Source of Induction and Sites of Primary Phloem Fibre Differentiation in Coleus blumei

The fact that fibre induction is strictly basipetal is usedhere to study the long distance effect of young growing leaveson acropetal primary phloem fibre differentiation. Excisionexperiments are used to show that young leaves induce fibredifferentiation around a wound a few internodes below them.No fibers appeared in the younger internodes between the youngleaves and the mature internode. Young leaves yield shorterfibres than those which differentiate under mature leaves, indicatingthat more than one stimulus is involved in the induction process.Fibre differentiation in nodes is faster than in subtendinginternodes. Wounding causes rapid differentiation of phloemfibres above and beside the wound. The rapid differentiationin the node as well as around the wound can be understood asan effect of a high local concentration of inductive stimulus.It is proved that the ability of the cells to respond to inductiondetermines the pattern of their differentiation which in thiscase is counter-directional to the induction. Coleus blumei, phloem fibres, differentiation     

Regulation of Auxin Levels in Coleus blumei by Ethylene

An investigation of the effects of ethylene pretreatment on several facets of auxin metabolism in Coleus blumei Benth “Scarlet Rainbow” revealed a number of changes presumably induced by the gas. Transport of indoleacetic acid-1-¹⁴C in excised segments of the uppermost internode was inhibited by about 50%. Decarboxylation of indoleacetic acid-1-¹⁴C by enzyme breis was not affected by the pretreatment. Levels of extractable native auxin in upper leaf and apical bud tissue of the pretreated plants were approximately one-half of those present in untreated plants. The rate of formation of auxin from tryptophan by enzyme breis from pretreated plants was approximately one-half that occurring in incubation mixtures containing the enzyme system from untreated plants. The conjugation of indoleacetic acid-1-¹⁴C in a form characterized chromatographically as indoleacetylaspartic acid was increased 2-fold in the upper stem region of plants pretreated with ethylene.     

The Effect of Kinetin on the Occurrence of Acid Auxin in Coleus blumei

Excised shoots and potted plants of Coleus blumei Benth, were subjected to different treatments with kinetin solutions. Control treatments were made with water. Free and bound auxin were extracted with ether. The acid fractions were purified by electrophoresis to remove all traces of kinetin, and were then analyzed with the Avena straight-growth test. As compared with the controls, kinetin treatment increases the bound auxin, whereas the corresponding free auxin is unchanged. Also methanol extracts of treated stems contain more acid auxin than corresponding extracts of water-treated stems. This indicates that on methanol extraction not only free auxin but also some bound auxin is obtained. The extracted auxin behaves like indoleacetic acid in paper chromatography with four different solvent systems, as well as in gel filtration through Sephadex. New formation or decreased breakdown of auxin seem the most likely explanations for the observed effects of kinetin.     

Gibberellin Effect on Tryptophan Metabolism, Auxin Destruction, and Abscission in Coleus

Application of gibberellic acid (GA) to the apical region of the stem enhances ¹⁴CO₂ release from tryptophan-l-¹⁴C in cell free preparations of the apical region. Although GA when applied to the apical region markedly accelerates abscission rates of debladed petioles at the 4th node, the enhancement effect on tryptophan metabolism appears to be restricted to the apical bud region. The increased levels of diffusible auxin in Coleus stems, observed earlier by Muir and Valdovinos (1965), appear to be due to the GA effect on auxin precursor conversion rather than to an altered rate of auxin destruction. GA pre-treatment does not significantly alter destruction rates of auxin in the stem tissue. This is demonstrated by the release of ¹⁴CO₂ from IAA-1-¹⁴C by sections of internode tissue. While a multiple deblading pattern retards abscission of debladed petioles considerably, application of GA to debladed petioles at the basal region of the stem restores the normal rates of abscission at debladed distal nodes. No significant change in the abscission rates at treated nodes is observed. The GA effect on abscission at distal nodes is attributed to the effect of the growth substance on auxin precursor conversion in the apical region. In these experiments, as in the case of plants treated in the apical region with GA, auxin destruction rates in the stem are not altered significantly.     

Polarity of IAA Effect on Sieve-Tube and Xylem Regeneration in Coleus and Tomato Stems

A technique is described for the processing of regenerated xylem and sieve tubes from the same wound area for microscopic and quantitative comparison.

Regeneration was examined in internodes of 2 developmental stages in Coleus: internode 2, elongating, characteristic of primary growth; and internode 5, non-elongating, characteristic of secondary growth.

Transport of indoleacetic acid (IAA) in excised number 5 internodes of Coleus is strictly polar, in a basipetal direction, judging by a regeneration bioassay involving both sieve tube strands and xylem cells. Similar results were obtained with tomato.

If isolated number 5 Coleus internodes are not treated with hormone, they regenerate no xylem cells and a small number of sieve tube strands. With increasing concentrations of IAA added apically, the number of regenerated sieve tube strands (and, with higher concentrations, of xylem cells) increases progressively up to 1% IAA, the highest concentration applied.

Internode 2 of Coleus regenerates fewer xylem cells or sieve tube strands than internode 5, whether on the otherwise intact plant or with a given concentration of IAA added apically. The amount of regenerated xylem increases with added apical IAA, except that the highest concentration gives no further increase. The number of xylem cells regenerated in intact plants occurs at the same interpolated IAA concentration as in number 5 internodes. No concentration of IAA tried provided replacement of intact number of sieve tube strands in internode 2.

IAA can exert a regenerative stimulus on both xylem and sieve tubes in the area immediately adjacent to the site of its application.

     

Phloem Loading in Coleus blumei in the Absence of Carrier-Mediated Uptake of Export Sugar from the Apoplast

Phloem loading in Coleus blumei Benth. leaves cannot be explained by carrier-mediated transport of export sugar from the apoplast into the sieve element-companion cell complex, the mechanism by which sucrose is thought to load in other species that have been studied in detail. Uptake profiles of the export sugars sucrose, raffinose, and stachyose into leaf discs were composed of two components, one saturable and the other not. Saturable (carrier-mediated) uptake of all three sugars was almost completely eliminated by the inhibitor p-chloromercuribenzenesulfonic acid (PCMBS). However, when PCMBS was introduced by transpiration into mature leaves it did not prevent accumulation of ¹⁴C-photosynthate in minor veins or translocation of labeled photosynthate from green to nonchlorophyllous regions of the leaf following exposure to ¹⁴CO₂. The efficacy of introducing inhibitor solutions in the transpiration stream was proven by observing saffranin O and calcofluor white movement in the minor veins and leaf apoplast. PCMBS introduced by transpiration completely inhibited phloem loading in tobacco leaves. Phloem loading in C. blumei was also studied in plasmolysis experiments. The carbohydrate content of leaves was lowered by keeping plants in the dark and then increased by exposing them to light. The solute level of intermediary cells increased in the light (phloem loading) in both PCMBS-treated and control tissues. A mechanism of symplastic phloem loading is proposed for species that translocate the raffinose series of oligosaccharides.     

The biosynthesis of rosmarinic acid in suspension cultures of Coleus blumei

Suspension cultures of Coleus blumei accumulate very high amounts of rosmarinic acid, an ester of caffeic acid and 3,4-dihydroxyphenyllactate, in medium with elevated sucrose concentrations. Since the synthesis of this high level of rosmarinic acid occurs in only five days of the culture period, the activities of the enzymes involved in the biosynthesis are very high. Therefore all the enzymes necessary for the formation of rosmarinic acid from the precursors phenylalanine and tyrosine could be isolated from cell cultures of Coleus blumei: phenylalanine ammonia-lyase, cinnamic acid 4-hydroxylase, hydroxycinnamoyl:CoA ligase, tyrosine aminotransferase, hydroxyphenylpyruvate reductase, rosmarinic acid synthase and two microsomal 3- and 3-hydroxylases. The main characteristics of these enzymes of the proposed biosynthetic pathway of rosmarinic acid will be described.Abbreviations DHPL 3,4-dihydroxyphenyllactate - DHPP 3,4-dihydroxyphenylpyruvate - pHPL 4-hydroxyphenyllactate - pHPP 4-hydroxyphenylpyruvate - RA rosmarinic acid     

彩叶草红色素的理论性质

天然色素可从动植物相应组织中提取。从吊竹梅（Zebrina pendula Schnizl．）中已得到非常稳定的天然色素,从Acalypha uilkesiana中得到大量的花青苷色素,从Setcrease purpurea中也得到非常稳定的天然紫红色素。彩叶草（Coleus blumei Benth）含有大量类黄酮物质,目前,对其色素的理化性质没有详细的报道。本文探讨彩叶草红色素的理化性质,旨在为该色素的开发应用提供科学依据。     

The Role of Gibberellin, Abscisic Acid, and Auxin in the Regulation of Developing Wheat Grains

Three forms of inhibition of germination of developing wheatgrains are described. One, due to the outer pericarp, may notinvolve growth substances. The others occur in the embryo itselfand are due also to the other grain tissues surrounding theembryo. Experiments with applied growth substances suggest thatthese may be regulated by a balance of endogenous gibberellinsand abscisic acid, but the results of extraction experimentsshow limited correlation with germination experiments, and indicatethat auxin may also be inhibitory.     

Phloem as Capacitor: Radial Transfer of Water into Xylem of Tree Stems Occurs via Symplastic Transport in Ray Parenchyma

The transfer of water from phloem into xylem is thought to mitigate increasing hydraulic tension in the vascular system of trees during the diel cycle of transpiration. Although a putative plant function, to date there is no direct evidence of such water transfer or the contributing pathways. Here, we trace the radial flow of water from the phloem into the xylem and investigate its diel variation. Introducing a fluorescent dye (0.1% [w/w] fluorescein) into the phloem water of the tree species Eucalyptus saligna allowed localization of the dye in phloem and xylem tissues using confocal laser scanning microscopy. Our results show that the majority of water transferred between the two tissues is facilitated via the symplast of horizontal ray parenchyma cells. The method also permitted assessment of the radial transfer of water during the diel cycle, where changes in water potential gradients between phloem and xylem determine the extent and direction of radial transfer. When injected during the morning, when xylem water potential rapidly declined, fluorescein was translocated, on average, farther into mature xylem (447 ± 188 µm) compared with nighttime, when xylem water potential was close to zero (155 ± 42 µm). These findings provide empirical evidence to support theoretical predictions of the role of phloem-xylem water transfer in the hydraulic functioning of plants. This method enables investigation of the role of phloem tissue as a dynamic capacitor for water storage and transfer and its contribution toward the maintenance of the functional integrity of xylem in trees.Physiological and hydraulic functioning of the two long-distance transport systems in trees, xylem and phloem, have intrigued plant researchers for more than a century. Since the pioneering work of Dixon and Joly (1895; cohesion-tension theory for xylem) and Münch (1930; pressure flow hypothesis for phloem), the majority of studies have investigated these systems independently of each other. Although the work of Stout and Hoagland (1939) as well as Biddulph and Markle (1944) laid the foundation for the physiological nexus between xylem and phloem, it is only recently that we have begun to understand the importance of the hydraulic nexus (Hölttä et al., 2006, 2009; Sevanto et al., 2011, 2014). Processes related to both nexus occur in parallel, and here the term physiological nexus covers all metabolite exchange, including the bidirectional flow of amino acids, minerals, and carbohydrates (Wardlaw, 1974; Ferrier et al., 1975; Pfautsch et al., 2009, 2015; De Schepper et al., 2013; for review, see van Bel, 1990, 2003). The term hydraulic nexus refers to the function of phloem as a capacitor, where water stored in phloem moves into xylem vessels to maintain the integrity of the transpiration stream (Zweifel et al., 2000, and refs. therein). Throughout this article, we use the term phloem collectively for cells that make up the transport phloem of woody plants (including sieve element/companion cell complexes, parenchyma cells, etc.), as opposed to collection and release phloem tissue, which differ in structure and function. Transport phloem is characterized by the retention of “high hydrostatic pressure by retrieval of leaked osmotica accompanied by water flux” (Patrick, 2013).According to the cohesion-tension theory, water in xylem vessels is constantly under tension and moves in a metastable state from roots to leaves along a hydrostatic pressure gradient. Depending on both the availability of soil moisture and the vapor pressure deficit of the atmosphere, this tension can exceed the cohesive forces that bind water molecules, resulting in the formation of a gas void that, after expanding, can lead to rupture of the water column inside individual vessels (termed cavitation; Zimmermann, 1983). Once cavitated, vessels become dysfunctional, and the transport of water and nutrients to leaves declines. However, water stored in woody tissues of trees can be mobilized to alleviate the risk of cavitation, and recent theory suggests that both water and carbohydrates from phloem may aid in the reversal of vessel embolism (i.e. air intrusion), although the evidence is indirect (Salleo et al., 2009; Brodersen et al., 2010; Nardini et al., 2011).All parts of plants have a water storage capacity (symplastic and apoplastic), and this capacitance increases with tree size and age (Phillips et al., 2003). The ability to mobilize stored water varies according to the force required to drag it out of storage (Holbrook, 1995). One-half century ago, Reynolds (1965) highlighted the importance of the volume of internally stored water to support the transpiration of trees. Since then, studies have quantified the fraction of stored water in total daily transpiration for a range of tree species. This fraction varies between 2% and 20% (Tyree and Yang, 1990; Čermák et al., 2007, and refs. therein; Barnard et al., 2011; Pfautsch and Adams, 2013) and is generally smaller in angiosperms compared with gymnosperms, where a maximum fraction of 50% was reported for Pinus sylvestris (Waring et al., 1979). Given that the daily water use of large adult trees can easily reach 260 to 380 L (Čermák et al., 2007; Pfautsch et al., 2011), considerable volumes of stored water must be mobilized from and restored back into capacitors on a daily basis. Remobilization of stored water also can prolong stomatal opening and thus increase carbon gain (Goldstein et al., 1998).The volume of stored water released depends on the elasticity of the storage tissue, its connectivity to xylem vessels, and the gradient of water potential (ψ) between the storage tissue and vessels. Cells with elastic walls represent ideal capacitors because they can change their volume as a consequence of small changes in ψ. Thus, phloem, cambium, and juvenile xylem cells are well suited for water storage and release (Yang and Tyree, 1992; Zweifel et al., 2014). The magnitude of release and refill of stored water in trees can be approximated by separately measuring the change in thickness of phloem and xylem during a diel cycle using high-precision dendrometers (Zweifel et al., 2014). Whitehead and Jarvis (1981) have calculated that around 90% of the diurnal change in stem radius can be attributed to changes in the water content of cambial and phloem tissues. To date, it is commonly accepted that tree bark, independent of the wood below, swells during the night and shrinks during the day (Zweifel et al., 2000), reflecting the water flow dynamics that characterize the dynamic exchange of water between phloem and xylem.Phloem and xylem tissues are separated by rows of intermediary cambial cells. However, depending on the species, phloem and xylem are connected through uniseriate or multiseriate strands of radially aligned ray parenchyma cells, commonly termed wood rays. These rays have been shown to be capable of symplastic water transport through plasmodesmata (Höll, 1975). Based on measurements of radial conductance, Sevanto et al. (2011) suggested that aquaporins also might be involved in the radial transfer of water. Both theoretical and experimental approaches have been developed to better understand the dynamic exchange of water between xylem and phloem. Hölttä et al. (2006, 2009) developed a model based on Münch’s hypothesis and included a term that represents the hydraulic connection between the two tissue types. Through incorporating this term, model outputs suggest the occurrence of a constant exchange of water between xylem and phloem along gradients of ψ. However, some authors suggested that changes in ψ of xylem alone might be insufficient to account for the observed diurnal shrinkage and swelling of bark (Sevanto et al., 2003). Along this line of argument, loading and unloading of carbohydrates in phloem tissue has been suggested to further impact the radial transfer of water and associated changes in bark thickness (Mencuccini et al., 2013).Nevertheless, to date, all approaches remain indirect, and the routes of water transfer between phloem and xylem have yet to be determined. Here, we present a technique that enables the visualization of water transfer from phloem to xylem tissues and resolves the apoplastic and symplastic pathways and cell types. The method involves the injection of an aqueous solution that contains fluorescent dye into phloem followed by analyses of woody tissues using confocal laser scanning microscopy. We assess the effectiveness of three different dyes to stain possible transfer pathways. We also introduce dye during different time intervals of the diel transpiration cycle to test the effect of predicted dynamic changes in ψ between phloem and xylem on the transfer processes. We hypothesized that radial transfer of water would be most pronounced during periods where conditions of the hydraulic nexus between phloem and xylem differ the most. These differences are expected during high rates of transpiration that cause a steep decline in xylem ψ, commonly observed during morning hours. We use leaf water potential (ψ_L) and high-precision dendrometer measurements to identify relevant time intervals. The simultaneous assessment of ψ_L and the independent diameter fluctuation of phloem and xylem may provide empirical evidence for the role of phloem as a water storage capacitor that helps mitigate increasing tension in the transpiration stream.     

Growth and production characteristics of permeabilized Coleus blumei cells in immobilized fed-batch culture

Summary Permeabilized Coleus blumei cells were cultivated in an immobilized state to study the effect of dimethyl sulfoxide (DMSO) concentrations and growth regulators on cell growth and rosmarinic acid (RA) production characteristics. Luffa (the fibrous skeleton of mature fruit of Luffa cylindrica) was a good support matrix for cell immobilization because of its high void volume. Maximum cell loading capacity was 1.33 g dry cell weight (DCW)/g dry Luffa. The experiments were done in shake flasks with no free medium. The medium was supplied in a fed-batch mode to avoid the flotation of Luffa pieces. The sucrose in the medium was completely hydrolyzed to glucose and fructose without any sugar accumulation in the medium. The cell viability was slightly higher in the cells on top of the Luffa than those in the middle. Cell growth rate and rosmarinic acid (RA) production were approximately half that obtained in cell suspension cultures. Cell yield (g DCW/g glucose) was similar to that of cell suspension cultures. The absence of growth regulators did not promote an increase of RA production but did decrease the cell mass. The second step preconditioning with 0.5% DMSO did not improve the cell's adaptability to higher DMSO concentrations and the cell mass did not increase with 2.5% DMSO.     

Arsenic Speciation in Phloem and Xylem Exudates of Castor Bean

How arsenic (As) is transported in phloem remains unknown. To help answer this question, we quantified the chemical species of As in phloem and xylem exudates of castor bean (Ricinus communis) exposed to arsenate [As(V)], arsenite [As(III)], monomethylarsonic acid [MMA(V)], or dimethylarsinic acid. In the As(V)- and As(III)-exposed plants, As(V) was the main species in xylem exudate (55%–83%) whereas As(III) predominated in phloem exudate (70%–94%). The ratio of As concentrations in phloem to xylem exudate varied from 0.7 to 3.9. Analyses of phloem exudate using high-resolution inductively coupled plasma-mass spectrometry and accurate mass electrospray mass spectrometry coupled to high-performance liquid chromatography identified high concentrations of reduced and oxidized glutathione and some oxidized phytochelatin, but no As(III)-thiol complexes. It is thought that As(III)-thiol complexes would not be stable in the alkaline conditions of phloem sap. Small concentrations of oxidized glutathione and oxidized phytochelatin were found in xylem exudate, where there was also no evidence of As(III)-thiol complexes. MMA(V) was partially reduced to MMA(III) in roots, but only MMA(V) was found in xylem and phloem exudate. Despite the smallest uptake among the four As species supplied to plants, dimethylarsinic acid was most efficiently transported in both xylem and phloem, and its phloem concentration was 3.2 times that in xylem. Our results show that free inorganic As, mainly As(III), was transported in the phloem of castor bean exposed to either As(V) or As(III), and that methylated As species were more mobile than inorganic As in the phloem.Arsenic (As) is an environmental and food chain contaminant that has attracted much attention in recent years. Soil contamination with As may lead to phytotoxicity and reduced crop yield (Panaullah et al., 2009). Food crops are also an important source of inorganic As, a class-one carcinogen, in human dietary intake, and there is a need to decrease the exposure to this toxin (European Food Safety Authority, 2009). Paddy rice (Oryza sativa) is particularly efficient in As accumulation, which poses a potential risk to the population based on a rice diet (Meharg et al., 2009; Zhao et al., 2010a). Other terrestrial food crops generally do not accumulate as much As as paddy rice; however, where soils are contaminated, relatively high concentrations of As in wheat (Triticum aestivum) grain have been reported (Williams et al., 2007; Zhao et al., 2010b). On the other hand, some fern species in the Pteridaceae family are able to tolerate and hyperaccumulate As in the aboveground part to >1,000 mg kg⁻¹ dry weight (e.g. Ma et al., 2001; Zhao et al., 2002); these plants offer the possibility for remediation of As-contaminated soil or water (Salido et al., 2003; Huang et al., 2004). A better understanding of As uptake and long-distance transport, metabolism, and detoxification is needed for developing strategies for mitigating As contamination, through either decreased As accumulation in food crops or enhanced As accumulation for phytoremediation.The pathways of As uptake by plant roots differ between different As species; arsenate [As(V)] enters plant cells via phosphate transporters, whereas arsenite [As(III)] is taken up via some aquaporins (for review, see Zhao et al., 2009). In rice, a silicic acid efflux protein also mediates As(III) efflux toward stele for xylem loading (Ma et al., 2008). Methylated As species, such as monomethylarsonic acid [MMA(V)] and dimethylarsinic acid [DMA(V)], which may be present in the environment as products of microbial or algal methylation of inorganic As or from past uses of methylated As pesticides, are taken up by rice roots partly through the aquaporin NIP2;1 (for nodulin 26-like intrinsic protein; also named Lsi1; Li et al., 2009). Once inside plant cells, As(V) is reduced to As(III), possibly catalyzed by As(V) reductase(s) such as the plant homologs of the yeast (Saccharomyces cerevisiae) ACR2 (Bleeker et al., 2006; Dhankher et al., 2006; Ellis et al., 2006; Duan et al., 2007). As(III) has a high affinity to thiol (-SH) groups and is detoxified by complexation with thiol-rich phytochelatins (PCs; Pickering et al., 2000; Schmöger et al., 2000; Raab et al., 2005; Bluemlein et al., 2009; Liu et al., 2010). As(III)-PC complexation in roots was found to result in reduced mobility for efflux and for long-distance transport, possibly because the complexes are stored in the vacuoles (Liu et al., 2010). Excess As(III) causes cellular toxicity by binding to the vicinal thiol groups of enzymes, such as the plastidial lipoamide dehydrogenase, which has been shown to be a sensitive target of As toxicity (Chen et al., 2010). The As hyperaccumulating Pteris species differ from nonhyperaccumulating plants because of enhanced As(V) uptake (Wang et al., 2002; Poynton et al., 2004), little As(III)-thiol complexation (Zhao et al., 2003; Raab et al., 2004), and efficient xylem loading of As(III) (Su et al., 2008). Recently, an As(III) efflux transporter, PvACR3, has been found to play an important role in As(III) detoxification by transporting As(III) into vacuoles in Pteris vittata (Indriolo et al., 2010).With the exception of As hyperaccumulators, most plant species have a limited root-to-shoot translocation of As (Zhao et al., 2009). The chemical species of As in xylem exudate have been determined in a number of plant species. As(III) was found to be the predominant species (80%–100%) in the xylem sap of rice, tomato (Solanum lycopersicum), cucumber (Cucumis sativus), and P. vittata even when these plants were fed As(V) (Mihucz et al., 2005; Xu et al., 2007; Ma et al., 2008; Su et al., 2010), suggesting that As(V) is reduced in roots before being loaded into the xylem. In other plant species, such as Brassica juncea (Pickering et al., 2000), wheat, and barley (Hordeum vulgare; Su et al., 2010), As(V) accounted for larger proportions (40%–50%) of the total As in the xylem sap. Studies using HPLC-inductively coupled plasma (ICP)-mass spectrometry (MS) coupled with electrospray (ES)-MS showed no evidence of As(III)-thiol complexation in the xylem sap of sunflower (Helianthus annuus; Raab et al., 2005). When rice plants were exposed to MMA(V) or DMA(V), both As species were found in the xylem sap (Li et al., 2009). Generally, methylated As species are taken up by roots at slower rates than inorganic As, but they are more mobile during the xylem transport from roots to shoots (Marin et al., 1992; Raab et al., 2007; Li et al., 2009).It has been shown that phloem transport contributes substantially to As accumulation in rice grain (Carey et al., 2010). However, little is known about how As is transported in phloem (Zhao et al., 2009). There are no reports on the chemical species of As in phloem exudate. The speciation of As in phloem is important because it dictates how As is loaded in the source tissues and unloaded in the sink tissues, such as grain. Questions with regard to the oxidation state, methylation, and complexation of As in phloem sap remain to be answered. Unlike xylem sap, phloem sap is much more difficult to obtain in sufficient quantities for analysis. In this study, we investigated As speciation in phloem and xylem exudates of castor bean (Ricinus communis), which is widely used as a model plant to investigate phloem transport of solutes (e.g. Hall et al., 1971; Hall and Baker, 1972; Allen and Smith, 1986; Bromilow et al., 1987).     

Between Xylem and Phloem: The Genetic Control of Cambial Activity in Plants

Abstract: Post-embryonic development is controlled by two types of meristems: apical and lateral. There has been considerable progress recently in understanding the function of root and shoot apical meristems at the molecular level. Knowledge of analogous processes in the lateral, or secondary, meristems, i.e. the vascular cambium or cork cambium, is, however, rudimentary. This is despite the fact that much of the diversity in the plant kingdom is based on the differential functions of these meristems, emphasizing the importance of lateral meristems in the development of different plant forms. The vascular cambium is particularly important for woody plants, but it also plays an important role during the development of various herbaceous species, such as Arabidopsis thaliana. In this review, we focus on the two basic functions of cambial activity: cell proliferation and pattern formation.     

Effect of Auxin and Gibberellin on Sporulation in Yeast

Effect of auxin and gibberellic acid on sporulation of a yeast, Saccharomyces ellipsoideus, was studied. When added to the sporulation media, gibberellic acid promoted sporulation. The sporulation rate was higher in the medium SGV with vitamins than in the vitamin-free SG, but the effect of gibberellic acid was more pronounced in the latter. Auxin (IAA, 2,4-D, and NAA) inhibited sporulation in SGV, but promoted it in SG. This sporulation-promoting effect of IAA was reversed by an antiauxin, 2,4,6-T. Preculturing in the presence of added IAA increased sporulation. Added to the preculture medium, gibberellic acid alone showed little effect on sporulation, but in combination with IAA it enhanced sporulation conspicuously. IAA and gibberellic acid were effective in sporulation promotion only when added before the nuclear enlargement occurred in sporulation culture.     

Carbohydrate Metabolism in Photosynthetic and Nonphotosynthetic Tissues of Variegated Leaves of Coleus blumei Benth

Mature, variegated leaves of Coleus blumei Benth. contained stachyose and other raffinose series sugars in both green, photosynthetic and white, nonphotosynthetic tissues. However, unlike the green tissues, white tissues had no detectable level of galactinol synthase activity and a low level of sucrose phosphate synthase indicating that stachyose and possibly sucrose present in white tissues may have originated in green tissues. Uptake of exogenously supplied [¹⁴C]stachyose or [¹⁴C]sucrose into either tissue type showed conventional kinetic profiles indicating combined operation of linear first-order and saturable systems. Autoradiographs of white discs showed no detectable minor vein labelling with [¹⁴C]stachyose, but some degree of vein labeling with [¹⁴C]sucrose. Autoradiographs of green discs showed substantial vein loading with either sugar. In both tissues, p-chloromercuribenzenesulfonic acid had no effect on the linear component of sucrose or stachyose uptake but inhibited the saturable component. Both tissues contained high levels of invertase, sucrose synthase and α-galactosidase and extensively metabolized exogenously supplied ¹⁴C-sugars. In green tissues, label from exogenous sugars was recovered as raffinose-series sugars. In white tissues, exogenous sugars were hydrolysed and converted to amino acids and organic acids. The results indicate that variegated Coleus leaves may be useful for studies on both phloem loading and phloem unloading processes in stachyose-transporting species.