Effects of Auxin Concentration on the Dimensions and Patterns of Tracheary Elements Differentiating in Pith Explants

The optimal concentration of IAA (0.03 mM) for tracheary elementdifferentiation in lettuce pith explants was about ten timesgreater than the optimal concentration for callus proliferation.Related to this, the mean volume per tracheary element increasedwith increasing IAA concentration, 18-fold between 0.001 mMand 0.3 mM IAA. At the highest concentrations, some pith cellsappeared to differentiate directly into tracheary elements,without cell division, resulting in especially large trachearyelements. Tracheary strands developed at intermediate concentrationsof IAA, and led to a small increase in the mean length/breadthratio of tracheary elements. For tracheary elements differentiating from stem cambial derivatives,a reassessment of previous studies indicates that increase inauxin concentration brings greater tracheary element size atconcentrations up to the 0.03 mM optimum. Above this optimum,however, further increase in auxin concentration brings progressivelysmaller tracheary elements, as the high auxin curtails enlargementof the differentiating cells. This contrasts with the pith explants,in which tracheary element size increases with IAA concentrationmost markedly above the optimum concentration. The interpretationof these relations requires an understanding of the effectsof auxin concentration on interacting quantities such as initialsize of cells, rate of enlargement, and rate of differentiation. Lactuca sativa, lettuce, IAA concentration, pith explants, tracheary element dimensions     

Inhibition of Lettuce Seed Germination and Root Elongation by Derivatives of Auxin and Reversal by Derivatives of Cycocel

Lettuce seed germination or lettuce root elongation after germination in water was inhibited by 5.7 × 10^-6M indoleacetic acid (IAA) and designated other IAA derivatives. These IAA-inhibited growth responses were reversed by 10^-5 to 10^-6M Cycocel, (2-chloroethyl) trimethylammonium chloride, which alone was without effect. Only those Cycocel analogs, which have previously been shown to be active as plant growth retardants, were effective in reversing IAA inhibition of germination or root elongation. These results are consistent with the concept that Cycocel at low concentrations acts as an auxin antagonist. However. Cycocel did not reverse the inhibitory effects from indole-3-propionic acid or indole-3-butyric acid.     

Auxin: its role in genetic tumor induction

Seedlings of the tumor-prone amphiploid Nicotiana suaveolens X N. langsdorffii were grown on nutrient medium supplemented with indoleacetic acid (IAA) and scored at regular intervals for the incidence of tumor formation. IAA at 2 x 10(-5)m caused a significant reduction in the rate of tumor formation. Plants were also grown on nutrient medium under two different intensities of illumination, and the endogenous level of IAA was determined in 23-day-old seedlings. Those grown under 2000 ft-c of illumination had a higher incidence of tumors and a significantly lower level of endogenous IAA than those grown under 500 ft-c of illumination. A correlation in time between decline in the endogenous level of IAA and onset of tumor formation was demonstrated in greenhouse-grown plants.     

Cambium Formation in Wounded Solanaceous Stems

When stems of certain Solanaceous species are wounded the internalphloem strands that lie near to the damaged surface become enlargedthrough cell division, and some of them develop a vascular cambium.This ‘internal cambium’ forms phloem inwards andxylem outwards; it is thus in inverted orientation. Such a structuredoes not occur in the normal stem of any Solanaceous plant.Further, during the regeneration of a cambial cylinder afterwounding, the regenerating cambium may turn inward to meet woundedinternal phloem strands. Where this happens, subsequent secondarythickening leads to the formation of thin tubes of cambium runningradially through the xylem and forming a limited amount of enclosedphloem which connects the internal and external phloem systemsof the stem. The jpositions in which these cambia arise are explicable bythe ‘gradient induction’ hypothesis of cambial regeneration,but not by the ‘free surfacfe’ and ‘cambialring’ theories.     

Auxin Content and Auxin Catabolism in Relation to the Growth Polarity

The auxin level in the root fragments of carrot cultivated in vitro is inversely related to the auxin-oxidase activity. In the morphological basal region, auxin catabolism is low and, in consequence, auxin content is high. This accumulation of the endogenous auxin leads to the induction of callus. In such new tissues, IAA-oxidase activity is also very low and, similarly, the auxin content is high: thus, cells can growth rapidly. Consequently the growth polarity is directly related to the auxin catabolism.     

杜仲形成层休眠机理

对杜仲(Eucommia ulmoides Oliv.)一年生枝条休眠中的芽和维管形成层的结构和蛋白质含量进行了研究,探讨了杜仲不同休眠期转化的生理生化机理.结果证实了杜仲树的休眠期包括2个被动休眠期和一个生理休眠期.在生理休眠期,无论用外源IAA处理,还是给予适当的温度和光照,形成层都不能恢复活动.而且,雌株进入各个休眠阶段的时间都比雄株早.树皮中的蛋白质含量在第一被动休眠期间(Q1)显著地逐步增高(P<0.01),进入生理休眠期(R)后,急剧降低,但第二被动休眠期(Q2)开始后又显著升高(P<0.01).杜仲雌雄株树皮中的蛋白质含量变化趋势基本一致,但雄株发生变化的时间比雌株早.SDS-PAGE电泳结果表明,在Q1-R-Q2的转变期出现一11.8 kD的特异蛋白条带.此特异蛋白条带可能与形成层休眠期中各阶段的转变调节有关.     

Auxin Receptors and Auxin Binding Proteins

In the last few years, a large number of auxin-binding proteins (ABPs) have been reported. Implicitly or explicitly, interest in such proteins resides in their possible role as auxin receptors. Many of these proteins are characterized as ABPs solely by their susceptibility to covalent photolabeling by tritiated azido-indole-3-acetic acid. In most cases where the labeled polypeptides have been identified, they turn out to have roles unconnected with primary auxin perception. It seems likely that auxin is binding to sites of catholic specificity in these cases and the influence of experimental protocols on the data is discussed. Because the term ABP implies that auxin binding affects the function of that protein, the importance of establishing further criteria before photolabeled peptides can be termed ABPs is emphasized. Applying such criteria, only a very few ABPs are currently of interest and only one of these, maize ABP1, has been characterized in detail. This protein is located primarily within the lumen of the endoplasmic reticulum, although an important fraction appears to function on the outside of the plasma membrane. The protein has a wide species distribution and it now seems highly probable that it is a genuine auxin receptor, the only protein for which such a function has yet been established. This conclusion is based on three independent lines of electrophysiological evidence, together with confocal imaging of cytoplasmic pH changes.     

杜仲形成层休眠机理

对杜仲 (EucommiaulmoidesOliv .)一年生枝条休眠中的芽和维管形成层的结构和蛋白质含量进行了研究 ,探讨了杜仲不同休眠期转化的生理生化机理。结果证实了杜仲树的休眠期包括 2个被动休眠期和一个生理休眠期。在生理休眠期 ,无论用外源IAA处理 ,还是给予适当的温度和光照 ,形成层都不能恢复活动。而且 ,雌株进入各个休眠阶段的时间都比雄株早。树皮中的蛋白质含量在第一被动休眠期间 (Q1)显著地逐步增高 (P <0 .0 1) ,进入生理休眠期 (R)后 ,急剧降低 ,但第二被动休眠期 (Q2 )开始后又显著升高 (P <0 .0 1)。杜仲雌雄株树皮中的蛋白质含量变化趋势基本一致 ,但雄株发生变化的时间比雌株早。SDS_PAGE电泳结果表明 ,在Q1 R Q2的转变期出现一11.8kD的特异蛋白条带。此特异蛋白条带可能与形成层休眠期中各阶段的转变调节有关。     

An Electron-microscopic Investigation of the Walls of Conifer Cambium

Electron-micrographs of the primary walls of conifer cambiumreveal the type of structure already found in other primarywalls, except that no area of ‘loose’ microfibrilsappear to be present. In addition, groups of fibrils are visibleradiating from a centre which appears to be granular and recallingstrongly the putative islands of synthesis reported in Valonia.     

泡桐维管形成层及木质部区的转录组分析

采用Illumina HiSeqTM2500高通量测序技术,获得泡桐维管形成层及木质部区组织转录组的109021918条clean reads(16.35 Gb)。将clean reads从头组装得到104432个单基因簇(Unigene),平均长度662 nt。将组装得到的Unigenes与公共数据库进行序列比对,分别有40789(Nr:39.05%)、31675(NT:30.33%)、15539(COG:14.87%)、29168(GO:27.93%)、16316(KEGG:15.62%)、30499(SwissProt:29.20%)以及28828(Pfam:27.6%)个Unigenes获得功能注释。通过与GO数据库的比对分析,注释的29168个Unigenes归于生物过程、细胞组分及分子功能三大类的55个功能组;15539条Unigenes注释到COG数据库,被分为25个类别中;基于KEGG数据库可将16316个Unigenes归于130个代谢途径。此外,在泡桐的维管形成层及木质部区转录组中共检测出16118个简单序列重复(SSR)位点。为进一步挖掘泡桐重要功能基因提供了大量数据。     

Timing of the Auxin Response in Coleoptiles and Its Implications Regarding Auxin Action

The timing of the auxin response was followed in oat and corn coleoptile tissue by a sensitive optical method in which the elongation of about a dozen coleoptile segments was recorded automatically. The response possesses a latent period of about 10 min at 23°C, which is extended by low concentrations of KCN or by reducing the temperature, but is not extended by pretreatments with actinomycin D, puromycin, or cycloheximide at concentrations that partially inhibit the elongation response. Analysis of the data indicates that auxin probably does not act on the elongation of these tissues by promoting the synthesis of informational RNA or of enzymatic protein. Not excluded is the possibility that auxin acts at the translational level to induce synthesis of a structural protein, such as cell wall protein or membrane protein. While the data do not provide direct support for this hypothesis, the speed with which cycloheximide inhibits elongation suggests that continual protein synthesis may be important in the mechanism of cell wall expansion.     

Cambium Destruction in Conifers Caused by Pinewood Nematodes

Percentage and rate of mortality in 2-4-year-old conifers depended upon the numbers of pinewood nematodes Bursaphelenchus xylophilus inoculated into their stems. In addition, percentage of conifer mortality was greater for spring inoculations when cambial activity was greater than for late summer and fall inoculations. Gross and histological examination of stems revealed destruction of the cambial layer, including fusiform and ray intitials and their derivatives. These data suggest that cambial and ray destruction causes tree death through blockage of tracheids by gas, oleoresin, or metabolites from dying ray tissues.     

生长素受体与信号转导机制研究进展

对生长素受体ABP1和TIR1及调控泛素化蛋白降解的生长素信号转导途径研究进展进行综述。     

Role of the Arabidopsis PIN6 Auxin Transporter in Auxin Homeostasis and Auxin-Mediated Development

Plant-specific PIN-formed (PIN) efflux transporters for the plant hormone auxin are required for tissue-specific directional auxin transport and cellular auxin homeostasis. The Arabidopsis PIN protein family has been shown to play important roles in developmental processes such as embryogenesis, organogenesis, vascular tissue differentiation, root meristem patterning and tropic growth. Here we analyzed roles of the less characterised Arabidopsis PIN6 auxin transporter. PIN6 is auxin-inducible and is expressed during multiple auxin–regulated developmental processes. Loss of pin6 function interfered with primary root growth and lateral root development. Misexpression of PIN6 affected auxin transport and interfered with auxin homeostasis in other growth processes such as shoot apical dominance, lateral root primordia development, adventitious root formation, root hair outgrowth and root waving. These changes in auxin-regulated growth correlated with a reduction in total auxin transport as well as with an altered activity of DR5-GUS auxin response reporter. Overall, the data indicate that PIN6 regulates auxin homeostasis during plant development.