluble sugars, malondialdehyde (MDA), and oxygen were measured in garlic shoot tips undergoing cryopreservation. Using microsensors, a very low oxygen concentration (<0.1 μM) was detected within the central meristem region of the shoot apex. When apices were immersed in cryoprotectant solution, the well-oxygenated peripheral regions (foliage leaf bases) became likewise hypoxic within a few minutes, probably resulting from strongly restricted gaseous diffusion.ConclusionsTissue level oxygen measurements supported the occurrence of hypoxia while biochemical analysis indicated adaptive responses, in particular the modulation in alanine and glutamate metabolism. The possible role of serine and glycine metabolism during cryopreservation is also discussed.

Physiological and Molecular Mechanisms of Differential Sensitivity of Palmer Amaranth (Amaranthus palmeri) to Mesotrione at Varying Growth Temperatures.

Herbicide efficacy is known to be influenced by temperature, however, underlying mechanism(s) are poorly understood. A marked alteration in mesotrione [a 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor] efficacy on Palmer amaranth (Amaranthus palmeri S. Watson) was observed when grown under low- (LT, 25/15°C, day/night temperatures) and high (HT, 40/30°C) temperature compared to optimum (OT, 32.5/22.5°C) temperature. Based on plant height, injury, and mortality, Palmer amaranth was more sensitive to mesotrione at LT and less sensitive at HT compared to OT (ED50 for mortality; 18.5, 52.3, and 63.7 g ai ha-1, respectively). Similar responses were observed for leaf chlorophyll index and photochemical efficiency of PSII (Fv/Fm). Furthermore, mesotrione translocation and metabolism, and HPPD expression data strongly supported such variation. Relatively more mesotrione was translocated to meristematic regions at LT or OT than at HT. Based on T50 values (time required to metabolize 50% of the 14C mesotrione), plants at HT metabolized mesotrione faster than those at LT or OT (T50; 13, 21, and 16.5 h, respectively). The relative HPPD:CPS (carbamoyl phosphate synthetase) or HPPD:β-tubulin expression in mesotrione-treated plants increased over time in all temperature regimes; however, at 48 HAT, the HPPD:β-tubulin expression was exceedingly higher at HT compared to LT or OT (18.4-, 3.1-, and 3.5-fold relative to untreated plants, respectively). These findings together with an integrated understanding of other interacting key environmental factors will have important implications for a predictable approach for effective weed management.

High expression of SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE coincides with initiation of various developmental pathways in in vitro culture of Trifolium nigrescens.

The aim of this study was to identify and examine the expression pattern of the ortholog of SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE gene from Trifolium nigrescens (TnSERK) in embryogenic and non-regenerative cultures of immature cotyledonary-stage zygotic embryos (CsZEs). In the presence of 1-naphthaleneacetic acid and N6-[2-isopentenyl]-adenine, the CsZE regenerated embryoids directly and in a lengthy culture produced callus which was embryogenic or remained non-regenerative. As revealed by semi-quantitative reverse transcription polymerase chain reaction (RT-PCR), the TnSERK was expressed in both embryogenic and non-regenerative cultures, but the expression level was significantly higher in embryogenic ones. An in situ RNA hybridization assay revealed that the expression of TnSERK preceded the induction of cell division in explants, and then, it was maintained exclusively in actively dividing cells from which embryoids, embryo-like structures (ELSs), callus or tracheary elements were produced. However, the cells involved in different morphogenic events differed in intensity of hybridization signal which was the highest in embryogenic cells. The TnSERK was up-regulated during the development of embryoids, but in cotyledonary embryos, it was preferentially expressed in the regions of the apical meristems. The occurrence of morphological and anatomical abnormalities in embryoid development was preceded by a decline in TnSERK expression, and this coincided with the parenchymatization of the ground tissue in developing ELSs. TnSERK was also down-regulated during the maturation of parenchyma and xylem elements in CsZE and callus. Altogether, these data suggest the involvement of TnSERK in the induction of various developmental programs related to differentiation/transdifferentiation and totipotent state of cell(s).Electronic supplementary materialThe online version of this article (doi:10.1007/s00709-015-0814-5) contains supplementary material, which is available to authorized users.

Evaluation of protocorm formation in meristematic regions of roots and leaves of Miltonia spectabilis moreliana (Orchidaceae).

The aim of this study was to evaluate the effect of 2.4-D and BAP on protocorm formation in meristematic regions of root and leaf of Miltonia spectabilis moreliana, and to test the effect of sucrose concentrations and pH levels on the growth of protocorms. Root and leaf segments of in vitro-germinated plants were cultured in MS/2 culture medium supplemented with 2.4-D and BAP, and kept in the dark for 210 days. The combination of 3 mg.L-1 2.4-D and 1 or 3 mg.L-1 BAP provided the best results. The concentrations of 15 and 30 g.L-1 sucrose, independently of the pH, were more efficient for the in vitro culture of this species, as they promoted an increase in the number and length of roots, height, and fresh weight of the plantlets. The pH was significant only in combination with 15 g.L-1 sucrose for the length of the largest root and fresh weight.

Cytoplasmic segregation in onion root tip cells and formation of vacuoles

Onion root tips were studied both with transmission and scanning electron microscope. The cells in the meristematic region of initials were found to be little vacuolated. At early stages of cell differentiation areas free of ribosomes are segregated in the cytoplasm. No (or only incomplete) membranes delimiting such areas could be distinguished in most cases. Seemingly, the membraneous structures may form later or simultaneously with the progress of breakdown of biostructure of the cytoplasm in the segregated area. The microscopic image of cytoplasm in the segregated areas (and even of the vacuolar sap at early stages of vacuole formation) resembles the matrix of cytoplasm populated with ribosomes. The cytoplasm in the whole central area is segregated at early stages of differentiation of root cap cells. The process of autophagic vacuoles formation in which the preexisting endomembranes seemingly are involved is described. It is proposed that such vacuoles may form after separation of two unit membranes of a cisternae surrounding a portion of the cytoplasm or an organelle, followed by independent growth of an outer unit membrane.

Development of Shoot Architecture of Japanese Privet in Response to Soil Moisture

Bud outgrowth dynamics and their implications for shoot architecture were examined in japanese privet (Ligustrum japonicum) plants under well-irrigated [short irrigation cycle (SC)] and water-limitation [long irrigation cycle (LC)] conditions. New buds had limited sensitivity to dormancy, whereas preformed buds required more than one growing season to outgrow naturally. The first spring flush of shoot growth was mostly the result of lateral bud outgrowth, whereas latter flushes had prominent contributions of new apex buds. First flush terminal stems had mainly determinate growth (episodic). First flush lateral stems had increased occurrence of indeterminate growth (continuous). Water limitation influenced shoot architecture by enhancing apical dominance. Lateral branching was diminished 51% in LC plants compared with SC plants. As plants adapted to the stress imposed, indeterminate growth was triggered more often in meristematic regions of terminal buds of LC plants. In shoot flushes that occurred later in the stress treatment, old buds burst more frequently than the newly formed apex lateral buds. Plants under SC were more compact and better formed as an inverse triangle, whereas plants under LC had considerably less new branches and instead had long branches that would require pruning to maintain aesthetically pleasing shapes.

Oxic microshield and local pH enhancement protects Zostera muelleri from sediment derived hydrogen sulphide.

Seagrass is constantly challenged with transporting sufficient O₂ from above- to belowground tissue via aerenchyma in order to maintain aerobic metabolism and provide protection against phytotoxins. Electrochemical microsensors were used in combination with a custom-made experimental chamber to analyse the belowground biogeochemical microenvironment of Zostera muelleri under changing environmental conditions. Measurements revealed high radial O₂ release of up to 500 nmol O2 cm(-2) h(-1) from the base of the leaf sheath, maintaining a c. 300-μm-wide plant-mediated oxic microzone and thus protecting the vital meristematic regions of the rhizome from reduced phytotoxic metabolites such as hydrogen sulphide (H₂S). H₂S intrusion was prevented through passive diffusion of O₂ to belowground tissue from leaf photosynthesis in light, as well as from the surrounding water column into the flow-exposed plant parts during darkness. Under water column hypoxia, high belowground H₂S concentrations at the tissue surface correlated with the inability to sustain the protecting oxic microshield around the meristematic regions of the rhizome. We also found increased pH levels in the immediate rhizosphere of Z. muelleri, which may contribute to further detoxification of H₂S through shifts in the chemical speciation of sulphide. Zostera muelleri can modify the geochemical conditions in its immediate rhizosphere, thereby reducing its exposure to H₂S.