The Developmental Anatomy of the Seminal Root of Wheat

Wheat embryo usually gives rise to five seminal roots in matured caryopsls, although, the sixth root might develop in some cases. The first one is known as the primary root. Primary root emerged early, and its primodium was distinctly originated from the proembryo and could be gradually identified as three layers of initials. Lateral seminal roots emerged later from the embryonic axis in pairs, and originated from the surrouding cells of the procambium. Differentiation of lateral roots was much more vigorous than that of the first seminal root (primary root), and, its mother cells of metaxylem vessel appeared soon, Lateral seminal roots usually had more metaxylem vessels. In short, only the first root is the primary root, the lateral seminal roots are adventitious in nature, since their structures are similar to those of other adventitious roots.     

小麦种子根的发育解剖

小麦胚胎发育过程中通常形成5条幼根(少数可形成6条),这些根统称为种子根,中间最先发生的为初生根.初生根的原基在胚胎发育的早期就在胚轴的一侧发生,原基细胞由不规则到规则排列。侧生种子根的原基在胚胎发育后期才出现,通常成对发生,并且是由胚轴上的节(盾片节和胚芽鞘节)维管束外方的细胞形成。侧生种子根的发育明显较初生根的快,分化能力也较强,后生木质部导管母细胞出现早,数目较多.因此,小麦胚胎发育过程中从胚轴上形成的这些侧生的种子根,形态上,仍应看作是一些不定根,其结构特征与后来形成须根系的不定根的比较近似。     

Adventitious root induction in Ophiorrhiza prostrata: a tool for the production of camptothecin (an anticancer drug) and rapid propagation

Roots of Ophiorrhiza prostrata D. Don serve as a rich source of camptothecin (CPT), an anticancer drug. Because of the large-scale collection of its roots, the plant has become a threatened species. The present study accomplishes the induction of adventitious roots as a means for the production of CPT as well as for the large-scale propagation of this anticancer drug plant using leaf and internode explants. The biomass yield and CPT content of adventitious roots induced from different explants were compared to roots developed on ex vitro rooted stem cuttings. Adventitious roots were produced on half-strength Murashige and Skoog (MS) medium supplemented with 10.74 μM α-naphthaleneacetic acid and 2.32 μM kinetin at mean fresh weights of 0.753, 0.739 and 0.748 g roots from leaf, internode and shoot, respectively. CPT yield from in vitro derived roots after 50, 80 and 120 days of incubation (0.028, 0.06 and 0.1% dry weight, respectively) was not significantly different from those harvested at the same age from ex vitro rooted (0.03, 0.06 and 0.13%, respectively) stem cuttings. CPT from subcultured roots derived from solid (0.08%) medium was lower than from suspension culture medium (0.12%). Subsequent cultures of the adventitious roots showed a stable production of CPT (0.16%). The yield of CPT from 360-day-old plant-derived roots was 0.19%. Elicitation using methyl jasmonate and acetyl salicylic acid exhibited no enhancement in CPT yield. In vitro propagation through direct shoot regeneration was achieved from the adventitious roots upon transfer to MS medium with 8.87 μM N ⁶-benzyladenine (BA) and 2.46 μM indole-3-butyric acid (IBA) with a mean of 21.2 shoots per culture in 50 days. The shoots upon subculture on medium having the same level of BA and IBA underwent rapid proliferation. The shoots transferred to field conditions after in vitro rooting exhibited 95% survival. Adventitious root induction, from leaf and internode explants, enables the feasible production of CPT as well as the large-scale rapid propagation of this species which can safeguard it from extinction.     

Functional xylem anatomy in root-shoot junctions of six cereal species

In cereals, the formation of safety zones in the root-shoot junction could protect the vessels of roots from embolism originating in the shoot. The root-shoot junction was examined both anatomically, with a light microscope, and experimentally, using a pressurized-air method, in the base of seminal and adventitious roots of maize (Zea mays L. cv. Seneca 60-II), a corngrass mutation of maize (Cg mutant), sorghum (Sorghum bicolor L. cv. Ho-Pak), winter oats (Avena sativa L. cv. Ogle), spring wheat (Triticum aestivum L. cv. Glenlea), winter wheat (T. aestivum cv. Monopol), winter barley (Hordeum vulgare L. cv. Wysor), spring rye (Secale cereale L. cv. JO-02 Finland), and winter rye (S. cereale cv. Musketeer). Two types of hydraulic architecture were found in the cereal roots: (i) a very safe root vessel system, as in winter rye, in which the vessels of the roots are separated from those of the shoots by tracheids, versus (ii) a completely unsafe system, as in corngrass, where the vessels in the root are continuous with the vessels in the shoot. The xylem anatomy of the seminal roots is generally correlated with the species-specific overall root morphology. Rye, wheat and barley, which develop four to six seminal roots, show a high degree of vascular segmentation resulting in, the formation of safe root vessels; maize, sorghum and oats, which typically develop a primary seminal root, contain unsafe vessels that are continuous through the mesocotyl and through the first node. In adventitious roots, vascular segmentation is not related to overall root morphology. Differences in the proportion of safe adventitious roots in which all the vessels end in the root-shoot junction range from 9 to 98% in the cereals studied. In the unsafe roots of these cereals, the number of vessels per root that are continuous through the junction range from 1 to 14. As significant differences in vascular segmentation of the root-shoot junction occur not only between species, but also between cultivars, we suggest that selection based on the occurrence of safety zones might be used in breeding programs designed to improve adaptation of cereals to drought and cold temperatures.This research project was supported by the Natural Sciences and Engineering Research Council of Canada through an International Scientific Exchange Award to R.A. and Dr. C.A. Peterson, and through an Operating Grant to M.G. We thank Dr. G. McLeod (Agriculture Canada, Swift Current, Sask., Canada), Dr. N.P.A. Huner (University of Western Ontario, London, Ont., Canada) and Dr. W.F. Tracy (University of Wisconsin, Madison, USA) for providing seeds; Dr. C.A. Peterson and Dr. W.B. McKendrick (University of Waterloo) for use of the Zeiss photomicroscopes; Dr. M.A. Dixon (University of Guelph, Guelph, Ont.) for use of the Moore pressure gauge; and Dr. R.J. O'Hara-Hines (University of Waterloo) for statistical advice.     

茎杆的第一节间离体再生空心菜

以空心菜（Ipomoea aquatica Forsk.）品种‘白骨柳叶’为材料,通过筛选植物外植体和调整培养基激素配比等方法,首次建立了茎秆第一节间为外植体的空心菜离体再生体系。结果表明,在MS基本培养上添加0.05% 的植物组织培养抗菌剂PPM可获得大量空心菜无菌苗;植株子叶和下胚轴的切段均未诱导出不定芽,而茎秆第一节间为外植体能成功诱导出不定芽,诱导成功率为20%,最佳培养基配方为MS+1.0 mg/L 6-BA+0.1 mg/L IAA;不定芽诱导生根的最佳培养基配方为1/2 MS+0.1 mg/L NAA,生根率为100%。诱导成功后,将完整的再生苗移栽至基质土中,成活率可达100%。     

Changing Kinetic Properties of Barley Alcohol Dehydrogenase during Hypoxic Conditions

The Finnish barley cultivar (Hordeum vulgare L, cv. Hankkija-673)was grown in solution culture for periods of one and two months.The one month old plants had seminal roots, whereas the twomonth old plants grew adventitious roots from the lower nodes.The roots were tested for ADH activity during aeration, during3 d of hypoxic treatment (brought about by passing nitrogenthrough the nutrient solution), and during a 4 d recovery period.The ADH activity, calculated on a protein basis, rose about4-fold during the nitrogen treatment, the greatest increaseoccurring in the adventitious roots. Differences in the kineticproperties of ADH during the hypoxic period were also foundbetween seminal and adventitious roots. The K_m for acetaldehydechanged little in the seminal roots during the hypoxic treatment,but in the adventitious roots it decreased considerably. Thephysiological significance of these changes is discussed. Key words: Hordeum vulgare, alcohol dehydrogenase, hypoxia, enzyme kinetics     

The hydraulic safety zone at the base of barley roots

A hydraulic constriction of the vessels occurs at the base of the primary roots of barley (Hordeum vulgare L.). The constriction and consequent hydraulic protection result from an extreme shortening of the vessel elements, leading to the accumulation of perforation plates with simple, broad-rimmed perforations which are smaller than those in normal-length vessel elements. It is compensated for by a local increase in the number of tracheary elements and an increase in their diameter. A similar trend of development was observed both at the base of other seminal roots and at the base of stem-borne adventitious roots. The rate at which compensation for the hydraulic constriction occurs could be of crucial importance for the axial resistance of water transport.     

Growth of Zea mays L. plants with their seminal roots only. Effects on plant development, xylem transport, mineral nutrition and the flow and distribution of abscisic acid (ABA) as a possible shoot to root signal

Maize (Zea mays L.) was grown in quartz sand culture eitherwith a normal root system (controls) or with seminal roots only(‘single-rooted’). Development of adventitious rootswas prevented by using plants with an etiolated mesocotyl andthe stem base was positioned 5–8 cm above the sand. Eventhough the roots of the single-rooted plants were sufficientlysupplied with water and nutrients, the leaves experienced waterdeficits and showed decreased transpiration as trans plrationalwater flow was restricted by the constant number of xylem vesselspresent in the mesocotyl. As a consequence of this restriction,transpirational water flow velocities in the metaxylem vesselsreached mean values of 270 m h^–1 and phloem transportvelocities of 5.2 m h^–1. Despite limited xylem transportmineral nutrient concentrations in leaf tissues were not decreasedin single-rooted plants, but shoot and particularly stem developmentwas somewhat inhibited. Due to the lack of adventitious rootsthe shoot:root ratio was strongly increased in the single-rootedplants, but the seminal roots showed compensatory growth comparedto those in control plants. Consistent with decreased leaf conductance,ABA concentrations in leaves of single-rooted plants were elevatedup to 10-fold, but xylem sap ABA concentrations in these plantswere lower than in controls, in good agreement with the well-wateredconditions experienced by the seminal roots. Surprisingly, however,ABA concentrations in tissues of the seminal roots of the single-rooted plants were clearly increased compared to the controls,presumably due to increased ABA import via phloem from the water-stressedleaves. The results are discussed in relation to the role ofABA as a shoot to root signal. Key words: Zea mays, seminal roots, plant development, xylem transport, mineral nutrition, ABA, shoot-to-root signal     

Compensatory function for water transport by adventitious roots of <Emphasis Type="Italic">Ipomoea pes-caprae</Emphasis>

To determine the role of adventitious roots in supplying water to Ipomoea pes-caprae (L.) Sweet (Convolvulaceae), we examined the effects of water deficit on water uptake and the growth patterns of leaves and shoots. After stopping the water supply from the primary root or adventitious roots, the water-uptake rate of the other root system increased steeply within 90–100 min to a level of 90% of the pretreatment water-uptake rate of the whole plant. Thus, the primary and adventitious roots can compensate for a decrease in the water-uptake rate of the whole plant caused by dehydration. The continuous growth of leaves and shoots after dehydration suggests that an increase in the water-uptake rate by either root system can support plant growth, although the growth rates of immature leaves in plants with no water supply from the primary or adventitious roots were lower than in controls. We conclude that the water supply from adventitious roots contributes to the survival and growth of plants, and will be important for vegetative propagation.     

濒危药用植物桃儿七根的显微结构及其菌根真菌分布研究

本文研究了桃儿七Sinopodophyllum hexandrum根的显微结构及其真菌分布。结果表明,桃儿七的根为根状茎,节状,不定根形成的须根系发达。根的结构主要由表皮、皮层、维管柱三部分构成,其中,皮层所占比例最大,超过80%。根的木质部有四原型和五原型两种类型,五原型较为常见;四原型的根和五原型的根在皮层细胞形态上存在一定差异。在桃儿七的不定根和其上的侧根观察到真菌菌丝分布,其数量和种类与根的直径有关,在不定根较细(先端)的部位真菌以暗色有隔内生真菌(DSE真菌)为主,侵染率为77.9%;而较粗根中真菌菌丝为无隔菌丝为主,分布很少且仅存在于皮层细胞的一至二层,不侵染皮层深部和维管柱。不定根侧根中真菌以丛枝菌根真菌为主,丛枝菌根常常占据大部分的皮层细胞,侵染率高达90%以上。桃儿七根中没有发现根毛存在,因此,侧根中共生的丛枝菌根真菌可能是桃儿七养分和水分吸收的主要途径。     

Structure and conductivity of the corn root system

When comparing conductivity in 5 mm long segments from the basis of the primary seminal root with that in segments from adventitious roots of the first to fifth node it was revealed that the conductivity is not a general function of the transection area. The conductivity determined experimentally is minimal in the primary seminal root and gradually increases in the adventitious roots. However, when calculating per area unit, roots of the first coleoptile node appear the most efficient, with roots of the second and third node the values gradually decrease, and conductivity in roots of the fourth and fifth node approximately equals that of the primary seminal roots. The conductivity is not a function of the conducting area. The conducting capacity of tissues which do not function directly as conductors is substantially lower; however, they cannot be neglected in evaluating the conductivity because of their high percentual occurence. The total conductivity in the individual root types is influenced by the ratio of the participation of water-conducting and non-conducting tissues.     

Vegetative propagation of Cecropia obtusifolia (Cecropiaceae)

Cecropia is a relatively well-known and well-studied genus in the Neotropics. Methods for the successful propagation of C. obtusifolia Bertoloni, 1840 from cuttings and air layering are described, and the results of an experiment to test the effect of two auxins, naphthalene acetic acid (NAA) and indole butyric acid (IBA), on adventitious root production in cuttings are presented. In general, C. obtusifolia cuttings respond well to adventitious root production (58.3% of cuttings survived to root), but air layering was the better method (93% of cuttings survived to root). The concentration of auxins used resulted in an overall significantly lower quality of roots produced compared with cuttings without auxin treatment. Future experiments using Cecropia could benefit from the use of isogenic plants produced by vegetative propagation.     

红皮云杉茎的解剖结构与插条不定根形成的研究

１９９２年７－８月定时固定红皮云杉插条基部材料于ＦＡＡ液中,石蜡制片法室内解剖研究不定根的发生。结果表明：红皮云杉插条诱发根原基的来源有两种途径。一种是愈伤组织生根型,在愈伤组织的再生形成层处,或茎的维管形成层诱发根原基;另一种是非愈伤组织生根型,在插条切口处的维管形成层、皮层或初生木质部与次生木质部间的薄壁组织较深的部位,直接产生纵向不定根原始体,有的在距离切口０．１－０．５ｃｍ以上茎的维管形成层,维管形成层与木射线的交界处及叶隙等薄壁组织产生径向不定根。不同个体间产生的不定根数量及发育的早晚差异较大。     

Resistance to water flow in the intracoleoptile internode of wheat

Summary Measurements of xylem vessel number and radii in the seminal roots and intra-coleoptile internode (I.C.I.) of five wheat genotypes showed that the conducting capacity of the I.C.I. was close to the main seminal axis, and would restrict flow when the usual 3–5 seminal axes contributed to uptake. The length and hence resistance of the I.C.I. increased with sowing depth, whilst xylem diameter also fell in two genotypes, which would further restrict flow. The resistance per unit length of I.C.I., assuming Poiseuille flow, was 4×10^–4 cm^–4 day MPa. A pressure drop of 0.15 MPa along an I.C.I. 5 cm long would be required to maintain transpiration under typical field conditions in southern Australia in spring.In a second study of eleven wheat varieties sown up to 10 cm deep, maximum I.C.I. length ranged from 3.6–6.8 cm amongst varieties with similar maximum coleoptile lengths (6–8 cm). Thus considerable variation in hydraulic resistance may be achieved by the appropriate combination of genotype and planting depth. It was concluded that potentially useful differences in the rate of subsoil water use could result.     

桤木插穗不定根发生与发育的解剖学观察

采用常规石蜡切片法对桤木插穗进行解剖观察,研究茎的次生结构及不定根的起源和发生发育过程,探讨影响不定根发生的因素。结果表明:桤木茎的次生构造从外至内由周皮、皮层和次生维管组织3部分组成。皮孔有2种类型。不定根的发育过程可分为4个阶段:(1)维管形成层与髓射线交叉处的细胞活动,产生具有典型分生组织特点的薄壁细胞团;(2)薄壁细胞不断分裂,形成不定根原基发端细胞;(3)分裂分化形成的不定根沿着韧皮射线向皮层延伸;(4)随着不定根内部的维管系统的发育,不定根从皮孔或下切口伸出。     

植物生长调节剂对鹿角杜鹃扦插繁殖的影响

以腐殖土为基质,研究了5种植物生长调节剂的4个浓度处理、以及萘乙酸(NAA)不同浓度与浸泡时间处理对鹿角杜鹃(Rhododendron latoucheae)当年生枝条扦插繁殖12个育苗指标的影响及各指标间的相关性,并运用隶属函数法对各处理组合的育苗效果进行了综合评价。结果表明:5种生长调节剂中,赤霉素(GA3)、吲哚丁酸(IBA)处理在大部分育苗指标上表现良好,为鹿角杜鹃扦插育苗的理想调节剂,吲哚乙酸(IAA)效果次之,6-苄氨基嘌呤(6-BA)、NAA处理的育苗指标表现较差;4个浓度水平上,愈伤率、腐烂率及老叶留存率总体以低浓度处理最佳,随着浓度升高效果下降;其它9个指标对浓度的响应因生长调节剂种类而异。各指标相关性分析发现,4个根系生长指标,即不定根数、最长不定根长、总根数及根系直径之间呈极显著正相关,但它们与愈伤率、腐烂率、生根率及老叶留存率、新梢率间的相关性较弱。隶属函数综合评价表明,50 mg/L GA3处理为鹿角杜鹃扦插育苗的最佳组合,其次为100 mg/L GA3和400 mg/L IBA处理。本研究为杜鹃花产业化育苗提供了科学依据。     

Relationships between the development of adventitious roots and the biosynthesis of anthocyanins in first internodes of sorghum

The initiation and subsequent growth of adventitious roots in excised first internodes of Sorghum vulgare var. Wheatland milo were studied to determine the effect of these processes on anthocyanin biosyntheses. Segmentation of the internodes inhibited both adventitious root growth and accumulation of cyanidin equally in all segments; these results can be interpreted as a common requirement for bidirectional longitudinal transport. The presence of the coleoptile, especially in the absence of the base of the internode, inhibited the growth of the roots, but increased the number of root initials. High intensities of white and blue light which induced cyanidin synthesis slightly decreased adventitious root growth. Anaerobic conditions produced by solution infiltration strongly inhibited the growth of adventitious roots and greatly increased the accumulation of apigeninidin and luteolinidin. Addition of indoleacetic acid, kinetin and cofactors such as pyridoxine produced effects on the initiation and subsequent growth of these roots similar to those effects reported in the literature. But unlike root formation in hypocotyls, the initiation of adventitious roots in Sorghum internodes was not always directly correlated with the accumulation of anthocyanins, and the subsequent growth of these roots was frequently inversely correlated with some of the anthocyanin biosyntheses. The possible nature of these correlations is discussed. Comparisons are made with related Sorghum lines and mutants.     

入侵植物水花生解剖学和组织化学染色研究

水花生(Alternanthera philoxeroides)因其表型可塑性、高生长速率和快速无性繁殖能适应水、陆生境.该文利用光学显微镜和荧光显微镜对水、陆生境的水花生不定根、茎解剖结构、组织化学特征及质外体通透性进行了研究.结果表明:(1)水生境下,其不定根皮层中具较大裂生型通气组织,无次生生长,内皮层具凯氏带且...     

On the Physiological Significance of Seminal Roots in Perennial Grasses

Measurements of yield and composition of plants of timothy (PhleumparatenseL.) show that nutrient uptake and growth are restricted if nutrientsare supplied only to the seminal roots. Plants whose nutrientswere supplied entirely through their adventitious roots didnot differ significantly in any of the characters studied fromthose in which all the roots had a nutrient supply available. It is therefore concluded that seminal roots have no specialphysiological significance.     

A Dominant Mutation in ARL2 Causes Impaired Adventitious Root Development in Rice

Adventitious roots are vital for water and nutrient assimilation by cereal crops because they comprise the bulk of the fibrous root system. We isolated and analyzed a rice mutant, adventitious rootless 2 (arl2), which failed to initiate adventitious root primordia during early development. Its seminal root produced fewer lateral roots than from the wild type. This mutant also exhibited pleiotropic phenotypes of longer and thicker seminal roots, a different morphology for the first leaf, delayed heading, and a greater tiller angle. Physiological experiments showed that exogenous auxin and ethylene could rescue adventitious root growth, a response opposite that for two previously reported mutants, arl1 and gnom1. Activity in the auxin signal pathway and the polar auxin transport system was normal for arl2. Compared with the wild type, arl2 plants showed enhanced sensitivity to ethephon but decreased sensitivity to AgNO₃, an inhibitor of ethylene. Genetics analysis demonstrated that this mutant is controlled by a single dominant gene; ARL2 was mapped within a 100-kb interval on the short arm of chromosome 2.