长柄水青冈幼苗根系构型及动态变化

长柄水青冈（Fagus longipetiolata）是我国亚热带山地林的重要组成树种,本研究在温室中用河砂培养长柄水青冈幼苗,采用直接测量法研究了长柄水青冈的根系构型。结果表明,生长50 d的长柄水青冈幼苗的根系呈倒圆锥形,根宽小于根深;基根平均生长角度较小,基根的向地性小;一级侧根与主根的夹角从根系上部至下部逐渐变小;二级侧根首先发生于根系的中下部,然后其发生范围向根系上、下部扩展。虽然长柄水青冈幼苗根系构型存在较大的个体差异性,但一级侧根与主根的夹角则具有较好的稳定性。研究揭示了实验条件下长柄水青冈幼苗的根系构型及其在幼苗建成过程中的生长变化规律,为长柄水青冈的进一步研究提供科学依据。     

Distribution of growth regulators in relation to the light-induced geotropic responsiveness in Zea roots

Growth regulators were measured in extracts from the upper and lower halves of 7-mm apical segments of horizontally oriented, red-light-irradiated and non-irradiated roots of Zea mays L. cv. Golden Cross Bantam 70 which exhibit a georesponse only after an exposure to light. Abscisic acid (ABA) was measured by gas-liquid chromatography, auxin (indole-3-acetic acid, IAA) by the Avena straight-growth assay, and an unidentified growth inhibitor by a Zea root-growth assay. The ratio of ABA in the upper and lower halves was 1.6 in the irradiated roots and 1.0 in the non-irradiated ones. The total amount of ABA after irradiation was increased by a factor of ca. 1.8. The ratio of IAA in the upper and lower halves of irradiated and non-irradiated roots was 1:3.4 and 1:2.9, respectively. The content (or activity) of an unidentified growth inhibitor was highest in the lower halves of horizontally oriented roots which had been irradiated with red light. The unidentified growth inhibitor, rather than IAA or ABA, may be the major factor in the light-induced geotropic responsiveness in Zea roots.     

Radial transport of water across cortical sleeves of excised roots ofZea mays L.

The stationary radial volume flows across maize (Zea mays L.) root segments without steles (sleeves) were measured under isobaric conditions. The driving force of the volume flow is an osmotic difference between the internal and external compartment of the root preparations. It is generated by differences in the concentrations of sucrose, raffinose or polyethylene glycol. The flows are linear functions of the corresponding osmotic differences ( ) up to osmotic values which cause plasmolysis. The straight lines obtained pass through the origin. No asymmetry of the osmotic barrier could be detected within the range of driving forces applied ( =±0.5 MPa), corresponding to volume-flow densities of j_{v, s}=±7·10^–8 m·s^–1. Using the literature values for the reflection coefficients of sucrose and polyethylene glycol in intact roots (E. Steudle et al. (1987) Plant Physiol.84, 1220–1234), values for the sleeve hydraulic conductivity of about 1·10^–7 m·s^–1 MPa^–1 were calculated. They are of the same order of magnitude as those reported in the literature for the hydraulic conductivity of intact root segments when hydrostatic pressure is applied.Abbreviations and symbols a _s outer surface of sleeve segment - c concentration of osmotically active solute - j _{v, s} radial volume flow density across sleeve segment - Lp_s hydraulic conductivity of sleeves - Lp_r hydraulic conductivity of intact roots - _N thickness of Nernst diffusion layer - reflection coefficient of root for solute - osmotic value of bulk phase - osmotic coefficient     

Toxicities of soluble Al, Cu, and La include ruptures to rhizodermal and root cortical cells of cowpea

Elevated levels of many metals are toxic to plant roots, but their modes of action are not well understood. We investigated the toxicities of aluminium (Al), copper (Cu), and lanthanum (La) in solution on the growth and external morphology of 3-d-old cowpea (Vigna unguiculata L.) roots for periods of up to 48 h. Root elongation rate decreased by 50% at ca. 30 μM Al, 0.3 μM Cu, or 2.0 μM La, accompanied by a decrease in the distance from the root tip to the proximal lateral root. Kinks developed in some roots 2.0 ± 0.4 mm from the root apex on exposure to Al or La (but not Cu). Light and scanning electron microscopy showed that soluble Al, Cu, or La caused similar transverse ruptures to develop > 1 mm from the root apex through the breaking and separation of the rhizodermis and outer cortex from inner-layers. The metals differed, however, in the range in concentration at which they had this effect; developing in solutions containing 54 to‑600 μM Al, but only from 0.85 to 1.8 μM Cu or 2.0 to 5.5 μM La. These findings suggest that Al, Cu, and La bind to the walls of cells, causing increased cell wall rigidity and eventual cell rupturing of the rhizodermis and outer cortex in the elongating zone. We propose that this is a major toxic effect of Al, and that Cu and La also have additional toxic effects.     

MOLECULAR CLONING OF TRYPSIN AND THE EFFECT OFDIETARY PROTEIN LEVELS AND STARVATION ON TRYPSINmRNA EXPRESSION AND ENZYME ACTIVITY IN JUVENILECHINESE SUCKER (MYXOCYPRINUS ASIATICUS BLEEKER)

The effect of dietary protein and starvation on the expression of trypsin was evaluated in the Chinesesucker (Myxocyprinus asiaticus Bleeker). The complete trypsin cDNA was cloned from juvenile Chinese suckerpancreatic tissue by using RACE and PCR methods. We used semi-quantitative RT-PCR and enzymatic activitymeasurements to quantify mRNA expression and trypsin activity in fish that were either starved or fed differinglevels of dietary casein (35%, 45% and 55%). The results showed that the Chinese sucker trypsin cDNA sequencewas 912 bp in length. Trypsin activity and mRNA levels were higher in fish that were fed moderate (45% casein)levels of protein than those that were fed high or low levels. Starvation significantly decreased mRNA expressionlevel and trypsin activity. The changes in trypsin activity tended to lag behind the changes in mRNA levels. Therewas no direct relationship between the trypsin activity and mRNA level. Given this, the trypsin synthesis is acomplex process regulated by a balance of several factors in the Chinese sucker.     

Cytokinin biosynthesis in roots of corn

Removal of the quiescent center (QC) from the root apex of maize (Zea mays L., cv. Kelvedon 33) initiates a set of events which culiminate in the regeneration of an intact apex with a newly formed QC. Concomitant with the formation of a new QC is a marked reduction in extractable cytokinins in the tissue of the proximal meristem. Replacing the excised QC with a Dowex (acidic cation-exchange resin) bead affects both root growth and QC regeneration. Root growth is inhibited by plain Dowex beads and Dowex beads treated with zeatin; this inhibition is reversed if the beads have been treated with CaCl₂ (±zeatin). Dowex beads treated with zeatin delay the formation of a new QC; this effect is the same whether or not the beads also contain CaCl₂. The results of this investigation support the notions that cytokinin biosynthesis in roots is a result of activities of both the QC and the proximal meristem, and that cytokinins, at least if supplied exogenously, can play a role in root morphogenesis by delaying the regeneration of the QC.Abbreviations used throughout the text PM proximal meristem - QC quiescent center - RC root cap     

Root–root interactions: extending our perspective to be more inclusive of the range of theories in ecology and agriculture using in-vivo analyses

Background

There is a large body of literature on competitive interactions among plants, but many studies have only focused on above-ground interactions and little is known about root–root dynamics between interacting plants. The perspective on possible mechanisms that explain the outcome of root–root interactions has recently been extended to include non-resource-driven mechanisms (as well as resource-driven mechanisms) of root competition and positive interactions such as facilitation. These approaches have often suffered from being static, partly due to the lack of appropriate methodologies for in-situ non-destructive root characterization.

Scope

Recent studies show that interactive effects of plant neighbourhood interactions follow non-linear and non-additive paths that are hard to explain. Common outcomes such as accumulation of roots mainly in the topsoil cannot be explained solely by competition theory but require a more inclusive theoretical, as well as an improved methodological framework. This will include the question of whether we can apply the same conceptual framework to crop versus natural species.

Conclusions

The development of non-invasive methods to dynamically study root–root interactions in vivo will provide the necessary tools to study a more inclusive conceptual framework for root–root interactions. By following the dynamics of root–root interactions through time in a whole range of scenarios and systems, using a wide variety of non-invasive methods, (such as fluorescent protein which now allows us to separately identify the roots of several individuals within soil), we will be much better equipped to answer some of the key questions in root physiology, ecology and agronomy.     

Levels of tropinone-reductase activities influence the spectrum of tropane esters found in transformed root cultures of Datura stramonium L.

The nortropane sulphur analogues 8-thiabicyclo[3.2.1] octan-3-one, 8-thiabicyclo[3.2.1]octan-3a-ol and 8-thiabicyclo[3.2.1]octan-3-ol have been found to have differential effects in vitro on the activities of tropinone reductase I and tropinone reductase II from Datura stramonium L. It has been demonstrated that only tropinone reductase I is able to metabolise 8-thiabicyclo[3.2.1]octan-3-one and that only this enzyme is inhibited by 8-thiabicyclo[3.2.1]octan-3-ol and 8-thiabicyclo[3.2.1]octan-3-ol. A K _m of 0.035 mM was determined for 8-thiabicyclo[3.2.1]octan-3-one and I₅₀ values of 0.081 mM and 0.021 mM for 8-thiabicyclo[3.2.1]octan-3-ol and 8-thiabicyclo[3.2.1]octan-3-ol, respectively. The influence that these differential interactions might have on metabolism was investigated in transformed root cultures of D. stramonium. It was found that when these cultures were grown in the presence of either 8-thiabicyclo[3.2.1]octan-3-one or 8-thiabicyclo[3.2.1]octan-3-ol the spectrum of alkaloids that accumulated was altered from that found in control roots in the manner predicted from the observed effects of these inhibitors on the isolated reductases. The effect could be mimicked by feeding pseudotropine, the product of tropinone reductase II. It is concluded that the relative levels of activity of the two tropinone reductases might play an important role in regulating the balance of tropan-3-ols to tropan-3-ols seen in the spectrum of tropane-alkaloid-producing plants.Abbreviations GC/MS gas chromatography/mass spectrometry; - I₅₀ concentration of inhibitor required to reduce the rate of reaction to half the maximal value; - -TBOL 8-thiabicyclo[3.2.1]octan-3-ol; - -TBOL 8-thiabicyclo[3.2.1]octan-3-ol; - TBON 8-thiabicyclo[3.2.1]octan-3-one; - TR tropinone reductase We are most grateful to J. Eagles (I.F.R., Norwich) for GC/MS analysis, to colleagues at I.P.B.P. and I.F.R. for helpful discussions, to the technical staff (Chemistry, Glasgow) and to W. Millar (Chemistry, Glasgow) for assistance with the reduction of TBON. This work was, in part, supported by a grant to B Dräger from the Deutsche Forschungsgemeinschaft (Dr227/I-I). The research reported here was supported by an Academic Research Collaboration Cooperative Award (project No. 215) from the British Council and the Deutscher Akademischer Austauschdienst to R.J. Robins and B. Dräger.     

沙地云杉幼苗根表土体中NPK的梯度分布

采用水平根和垂直根两种处理方法对6年生沙地云杉幼苗进行栽培实验,应用分层取样方法对幼苗根表不同距离土体进行取样,并测定不同层次土体中速效N、速效P、速效K的含量。结果表明,在沙地云杉根表不同距离的土体中,速效N、P、K呈现有规律的梯度分布,即在根表近距离土体中营养元素由于根系的吸附作用而含量较高,同时根系生命活动对营养元素的大量消耗又使得营养元素随即出现严重的亏缺区,再向外延伸营养元素含量又逐渐上升而达到土壤本底值,在水平根处理中,由于沙地云杉对N、P、K吸收和利用的强度不同,亏缺区出现的位置不同,速效N和速效K的亏缺区出现在距离根表1cm处;速效P出现在距离根表0．5cm处,在垂直根处理中,速效N、速效P、速效K的梯度变化与水平根处理的相似速效N和速效K亏缺区出现在距离根表大约1cm处,而速效P在根表附近土壤中的含量始终少于根表远处,说明沙地云杉幼苗对速效P的吸收和利用强度大,速效P可能成为沙地云杉生长发育的限制因子。因此,在沙地云杉引种栽培时,应该选择含P丰富的土壤,或者对林地适当施用一些P肥。