Stimulation of cucumber hypocotyl elongation by dihydroconiferyl alcohol. Interactions between dihydroconiferyl alcohol and auxin or gibberellin

The effect of dihydroconiferyl alcohol (DCA) on elongation ofcucumber hypocotyl segments was studied. DCA did not influenceelongation when given alone, but synergistically enhanced IAA-inducedelongation. The stimulating effect of DCA was conspicuous particularlywhen it was given together with suboptimal concentrations ofIAA. DCA hardly influenced GA-induced elongation in the presenceof 2% sucrose. (Received May 22, 1974; )     

Nitrate reductase in cotyledons of cucumber seedlings as affected by nitrate, phytochrome and calcium

Regulation by the active form of phytochrome (P_FR) and the effect of Ca²⁺ was examined with nitrate reductase (NR) in etiolated cucumber ( Cucumis sativus cv. Beilpuig). Nitrate reductase activity (NRA) was studied in excised cotyledons of cucumber seedlings grown in distilled water and in darkness for seven days at 24 ± 0.5°C. All experiments were performed in the dark and a dim green safelight was used during analyses. In etiolated cucumber cotyledons NRA was induced by nitrate and a brief irradiation (15 min) with red light (R) resulted in 62% increase in NRA. This effect was nullified when R was followed immediately by a brief (5 min) far-red light (FR). NRA also showed a semidian (12 h) rhythmicity. Both P_FR, and nitrate effects were age dependent. Calcium seemed to be involved since the phytochrome effect was only observed when calcium was supplied in the external solution. The effect of R on NRA depended on the period of calcium nitrate incubation. An external supply of calcium ionophore mimicked the effect of R and, if supplied to R-irradiated cotyledons, produced a higher NR level than that caused by R alone. This suggested that intracellular free calcium was involved.     

Light quality influences germination, root growth and hypocotyl elongation in somatic embryos but not in seedlings of norway spruce

Summary We studied how light from different light sources influences germination and postgerminative growth of plants from somatic embryos and seeds of Norway spruce (Picea abies [L.] Karst). Somatic embryos of three spruce genotypes and seeds were subjected to light from commercially available light sources: Philips TLD Blue 18W/18 (BL), Osram Fluora (FL), Philips Cool White TL 50W/33 (CW), Osram Warm White 18W/30 (WW), Philips Yellow 36W/16 (YE) and Philips TLD Red 36W/15 (RE), 18 h a day, with a photon flux (PAR) at 30 μmol m⁻² s⁻¹. After 6 wk the germination frequencies of the somatic embryo-derived plantlets were 50% under BL and 98% under RE. The corresponding mean root lengths were 6.7 and 15.4 mm. In somatic embryo-derived plantlets cultured under BL, FL, CW and WW, both roots and hypocotyls turned brown, presumably due to production of phenolic substances. Browning was less severe in somatic embryo-derived plantlets cultured under RE and YE. Under RE, the epicotyl elongated in 37% of the plantlets after 6 wk, compared with 70% under the other light sources. Seed germination and postgerminative seedling growth was modestly influenced by light from these light sources. RE and WW initially delayed germination as compared with BL, FL and CW, but after 2 wk, more than 90% of the seeds had germinated under all light sources. In conclusion, germination and postgerminative growth of somatic embryos of spruce is sensitive to differences in light quality, whereas seed germination and seedling growth is not.     

Mannitol inhibits growth of intact cucumber but not pea seedlings by mechanically collapsing the root pressure

The positive xylem pressure (Px) in cucumber hypocotyls is a direct extension of root pressure and therefore depends on the root environment. Solutions of the electrolyte KCl (0-10 osm) reduced the hypocotyl Px transiently (biphasic response), while the Px reduction by mannitol solutions was sustained. The amplitudes of the induced Px reduction depended directly, and the degree of Px restoration after stress release depended indirectly, on the size of the initial positive Px indicating that mannitol released the root pressure by a mechanical rather than osmotic mechanism. Mannitol treatment and other means of root pressure reduction revealed two separate growth responses in the affected cucumber hypocotyls. Only steep Px drops (following root excision or root pressure release in mannitol) directly cause a rapid, transient drop in growth rate (GR). Both rapid and slow (after root incubation in KCN or NEM) decreases in root pressure, however, led to a sustained growth inhibition of cucumber hypocotyls after about 30 min. This delay characterizes the growth response as an indirect consequence of the Px change. Pea seedlings, which lacked root pressure and had a negative Px throughout, showed extremely small changes in epicotyl Px and GR after root incubation in mannitol. It is apparent that the higher sensitivity of cucumber growth to mannitol depended on the presence and release of root pressure.     

Sucrose transport by seedlings of Ricinus communis L: the export of sucrose from the cotyledons to the hypocotyl as a function of sucrose concentration in the cotyledons

Abstract Using seedlings of Ricinus communis L. sucrose export from the cotyledons to the hypocotyl and roots was measured at different levels of sucrose concentration in the cotyledons. Sucrose export followed Michaelis-Menten kinetics with a half-saturation of export at 35 mM sucrose in the cotyledons. A maximal export flux of 90 μmol h^?l g^?1 fresh weight of the cotyledons was obtained. Both these figures coincide with those obtained for sucrose uptake into the cotyledons. It is postulated that sucrose uptake and sucrose export occurs by the same mechanism and possibly by the same cells which then would have to be part of the phloem. Since sucrose uptake has been shown to proceed as proton-sucrose co-transport, phloem loading might also be energized by the protonmotive potential difference. The data, furthermore, are difficult to reconcile with the symplastic route of phloem loading.     

Auxin-gibberellin relationships in their effects on hypocotyl elongation of light-grown cucumber seedlings. Responses of sections to auxin, gibberellin and sucrose

The sensitivity of light-grown cucumber hypocotyl sections toIAA and GA₃ depends on the degree of aging of the tissue. Agreater response to GA₃ was obtained with young tissue, whilethat to IAA was obtained with relatively old tissue. The responseto IAA reached a maximum at about 15 hr of incubation; the youngerthe tissue the earlier the time of maximum response. The responseto GA₃ continued for more than 70 hr with a constant growthrate. Very young tissue started to respond to GA₃ without lagtime; the older the tissue the later the start of the response. Sucrose (2%) inhibited IAA-induced elongation, while there wasa distinct synergism between GA₃ and sucrose. The promotiveeffect of sucrose on GA₃-induced elongation was also obtainedwhen sections were pretreated with sucrose, then transferredto GA₃. Mannitol (1%) strongly inhibited IAA-induced elongation,but not GA₃-induced elongation. (Received December 6, 1972; )     

三唑酮对黄瓜幼苗生长及抗寒性的影响

研究了不同浓度三唑酮浸种对黄瓜幼苗生物量及抗寒性的影响。结果表明,20～100μmol·L^-1三唑酮能显著抑制黄瓜幼苗的株高、根长,增加了根重、根冠比和叶绿素含量,30d幼苗经过3d低温胁迫后,10～50μmol·L^-1三唑酮处理能保持较高的叶绿素含量,有效地降低质膜相对透性,维持较高的SOD活性,50μmol·L^-1三唑酮处理明显减缓低温胁迫过程中MDA的累积。另外,50μmol·L^-1三唑酮处理在低温胁迫第1d促进脯氨酸的累积,在第3d脯氨酸反而低于对照。但高浓度(>100μmol·L^-1)三唑酮不利于幼苗抵御低温伤害,总的来看,三唑酮增强了黄瓜幼苗的耐寒性。     

Fasting, but not adrenalectomy, reduces transport of leptin into the brain

Food deprivation and adrenalectomy are associated with low concentrations of leptin in blood and the absence of obesity. Because leptin is known to cross the blood-brain barrier (BBB) by a saturable transport system, we examined whether fasting and adrenalectomy (ADX) also act at the BBB. Multiple-time regression analysis showed that fasting, but not ADX, significantly decreased the entry of leptin into mouse brain. After 3 days of food deprivation, the influx of leptin became indistinguishable from that of the vascular control (albumin); 5 h of refeeding significantly reversed this reduced rate of influx. Thus, the results indicate that the BBB provides a dynamic site for the regulation of physiological processes involving leptin.     

Osmoregulation in hypocotyls of etiolated mung bean seedlings with or without cotyledons in response to water-deficient stress

Effects of water-deficient stress and cotyledon excision on osmoregulation in hypocotyls of dark-grown mung bean seedlings were studied, and following results were obtained. Water-deficient stress inhibited hypocotyl elongation either in intact or decotylized seedlings. The inhibition was more conspicuous in decotylized seedlings than in intact ones. Water-deficient stress decreased osmotic potential in hypocotyls, while cotyledon excision increased it. The concentrations of soluble sugars, free amino acids and potassium ions in hypocotyls of intact or decotylized seedlings increased in response to water-deficient stress. Cotyledon excision reduced the concentration of soluble sugars and free amino acids, but it did not change the concentration of potassium ions, suggesting that a part of soluble sugars and free amino acids is transported from cotyledons. Unlike cotyledon excision, excision of the apex or roots had no influence on osmoregulation in response to water-deficient stress. Segments excised from hypocotyls had the ability to osmoregulate in response to water-deficient stress. Based on these results, the role of cotyledons in osmoregulation in response to water-deficient stress and quantitative relationships between osmotic potential and hypocotyl elongation in etiolated mung bean seedlings are discussed.     

Inhibition of p38 reduces myocardial infarction injury in the mouse but not pig after ischemia-reperfusion

The MAPK family member p38 is activated in the heart after ischemia-reperfusion (I/R) injury. However, the cardioprotective vs. proapoptotic effects associated with p38 activation in the heart after I/R injury remain unresolved. Another issue to consider is that the majority of past studies have employed the rodent as a model for assessing p38's role in cardiac injury vs. protection, while the potential regulatory role in a large animal model is even more uncertain. Here we performed a parallel study in the mouse and pig to directly compare the extent of cardiac injury after I/R at baseline or with the selective p38 inhibitor SB-239063. Infusion of SB-239063 5 min before ischemia in the mouse prevented ischemia-induced p38 activation, resulting in a 25% reduction of infarct size compared with vehicle-treated animals (27.9 +/- 2.9% vs. 37.5 +/- 2.7%). In the pig, SB-239063 similarly inhibited myocardial p38 activation, but there was no corresponding effect on the degree of infarction injury (43.6 +/- 4.0% vs. 41.4 +/- 4.3%). These data suggest a difference in myocardial responsiveness to I/R between the small animal mouse model and the large animal pig model, such that p38 activation in the mouse contributes to acute cellular injury and death, while the same activation in pig has no causative effect on these parameters.     

Docosahexaenoic acid, but not eicosapentaenoic acid, reduces the early inflammatory response following compression spinal cord injury in the rat

Docosahexaenoic acid (DHA, 22 : 6) and eicosapentaenoic acid (EPA, 20 : 5) are omega-3 polyunsaturated fatty acids (n-3 PUFAs) with distinct anti-inflammatory properties. Both have neuroprotective effects acutely following spinal cord injury (SCI). We examined the effect of intravenous DHA and EPA on early inflammatory events after SCI. Saline, DHA or EPA (both 250 nmol/kg) were administered 30 min after T12 compression SCI, to female Sprague-Dawley rats. DHA significantly reduced the number of neutrophils to some areas of the injured epicentre at 4 h and 24 h. DHA also reduced C-reactive protein plasma levels, whereas EPA did not significantly reduce neutrophils or C-reactive protein. Laminectomy and SCI elicited a sustained inflammatory response in the liver, which was not reversed by the PUFAs. The chemokine KC/GRO/CINC and the cytokine IL-6 provide gradients for chemotaxis of neutrophils to the epicentre. At 4 h after injury, there was a significant increase in IL-6, KC/GRO/CINC, IL-1β and tumour necrosis factor-α in the epicentre, with a return to baseline at 24 h. Neither DHA nor EPA returned their levels to control values. These results indicate that the acute neuroprotective effects of n-3 PUFAs in rat compression SCI may be only partly attributed to reduction of some of the early inflammatory events occurring after injury.     

Exposure of mouse oocytes to bisphenol A causes meiotic arrest but not aneuploidy

Mouse oocytes isolated from large antral follicles were exposed to a wide range of concentrations of bisphenol A (BPA) during maturation in vitro (50 ng/ml to 10 microg/ml BPA in medium). Exposure to high concentrations of BPA (10 microg/ml) affected spindle formation, distribution of pericentriolar material and chromosome alignment on the spindle (termed congression failure), and caused a significant meiotic arrest. However, BPA did not increase hyperploidy at meiosis II at any tested concentration. Some but not all meiosis I arrested oocytes had MAD2-positive foci at centromeres of chromosomes in bivalents, suggesting that they had failed to pass the spindle checkpoint control. In a second set of experiments prepubertal mice were exposed sub-chronically for 7 days to low BPA by daily oral administration, followed by in vitro maturation of the denuded oocytes to metaphase II in the absence of BPA, as this treatment protocol was previously reported to induce chromosome congression failure and therefore suspected to cause aneuploidy in oocytes. The sub-chronic exposure subtly affected spindle morphology and oocyte maturation. However, as with the exposure in vitro, there was no evidence that low BPA doses increased hyperploidy at meiosis II. In conclusion, the data suggest that mouse oocytes from mice respond to BPA-induced disturbances in spindle formation by induction of meiotic arrest. This response might result from an effective checkpoint mechanism preventing the occurrence of chromosome malsegregation and aneuploidy. Low chronic BPA exposure in vivo as such does not appear to pose a risk for induction of errors in chromosome segregation at first meiosis in mouse oocytes. Additional factors besides BPA may have caused the high rate of congression failure and the temporary increase in hyperploidy in mouse metaphase II oocytes reported previously.     

Eastern deciduous tree seedlings advance spring phenology in response to experimental warming,but not wetting,treatments

Changing global climate, particularly rising temperatures, has been linked through observations with advanced spring phenology in temperate regions. We experimentally tested if regional climate change predictions of increased temperature and precipitation alter the spring phenology of eastern US tree seedlings. This study reports the results of a 3-year-field experiment designed to study the responses of eastern deciduous tree species planted in a post-harvest environment to a 2 °C increase in temperature and a 20 % increase in precipitation. Species were monitored for timing of germination and leaf out in four treatment combinations (ambient, warmed, irrigated, and warmed + irrigated) on 16 plots located in a recently harvested central Pennsylvania forest. The 2 °C warming advanced day of seed germination by an average of 2 weeks and seedling leaf out by 10 days among all species (both p < 0.001). However, increased precipitation did not result in a significant change in spring phenology. Species responded uniquely to treatments, with germination advancing in three of five species in response to warming and leaf out advancing in six of six species. Southern species projected to expand northward into the study region with rising temperatures did not show responses to warming treatments that would provide them an advantage over current resident species. Timing of germination and leaf out varied among years of the experiment, most likely driven by year-to-year variability in spring temperatures. The climate change experiment highlighted the potential of a moderate 2 °C temperature increase to advance spring phenology of deciduous tree seedlings by up to 2 weeks, with a lack of a phenological response to a 20 % increase in precipitation.     

Exposure of roots of cucumber (Cucumis sativus) to low temperature severely reduces root pressure, hydraulic conductivity and active transport of nutrients

When root temperature dropped below 25°C, there was a sharp drop in the root pressure ( P _r) and hydraulic conductivity of excised roots ( Lp _r) of young cucumber ( Cucumis sativus L.) seedlings as measured with the root pressure probe. A detailed analysis of root hydraulics provided evidence for a larger reduction in the osmotic component of Lp _r (77%) in comparison with the hydrostatic component (34%) in response to the exposure of the root system to 13°C. The activity of the plasma membrane H⁺-ATPase (EC 3.6.1.35) was reduced from 30 to 16 µmol Pi mg⁻¹ protein h⁻¹ upon exposure to 8°C for 1 day. Ultrastructural observations showed no evidence of loosening of the microstructure of endodermal cell walls in low temperature (LT)-treated roots. It is concluded that the rapid drop in the P _r in response to LT is largely caused by a reduction in the activity of the plasma membrane H⁺-ATPase rather than by loosening of the endodermal wall which would cause substantial solute losses. On the other hand, water permeability of root cell membrane at LT was related to changes in the activity (open/closed state) of water channels.     

Calmodulin binds to K-Ras, but not to H- or N-Ras, and modulates its downstream signaling

Activation of Ras induces a variety of cellular responses depending on the specific effector activated and the intensity and amplitude of this activation. We have previously shown that calmodulin is an essential molecule in the down-regulation of the Ras/Raf/MEK/extracellularly regulated kinase (ERK) pathway in cultured fibroblasts and that this is due at least in part to an inhibitory effect of calmodulin on Ras activation. Here we show that inhibition of calmodulin synergizes with diverse stimuli (epidermal growth factor, platelet-derived growth factor, bombesin, or fetal bovine serum) to induce ERK activation. Moreover, even in the absence of any added stimuli, activation of Ras by calmodulin inhibition was observed. To identify the calmodulin-binding protein involved in this process, calmodulin affinity chromatography was performed. We show that Ras and Raf from cellular lysates were able to bind to calmodulin. Furthermore, Ras binding to calmodulin was favored in lysates with large amounts of GTP-bound Ras, and it was Raf independent. Interestingly, only one of the Ras isoforms, K-RasB, was able to bind to calmodulin. Furthermore, calmodulin inhibition preferentially activated K-Ras. Interaction between calmodulin and K-RasB is direct and is inhibited by the calmodulin kinase II calmodulin-binding domain. Thus, GTP-bound K-RasB is a calmodulin-binding protein, and we suggest that this binding may be a key element in the modulation of Ras signaling.     

Overexpression of rice phytochrome A in tobacco seedlings modifies responsiveness but not competence to phytochrome

To analyse the control of rice phytochrome A (phyA) overexpression (wild type or variously mutated) on gene regulation, transgenic tobacco lines overexpressing various rice phyA constructs were crossed with transgenic tobacco lines containing mustard Lhcb1 or Chs1 promoters fused to the uidA reporter gene (-glucuronidase). It was demonstrated that the temporal pattern of competence to respond to phytochrome was not altered by rice phyA overexpression. Also, overexpression of rice phyA did not change the spatial pattern of gene expression. The responsiveness to red and far-red light, on the other hand, depended on the type of overexpressed rice phyA in a structure-function relation: the serine-to-alanine mutant mediated an enhanced response both under continuous red and far-red light, whereas the N-terminal deletion mutant showed a dominant negative effect under continuous far-red light and even after red light pulses. However, the effectiveness of rice phyA overexpression depended on the promoter construct and the developmental stage of the seedlings. The Lhcb1 promoter also conferred -glucuronidase activity in etiolated seedlings. This dark expression could be decreased by a long-wavelength farred light pulse given early in development (24 h after sowing), indicating that this phenomenon is under the control of stable types of phytochrome.Abbreviations Chs1 chalcone synthase - GUS -glucuronidase - Lhcb1 type 1 light-harvesting chlorophyll a/b-binding protein - NTD N-terminal deletion mutant of rice phyA - phyA phytochrome A - phyB phytochrome B - Pfr far-red absorbing form of phytochrome - Pr red-absorbing form of phytochrome - RW rice wild-type phyA - S/A serine-to-alanine mutant of rice phyA - XAN wild-type tobacco cv. Xanthi We thank N.-H. Chua (Rockefeller Univ., New York, USA) and J. Stockhaus (Heinrich-Heine-Universität, Düsseldorf, Germany) for providing seeds from tobacco lines overexpressing the diverse rice phyA proteins. The work was supported by a grant from the Human Frontier Science Program and a grant from Deutsche Forschungsgemeinschaft (SFB 388). K.E. is a recipient of a Landesgraduierten-förderung fellowship     

Dystroglycan does not contribute significantly to kidney development or function, in health or after injury

Dystroglycan (DG or DAG1) is considered a critical link between the basement membrane and the cytoskeleton in multiple tissues. DG consists of two subunits, an extracellular α-subunit that binds laminin and other basement membrane components, and a transmembrane β-subunit. DG-null mouse embryos die during early embryogenesis because DG is required for Reichert's membrane formation. DG also forms an integral part of the dystrophin-glycoprotein complex in muscle. Although no human DG mutations have been reported, multiple forms of muscular dystrophy have been linked to DG glycosylation defects, and targeted deletion of muscle DG causes muscular dystrophy in mice. Moreover, DG is widely distributed in endothelial and epithelial cells, including those in the kidney. There has therefore been significant interest in DG's role in the kidney, especially in podocytes. Previous reports suggested that DG's disturbance in podocytes might cause glomerular filtration barrier abnormalities. To fully understand DG's contribution to nephrogenesis and kidney function, we used a conditional DG allele and a variety of Cre mice to systematically delete DG from podocytes, ureteric bud, metanephric mesenchyme, and then from the whole kidney. Surprisingly, none of these conditional deletions resulted in significant morphological or functional abnormalities in the kidney. Furthermore, DG-deficient podocytes did not show increased susceptibility to injury, and DG-deficient kidneys did not show delayed recovery. Integrins are therefore likely the primary extracellular matrix receptors in renal epithelia.