Mesencephalic root fibers of the trigeminal nerve in the cat

The trigeminal nerve has three motor roots and one sensory root in the cat. One of the motor roots can be divided into two bundles: the larger and the smaller. These motor roots form the common root with the sensory root at the exit from the pons, sometimes being separated partially by the subarachnoidal space between the medial and the ventral part of the common root. The mesencephalic root fibers are observed numerously in all the motor roots. Some degenerated fibers are observed in the sensory root. The transitional zone of the trigeminal nerve root between central and peripheral nervous system is occupied by interlocking processes of the fibrous astrocyte.     

不同灌溉方式下土玉米根际硝态氮的分布

实验着重研究分根条件下常规灌溉、交替灌溉和固定灌溉玉米苗期根际硝态氮的分布, 研究结果表明不同灌水方式下,玉米根际硝态氮的分布不同.在这3种灌水方式的湿润区,NO-3-N的累积趋势为交替灌水＞固定灌水＞常规灌水.     

Effect of Lateral Root Formation on the Vascular Pattern of Barley Roots

The vascular pattern in the root of barley (Hordeum vulgare L.), characterized by discontinuous xylem, is markedly affected by its branching. The roots become divided into unbranched segments alternating with branched segments with a more complex vascular pattern, formed by two systems differing in origin and age: the primary vascular system derived from the procambium and ontogenetically younger connective vascular system derived from stelar parenchyma. Adjacent to the sites of the lateral root initiation, reprogramming of parent stelar parenchyma for connective vascular elements occurs. The connecting phloem is represented by small sieve elements and companion cells, the connecting xylem is composed of small vessel elements with reticulate or scalariform-reticulate wall thickenings and simple perforations. Development of the connective vascular system secures continuous lateral and axial vascular connection between lateral root and parent root. The extent of the vascular connection in the parent root increases in an acropetal direction. Hydraulic effects of connective vascular tissue formation and parent root segmentation are discussed.     

Inhibition of root-nodule formation in leguminous plants by EDTA

Summary Nodulation of pea plants was inhibited by low concentrations of Fe(III)-EDTA and to a smaller degree by K₂-EDTA. Using the divided root system, it was demonstrated that the inhibitory effect was only observed on that part of the root system which was in direct contact with the chelate. A simple device for the application of Fe(III)EDTA to either the upper or the lower part of the root system is described.on leave from the National Biological Institute, Bogor, Indonesia.     

欧美杂种山杨微扦插不定根发生过程的解剖学研究

采用石蜡切片技术,以欧美杂种山杨插穗基部茎段为实验材料,连续解剖观察插穗不定根发生发育过程,分析根原基发生部位与扦插生根的关系。结果显示:欧美杂种山杨插穗不定根的发生过程分为4个时期,为根原基诱导期,不定根起始期、表达期和伸长生长期。根原基诱导期维管形成层产生具有分生组织特点的薄壁细胞;不定根起始期,维管形成层及附近的薄壁细胞脱分化,形成不定根原基发端细胞;不定根表达期,根原基发端细胞不断分裂成具有方向性的根原基,根原基穿过韧皮射线和皮层,向皮孔方向发展;不定根伸长生长期,根原基从皮孔伸出,其内部的维管系统开始发育,形成不定根。研究认为,欧美杂种山杨为皮部诱导生根类型,不定根原基起源于维管形成层区,起源部位单一,扦插难生根。     

The Influence of Mineral Nutrition on the Root Development of Trees: II. THE EFFECT OF SECIFIC NUTRIENT ELEMENTS ON THE GROWTH OF INDIVIDUAL ROOTS OF SITKA SPRUCE

Sitka spruce seedlings were grown with divided root systemsin sand culture and the application of N, P, and K was variedwhile maintaining a complete supply of other nutrients. Therewas a localized stimulation of the growth of roots to whichnutrients were applied and N produced the greatest stimulation;P was also important but K did not enhance growth. Measurements of Ca and Mg concentrations in the roots showedthat differential root growth, which is influenced by the concentrationof N and P in the bathing medium, could not be adequately explainedby the effect of N or P on the uptake of the immobile cations. The two parts of the divided root system appeared to competefor assimilates; the enhanced growth of one root was accompaniedby reduced growth in the other, and vice versa.     

An auxin transport-based model of root branching in Arabidopsis thaliana

Root architecture is a crucial part of plant adaptation to soil heterogeneity and is mainly controlled by root branching. The process of root system development can be divided into two successive steps: lateral root initiation and lateral root development/emergence which are controlled by different fluxes of the plant hormone auxin. While shoot architecture appears to be highly regular, following rules such as the phyllotactical spiral, root architecture appears more chaotic. We used stochastic modeling to extract hidden rules regulating root branching in Arabidopsis thaliana. These rules were used to build an integrative mechanistic model of root ramification based on auxin. This model was experimentally tested using plants with modified rhythm of lateral root initiation or mutants perturbed in auxin transport. Our analysis revealed that lateral root initiation and lateral root development/emergence are interacting with each other to create a global balance between the respective ratio of initiation and emergence. A mechanistic model based on auxin fluxes successfully predicted this property and the phenotype alteration of auxin transport mutants or plants with modified rhythms of lateral root initiation. This suggests that root branching is controlled by mechanisms of lateral inhibition due to a competition between initiation and development/emergence for auxin.     

Modelling the branching growth fractal pattern of the maize root system

Using the technique of L-systems, a growth model of the maize root system is developed. From the observation of the root systems developed under various soil density in eight root boxes, a spatial hierarchy of growth rules was extracted. The rules were divided into three categories: a meta-rule for describing features of an entire root system, a branching growth rule and a tip elongation rule. Some variations in the entire features of the root system, such as the outline and the root distribution, were confirmed by observation, and then the respective meta-rules were re-defined. The branching properties of first- and second-order lateral roots were statistically almost equal in the observations, and this lead us to set up a single stochastic branching growth rule. Tip elongation movement was not observed here; its rule had to be assumed by reference to data in the literature. A single set of branching growth and tip elongation rules were coupled with the respective meta-rules corresponding to the root samples observed, where a small scale rule was loosely governed by a large scale rule. Computer simulations offered optimized drawings of the observed root systems, and they also reproduced a typical anisotropic power distribution of roots similar to those observed.     

Uptake and long-distance transport of phosphate,potassium and chloride in relation to internal ion concentrations in barley: evidence of non-allosteric regulation

The extent to which uptake and transport of either phosphate, potassium or chloride are controlled by the concentration of these ions within the root, perhaps through an allosteric mechanism, was investigated with young barley plants in nutrient solution culture. Plants were grown with their roots divided between two containers, such that a single seminal root was continuously supplied with all the required nutrient ions, while the remaining four or five seminal roots were either supplied with the same solution (controls) or, temporarily, a solution lacking a particular nutrient ion (nutrient-deficient treatment). Compared with controls, there was a marked stimulation of uptake and transport of labelled ions by the single root following 24 h or more of nutrient dificiency to the remainder of the root system. This stimulation, which comprised an increased transport to the shoot and, for all ions except Cl^-, increased transport to the remainder of the root system, took place without appreciable change in the concentration of particular ions within the single root. However, nutrient deficiency quickly caused a lower concentration of ions in the shoot and the remaining roots. The results are discussed in relation to various mechanisms, proposed in the literature, by which the coordination of ion uptake and transport may be maintained within the plant. We suggest that under our conditions any putative allosteric control of uptake and transport by root cortical cells was masked by an alternative mechanism, in which ion influx appears to be regulated by ion efflux to the xylem, perhaps controlled by the concentration of particular ions recycled in the phloem to the root from the shoot.     

Identifying soybean lines differing in gas exchange sensitivity to humidity

The ratios of root length and root weight to leaf area differed within and between cultivars of soybean. Plants with low ratios of root length or weight to leaf area had leaf conductances and net photosynthetic rates more reduced by a given increase in the leaf to air water vapour pressure difference around a single leaf than plants with high ratios. Plant and root system conductances to water were estimated as transpiration rate per unit leaf area divided by the difference between substrate and leaf water potentials, and by the rate of water flow through pressurised root systems. These conductances were greater in plants with large, as compared with small, root systems per unit leaf area. Cultivar rankings in sensitivity of gas exchange to humidity were consistent in controlled environment chambers and in field tests.     

The root system architecture of young Greek fir (Abies cephalonica Loudon) trees

Abstract

The root system architecture of young Greek fir (Abies cephalonica Loudon) trees was studied in Evritania, Central Greece. A sample of naturally regenerated fir plants were uprooted and divided into three age groups of 5 (5–6 years), 10 (9–11 years) and 15 (15–16 years) years old. Root architectural data (e.g. root length and volume, topology, branching structure) were obtained with a 3D digitizer (3SPACE Fastrak, Polhemus). In all nine trees the largest vertical root originating from the stump was selected, measured and coded as a taproot. The topological and geometrical information from the data file was analysed by computing the characteristics of each root segment. The AMAPmod software was used, providing the user with various tools for encoding, exploring and modelling plants. The findings showed that the age of fir trees is an important parameter that affects root architecture. Topological analysis revealed that the root system of Greek fir have almost a typical herringbone pattern during the first 10 years of tree life, and then the root systems changes to a less herringbone pattern. The root system is expanded with the tree age; however, the total root length and the total number of roots seems to increase in a linear trend, while the root volume appears to increase in a geometric way.     

The course of root differentiation from root primordia in poplar stems

Upon rooting of poplar stem cuttiags the total inductive stimulation does not take place, but the individual root primordia maintain a relative independence. This becomes evident by various time parameters of their differentiation. Under experimental conditions, in dormant cuttings from one year individuals of the hybrid I 214 the activation of the first root primordia occurs after 24 h, the pre-emergent development of the roots formed was completed after 72 h. The activated root primordium is divided into two regions. In the distal region with the predominating cell division the root apex with histogens is formed by the action of initials. From peripheral cell layers of the distal region the so-called “Wurzeltasche” develops which covers the root cap. Due to cell elongation in the proximal region the root apex is pushed up towards the stem surface. The beginning differentiation of the connective vascular tissue is a preparative step for the connection of the vascular system of the developing root with the secondary vascular system of the maternal stem. Following the penetration of the root through the peripheral stem tissues this connection is realized with progressing development. In the developed root the protoxylem elements differentiate continuously and acropetally in direct continuity with tracheids of the basal connective region.     

根区湿润方式对玉米根系生长发育的影响

将厚塑料紧密地固定在盆栽试验用桶壁和底的中央,玉米种子播种于厚塑料布的正上方,在均匀灌水、固定部分根区灌水和根系分区交替灌水3种方式下,分期测定两个1／2根区根系的长度、面积、干重以及单位面积的平均根长和比根长,研究不同根区根系的生长发育特征。结果表明,处理40d时,与其他根区相比,固定灌水非灌水区的比根长和单位面积平均根长明显增大,说明土壤水分减少使根系直径变小。根面积、长度以及干重的增长速率均表现为,处理0～5d内,与均匀灌水及其非灌水区相比,两种局部灌水的灌水区均显著增大;处理10～15d内,交替灌水的灌水区较其他根区明显增大,固定灌水的灌水区与均匀灌水相近。固定灌水时,灌水区根系的面积、长度、干重及其增长速率较之非灌水区显著增大;交替灌水时,两个根区的增长速率呈交替变化,其绝对数值随时间延长趋于相同。表明交替灌水不仅可刺激供水区根系的补偿生长,而且对恢复供水区也有补偿效应,并能够促使不同根区的根系均衡发展。     

The Influence of Mineral Nutrition on the Root Development of Trees: III. PLASTICITY OF ROOT GROWTH IN RESPONSE TO CHANGES IN THE NUTRIENT ENVIRONMENT

Lodgepole pine seedlings were grown in solution culture withtheir root systems divided between two contrasting nutrientregimes, viz. a high regime, which provided near optimum conditionsfor growth, and a low regime in which nutrients were limiting.The high nutrient regime stimulated root growth whereas theroots receiving a low level of nutrients grew comparativelyslowly and in certain instances stopped elongating and becamebrown. After differential root growth had been induced certainplants were transferred to a uniform high nutrient environmentand the previously deprived parts of the root system respondedby renewed growth and their growth rate increased in comparisonwith roots which remained in low nutrient conditions. The results show that initial nutritional differences in theenvironment do not lead to dominance in certain roots; the rootsystem remains remarkably plastic.     

根系分泌物对紫云英油菜间作的响应

根系分泌物是植物与土壤进行物质交换和信息传递的重要载体,也是间作体系中作物-土壤-微生物互作的重要调控者。为进一步揭示间作体系中作物之间的互作机制,本研究通过紫云英单作、油菜单作和紫云英油菜间作,重点分析了紫云英油菜间作下根系分泌物的响应特征。结果表明: 共检测到紫云英和油菜根系分泌物391种,定性93种,包括了9种代谢物类型,其中有机氧化物含量最高,主要是以核糖醇的形式存在。不同种植模式中,紫云英、油菜的根系分泌物含量差异显著,紫云英油菜间作时根系分泌物特征与油菜单作相似,与紫云英单作差异较大。不同种植模式的差异根系分泌物中,仅9-芴酮1与其他差异分泌物间呈负相关关系。不同种植模式的差异根系分泌物主要为苯系物、脂类和类脂分子、有机酸及其衍生物、有机氧化物等,其中苯系物、脂类和类脂分子是表征紫云英、油菜根系分泌物变化的重要类型。可见,紫云英油菜间作改变了作物的根系分泌物特征,其变化特征与苯系物、脂类和类脂分子关系密切。     

Relationship between tissue sugar content, phloem import and lateral root initiation in wheat

Split‐root experiments were conducted to test the hypothesis that adjustments in lateral root initiation, as might occur in response to localized soil conditions, are determined by the sugar content of the root and do not depend on changes in the import of phloem‐translocated phytohormones. Wheat ( Triticum aesticum L. cv. Alexandria) seedlings were grown in hydroponics with their seminal roots divided between two compartments within the culture vessel. Two seminal roots of treated plants were supplied with standard nutrient solution supplemented with 50 m M glucose, whilst the remaining three roots received nutrient solution without glucose. Control plants had their roots divided in the same ratio, but both 'halves' received nutrient solution without glucose. Feeding glucose to one 'half' of the root system increased the frequency (number per unit length) of lateral root primordia in the fed axes. The increase was first observed 15 h after the start of treatment and was located within the apical 30 mm of root. At this time there was no significant treatment effect on the frequency of primordia in non‐fed axes. The enhanced initiation of lateral roots in glucose‐fed root tips was associated with an increase in their concentration of glucose and sucrose plus low molecular mass fructans. In contrast, there was a reduction in partitioning of ¹⁴C‐photosynthate to these root tips compared to the non‐fed roots of treated plants and controls. The results indicate that lateral root initiation can be stimulated by sugars in the absence of an increase in phloem translocation. It is proposed that proliferation of lateral roots in response to localized soil conditions, such as nutrient patches, may be signalled by an increase in sugar content of the tissue, rather than an altered flux of phytohormones or other material co‐transported with sucrose in the phloem.     

WATER RELATIONS OF WATER-STRESSED,SPLIT-ROOT C4 (SORGHUM BICOLOR; POACEAE) AND C3 (HELIANTHUS ANNUUS; ASTERACEAE) PLANTS

Sorghum [Sorghum bicolor (L.) Moench] and sunflower (Helianthus annuus L.) were grown in a greenhouse with roots divided between sand irrigated with nutrient solution (–0.097 MPa) or nutrient solution containing polyethylene glycol (PEG) (–0.570 MPa) to compare the effect of unequal root zone stress on plant water relations of a C₄ (sorghum) and a C₃ (sunflower) plant. Roots also were divided between two pots of sand irrigated only with nutrient solution (controls) or only with PEG in nutrient solution. In addition to plant water-status measurements, photosynthetic rate, growth (height, root, and shoot dry weights), and evolution of ethylene (a gaseous hormone indicative of stress) were measured. Under all three split-root treatments, sunflower had a lower leaf water potential and produced more ethylene than sorghum. Sunflower was able to survive the PEG stress if half of its root system was under nonstressed conditions. Sunflower with half its root system irrigated with PEG usually had values of leaf water potential, osmotic potential, stomatal resistance, transpiration rate, photosynthetic rate, ethylene evolution, height, and dry weights that were close to those of the control plants. Sunflower with all roots exposed to PEG was wilted severely. Sorghum was little affected by PEG stress applied either to half or all the root system. Growth of sorghum was the same under all treatments. Apparently because stomata of sorghum were more closed in the partial stress test than those of sunflower, sorghum conserved water and had a higher leaf water potential, which might have permitted growth with stress.     

The effect of ethrel on nodulation inPisum sativum L.

Summary Nodulation of inoculated pea plants was severely inhibited when ethrel (2-chloroethane phosphonic acid) was applied to the roots. The inhibition was evident at ethrel concentrations of 2 ppm and above. Ethrel applied to the foliage at 10 ppm also depressed nodulation. At least part of the effect of ethrel on nodulation came from its inhibition of root growth. Nodulation was inhibited on half of a divided root system treated with ethrel, while there was no inhibition on the neighbouring untreated half.