A two-step control of basic and acidic peroxidases and its significance for growth and development

A generalized two-step and interdependent control of basic and acidic peroxidases (EC 1.11.1.7) is observed in plant responses to different physical and chemical stimuli. An interpretative model consisting of a pathway of reactions is presented on the basis of our own data and the literature. Stress-induced membrane depolarization would generate different species of free radicals and peroxides, which in turn initiate lipid peroxidation. The degradation of cell membranes is suggested to bring about rapid changes in ionic fluxes (especially release of K⁺ which would result in an enhanced endogenous Ca/K ratio) and in leakage of solutes (among them electron donors such as ascorbic acid and phenolic substances). The increased intracellular relative calcium level results in: 1) activated secretion of basic peroxidases into the free space where, in association with the electron donors and maybe with the circulating indole-3-acetic acid (IAA), they eliminate the peroxides; and 2) facilitated binding of basic peroxidases to membrane structures allowing a role as 1-aminocyclopropane-1-carboxylic acid (ACC)-oxidases. The resulting IAA and ACC oxidase-mediated changes in ethylene production would further induce (this time through the protein synthesis machinery) an increase in activity of phenylalanine ammonia-lyase (EC 4.31.5) and acidic peroxidases. The resulting lignification and cell wall rigidification determines the growth and/or the developmental response to the initial stress.     

Growth regulation, plastid differentiation and the development of a photosynthetic system in cultured carrot root explants as influenced by exogenous sucrose and various phytohormones

Chromoplasts, which exist in the cells of freshly isolated carrot root explants, seemed to be transformed in thylakoid containing plastids, and chlorophyll formation was initiated if the explants were cultured in a liquid medium containing inositol and IAA as a hormonal supplement. This process was intensified when kinetin was also added, but no dependence on a sucrose supply could be found.A sucrose supply of 2% in conjunction with the combination of all three hormones, however, was needed to achieve maximal thylakoid formation including stacking in individual chloroplasts and for the very extensive chloroplast multiplication in explants growing with high cell division activity. It should be noted that the number of plastids per cell is strongly increased by the sucrose supplement which leads also to starch accumulation. However, no transformation into chloroplasts occurred without the hormonal stimulus.     

Starch and triacylglycerol metabolism related to somatic embryogenesis in Papaver orientale tissue cultures

During somatic embryogenesis in Papaver orientale tissue cultures a permanent starch accumulation and a transient triacylglycerol accumulation were observed. The degradation of the lipids during plantlet development from embryoids was paralleled by an activity increase of the glyoxylate-cycle enzymes malate synthase (EC 4.1.3.2) and isocitrate lyase (EC 4.1.3.1). Fat accumulation and breakdown was interpreted as a reflection of seed formation and germination during normal development.     

Anaerobic fermentation in Cyanidium caldarium

Cyanidium caldarium cells kept anaerobically in the dark have no detectable gas exchange and form exclusively d-(-)-lactate at the expense of their starch content. The addition of acetate enhances both starch breakdown and lactate accumulation by a factor of two. During prolonged anaerobiosis Cyanidium is able to keep its energy charge at a low, but fairly constant level. The adenylate-kinase equilibrium, however, undergoes considerable changes, indicative of a regulatory mechanism which maintains a high energy charge particularly by accumlating AMP instead of ADP.     

High frequency callus formation from maize protoplasts

Summary A solid feeder layer technique was developed to improve callus formation of Black Mexican Sweet maize (Zea mays L.) suspension culture protoplasts. Protoplasts were plated in 0.2 ml liquid media onto a cellulose nitrate filter on top of agarose-solidified media in which Black Mexican Sweet suspension feeder cells were embedded. Callus colony formation frequencies exceeding 10% of the plated protoplasts were obtained for densities of 10³–10⁵ protoplasts/ 0.2 ml, which was 100- to 1,000-fold higher than colony formation frequencies obtained for conventional protoplast plating methods such as liquid culture or embedding in agarose media. Compared with conventional methods, the feeder layer method gave higher colony formation frequencies for three independently maintained Black Mexican Sweet suspension lines. Differences among the three lines indicated that colony formation frequencies might also be influenced by the suspension culture maintenance regime and length of time on different 2,4-dichlorophenoxyacetic acid concentrations. The callus colony formation frequency reported is an essential prerequesite for recovering rare mutants or genetically transformed maize protoplasts.     

Adventitious Bud Formation from Bulb-scale Explants of Lilium speciosum Thunb. in vitro Effects of aminoethoxyvinyl-glycine, 1-aminocyclopropane-1-carboxylic acid,and ethylene

Several representatives of marine brown macroalgae (Phaeophyceae) including Fucus serratus L., Fucus spiralis L. and Fucus vesiculosus L. as well as Laminaria digitata (Huds.) Lamour., Laminaria hyperborea (Gunn.) Foslie and Laminaria saccharina (L.) Lamour. were investigated with particular regard to features of biosynthesis of the storage product mannitol. The respective catalytic system involved in the last step of mannitol formation, mannitol-1-phosphate dehydrogenase, appears to be a cytoplasmic enzyme as may be judged from the degree of correlation with the chloroplast key enzyme ribulose-1,5-bisphosphate carboxylase in different tissues of Laminaria digitata and Laminaria saccharina. Activity of mannitol-1-phosphate dehydrogenase in vitro is not affected by mannitol-l-phosphate or free mannitol, suggesting that mannitol biosynthesis in vivo) is mainly controlled by the environment and/or developmental stage. Certain inorganic ions such as NO₃^- (including K⁺) exert a strong influence on the activity of mannitol1-phosphate dehydrogenase thus suggesting that the intracellular pools of stored NO₃^- and mannitol are confined to spatially separated cellular compartments.     

Segment- and nest-specific determination in the histoblasts of the housefly

Summary Using a novel grafting procedure for histoblasts, we have transplanted the fifth dorsal or ventral histoblast nests to heterotopic positions in the abdomen of the prepupa of the housefly to find out how rigid are these imaginai cells in their commitment to form their respective segmental pattern. Our results clearly show that these histoblasts survive in their new positions and form patterns according to their original determined state.     

Metabolic links between the biosynthesis of pyrrolizidine alkaloids and polyamines in root cultures of Senecio vulgaris

Isotope feeding and inhibitor experiments were performed in order to elucidate the pathway common to polyamine and alkaloid biosynthesis in root cultures of Senecio vulgaris L. -Difluoromethylarginine, a specific inhibitor of arginine decarboxylase, prevented completely the incorporation of radioactivity from [¹⁴C]arginine and [¹⁴C]ornithine into spermidine and the pyrrolizidine alkaloid senecionine N-oxide. In contrast, -difluoromethylornithine, a specific ornithine-decarboxylase inhibitor, had no effect on the flow of radioactivity from labelled ornithine and arginine into polyamines and alkaloids. Thus, putrescine, the common precursor of polyamines and pyrrolizidine alkaloids, is exclusively derived via the arginine-agmatine route. Ornithine is rapidly transformed into arginine. Recycling of the guanido moiety of agmatine back to ornithine can be excluded. Putrescine and spermidine were found to be reversibly interconvertable and to excist in a highly dynamic state. In contrast, senecionine N-oxide did not show any turnover but accumulated as a stable metabolic product. In-vivo evidence is presented that the carbon flow from arginine into the polyamine/alkaloid pathway may be controlled by spermidine. The possible importance of the metabolic coupling of pyrrolizidine-alkaloid biosynthesis to polyamine metabolism is discussed.Abbreviations DFMA D,l--difluoromethylarginine - DFMO D,l--difluoromethylornithine - FW fresh weight     

Expression of gooseberry-proximal in the Drosophila developing nervous system responds to cues provided by segment polarity genes

Summary Segment polarity genes define the cell states that are required for proper organization of each metameric unit of the Drosophila embryo. Among these, the gooseberry locus has been shown to be composed of two closely related genes which are expressed in an overlapping single-segment periodicity. We have used specific antibodies raised against the protein product of the gooseberry proximal (gsb-p) gene to determine the spatial distribution of this antigen in wild type embryos, and to monitor the effects of segment polarity mutants on the pattern of the gsb-p protein distribution. We find that the gsb-p protein accumulates beneath each posterior axonal commissure in the progeny of neuroblasts deriving from the epidermal compartments of wingless (wg) and engrailed (en) expression. The results of this analysis support the idea that gsb-p has a specific role in the control of cell fates during neurogenesis, and indicate that en and wg provide critical positional cues to define the domain in which gsbp will be activated. Furthermore, these data suggest that, in order to be expressed in the embryonic CNS, gsb-p may preliminarily require activity of the gooseberry-distal gene in the epidermis. Offprint requests to: S. Côté     

The kinetics of oocyte activation and polar body formation in bovine embryo clones.

The kinetics of polar body formation were examined in parthenogenetically activated, in vitro matured and aged bovine oocytes. Subsequently, the presence or absence of polar body formation was determined in bovine embryo clones. Polar body formation, defined as telophase II, occurred by 1 (13/40, 43%) and 2 h (15/21, 71%) postparthenogenetic activation of metaphase II stage oocytes. Parthenogenetically activated oocytes readily formed pronuclei by 4 h. Some oocytes had chromatin in a highly condensed state at 1, 2, and 4 h postactivation (13/72, 18%). These oocytes often (10/13, 77%) appeared to be "self-enucleated," as the condensed chromatin was found in a membrane-bound extrusion. The phenomenon was most prevalent when oocytes were handled at room temperature (25-27 degrees C). Nuclear transfer procedures were established to bring about synchronous blastomere fusion and oocyte activation conditions. Synchronous conditions were achieved only when oocytes were handled and manipulated at 37-39 degrees C. Embryo clones examined 2 h postfusion did not form a polar body. Conversely, nucleate demi-oocyte controls were at the late telophase II stage of meiosis. The results are discussed in relation to cell cycle effects on bovine nuclear transfer.