QUANTITATIVE LAWS IN REGENERATION. II

This paper contains the results of a reexamination of a law expressed in a previous paper; namely, that when a piece of stem inhibits the growth of shoots and roots in a leaf connected with it the dry weight of the stem increases and that this gain equals approximately the mass of shoots and roots the leaf would have produced if it had been detached from the stem. This has been confirmed and it has been shown that the gain of the stem as a rule even exceeds slightly the mass of shoots and roots the leaf would have produced if it had not been inhibited by the stem. This supports the idea that the inhibitory influence of the stem upon the formation of roots and shoots in the leaf is due to the fact that the material available and required for this process naturally flows into the stem.     

THE PHYSIOLOGICAL BASIS OF MORPHOLOGICAL POLARITY IN REGENERATION. II

1. The experiments show that the mass of air roots formed in a stem increases with the mass of the leaf attached to the stem, though it has not been possible to establish an exact mathematical relation between the two masses, owing to unavoidable sources of error. 2. Darkened leaves do not increase the mass of roots formed. 3. In stems suspended horizontally air roots appear on the lower side of the stem, with the exception of the cut end where they usually appear around the whole circumference of the stem. When the lower half of a stem suspended horizontally is cut off, roots are formed on the upper side. It is shown by experiments on leaves suspended horizontally that the more rapidly growing roots and shoots on the lower side inhibit the root and shoot formation in the upper half of such a leaf; and likewise the more rapid formation of roots on the lower side of a horizontally suspended stem seems to account for the inhibition of root formation on the upper side of such a stem. Likewise the more rapid growth of shoots on the upper side of a stem suspended horizontally is likely to inhibit the growth of shoots on the lower side. 4. Each leaf contains in its axil a preformed bud capable of giving rise to a root, which never grows out in the normal stem on account of the inhibitory influence of the normal roots at the base of the plant. These dormant root buds are situated above (apically from) the dormant shoot bud. The apical root buds can be caused to develop into air roots when a piece of stem is cut out from a plant from which the leaves except those in the basal node of the piece are removed. The larger these basal leaves the better the experiments succeed. 5. These apical air roots grow out in a few days, while the roots at the basal end of the stem (which in our experiments dip into water) grow out about a week later. As soon as the basal roots grow out in water they cause the air roots in the more apical region of the stem to dry out and to disappear. 6. In addition to the basal roots, basal nodes have also an inhibitory effect on the growth of the dormant root buds in the apical region of a stem. This is indicated by the fact that a stem with one pair of leaves near the base will form apical air roots more readily when no node is situated on the stem basally from the leaf than if there is a node basally from the leaf.     

QUANTITATIVE LAWS IN REGENERATION. I

1. Equal masses of sister leaves of Bryophyllum calycinum produce equal masses of shoots and roots in equal time and under equal conditions. 2. The mass of shoots and roots produced by different masses of sister leaves in equal time and under equal conditions is approximately in direct proportion to the masses of the leaves. 3. When a piece of stem inhibits the production of shoots and roots in a leaf of Bryophyllum connected with it, the stem gains in mass and this gain in mass equals approximately the mass of shoots and roots the leaf would have produced if it had been detached from the stem. 4. This suggests that the inhibitory influence of the stem upon the formation of shoots and roots in the leaf is due to the fact that the material available for this process naturally flows into the stem.     

Hyoscyamine 6 beta-hydroxylase, an enzyme involved in tropane alkaloid biosynthesis, is localized at the pericycle of the root

Hyoscyamine 6 beta-hydroxylase (H6H; EC 1.14.11.11) catalyzes the first reaction in the biosynthetic pathway from hyoscyamine to scopolamine in several solanaceous plants. Four monoclonal antibodies were raised against H6H purified from cultured roots of Hyoscyamus niger. The IgG1 antibody mAb5 inhibited H6H activities present in cell-free extracts of H. niger roots and specifically recognized 38-40-kDa proteins from six different scopolamine-producing plant species in Western blot analysis after sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. The other three monoclonal antibodies all recognized SDS-denatured H6H protein from Hyoscyamus species, but did not bind to native H6H. Western blot analysis of protein extracts from various tissues of H. niger using these antibodies showed that H6H is abundant in cultured roots, present in plant roots, but absent in leaf, stem, calyx, cultured cells, and cultured shoots. Immunohistochemical studies using monoclonal antibody and immunogold-silver enhancement detected H6H only in the pericycle cells of the young root in several scopolamine-producing plants. Mature roots that underwent secondary growth and lacked the pericycle did not react with the antibody. This pericycle-specific localization of scopolamine biosynthesis provides an anatomical explanation for the tissue-specific biosynthesis of tropane alkaloids and may be important for translocation of tropane alkaloids from the root to the aerial parts.     

Non-oncogenic T-region mutants ofAgrobacterium tumefaciens do transfer,T-DNA into plant cells

A new procedure for site-directed mutagenesis has been applied to the shooting and rooting loci of T-DNA of an octopine Ti-plasmid ofAgrobacterium tumefaciens. Mutants have been obtained which induced tumours that either developed shoots or produced more roots than normally observed. Double mutations, in which both types of T-DNA loci were affected, resulted in non-oncogenic strains. Indications have been obtained, showing that T-DNA coded oncogenic functions can be eliminated without affecting T-DNA transfer into plant cells.     

买麻藤根的异常次生生长

买麻藤(Cnetum montanum)根的异常次生生长与茎的异常次生生长相似,位于维管束外围的薄壁组织细胞可以形成维管束,以这种方式使根加粗。并且在生长过程中以同样的方式,在维管束的外围不断形成新的维管束。这些新的维管束成环状排列,因此,在老根中呈多圈的维管束。与茎唯一不同的是根的异常次生生长为不均等的,在两个宽大的射线区外侧,没有异常的维管束形成,因此,根主要向着与两条宽大射线相垂直的方向扩展,故外形呈扁圆形。     

Engineering a root-specific, repressor-operator gene complex

Strong, tissue-specific and genetically regulated expression systems are essential tools in plant biotechnology. An expression system tool called a 'repressor-operator gene complex' (ROC) has diverse applications in plant biotechnology fields including phytoremediation, disease resistance, plant nutrition, food safety, and hybrid seed production. To test this concept, we assembled a root-specific ROC using a strategy that could be used to construct almost any gene expression pattern. When a modified E. coli lac repressor with a nuclear localization signal was expressed from a rubisco small subunit expression vector, S1pt::lacIn, LacIn protein was localized to the nuclei of leaf and stem cells, but not to root cells. A LacIn repressible Arabidopsis actin expression vector A2pot was assembled containing upstream bacterial lacO operator sequences, and it was tested for organ and tissue specificity using beta-glucuronidase (GUS) and mercuric ion reductase (merA) gene reporters. Strong GUS enzyme expression was restricted to root tissues of A2pot::GUS/S1pt::lacIn ROC plants, while GUS activity was high in all vegetative tissues of plants lacking the repressor. Repression of shoot GUS expression exceeded 99.9% with no evidence of root repression, among a large percentage of doubly transformed plants. Similarly, MerA was strongly expressed in the roots, but not the shoots of A2pot::merA/S1pt::lacIn plants, while MerA levels remained high in both shoots and roots of plants lacking repressor. Plants with MerA expression restricted to roots were approximately as tolerant to ionic mercury as plants constitutively expressing MerA in roots and shoots. The superiority of this ROC over the previously described root-specific tobacco RB7 promoter is demonstrated.     

QUANTITATIVE LAWS IN REGENERATION : III. THE QUANTITATIVE BASIS OF POLARITY IN REGENERATION.

It is well known that a long defoliated piece of stem of Bryophyllum calycinum forms shoots only at the apical or the two apical nodes, while when such a stem is cut into as many pieces as there are nodes each node produces shoots. It is shown in this paper that the dry weight of shoots produced in the apical nodes of a long piece of stem is approximately equal to the dry weight of shoots the same stem would have produced if it had been cut into as many pieces as it possesses nodes. Hence all the material which can be used for the growth of shoots goes into the most apical part of the stem and this accounts for the polar character of regeneration in this case. It seems that the mass of basal roots produced by a piece of defoliated stem also increases with the mass of the stem.     

Age versus stage: does ontogeny modify the effect of phosphorus and arbuscular mycorrhizas on above‐ and below‐ground defence in forage sorghum?

Arbuscular mycorrhizas (AM) can increase plant acquisition of P and N. No published studies have investigated the impact of P and AM on the allocation of N to the plant defence, cyanogenic glucosides. We investigated the effects of soil P and AM on cyanogenic glucoside (dhurrin) concentration in roots and shoots of two forage sorghum lines differing in cyanogenic potential (HCNp). Two harvest times allowed plants grown at high and low P to be compared at the same age and the same size, to take account of known ontogenetic changes in shoot HCNp. P responses were dependent on ontogeny and tissue type. At the same age, P‐limited plants were smaller and had higher shoot HCNp but lower root HCNp. Ontogenetically controlled comparisons showed a P effect of lesser magnitude, and that there was also an increase in the allocation of N to dhurrin in shoots of P‐limited plants. Colonization by AM had little effect on shoot HCNp, but increased root HCNp and the allocation of N to dhurrin in roots. Divergent responses of roots and shoots to P, AM and with ontogeny demonstrate the importance of broadening the predominantly foliar focus of plant defence studies/theory, and of ontogenetically controlled comparisons.     

How genetic modification of roots affects rhizosphere processes and plant performance

Genetic modification of plants has become common practice. However, root-specific genetic modifications have only recently been advocated. Here, a review is presented regarding how root-specific modifications can have both plant internal and rhizosphere-mediated effects on aboveground plant properties and plant performance. Plant internal effects refer to pleiotropic processes such as transportation of the modified gene product. Rhizosphere-mediated effects refer to altered plant-rhizosphere interactions, which subsequently feed back to the plant. Such plant-soil feedback mechanisms have been demonstrated both in natural systems and in crops. Here how plant internal and rhizosphere-mediated effects could enhance or counteract improvements in plant properties for which the genetic modification was intended is discussed. A literature survey revealed that rice is the most commonly studied crop species in the context of root-specific transgenesis, predominantly in relation to stress tolerance. Phytoremediation, a process in which plants are used to clean up pollutants, is also often an objective when transforming roots. These two examples are used to review potential effects of root genetic modifications on shoots. There are several examples in which root-specific genetic modifications only lead to better plant performance if the genes are specifically expressed in roots. Constitutive expression can even result in modified plants that perform worse than non-modified plants. Rhizosphere effects have rarely been examined, but clearly genetic modification of roots can influence rhizosphere interactions, which in turn can affect shoot properties. Indeed, field studies with root-transformed plants frequently show negative effects on shoots that are not seen in laboratory studies. This might be due to the simplified environments that are used in laboratories which lack the full range of plant-rhizosphere interactions that are present in the field.     

Expression of the fission yeast cell cycle regulator cdc25 induces de novo shoot formation in tobacco: evidence of a cytokinin-like effect by this mitotic activator.

During the last decade, the cell cycle and its control by cyclin-dependent kinases (CDKs) has been extensively studied in eukaryotes. The regulation of CDK activity includes, among others, its activation by Cdc25 phosphatase at G2/M. However, within the plant kingdom studies of this regulation have lagged behind and a plant cdc25 homologue has not been identified yet. Here, we report on the effects of transformation of tobacco (Nicotiana tabacum L., cv. Samsun) with fission yeast (Schizosaccharomyces pombe) cdc25 (Spcdc25) on de novo plant organ formation, a process dependent on rate and orientation of cell division. On shoot-inducing medium (low 1-naphthylacetic acid (NAA), high 6-benzylaminopurine (BAP)) the number of shoots formed on internode segments cultured from transgenic plants was substantially higher than in the non-transformed controls. Anatomical observations indicated that the shoot formation process was accelerated but with no changes in the quality and sequence of shoot development. Surprisingly, and in contrast to the controls, when on root-inducing medium (high NAA, low BAP) cultured segments from transgenic plants failed to initiate hardly any roots. Instead, they continued to form shoots at low frequencies. Moreover, in marked contrast to the controls, stem segments from transgenic plants were able to form shoots even without the addition of exogenous growth regulators to the medium. The results indicate that Spcdc25 expression in culture tobacco stem segments mimicked the developmental effects caused by an exogenous hormone balance shifted towards cytokinins. The observed cytokinin-like effects of Spcdc25 transformation are consistent with the concept of an interaction between cell cycle regulators and phytohormones during plant development.     

Variation in structure and plant regeneration of Agrobacterium rhizogenes transformed and control roots of the potato cv. Bintje

Agrobacterium rhizogenes transformed and control roots of the tetraploid potato cv. Bintje were compared. Transformed roots were obtained after infection by A. rhizogenes 15834 or 1855. Both in leaf and stem segments, more roots were formed at the basal side of the segments, indicative for a polarity in root formation. As compared to control roots the transformed roots are characterized by smaller and more densely stained cells, a zone of cell division, and smaller statoliths. These characteristics are correlated with vigorous growth, high branching incidence and diminished geotropism. The plant regeneration procedure according to Ooms et al. [1] was modified. The transformed roots required less 2,4-D than control roots for the induction of shoot-competent calli. The callus and shoot induction phases were reduced from 8 and 6 weeks to 3 and 3 weeks, respectively. Upon induction, 25%, 58% and 61% of the root clones originating from tuber, stem and leaf, respectively, produced shoots, whereas all of the control roots produced shoots. Shoot outgrowth occurred on liquid MS medium in the absence of hormones.Abbreviations Ri-root Agrobacterium rhizogenes transformed root - BAP benzylaminopurine - IAA indoleacetic acid - GA₃ gibberellic acid - NAA naphthaleneacetic acid - 2,4-D 2,4 dichlorophenoxyacetic acid     

植物根系吸水机理的研究进展

近年来,植物根系吸水机理在细胞、组织和整体水平上的研究进展非常迅速,对阐明植物抗旱机制及其高效利用有限水资源途径的探讨具有重要意义。本文主要对植物根的复合结构和根系在土壤中的分布、根系中水流性质等方面的最新研究状况进行了概述,特别详细地论述了水通道蛋白的表达及功能与根系中水分运动的关系、以及根系输水的调节和根系吸水过程中的信号传导方面的研究动态,并且评价了根的复合运输模型和根系吸水的数学模型等,最后就其可能生理意义及其应用前景作了评述。     

Tissue-specific and pathogen-induced regulation of a Nicotiana plumbaginifolia beta-1,3-glucanase gene.

The Nicotiana plumbaginifolia gn1 gene encoding a beta-1,3-glucanase isoform has been characterized. The gn1 product represents an isoform distinct from the previously identified tobacco beta-1,3-glucanases. By expressing gn1 in Escherichia coli, we have determined directly that the encoded protein does, indeed, correspond to a beta-1,3-glucanase. In N. plumbaginifolia, gn1 was found to be expressed in roots and older leaves. Transgenic tobacco plants containing the 5'-noncoding region of gn1 fused to the beta-glucuronidase (GUS) reporter gene also showed maximum levels of GUS activity in roots and older leaves. No detectable activity was present in the upper part of the transgenic plants with the exception of stem cells at the bases of emerging shoots. The expression conferred by the gn1 promoter was differentially induced in response to specific plant stress treatments. Studies of three plant-bacteria interactions showed high levels of GUS activity when infection resulted in a hypersensitive reaction. Increased gene expression was confined to cells surrounding the necrotic lesions. The observed expression pattern suggests that the characterized beta-1,3-glucanase plays a role both in plant development and in the defense response against pathogen infection.     

Hormonal requirement and tissue competency for shoot organogenesis in two cultivars of Brassica napus

An investigation of the regeneration ability of explants taken from the floral stem of Brassica napus var. oleifera was performed in the winter cultivars Darmor and Bienvenu. Our purpose was to compare the regeneration ability of the two genotypes, to compare the competence of the different tissues of the stem and then to study histologically the regeneration of shoots. A strong genotypic effect was observed between the two cvs; Bienvenu had a poorer ability to produce shoots when cultured in the presence of benzyladenine: regeneration commenced later; the percentage of explants producing shoots and the number of shoots per regenerating explant were much lower. The comparison between the regeneration ability of different explants, i.e stem segments, internal stem segments, thin cell layer and peels, showed that the superficial tissues were able to regenerate roots but not shoots. Contrariwise, internal stem segments regenerated only shoots. The origin of shoots was investigated in stem segments of cv. Darmor. A kinetic histological analysis showed the basic role played by phloem and phloem-associated cells in shoot formation.     

DEVELOPMENTAL ANATOMY OF JUVENILE AND ADULT SHOOTS OF MARCGRAVIA RECTIFOLIA L

Marcgravia rectifolia L. is a dimorphic vine having distinct juvenile and adult shoots. The juvenile shoot is a climber characterized by an orthotropic growth habit, a flattened stem, adventitious roots, and ovate leaves. The adult shoot, on the other hand, possesses a plagiotropic growth habit, has a cylindrical stem, few or no adventitious roots, and lanceolate leaves. Both phases have distichous phyllotaxy, however the plastochron is shorter for the adult phase than for the juvenile. Internode elongation occurs earlier for adult shoots than for juvenile shoots. Cytological analyses show the flattened stem of the juvenile results from differential production of cells, especially in the pith region. On the other hand, internodes of the adult phase are longer than juvenile internodes, a result of more cells produced rather than longer cells. In juvenile stems a perivascular band of elongated fibers develops, while in adult stems this band consists of brachyosclereids. Both phases undergo secondary growth and have non-storied cambia. Cambial activity begins in the 6th internode of each phase. As secondary growth proceeds, the adult stem produces much more xylem than juvenile stems of the same age. Adventitious roots produced in the juvenile stem are located in vertical rows at the “corners” of flattened stems and are attachment structures aiding the climbing habit of this vine. Phase changes occur regularly in this species. The juvenile phase usually transforms into the adult, however the adult phase can spontaneously revert back into the juvenile phase. The anatomical features and the phase changes are discussed and compared to Hedera helix, a vine whose phase changes have been studied in some detail. It is suggested that the anatomical features of Marcgravia rectifolia L. including its phase changes, may provide an alternative system to study physiological changes similar to those done with Hedera helix.     

褐飞虱侵害后不同水稻品种根及地上部氮、磷、钾含量的变化

利用浓硫酸-过氧化氢消煮法,研究了不同耐、感虫品种水稻分蘖期在褐飞虱侵害胁迫后根及地上部间营养成分含量的变化情况。结果表明：褐飞虱侵害协优963后3天,根及地上部N、P、K含量、6天根及地上部N含量、9天地上部N含量在60、120头/株侵害后变化不明显;6天根及地上部P含量、6天根K含量、9天地上部P含量、9天根及地上部K含量在120头/株侵害后显著下降,60头/株侵害后变化不明显;6天地上部K含量、9天根N含量在60、120头/株侵害后均显著下降。对于协优63,3天地上部N含量、3天根及地上部P含量、6天及9天地上部N、P含量在60、120头/株侵害后变化不明显;6天根N、P含量、根及地上部K含量、9天根N含量在120头/株侵害后显著下降,60头/株侵害后下降不明显;3天、9天根及地上部K含量、9天根部P含量在60、120头/株侵害后均显著下降。表明不同水稻品种体内不同营养物质含量在褐飞虱侵害后变化不同,协优63较协优963敏感;K含量变化最明显,其次为P,最后为N;而且根比地上部对褐飞虱的反应敏感。     

Relationship of Apical Dominance to the Nutrient Accumulation Pattern in Pisum sativum var. Alaska

Decapitation of the pea plant resulted in the growth of all the lateral shoots. The initial growth of all lateral buds was somewhat similar. The differential growth rates developed later on. The pattern of growth of lateral shoots varied with the age of the plant when decapitation was performed. The basal shoots dominated when the plants were decapitated at the 2-leaf stage. At 3-leaf stage decapitation resulted in the dominance of shoot 5. Decapitation at 4-or-more-leaf stage resulted in the eventual dominance of the suhterminal lateral shoot. As a rule P-32 moved to the most actively growing part of the plant, i.e. apex in intact vegetative plant, the growing lateral shoots in a decapitated plant, the elongating subapical parts of the stem and the roots. The various metabolic sinks seemed to compete actively for this nutrient, therefore P-32 accumulation in any particular growing region of the plant was taken as an indicator of nutrient utilization potential of that part. The stem apex of an intact plant seemed to loose its dominance with the increasing age of the plant. The loss of apical dominance was almost complete during the reproductive phase of the plant, during which the upper lateral shoots initiated growth. Their growth, however, was inhibited soon because of competition with the other developing sinks, viz., the flower and the fruit. The amount of soluble carbohydrates in various parts of the pea plant followed essentially the same pattern as did P-32 accumulation. These distribution patterns were apparently correlated with the growth of the plant.     

Ultrastructure of unique plasmodesmata in Selaginella willdenowii

Summary All meristematic cells of dorsal angle meristems of Selaginella willdenowii Baker cultured in vitro possessed expanded plasmodesmata, unlike the conventional plasmodesmata which were also found in these cells. Apical tissues of stems, roots and shoots from intact plant also possessed these structures though to a lesser degree than angle meristems. Root tips and stem apices had numerous conventional plasmodesmata in their walls. The expanded plasmodesmata, with their marked symmetry, represent a unique variation of plasmodesmatal structure.This study was partially supported by NSF Grant GB 37945 to Zachary S. Wochok.