植物生长调节剂的研究及应用进展

植物生长调节剂是合成植物激素,其可以调节植物的代谢和生理功能,并且已广泛用于农业、林业和其他领域.而植物生长调节剂本身存在的毒副作用所引起的安全问题也不容忽视,在使用调节剂时应保证其安全性和有效性.文章概述了植物生长调节剂的种类、作用功效、国内外植物生长剂的研究和应用情况及在使用中存在的问题,分析了调节剂药效的影响因素...     

Exploration of Modulated Genetic Circuits Governing Virulence Determinants in <Emphasis Type="Italic">Staphylococcus aureus</Emphasis>

The expression of virulence genes in the human pathogen Staphylococcus aureus is strongly influenced by the multiple global regulators. The signal transduction cascade of these global regulators is accountable for recognizing and integrating the environmental cues to regulate the virulence regulon. While the production of virulent factors by individual global regulators are comparatively straightforward to define, auto-regulation of these global regulators and their impact on other regulators is more complex process. There are several reports on the production of virulent factors that are precisely regulated by switching processes of multiple global regulators including some prominent accessory regulators such as agr, sae and sar which allows S. aureus to coordinate the gene expression, and thus, provide organism an ability to act collectively. This review implicates the mechanisms involved in the global regulation of various virulence factors along with a comprehensive discussion on the differences between these signal transduction systems, their auto-induction and, coordination of classical and some comparatively new bacterial signal transduction systems.     

Long-term effects of growth regulators on growth and turnover of symplastic and apoplastic sugars in the suspension subculture of kidney bean

Suspension cells of kidney bean were grown for 42 d in MS medium supplemented with growth regulators (2.0 mgL^-1 2,4-D and 0.5 mgL^-1 kinetin) or without At the stationary growth phase (42 d), the sugars were fractionated into the symplastic (ethanol and starch) and apoplastic [low-molecular pectin (lm-pectin), high-molecular pectin (hm-pectin), hemicellulose, and cellulose] sugars. The neutral sugars (NS) of hm-pectin and hemicellulose fractions were analyzed by GLC. The growth of the suspension cells in the liquid MS media, in terms of settled cell volume (SCV), remained similar, to the end of the experiment, irrespective of the presence or absence of growth regulators, indicating the nonnecessity of the exogenous growth regulators for the subculture. Total sugar (TS) of the ethanol fraction and NS of the Im-pectin of the suspension cells grown in the medium with growth regulators were higher than in the medium without growth regulators. However, starch content in the starch fraction and uronic acid (UA) content of the Im-pectin fraction did not exhibit any differences. From these results, it was suggested that the growth regulators modulated the structure of the cell wall polysaccharide. Analysis of the NS composition of the hm-pectin fractions revealed that the Rha, Arb, and Gal contents in the presence of growth regulators were higher than in the absence, while the Xyl, Man, and Glc contents in the presence of growth regulators were higher than in the absence, indicating the turnovers of rhamnogalacturonan and/or arabinogalactan. On the other hand, analysis of NS composition of hemicellulose fractions revealed that the Ara and Glc contents in the presence of growth regulators was higher than in the absence, whereas Xyl and Glc contents were nearly consistent, indicating the turnovers of arabinaogalactan I or II. The cellulose contents remained similar, irrespective of the presence (19.1%) or absence (18.7%) of growth regulators.     

Expression of cell-cycle regulators during Xenopus oogenesis

In full-grown Xenopus oocytes, cell-cycle regulators and an inactive form of maturation/M phase promoting factor (pre-MPF) are stored ready to bring about a specific cell cycle for oocyte maturation. We examined the expression pattern of these cell-cycle regulators as well as pre-MPF formation during oogenesis. Cdc2 and Cyclin B2 were already present in stage I oocytes and pre-MPF formation was also detected in stage I oocytes. Some negative regulators of MPF, Myt1 and Chk1, were synthesized early in oogenesis. In contrast, positive regulators of MPF, MEK, MAPK and Cdc25C, were mainly synthesized late in oogenesis. Northern blotting analysis suggested that the synthesis of these cell-cycle regulators was controlled by translation.     

Regulator-driven functional diversification of protein phosphatase-1 in eukaryotic evolution

We have used the (nearly) completed eukaryotic genome sequences to trace the evolution of thirteen families of established vertebrate regulators of type-1 protein phosphatases (PP1). Two of these families are present in all lineages of the eukaryotic crown and therefore qualify as candidate primordial regulators that determined the surface of PP1. The set of regulators of PP1 has continued to expand ever since, often in response to functional innovations in different eukaryotic lineages. In particular, the development of metazoan multicellularity was accompanied by an explosive increase in the number of regulators of PP1. The further increase in the functional diversity of PP1 in the vertebrate lineage was mainly achieved by the duplication of genes for regulatory subunits and by the conversion of already existing proteins into regulators of PP1. Unexpectedly, our analysis has also enabled us to classify nine poorly characterized proteins as likely regulators of PP1.     

NON-HORMONAL STIMULATORS AND INHIBITORS OF PLANT GROWTH AND DEVELOPMENT

1. Plants contain growth regulators that are non-hormonal in nature. These regulators change in concentration during ontogeny and when applied exogenously, can either stimulate or depress growth. While the bulk of either the phenolic or terpenoid regulators are localized within the vacuole, they can also be found within other cellular compartments where they may act upon metabolic pathways, modifying either cell multiplication or elongation. 2. Non-hormonal growth regulators may affect the synthesis and/or destruction of phytohormones, mainly indole-3-acetic acid (IAA). These regulators behave non-specifically, modifying the actions of auxins, gibberellins and cytokinins upon growth. 3. A variety of both uncertainties and unresolved contradictions exist that have prevented a thorough elucidation of the mechanisms of actions of both phenolic and terpenoid regulators. These uncertainties and unresolved contradictions include lack of data regarding compartmentalization of many of the inhibitors. This raises the question of whether their intracellular concentrations become elevated sufficiently to affect metabolic pathways in vivo. Exogenously applied regulators of non-hormonal nature usually interfere with growth only at high concentrations. Therefore, the possibility cannot be excluded that under these conditions, reactions occur within the cell that are absent in vivo. 4. The specific properties of natural non-hormonal regulators are similar in certain respects to phytohormones. For example, both of them may be biogenetically bound within metabolic centres: shikimate (phenolics, indoles, alkaloids), bi-benzi (coumarins) or acetate-mevalonate (terpenoids, fluorens, sesquiterpenes, cytokinins). In addition, both non-hormonal regulators and phytohormones exhibit biological activity in growth bioassays. 5. Non-hormonal regulators may possess a number of useful purposes, e.g. test substances such as fusicoccin permit the investigation of the mode of action of phytohormones, specific inhibitors blocking special forms of growth and protectors of phytohormone activity in culture.     

Hormonal autonomy ofArabidopsis thaliana calli

The growth ofArabidopsis thaliana calli on media without growth regulators was studied Calli under study showed autonomy for cytokmms independently whether cultivated on the light or m the dark When cultivated in intense light, they were able to grow, either transiently or permanently, on the medium without any growth regulators In the dark, they were strictly dependent on 2,4 D m the medium Both the intensity of growth and the duration of the transient growth on the medium without growth regulators m the light decreased with the duration of the previous cultivation on the medium with growth regulators The intensity of growth on the medium without grow th regulators was best and the growth was permanent m the callus clone of spontaneous origin which was never treated by growth regulators The degree of chromosomal variability (assessed as the number of chromocentres) m this callus line was lower than that in calli induced on media with growth regulators and then transferred onto medium without growth regulatois.     

Root organogenesis from single cells released from the root cap of Medicago sp.

Root border cells were isolated from alfalfa seedlings, and incubated in culture medium with growth regulators. Alfalfa seedlings yielded 1500±100 cells per root, and initial viability of the cells was 95±5%. Multiple cell divisions occurred in the border cells within two weeks. Cell clusters transferred to solidified medium containing growth regulators developed into rapidly growing, friable callus. When transferred to growth regulator-free medium, some of the calluses generated normal roots.Abbreviations BRD cells border cells - SHDN Schenk & Hildebrandt salts medium with growth regulators - SHO Schenk & Hildebrandt salts medium without growth regulators - NAA I-naphthaleneacetic acid     

Slit proteins: key regulators of axon guidance, axonal branching, and cell migration

In the past year, Slit proteins have been identified as important regulators of axon guidance and cell migration in Drosophila and vertebrates. Remarkably, they were simultaneously identified as negative regulators, repelling various axonal and cell migrations in both invertebrates and vertebrates, and as positive regulators, stimulating branching and extension of at least one class of axons in vertebrates.