Forest structure of a subtropical mangrove along a river inferred from potential tree height and biomass

The hypothesis was tested that potential tree height and biomass in mangroves decrease downstream with the tidal gradient along the Okukubi River in Okinawa Island, Japan. The mangrove stands consisted of Bruguiera gymnorrhiza (L.) Lamk. and Kandelia obovata (S., L.) Yong (Rhizophoraceae). Four sites were selected considering the distance from the mouth of the river. Soil salinity increased downstream, while soil total nitrogen content decreased. The soil redox potential did not vary along the river. Maximum gross photosynthesis and tree height for each species decreased downstream. The potential tree height (H_max) inferred from the stem diameter (D_0.1)–tree height (H) relationship ( a, h, coefficient) in each species decreased downstream. The tree density (ρ)–mean tree size () relationships ( K, α, coefficient) determined for four sites revealed that the mean tree size at any given tree density decreased downstream, which indicates the decrease of potential biomass. Furthermore, an index for biomass () was homogeneous within a site regardless of tree density, i.e. the value of α at each site did not differ significantly from 1.0 (p > 0.05). The decreases in potential tree height and biomass may be partially ascribed to the stressful environments at the downstream sites characterized by high salinity (>2.6%) and nitrogen-poor soils (<0.25 ppt) in our study area.     

Expression of defence-related peroxidases Prx7 and Prx8 during abiotic stresses in barley roots

The expression of defence-related peroxidases Prx7 and Prx8 in barley roots grown under selected abiotic stress conditions (toxic metals: Cd, Al, Co, Cu, Hg; drought, salinity, extreme temperatures: heat, cold) and compounds activating (2,4-D) or inhibiting (SHAM) POD activity as well as H₂O₂ and H₂O₂ scavenger (DTT) was characterized. Strong Cd concentration dependent expression of Prx8 peroxidase gene was observed, which correlated with root growth inhibition induced by Cd- and some other stress factors (heavy metals, heat and salinity). Application of H₂O₂ did not cause changes in expression of Prx8, but H₂O₂ scavenger (DTT) as well as the inhibitor (SHAM) and the activator (2,4-D) of PODs induced increase in Prx8 expression. Our results demonstrate that root growth inhibition during any disturbance of active oxygen species (AOS) in root tissue is correlated with up-regulation of Prx8 gene expression in barley roots.     

An energy balance from absorbed photons to new biomass for Chlamydomonas reinhardtii and Chlamydomonas acidophila under neutral and extremely acidic growth conditions

Chlamydomonas is one of the most well-studied photosynthetic organisms that had important biotechnological potential for future bioproductions of biofuels. However, an energy balance from incident photons to the energy stored in the new biomass is still lacking. In this study, we applied a recently developed system to measure the energy balance for steady state growth of Chlamydomonas reinhardtii grown at pH 6.5, and C. acidophila that was grown at pH 6.5 and 2.6. Energy use efficiency was quantified on the basis of light absorption, photosynthetic quantum yield, photosynthetic and respiratory quotient, and electron partitioning into proteins, carbohydrates and lipids. The results showed that lower growth rates of C. acidophila under both pH conditions were not caused by the differences in the photosynthetic quantum yield or in alternative electron cycling, but rather by differences in the efficiency of light absorption and increased dark respiration. Analysis of the macromolecular composition of the cells during the light phase showed that C. acidophila uses biosynthetic electrons preferentially for carbohydrate synthesis but not for synthesis of lipids. This led to a strong diurnal cycle of the C/N ratio and could explain the higher dark respiration of C. acidophila compared with C. reinhardtii .     

Cascade transduction and production of the light-nitric oxide signal from shoots to roots in maize seedlings exposed to enhanced UV-B radiation

The biomasses, rate of apparent nitric oxide (NO)-release, nitric oxide synthase (NOS) activity as well as β-d-endo and exo-glucanase activity of the cell wall were analyzed and determined in the roots of maize seedlings. It was found that rhizospheric treatments of 2-phenyl-4,4,5,5-tetramethlimida-zoline-l-oxyl-3-oxide (PTIO), a NO scavenger, and radiation of enhanced ultraviolet-B (UV-B) to aerial parts of the seedling markedly inhibited the rate of NO release in roots, raised the activity of β-d-endo and exo-glucanase, and increased the biomasses of roots. The patent inhibitor, N-nitro-l-arginine (LNNA), of NOS was unable to inhibit NOS activity and NO generation. Inversely, reactive oxygen species (ROS) eliminator, N-acetyl-cysteine (NAC), stimulated the rate of NO release. There is no relationship between NOS activity and the rate of NO release. The latter showed a positive correlation with nitrate reductase (NR) activity, whereas it showed a negative correlation with the bio-masses and the activity of β-d-endo and exo-glucanase. All results implicated that NO was a by-product generated by NR catalysis, whereas NR activity was sensitively repressed by the systemic signal network (involved in ROS) induced by enhanced UV-B. It indicated that the downstream signal molecule of enhanced UV-B light is probably ROS which decreased NO generation through inhibiting NR activity. The endogenous NO generated by NR catalysis is perhaps such a messenger for restraining β-d-endo and exo-glucanase activity that the root growth was retarded.     

In vitro propagation of seven <Emphasis Type="Italic">Daphne</Emphasis> L. species

Cultures of seven Daphne species: Daphne caucasica, D. cneorum, D. giraldii, D. retusa, D. jasminea, D. laureola and D. tangutica were established in vitro on MS/WPM based media. Five of the species responded best on MS-based media (D. tangutica, D. laureola, D. caucasica, D. retusa and D. giraldii), while the remaining two species performed best on WPM-based media (D. cneorum, and D. jasminea). Shoot proliferation was achieved from both apical and nodal explants. Shoots were sub-cultured from stock cultures, cut into nodal explants 3–5 cm long and place vertically on basal media supplemented with different concentrations and combinations of cytokinins and auxins. Individual species displayed different responses to the various cytokinins and auxins. Among species, D. jasminea produced the greatest proliferation rate with an average of 7.84 + 0.6 shoots per explant on WPM supplemented with 2.32 μM BA + 0.0045 μM TDZ + 0.054 μM NAA, while the best multiplication rate for the same species grown on the same media supplemented with a single cytokinin (BA) and no auxin was 2.60 + 1.3 shoots per explant. Following multiplication, new shoots transferred to the elongation trails and then 50–100 mm Shoots used for rooting experiments. Increased rooting efficiencies were observed on in vitro-generated shoots with the two-layer medium or dipping methods over when PGRs were uniformly incorporated into the medium. Maximum rooting frequencies (average) ranged from 59% in D. tangutica to 85% in D. jasminea. Following in vitro rooting, rooted shoots immersed in 0.01% solution of humates and planted into a standard horticultural substrate composed and watered weekly with a solution containing half-strength MS salts.     

Effects of brassinosteroids on barley root growth,antioxidant system and cell division

Homobrassinolide (HBR), which is one of the most biologically active forms of Brassinosteroids (BRs), was used to examine the potential effects of hormone on root germination, antioxidant system enzymes and cell division of barley (Hordeum vulgare L.). Seeds were germinated between filter papers in 0.1, 0.5 and 1.0 μM HBR-supplemented distilled water for 48 h at dark with their controls. HBR application increased especially the primary root growth significantly with increasing concentrations when compared with the control materials and reached two fold increase in 1.0 μM HBR treated material. Treated and untreated control group roots were fixed in 1:3 aceto-alcohol and aceto-orcein preparations were made. Roots treated with HBR showed more mitotic activity, mitotic abnormalities and significant enlargements at the root tips when compared with control material. HBR application decreased total soluble protein content, superoxide dismutase (EC 1.15.1.1), catalase (EC 1.11.1.6) and peroxidase (EC 1.11.1.11) activities significantly at 1.0 μM HBR concentration. Data presented here is one of the first detailed analyses of HBR effect on barley root development.     

Soil water availability and rooting depth as determinants of hydraulic architecture of Patagonian woody species

Adaptations of species to capture limiting resources is central for understanding structure and function of ecosystems. We studied the water economy of nine woody species differing in rooting depth in a Patagonian shrub steppe from southern Argentina to understand how soil water availability and rooting depth determine their hydraulic architecture. Soil water content and potentials, leaf water potentials (Ψ_Leaf), hydraulic conductivity, wood density (ρ_w), rooting depth, and specific leaf area (SLA) were measured during two summers. Water potentials in the upper soil layers during a summer drought ranged from −2.3 to −3.6 MPa, increasing to −0.05 MPa below 150 cm. Predawn Ψ_Leaf was used as a surrogate of weighted mean soil water potential because no statistical differences in Ψ_Leaf were observed between exposed and covered leaves. Species-specific differences in predawn Ψ_Leaf were consistent with rooting depths. Predawn Ψ_Leaf ranged from −4.0 MPa for shallow rooted shrubs to −1.0 MPa for deep-rooted shrubs, suggesting that the roots of the latter have access to abundant moisture, whereas shallow-rooted shrubs are adapted to use water deposited mainly by small rainfall events. Wood density was a good predictor of hydraulic conductivity and SLA. Overall, we found that shallow rooted species had efficient water transport in terms of high specific and leaf specific hydraulic conductivity, low ρ_w, high SLA and a low minimum Ψ_Leaf that exhibited strong seasonal changes, whereas deeply rooted shrubs maintained similar minimum Ψ_Leaf throughout the year, had stems with high ρ_w and low hydraulic conductivity and leaves with low SLA. These two hydraulic syndromes were the extremes of a continuum with several species occupying different portions of a gradient in hydraulic characteristics. It appears that the marginal cost of having an extensive root system (e.g., high ρ_w and root hydraulic resistance) contributes to low growth rates of the deeply rooted species.     

Malate. Jack of all trades or master of a few?

The dicarboxylic acid malate has long been thought to play important roles in plant physiology. In addition to being a major photosynthate in C4 and CAM plants and an intermediate of the tricarboxylic acid cycle it has been proposed to play essential roles in pH regulation and important roles in pathogen response, as a component of the root exudates and as a regulatory osmolyte affecting stomatal function. Recent years have seen the cloning and functional analysis of a wide range of enzymes and transporters associated with malate metabolism. Here we attempt to provide a synthesis of research in this field as well as re-evaluating the role of this metabolite in mediating guard cell function.     

Cytokinin Profiles in the Conifer Tree <Emphasis Type="Italic">Abies nordmanniana</Emphasis>: Whole-Plant Relations in Year-Round Perspective

Conifer trees are routinely manipulated hormonally to increase flowering, branching, or adjust crown shape for production purposes. This survey of internal cytokinin levels provides a background for such treatments in Abies nordmanniana, a tree of great economic interest. Reference points in the crown and root system were sampled destructively in 4- and 6-year-old trees and analyzed for a range of cytokinins by LC-MS/MS. No seasonal patterns were detected in the root samples, and a major portion of cytokinin was in conjugated forms. Dramatic and consistent seasonal changes occurred in the crown, at levels 17–65 times higher than in the root. Predominant among crown cytokinins was ZR, except in the needles where IPR was also prominent. Within the crown, cytokinin profiles in different organs differed consistently. The leader bud showed a pronounced mid-June minimum, and a maximum later in summer. Subapical buds showed the same June minimum but peaked in mid autumn at a much lower level. Maxima in these buds were preceded by peaks in the subapical stem. Parallel patterns were observed in homologous tissues on branches.This pattern is consistent with two surges beginning in the uppermost stem tissues leading to subsequent accumulation or stimulated production within the buds. Strong differential hormonal profiles between adjacent buds with different fates agree with recent evidence of localized cytokinin production. The data suggest a reduced role of root-derived cytokinins in crown development. Practical cytokinin treatments for crown-shape regulation require close attention to dosage as well as precise timing and positioning.     

Plant meristems: <Emphasis Type="Italic">CLAVATA3/ESR</Emphasis>-related signaling in the shoot apical meristem and the root apical meristem

The plant meristems, shoot apical meristem (SAM) and root apical meristem (RAM), are unique structures made up of a self-renewing population of undifferentiated pluripotent stem cells. The SAM produces all aerial parts of postembryonic organs, and the RAM promotes the continuous growth of roots. Even though the structures of the SAM and RAM differ, the signaling components required for stem cell maintenance seem to be relatively conserved. Both meristems utilize cell-to-cell communication to maintain proper meristematic activities and meristem organization and to coordinate new organ formation. In SAM, an essential regulatory mechanism for meristem organization is a regulatory loop between WUSCHEL (WUS) and CLAVATA (CLV), which functions in a non-cell-autonomous manner. This intercellular signaling network coordinates the development of the organization center, organ boundaries and distant organs. The CLAVATA3/ESR (CLE)-related genes produce signal peptides, which act non-cell-autonomously in the meristem regulation in SAM. In RAM, it has been suggested that a similar mechanism can regulate meristem maintenance, but these functions are largely unknown. Here, we overview the WUS–CLV signaling network for stem cell maintenance in SAM and a related mechanism in RAM maintenance. We also discuss conservation of the regulatory system for stem cells in various plant species. S. Sawa is the recipient of the BSJ Award for Young Scientist, 2007.