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The stages of floral development in staminate and pistillate plants of hop (Humulus lupulus) were defined using scanning electron microscopy and light microscopy. Vegetative meristems of male and female plants are morphologically indistinguishable. On transition to the reproductive phase, inflorescence apices reduce greatly in size and striking developmental sex differences become apparent. The first sex-specific differences occur extremely early in floral ontogeny. Both male and female plants initiate inflorescence meristems at each leaf node, each meristem being enclosed within a bract. Male secondary inflorescence meristems give rise to clusters of asynchronously developing flowers. Female inflorescence meristems produce flowers arranged in 'cones'. Each male floral meristem initiates a whorl of five sepal primordia, followed by an inner whorl of five stamen primordia. There is no sign of carpel development at any stage. In females, two carpel primordia are initiated, surrounded at their base by a vestigial perianth whorl. No stamen development is observed. Several monoecious lines carry bisexual flowers, either within cymose panicles or within the basal bracts of terminal female inflorescences. Bisexual flowers usually possess perianth, stamen and carpel whorls. The central whorls are often highly variable, and range from a pair of stigmas fused to a thin central filament to a well developed gynoecium. Chimaeric central whorls consisting of fused staminoid-carpelloid structures also occur. Sex differences in unisexual hop flowers are determined at an extremely early stage in ontogeny. The inappropriate set of sex organs is suppressed before it becomes visible or, more probably, it is not initiated at all. Genes directing the development of sex are likely to act at an extremely early stage, well in advance of floral organogenesis. The sex chromosomes of dioecious hop plants are described, as well as the chromosome constitutions of monoecious plants and those carrying bisexual flowers.

Objectives The aim was to identify and characterize all incident adult cases of idiopathic inflammatory myopathies (IIM) between 1 January 2007 and 31 December 2016 in the City of Salford, UK. Methods Adults first diagnosed with IIM within the study period were identified by: a Salford Royal NHS Foundation Trust (SRFT) inpatient episode IIM-specific ICD-10 coding search; all new patient appointments to SRFT neuromuscular outpatient clinics; and all Salford residents enrolled within the UKMYONET study. All patients with definite IIM by the 2017 EULAR/ACR classification criteria were included, as were probable cases if consensus expert opinion agreed. Cases were excluded if

Because of its ease of implementation and insensitivity to indenter drift, dynamic indentation techniques have been frequently used to measure mechanical properties of bulk and thin film materials as a function of indenter displacement. However, the actual effect of the oscillating tip on the material response has not been examined. Recently, it has been shown that the oscillation used with dynamic indentation techniques alters the measured hardness value of ductile metallic materials, especially at depths less than 200 nm. The alteration in the hardness is due to the added energy associated with the oscillation which assists dislocation nucleation. Atomistic simulations on nickel thin films agree with experiments that more dislocations are nucleated during dynamic indents than with quasi-static indents. Through the analysis of quasi-static and dynamic indents made into nickel single crystals and thin films, a theory to describe this phenomenon is presented. This is coined the Nano-Jackhammer effect, a combination of dislocation nucleation and strain rate sensitivity caused by indentation with a superimposed dynamic oscillation.

Grain development, germination and plant development under abiotic stresses are areas of biology that are of considerable interest to the cereal community. Within the Investigating Gene Function programme we have produced the resources required to investigate alterations in the transcriptome of hexaploid wheat during these developmental processes. We have single pass sequenced the cDNAs of between 700 and 1300 randomly picked clones from each of 35 cDNA libraries representing highly specific stages of grain and plant development. Annotated sequencing results have been stored in a publicly accessible, online database at http://www.cerealsdb.uk.net. Each of the tissue stages used has also been photographed in detail, resulting in a collection of high-quality micrograph images detailing wheat grain development. These images have been collated and annotated in order to produce a web site focused on wheat development (http://www.wheatbp.net/). We have also produced high-density microarrays of a publicly available wheat unigene set based on the 35 cDNA libraries and have completed a number of microarray experiments which validate their quality.

Hungerford Bridge Millennium Project in London, UK—a complex seven-span multi-cable-stayed structure—was under construction at the time of the oscillations of the nearby Bankside Millennium Footbridge. The design criteria and methods of calculation used to assess oscillation and displacement are described. The results of physical testing of the bridge by mechanically induced vibration and by a walkover test are compared to the calculated values. The calculations predicted performance in service with adequate accuracy. Measurement of structural damping during the physical tests indicated that it was lower than expected.

We report a detailed study of the morphology of TiO2:Co films grown on both LaAlO3 (001) and SrTiO3 (001) substrates by pulsed laser deposition. The films are optically transparent and ferromagnetic at room temperature with a magnetic moment of 1.7±0.4 μB/Co. Plan view transmission electron microscope studies show clear evidence of cobalt segregation with the clustering more pronounced for higher cobalt concentrations. Films grown on SrTiO3 substrates show the presence of a thin surface rutile (111) layer, into which the cobalt appears to migrate. These results are supported by x-ray structure determination and resistivity measurements.

Professor of botany from 1825 until his death, John Stevens Henslow (1796–1861) revived and greatly advanced the study of plants at Cambridge. His influence helped to make the University Botanic Garden an important centre for teaching and research. Originally published over a period of seventeen years, and now reissued here together, these thirteen papers reveal the impressive breadth of Henslow's scientific knowledge. The first two items, from 1821, address the geology of the Isle of Man and Anglesey respectively, preceding his five-year tenure as chair of mineralogy at Cambridge from 1822. The rest of the papers, dating from 1829 to 1838, address botanical topics. Professor John Parker, Director of Cambridge University Botanic Garden, has provided a new introduction that traces Henslow's developing interests and contextualises the items in this collection. Several of Henslow's other publications, including his Catalogue of British Plants (1829), are reissued separately in this series.

The final stage of map-based gene isolation is complementation of the mutant phenotype with wild-type DNA to determine the exact location of the gene of interest. This usually involves Agrobacterium tumefaciens-mediated transformation, which is reliable and produces stable transformants. However, the process of Agrobacterium transformation may take up to three months to complete. If the mutant phenotype can be seen in a single cell, and the wild-type copy of the gene can act cell autonomously, then complementation of the whole plant is not strictly necessary. We have developed a technique for the biolistic transformation of Arabidopsis thaliana root hairs, and used this to test large insert clones for complementation of two recessive mutant phenotypes, a procedure that takes less than a day. Our results show that biolistic transformation can be used with transient assays to conduct rapid tests for complementation by large insert clones.

The cuckoo chromosome 4S(L) from Aegilops sharonensis is preferentially transmitted when introduced by hybridization into common wheat, Triticum aestivum. Gametocidal (Gc) factors carried in 4S(L) induce chromosome breakage in meiospores not containing them, ensuring their transmission to the progeny. Chromosome breakage and break-fusion-bridge (BFB) cycles can also be observed during early embryo sac development of chromosome 4S(L) addition lines to wheat, often leading to the presence of dicentric chromosomes in the subsequent progeny. However, the process responsible for inducing the primary chromosomal breaks only appears to occur during the initial divisions of the embryo and endosperm. In the presence of chromosome 4S(L), treatment with the hypomethylating agent 5-azacytidine induces chromosome breakage in root tips. This suggests that the process of chromosome fragmentation, induced by the Gc factors during early seed development, is repressed at later stages by DNA methylation.

After a decade of Arabidopsis genetics many genes with important roles in root hair development have been identified. Mutants have been used to discover genes, define their roles, and identify their DNA sequences. Plant growth regulator signaling and transcription factor genes determine which root epidermal cells form hairs. A network of gene activity has been characterized that produces a swelling on the surface of each hair cell and a single tubular outgrowth from each swelling. The molecular functions of some genes in this network have been revealed. We are approaching a molecular understanding of root hair development that will provide exciting opportunities in plant cell biology and physiology.

Studies of pollination ecology have been hindered by an absence of biochemical information about the basis of polymorphism. Using model plants and mutant lines described by molecular genetics may circumvent this difficulty. Mutation of genes controlling petal colour and petal epidermal cell shape in Antirrhinum majus was previously shown to influence fruit set. White flowers set less fruit than magenta flowers and mutants with flat petal epidermal cells set less fruit than flowers with conical cells. Here we analyse the causal pathway underlying this phenomenon through a study of floral characteristics and bee behaviour. Results indicate that bees recognized plants with magenta conical-celled flowers at a distance and did not approach white flowers or magenta flat-celled flowers so frequently. Petal cell shape interacted with colour in determining whether an approaching bee landed on a flower within a plot and whether a bee landing on a flower would probe it. The intrafloral temperature of flowers with conical petal cells was shown to increase with solar irradiance, unlike the intrafloral temperature of flowers with flat petal cells. The difference in fruit set may reflect pollinator discrimination between genotypes as a consequence of the effect of intrafloral temperature on nectar quality and quantity.

Key words: Cell cycle, DNA replication, licensing factor,MCM proteins, plant.A partial cDNA from maize, ROA, encoding a proteinhomologous to the MCM3 family of essential factorsfor the initiation of DNA replication, has been isolated Introduction previously. In the present work, a longer version of theoriginal ROA cDNA, encoding a full-length protein, was The eukaryotic genome is generally replicated exactlyisolated and termed ZmROA1. In addition, three other once, during the S phase of the somatic cell cycle, andclosely related cDNAs, ZmROA2, ZmROA3 and this is essential to maintain the DNA content throughZmROA4, were also isolated. ZmROA2 end ZmROA3 numerous generations of cells. The once-per-cell cycleappear to encode full-length proteins, whereas control over DNA replication ensures that DNA synthesisZmROA4 a partial polypeptide. Two clusters of basic is initiated only once, and that re-replication is inhibitedamino acids comprising putative nuclear localization during S phase (reviewed by Coverly and Laskey, 1994).signals were identified in the N-terminal domain This involves a tight control over replication origins,of these proteins, together with a potential leucine which must be timed to activate upon S phase entry,zipper. Immunofluorescence studies on cycling meris- but then rendered unable to support further rounds oftematic root-tip cells revealed that these proteins are DNA synthesis until cells complete mitosis and enter thelocalized in the nucleus throughout interphase with a next interphase. A complex array of interactions betweenpattern overlapping that of chromatin. However, as initiation factors and chromosomal origins is essential tochromatin condenses at prophase, ZmROA proteins make origins competent for DNA replication, to fire thembecome increasingly distinct from chromatin and during S phase, and to prevent them from firing again inappear totally dissociated from the segregating chro- the same cell cycle (reviewed by Kearsey

The Mars Global Surveyor (MGS) z -axis accelerometer has obtained over 200 vertical structures of thermospheric density, temperature, and pressure, ranging from 110 to 170 kilometers, compared to only three previous such vertical structures. In November 1997, a regional dust storm in the Southern Hemisphere triggered an unexpectedly large thermospheric response at mid-northern latitudes, increasing the altitude of thermospheric pressure surfaces there by as much as 8 kilometers and indicating a strong global thermospheric response to a regional dust storm. Throughout the MGS mission, thermospheric density bulges have been detected on opposite sides of the planet near 90°E and 90°W, in the vicinity of maximum terrain heights. This wave 2 pattern may be caused by topographically-forced planetary waves propagating up from the lower atmosphere.

A detailed cytogenetical study of inbred lines of pea and their F1hybrids has been undertaken to study the relationship between the cytogenetic map and the molecular linkage map. The mitotic karyotypes of a standard pea line, JI15, a translocation line, JI61, and line JI281, a line used in the production of a mapping population, are given. A chromosome rearrangement detected by cytogenetic analysis of mitotic chromosomes has been further defined by synaptonemal complex (SC) analysis and the study of metaphase I chromosome behaviour. This meiotic analysis has allowed a comparison of SC physical lengths, observed chiasma frequencies, and recombination frequencies, as estimated from the genetic map, as a means of comparing physical and genetic distances.Key words: Pisum, linkage map, cytogenetics, chromosome rearrangement, synaptonemal complex.

A cytogenetic analysis of inbred lines that have been used to generate genetic maps of pea is presented. Mitotic karyotyping of the inbred lines and meiotic studies of their F1hybrids have been used to test the prediction that structural differences exist between the parental lines. The results are not compatible with the previously published molecular data. A reordered and updated linkage map of pea is presented that is consistent with the cytogenetic data.Key words: Pisum, linkage map, recombination, synaptonemal complex, chiasmata.

The present study evaluated the effects of bright light therapy on a patient with cortical blindness. Behavioral indices of functioning included the appraisal of mood, fatigue, appetite and orientation. Physiological measures assessed were blood pressure and temperature. Blood serum samples were analyzed for 5-HIAA and norepinephrine (NE). For the control and follow-up, the patient was exposed to 30 minutes of red light (300-lux), and thirty minutes of white light (10,000-lux) was used for treatment. High-pressure liquid chromatography analyses of blood serum samples revealed no change in serotonin (5-HT). However, an increase in blood NE was indicated following light treatment (red light: 12.7 ng/ml, white light: 43.5 ng/ml and, red light: 27.5 ng/ml). Analysis of data revealed significant differences in baseline and treatment scores for 4 of the outcome measures.

The overall composition of the maize B is similar to that of the standard chromosome complement (A-chromosomes). This has been demonstrated by the use of several methods including: (a) genomic in situ hybridization (GISH), (b) analysis of highly repetitive sequences by the comparison of restriction digests of 0B and +B DNA and (c) the characterization of middle-repetitive cloned sequences. By the use of the technique of random amplification of polymorphic DNA-polymerase chain reaction, we have identified a B-specific repetitive sequence family. Sequence analysis of the B-specific clone reveals a relationship to the PREM-1 family of maize retroelements, which are preferentially transcribed in pollen. These results suggest an internal origin of the B-chromosome from within the maize genome, but demonstrate also that specific sequences can evolve by rapid processes of genomic turnover. Models for the origin of the maize B are discussed in the context of the present data.

Summary Using indirect immunofluorescence, the system of radiating e ndoplasmic m icro t ubule s (REMTs) within intact cells of meristematic root tissues of maize has been examined throughout the cell cycle, paying special attention to its relationship with the pre- and post-mitotic nuclei with which it is associated. At early interphase, REMTs are not uniformly disposed around the nucleus but grow out from feint, though easily recognizable, perinuclear foci. During S and G2 phases, REMTs increase in number and have a close association with the assembly of the p re p rophase b and (PPB) MT array. Later, when the cortical part of the PPB disintegrates, the REMTs align along the nuclear surface, predicting the long axis of the future mitotic spindle. In contrast to naturally wall-less cells, or to cells with perturbed cell walls, these pre-mitotic, as well as the subsequently formed post-mitotic cells display symmetrical rearrangements of their REMTs around the nuclear surface. Mitotic cells sectioned in the median plane show a symmetrical quadripolar MT organization which is obvious at all stages of mitosis. The symmetrical redistributions of the REMTs which occur during the cell cycle are perturbed, or even prevented, by treatments with chemical or with physical anti-MT agents. Nuclei of cells so treated accumulate REMTs, but fail to redistribute them symmetrically. As a result, the pre- and post-mitotic nuclei of root cells treated with anti-MT agents resemble, with respect to their REMTs, the corresponding nuclei of wall-less plant cells, or of cells which have perturbed cell walls. The dynamic REMTs which connect the pre- and post-mitotic nuclei with the cell periphery are suggested as being involved in sensing the position of dividing cells within the intact plant organ. This property of REMTs enables them to spatially control the sequential alignment of cell division planes of immobile walled plant cells which underlies the morphogenesis of higher plant organs.

A spontaneous chromosome fission in the plant Hypochoeris radicata has been characterized by Feulgen staining, in situ hybridization of the rDNA probe pTA71 and silver staining for active nucleolus organizing regions. The parental acrocentric chromosome has no detectable ribosomal genes at the centromere, but both fission derivatives possess active NORs at their centric ends. In fission heterozygotes, pachytene configurations studied by synaptonemal complex spreading show that the ribosomal cistrons form short arms on each telocentric which pair together to form a triradial. The paired short arms are associated with the single nucleolus at pachytene. It is proposed that the origin and stabilization of the fission rearrangement involved transposition of rDNA from the nucleolus organizing region of chromosome 3 into the centromeric region of chromosome 1.

A large euchromatic supernumerary segment (ss) occurs at a high frequency in a natural population of Scilla autumnalis from the west of the Iberian Peninsula. Mother-offspring analyses have shown random pollination of all bulbs lacking the extra segment but non-random pollination of some bulbs carrying it. With a single exception, ss transmission appeared to be Mendelian through the eggs of heterozygous bulbs, which was consistent with results of controlled crosses. An analysis of the effects of this ss on some female fitness components demonstrated significant differences between genotypes for mean seed weight. Heterozygous bulbs yielded significantly heavier seeds than standard homozygous bulbs, and slightly (but not significantly) heavier seeds than segment homozygotes. No trade-off was observed between seed number and seed size in this population. In heterozygotes there was a surprising positive correlation between fruit fertility (number of seeds per fruit) and seed weight. These results are discussed in relation to the maintenance of the segment in natural populations.

summary Results from studies with metabolic inhibitors suggest that, in growing cells of the maize root apex, nuclear metabolism is involved in the organization of the cortical microtubular arrays (CMTs) located at the cell periphery. Nucleus-derived factors intrinsic to each individual cell are inferred as being responsible for the accomplishment of the MT-dependent transition from the approximately isodiametric mode of cellular growth, characteristic of the immediate post-mitotic root region, to the strictly directional cell lengthening in the elongation zone. These hypothetical factors seem to be related to RNA but not DNA synthesis, as indicated by our inhibitor studies. For instance 5-fluorodeoxyuridine, an inhibitor of DNA synthesis, had little effect on orientation of CMTs, when these were present, and allowed the developmental switch from more or less isodiametric mode of cell growth into highly polarized cell elongation to occur. In contrast, actinomycin D, a specific inhibitor of nuclear metabolism which rapidly halts rRNA synthesis, affected both the polarity and efficacy of postmitotic cell growth and impaired the transversal arrangement of CMTs as well as inducing the appearance of prominent ‘holes’ in their bundled arrays. These latter effects of actinomycin D cannot be simply explained by its indirect effect on translation, through impairment of functional ribosome assembly, as they were visible after only 15 min. Moreover, inhibition of protein synthesis by cycloheximide resulted in a different response. There was rapid and complete loss of the preferred transverse orientation of CMTs and the individual CMTs failed to organize themselves into bundles. Endoplasmic microtubules (EMTs), located more internally between plasma membrane and nucleus, seem to be important for determining nuclear size and chromatin architecture, since whenever EMTs were caused to disintegrate (cold and anti-MT drug treatments), meristematic nuclei swelled and their chromatin dispersed. By contrast, when EMTs were stabilized and increased in number by taxol, which specifically favours MT polymerization, the nuclei became smaller and the chromatin more condensed. Nevertheless, the mechanisms of these complex interplays between the MT cytoskeleton and the nuclear organization remain unclear.

The B chromosome of Crepis capillaris was isolated from the standard chromosomes by microdissection, and the chromosomal DNA amplified using the degenerate oligonucleotide-primed polymerase chain reaction (DOP-PCR). The PCR product was cloned and a B-specific library created and characterised. Southern and in situ hybridisation analyses of the DOP-PCR product from microdissected B chromosomes confirmed that the B chromosome is composed mainly of sequences also present in the A chromosomes but lacks the main repeated DNA families located in the A-chromosomal heterochromatin. From 100 clones analysed, 12% of the generated B-chromosomal library was shown to be composed of dispersed repeats located in both the A and B chromosomes. No B-specific repeated sequence was detected. One of the most abundant repeated DNAs within the library, the family B134, was further characterised. Repeating units show a sequence similarity range from 69% to 90% and are characterised by their richness in (CA)n repeats. In situ hybridisation revealed that members of this family are dispersed throughout the A and B chromosomes but are more concentrated in the pericentromeric heterochromatin of the B, indicating that the molecular organization of B heterochromatin is different from that of the A chromosomes. Compared with the A chromosomes, the Bs contain about 20,000 copies per micron more of the B134 sequence. This indicates that B134 was amplified on the B chromosome after its origin. The B134 sequences in the B chromosomes have also diverged from those on the A chromosomes. Although the DNA composition of A and B chromosomes is similar, Bs are evolving separately from A chromosomes at the molecular level.

Recent reports of room temperature ferromagnetism in thin films of TiO2 doped with small amounts of cobalt have excited a great deal of interest due to the possible applications of this ferromagnetic, transparent semiconductor to spintronics devices. Ferromagnetism has been reported for TiO2 grown in both the anatase and rutile phases, although a range of magnetic moments has been reported by different groups. We have grown epitaxial thin films of Ti1−xCoxO2, with x=0.01–0.07 by pulsed laser deposition in both the anatase and rutile forms on single crystal substrates of LaAlO3, SrTiO3, and Al2O3. These films are ferromagnetic at room temperature with a magnetic moment of ∼1.7 μB/Co in the anatase phase and ∼0.6 μB/Co in the rutile phase. Detailed transmission electron microscopy measurements show a variation in the cobalt distribution in these materials that corresponds to the different magnetic moments. The cobalt does not appear to enter the anatase phase of TiO2, but rather forms crystallites of cobalt metal on the surface of anatase films. This results in a magnetic moment similar to that of bulk cobalt. In the rutile phase the cobalt has substituted uniformly throughout the lattice. We present the morphology and magnetization of TiO2:Co as a function of the TiO2 growth phase and substrate material. Preliminary electrical measurements are also mentioned.

The tips of roots and shoots commonly show lateral movements as they grow forwards. These occur as both circumnutations (with long periods and large amplitudes) and micronutations (with short periods and small amplitudes). Their properties are reviewed, with emphasis on roots, and possible ways in which they could be regulated are discussed. The mechanisms could include long-range controls (for circumnutations) that depend on transmissible signals using steps common to gravitropism, and short-range controls (for micronutations) that operate within the elongation zone. The former are a property of the apex as a whole, while the latter may be confined to localized groups of cells. Simulation of nutations is presented with a view to isolating key physiological processes. However, this approach is limited by the current inadequate understanding of the growth mechanisms involved.

A repeated sequence of 180 bp in tandem array has been isolated from the dioecious plant species Rumex acetosa which has a multiple sex chromosome system, XX♀/XY1Y2♂. There are two or three thin C-bands on the X while the Ys are almost entirely heteropycnotic and DAPI-positive but contain no C-band material. The Ys thus represent massive blocks of facultative heterochromatin. The 180 bp sequence has been localized to the X and both Y chromosomes by in situ hybridization. The molecular data support an origin of the sex-multiple from a homomorphic chromosome pair rather than from a sex chromosome/autosome translocation.

The growth of thin films of the ferromagnetic semiconductor EuS on [100] oriented GaAs substrates by electron-beam evaporation is demonstrated. Structural characterization by X-ray diffraction reveals [100] oriented growth. In general, the magnetic and transport properties can strongly be influenced by the deposition parameters. We systematically investigate the influence of the growth temperature T/sub S/ in the range T/sub S/=235 K-675 K on the above properties. The Curie temperature increases with decreasing growth temperature, while the magnetic transition becomes broader. The resistivity decreases over four orders of magnitude with decreasing substrate temperature. The behavior of the magnetic properties and the resistivity can be explained by a change in stoichiometry, leading to higher carrier concentrations for lower substrate temperatures. Hall-effect measurements, magnetoresistance, and temperature dependence of the resistivity show a qualitative behavior known from bulk EuS samples. The demonstrated tunability of the magnetic and transport properties opens a wide range of possible applications for EuS in spin-electronics.

The organization and behaviour of nucleolar-organizer regions (NOR) of Scilla autumnalis were studied in two diploid races, their allotetraploid and autoallohexaploid derivatives and hybrids between them. The diploids of genome constitution AA and B7B7 each have a pair of nucleolar-organizer chromosomes while the polyploids AAB7B7 and AAB7B7B7B7 only carry visible organizers on the B7 chromosomes. In situ hybridization using ribosomal probe pTA71 was used to localize ribosomal cistrons. In polyploids the sites of hybridization are limited to the B7-derived nucleolar-organizer chromosomes and ribosomal cistrons have thus been deleted from the A genome. A NOR-associated C-band has also been deleted.

The role of gibberellins and cortical microtubules in determining the polarity of cell growth in the root cortex of maize (Zea mays L.) was examined. Inhibition of gibberellin biosynthesis, either naturally through mutation (d5 mutant) or by means of chemicals such as 2S,3S paclobutrazol, caused thickening of root apices and increased their starch content. Immunofluorescence microscopy of cortical microtubules, coupled with a comparison of cell widhts, lengths and shapes, indicated that the meristem and immediate post-mitotic zone were the targets of gibberellin deficiency. Cortical cells in these regions were impaired in their ability to develop highly ordered transversal arrays of cortical microtubules. Consequently, the cells became wider and shorter. Application of gibberellic acid re-established the arrangements of cortical microtubules and the polarity of cell growth characteristic for roots having normal levels of gibberellins, it also decreased the starch content. These results indicate that gibberellins are morphogenetically active substances, not only in shoots but also in roots of maize.

Microtubules (MTs) in cells of various tissues at different distances from the apex of the maize root exhibited different sensitivities to cold (5 °C), as judged by MT reorientation and tendency to depolymerization. Their responses seem to be related to their initial intracellular arrangements. Generally, MTs in cells which were ceasing elongation were the least sensitive during the early stages (6–24 h) of cold treatment, but during the later stages (5–7 d) MTs in most of these cells eventually depolymerized. Pericycle cells showed a unique cold response. Here the MTs were conspicuously cold-labile and quickly depolymerized near the root-tip. However, after 1 d many pericycle cells in more proximal regions had repolymerized their MTs as dense, randomly organized arrays. These persisted for the remainder of the cold treatment. A similar resistance to longterm chilling, by means of MT repolymerization, was found in cells of the root cap, quiescent centre and cells of the distal part of the former meristem. MT repolymerization in the cold may enable the apex to resume growth when more favourable (warmer) conditions return.