Does abscisic acid influence proline accumulation in stressed leaves?

Root treatments of barley (Hordeum distichum L.) plants with 10^-7 to 10^-4 M abscisic acid (ABA) caused an increase in proline content, especially at higher concentrations, within 2–3 h. Even 3 h after the removal of ABA from the medium the plants continued to accumulate proline. The higher the concentration of the ABA, the higher was the proline level at 6 h. When the highest ABA concentration, 10^-4 M, was tested with polyethylene glycol (PEG) (-5.0 bars) in the medium, the ABA treatment resulted in a higher proline content than in control plants. The treatments PEG alone and PEG + ABA resulted in heavy accumulation of proline, especially, 3 h after releasing the plants from the stress. The proline content in PEG+ABA-treated plants was always higher than plants treated with PGE or ABA alone. In peas (Pisum sativum L. cv Alaska) the same trend occurred although to a lesser degree. These findings indicate an influence of ABA on proline accumulation in water-stressed plants.Abbreviations ABA abscisic acid - PEG polyethylene glycol - RWC relative water content     

Gross nitrogen transformations in soils from uncut and cut boreal upland and peatland coniferous forest stands

Gross and net nitrogen (N) ammonification and nitrification were measured in soils from an uncut and recently cut upland and peatland conifer stand in northwestern Ontario, Canada. Rates of gross total inorganic N immobilization were similar to gross mineralization, resulting in low net mineralization rates in soils from all four upland and peatland conifer stands. Gross ammonification rates were variable but similar in soils from uncut and cut peatland hollows (18–19mgNkg^–1day^–1) and upland forest floor soils (14–19mgNkg^–1day^–1). Gross ammonium ( ) immobilization rates were also variable but similar to ammonification rates. Median gross nitrification rates were within 0–2mgNkg^–1day^–1 in soils from all four upland and peatland cut and uncut stands, although rates were consistently higher for the soils from the cut stands. Large variability in gross nitrification rates were observed in peatland soils, however the highest gross nitrification rates were measured in saturated peatland soils. Net rates remained low in the soils from all four stands due to high nitrate ( ) immobilization and very fast turnover (<0.2 day). Our results suggest that potential losses may be negated by high immobilization in uncut and cut boreal forest stands. This study reveals the potential for the interaction of N production and consumption processes in regulating N retention in upland and peatland conifer forests, and the resilience of the boreal forest to disturbance.     

Nuclear Overhauser effect investigation on GM1 ganglioside containingN-glycolyl-neuraminic acid (II3Neu5GcGgOse4Cer)

The conformational properties of the oligosaccharide chain of GM1 ganglioside containingN-glycolyl-neuraminic acid, -Gal-(1-3)--GalNAc-(1-4)-[-Neu5Gc-(2-3)]--Gal-(1-4)--Glc-(1-1)-Cer, were studied through NMR nuclear Overhauser effect investigations on the monomeric ganglioside in dimethylsulfoxide, and on mixed micelles of ganglioside and dodecylphosphocholine in water. Several interresidual contacts for the trisaccharide core--GalNAc-(1-4)-[-Neu5Gc-(2-3)]--Gal-were found to fix the relative orientitation of the three saccharides, while the glycosidic linkage of the terminal -Gal-was found to be quite mobile as the -Gal-(1-3)--GalNAc-disaccharide exists in different conformations. These results are similar to those found for two GM1 gangliosides containingN-acetyl-neuraminic acid and neuraminic acid [1].Abbreviations Ganglioside nomenclature is in accordance with Svennerholm [23] and the IUPAC-IUB Recommendations [24] GM3(Neu5Ac) II³Neu5AcLacCer, -Neu5Ac-(2-3)--Gal-(1-4)--Glc-(1-1)-Cer - GM3(Neu5Gc) II³Neu5GcLacCer, -Neu5Gc-(2-3)--Gal-(1-4)--Glc-(1-1)-Cer - GM1(Neu5Ac) II³Neu5AcGgOse₄Cer, -Gal-(1-3)--GalNAc-(1-4)-[-Neu5Ac-(2-3)]--Gal-(1-4)--Glc-(1-1)-Cer - GM1(Neu5Gc) II³Neu5GcGgOse₄Cer, -Gal-(1-3)--GalNAc-(1-4)-[-Neu5Gc-(2-3)]--Gal-(1-4)--Glc-(1-1)-Cer - GM1(Neu) II³NeuGgOse₄Cer, -Gal-(1-3)--GalNAc-(1-4)-[-Neu-(2-3)]--Glc-(1-1)-Cer - GD1a IV³Neu5AcII³Neu5AcGgOse₄Cer, -Neu5Ac-(2-3)--Gal-(1-3)--GalNAc-(1-4)-[-Neu5Ac-(2-3)]--Gal-(1-4)--Glc-(1-1)-Cer - GalNAc-GD1a IV⁴GalNAcIV³Neu5AcII³Neu5AcGgOse₄Cer, -GalNAc-(1-4)-[-Neu5Ac-(2-3)]--Gal-(1-3)--GalNAc-(1-4)-[-Neu5Ac-(2-3)]--Gal-(1-4)--Glc-(1-1)-Cer - Neu neuraminic acid - Neu5Ac N-acetyl-neuraminic acid - Neu5Gc N-glycolyl-neuraminic acid - Cer ceramide     

Tissue culture ofKarwinskia humboldtiana—a plant producing toxins with antitumoural effects

Isolated embryos ofKarwinskia humboldtiana were cultured in vitro. The growth of embryos and development to plantlets on woody plant medium supplemented with indole-3-acetic acid 6.10^-2 mol l^–1, gibberellic acid (GA₃) 3.10^-2 mol l^–1, and 6-benzylaminopurine (BA) 2 mol l^–1 was obtained. Multiplication of shoots and rooting of excised shoots has been achieved. Callus formation on modified Murashige-Skoog medium supplemented with 1-naphthaleneacetic acid 10 mol l^–1, GA₃ 14 mol l^–1, and kinetin 5 mol l^–1 on hypocotyls, or on root cultures on medium supplemented with 2.4-dichlorophenoxyacetic acid 10 mol l^–1 and BA 10 mol l^–1 was induced.Abbreviations BA 6-benzylaminopurine - 2,4-d 2,4-dichlorophenoxyacetic acid - GA₃ gibberellic acid - IAA indole-3-acetic acid - NAA 1-naphthaleneacetic acid - TEM transmission electron microscopy     

Glucomannan-synthase activity in differentiating cells of Pinus sylvestris L.

Particulate membrane preparations have been isolated from cambial cells, and from differentiating and differentiated xylem cells of the main stem of pine trees. These preparations synthesise a 14 glucomannan from guanosine 5-diphosphate-mannose. The polysaccharide and the synthase have been characterized and the K_m and V_max for the synthase determined as 85 M and 52.9 M·min^-1, respectively. The enzymic activity was inhibited by the addition of guanosine 5-diphosphate-D-glucose so that the presence of an epimerase on the particulate fraction in conjunction with the synthase probably allowed the heteropolymer to be formed with the optimal ratio of the concentrations of the nucleoside-diphosphate sugar donors. No evidence for a polyprenyl-phosphate derivative as an intermediate during the polymer synthesis was obtained. Part of the control mechanism for the deposition of the large amounts of the glucomannan during the secondary thickening of the tracheids of the vascular system is by an increase in the amount of synthase activity at the endomembrane system of the cells. This probably occurs by an increase in the amount of enzyme which is modulated by gene regulation during differentiation.Abbreviations GDP guanosine 5-diphosphate - GLC gasliquid chromatography     

Plant regeneration through direct shoot bud formation from leaf cultures of Paphiopedilum orchids

Leaf explants of Paphiopedilum phiIippinense hybrids (hybrid PH59 and PH60) directly formed adventitious shoots from wound regions within 1 month, when cultured on modified Murashige and Skoog medium (1/2-strength macro- and full-strength micro-elements) free of plant growth regulator in darkness. The combinations of 2,4-dichlorophenoxyacetic acid ((2,4-D) acid (0, 4.52 and 45.25 M) and 1-phenyl-3-(1,2,3-thiadiazol-5-yl)-urea (TDZ) (0, 0.45, 4.54 and 22.71 M) were used to test their effects on direct shoot bud formation from two types of explants (1.5-cm long intact leaf explants and 0.5-cm long leaf segment explants). In hybrid PH59, 4.54 M TDZ increased mean numbers of shoots per explant with leaf segment explants. In hybrid PH60, 4.52 M 2,4-D plus 0.45 M TDZ promoted direct shoot bud formation from leaf segment explants. In addition, three treatments (4.52 M 2,4-D, 22.71 M TDZ, 4.52 M 2,4-D plus 4.54 M TDZ) gave a higher response than control on mean numbers of shoots per explant with intact leaf explants. Healthy plantlets each with one to three roots were obtained from leaf-derived shoots after transfer onto a hormone-free medium for 22 months. These plantlets were acclimatized in a greenhouse and grew well with 100% survival rate.     

The spermatozoon of Oikopleura dioica Fol (Larvacea,Tunicata)

Summary The spermatozoon of Oikopleura dioica is about 30 m long, with a spherical head, about 1 m wide, a 3 m long and 1 m wide midpiece, and a 25 m long tail with a tapered end piece. The head contains a nucleus with the chromatin volume limited to about 0.1 m³. A small acrosome is found in an anterior inpocketing, and a flagellar basal body in a posterior inpocketing of the nucleus. The midpiece contains a single mitochondrion with the flagellar axoneme embedded in a groove along its medial surface. The flagellar axoneme has the typical 9 + 2 substructure, and the basal body the typical 9+0 substructure. A second centriole and special anchoring fibres are absent.     

Structure of a new nonasaccharide isolated from human milk: VI2Fuc,V4Fuc,III3Fuc-p-lacto-N-hexaose

The structure of a new nonasaccharide isolated from human milk has been investigated. By using methylation analysis, FAB-MS and¹H-and¹³C-NMR spectroscopy as basic methods of structural investigation, this oligosaccharide was identified as VI²--Fuc,V⁴-Fuc,III³--Fuc-p-lacto-n-hexaose: Fuc1-2Gal1-3[Fuc1-4]GlcNAc1-3Gal1-4[Fuc1-3]GlcNAc1-3Gal1-4Glc.Abbreviations COSY correlation spectroscope - DP degree of polymerisation - FAB-MS fast atom bombardment-mass spectrometry - HPLC high performance liquid chromatography - NMR nuclear magnetic resonance - GLC gas-liquid chromatography     

Saponin-like substances inhibit α-galactosidase production in the endosperm of fenugreek seeds

When fenugreek (Trigonella foenum-graecum L.) endosperms plus testa (endosperms), which had been isolated from 5-h-imbibed seeds, were incubated for at least 2 h under germination conditions, they leaked substances which, like exogenous abscisic acid (ABA), inhibited the production of fenugreek endosperm -galactosidase. However, unlike ABA, 8 h treatment with these inhibitors had no effect on fenugreek endosperms which had been isolated from 15-h-imbibed seeds and leached for 2 h. This indicated that either their inhibitory action was on processes which were related to the production of -galactosidase and had been completed by this time, or that there might be factors present which inactivate these inhibitors. It was also concluded that the action of the endosperm leachate could not be attributed to the presence of ABA. The activity of the leachate decreased when it originated from endosperms imbibed for periods longer than 25 h and thin-layer chromatography (TLC) of extracts from these endosperms showed decreased contents of the leachable inhibitors as imbibition proceeded. From the seed leachate, which had a TLC pattern and inhibitory action similar to that of the endosperm, were isolated three substances which, when applied to endosperms, inhibited the production of -galactosidase activity. According to their chromatographic behaviour and their reaction with specific reagents, there are strong indications that these substances are saponins. These diffusible saponin-like substances were located in both endosperm and perisperm and their physiological role is discussed.Abbreviations ABA abscisic acid - PEG polyethylenglycol - TLC thin-layer chromatography We wish to thank the Alexander S. Onasis Public Benefit Foundation for a grant to K.Z. and Dr. J.S.G. Reid (University of Stirling, Scotland) for a kind gift of fenugreek seeds.     

Meiotic studies ofElymus nutans andE. jacquemontii (Poaceae,Triticeae) and their hybrids withPseudoroegneria spicata and seventeenElymus species

Hybridizations ofElymus nutans andE. jacquemontii were carried out with one species ofPseudoroegneria (S genome), and 20Elymus species, each containing either of the SH, SY, SYH, or SYW genomes. Chromosome configurations were analysed at metaphase I of the two target taxa and their interspecific hybrids. It is concluded that (i)E. nutans is an allohexaploid containing the SYH genomes, andE. jacquemontii is an allotetraploid having the SY genomes; (ii) the genomic affinity is associated with the geographic distance between the species studied; (iii) minor genomic structural rearrangements have occurred within the hexaploid taxon ofE. nutans.     

Hormonal regulation of gene expression in the “slender” mutant of barley (Hordeum vulgare L.)

The slender mutant of barley resembles a normal barley plant treated with high doses of gibberellic acid (GA₃). Expression of GA₃-regulated and abscisic acid (ABA)-regulated mRNAs was studied in the endosperm and roots of mutant and wild-type (WT) plants.Production of -amylase (EC 3.2.1.1) by WT embryoless half-grains was dependent on the presence of GA₃, and was prevented by ABA. In contrast, -amylase was produced by half-grains of the slender mutant in the absence of added GA₃, although it was still reduced by ABA. The spectrum of -amylase mRNAs in slender embryoless half-grains incubated in the absence of added GA₃ was the same as in WT endosperm half-grains incubated in the presence of GA₃. These results indicate that the endosperm of the slender mutant exhibits similar properties to WT endosperm treated with GA₃.In roots the expression of an ABA-inducible mRNA was similar in slender and WT seedlings either treated with exogenous ABA or exposed to dehydration. This result, and the effect of ABA on -amylase production by the endosperm, indicate that the slender plants retain sensitivity to ABA.Abbreviations ABA abscisic acid - AMV avian myeloblastosis virus - GA gibberellin - GA₁ gibberellin A₁ - GA₃ gibberellic acid - WT wild-type     

Isolation and characterization of a barley mutant with abscisic-acid-insensitive stomata

A barley (Hordeum vulgare L.) mutant (cool) with leaf transpiration unaffected by the application of 1 mM abscisic acid (ABA) was isolated from the population of M2 seedlings using thermography (electronic visualization, and quantitation of the temperature profiles on the surface of the leaves). Stomata of the mutant plants were insensitive to exogenously applied ABA, darkness, and such desiccation treatments as leaf excision and drought stress. The evaporative cooling of the leaves of the cool barley was always higher than that of the wild-type barley, even without ABA application, indicating that the diffusive resistance of the mutant leaves to water loss was always lower. Guard-cell morphology and stomatal density as well as ABA level and metabolism were seemingly unaltered in the mutant plants. In addition, gibberellin-induced -amylase secretion and precocious embryo germination in the mutant barley was inhibited by ABA to the same extent as in the wild-type barley.Abbreviations ABA (±) cis-trans abscisic acid - GA gibberellin     

Mutants of Arabidopsis thaliana with altered phototropism

Thirty five strains of Arabidopsis thaliana (L.) Heynh. have been identified with altered phototropic responses to 450-nm light. Four of these mutants have been more thoroughly characterized. Strain JK224 shows normal gravitropism and second positive phototropism. However, while the amplitude for first positive phototropism is the same as that in the wild-type, the threshold and fluence for the maximum response in first positive phototropism are shifted to higher fluence by a factor of 20–30. This mutant may represent an alteration in the photoreceptor pigment for phototropism. Strain JK218 exhibits no curvature to light at any fluence from 1 mol·m^-2 to 2700 mol·m^-2, but shows normal gravitropism. Strain JK345 shows no first positive phototropism, and reduced gravitropism and second positive phototropism. Strain JK229 shows no measurable first positive phototropism, but normal gravitropism and second positive phototropism. Based on these data, it is suggested that: 1. gravitropism and phototropism contain at least one common element; 2. first positive and second positive phototropism contain at least one common element; and 3. first positive phototropism can be substantially altered without any apparent alteration of second positive phototropism.Abbreviation WT wild-type     

Possible involvement of abscisic acid in the induction of secondary somatic embryogenesis on seed-coat-derived carrot somatic embryos

When seed coats (pericarps) were picked from 14-day-old carrot (Daucus carota) seedlings and cultured on agar plates, embryogenic cell clusters were produced very rapidly at a high frequency on the open side edge. Embryo induction progressed without auxin treatment; indeed treatment caused the formation of non-embryogenic callus. The embryogenic tissues (primary embryos) developed normally until the torpedo stage; however, after this a number of secondary somatic embryos were produced in the hypocotyl and root regions. Tertiary embryos were formed on some of the secondary embryos, but many developed into normal plantlets. The primary embryos contained significantly higher levels of abscisic acid (ABA) than the hypocotyl-derived normal and seed-coat-derived secondary embryos. Fluridone inhibited the induction of secondary embryogenesis, while exogenously supplied ABA induced not only tertiary embryogenesis on the seed-coat-derived secondary embryos, but also secondary embryos on the hypocotyl-derived normal somatic embryos. These results indicate that ABA is one of the important endogenous factors for the induction of secondary embryogenesis on carrot somatic embryos. Higher levels of indole-3-acetic acid (IAA) in primary embryos also suggest the presence of some concerted effect of ABA and IAA on the induction of secondary embryogenesis in primary embryos.     

Effects of G-protein probes on interactions between auxin efflux carriers and phytotropin receptors in zucchini (Cucurbita pepo L.) microsomal membranes

Microsomal vesicles prepared from etiolated hypocotyl tissue of zucchini (Cucurbita pepo L. cv. All Green Bush) exhibited saturable N-1-naphthylphthalamic acid ([³H]NPA) binding, NPA-stimulated association of indol-3yl-acetic acid ([³H]IAA), and saturable binding of guanosine 5-O-[3-thiotriphosphate] (GTP--[³⁵S]). These vesicles were used to test the possibility that NPA receptors might interact with IAA-anion efflux carriers by coupling through a GTP-binding protein (G-protein). Unlabelled GTP--S or guanosine 5-O-[2-thiodiphosphate] (GDP--S) had no effect on saturable NPA binding or on the NPA-stimulated association of IAA with microsomes. NPA did not affect saturable binding of GTP--[³⁵S] to microsomes, either in the presence or absence of saturating concentrations of unlabelled GTP--S or GDP. It is concluded that the occupancy of phytotropin receptors is not transduced to auxin efflux carriers by a GTP-binding protein.     

Further cytogenetic analyses of the Croatian triploid shallot “Ljutika” (Allium cepa var.viviparum, Alliaceae) and its comparison with the Indian triploid “Pran”

Feulgen and silver-stained karyotypes and meiosis of two triploid viviparous onion forms (Allium cepa var.viviparum), the Croatian Ljutika and the Indian Pran, were comparatively analyzed. The results of chromosome measurements show that Ljutika and Pran are karyologically not identical, although significant similarities were found in the morphology of their chromosomes. Five geographically distant clones of Ljutika showed good agreement in the number and gross morphology of the chromosomes and in the number and position of NORs and interphase nucleoli. Heterotrivalents were predominant in meiosis of Ljutika but a relatively high frequency of higher multivalents together with univalents and bivalents were also observed. The relationship between Ljutika and Pran and their possible origin are discussed.     

In vitro regeneration through organogenesis of Meconopsis simplicifolia — An endangered ornamental species

Meconopsis simplicifolia (D.Don) Walp. could be propagated by induction of adventitious shoots from callus produced on hypocotyl, cotyledon and rosette leaf explants of 4-month-old seedlings. Callus was initiated on agar-solidified Murashige and Skoog medium supplemented with 1 M kinetin +10 M -naphthaleneacetic acid (NAA). Shoots formed when the callus was subcultured on medium supplemented with kinetin or benzyladenine (BA) in combination with NAA, indoleacetic acid, indolebutyric acid or gibberellic acid. Excised shoots were rooted on medium containing auxin with 10 M NAA producing the best rooting (55%).Abbreviations BA 6-benzyladenine - 2,4-d 2,4-dichlorophenoxy-acetic acid - FAA formalin-acetic acid-alcohol - GA₃ gibberellic acid - IAA indole-3-acetic acid - IBA -indolebutyric acid - NAA -naphthaleneacetic acid     

Abscisic acid metabolism —vacuolar/extravacuolar distribution of metabolites

The biotransformation of abscisic acid (ABA) was studied in cell suspension cultures of Lycopersicon esculentum. The ABA was converted by the cells to phaseic acid, nigellic acid, dihydrophaseic acid, abscisic acid--D-glucopyranosyl ester (ABA-Glc) and other ABA and phaseic acid conjugates. Investigation of their cellular distribution showed that the conjugated forms were located only in the vacuoles whereas ABA and its acidic metabolites were found mainly in the extravacuolar fractions. Our results, together with a number of studies on the increase of ABA-Glc as a response to stress, allow us to propose that ABA-Glc is irreversibly compartmented in the vacuoles of plant cells.Abbreviations ABA abscisic acid - ABA-Glc -D-glucopyranosyl ester of ABA - DPA 4-dihydrophaseic acid; nigellic acid=3-methyl-5-(1-hydroxy-2-hydroxymethyl-6-dimethyl-4-oxo-cyclohex-2-enyl)-penta-2Z, 4E-dienoic acid - PA phaseic acid     

Cell multiplication and ultrastructure ofMicrasterias denticulata (Desmidiaceae) grown under salt stress

Cells ofMicrasterias denticulata Bréb. were kept in nutrient solution of high osmolality (salt stress) for four weeks. In a special cell multiplication test it was established that cell division is gradually inhibited at increasing salt concentrations and totally arrested at the highest concentration (26 mosm/kg). Recovery studies proved that even cells from the highest concentration range start dividing immediately after being placed in aqua bidest. thus indicating the full reversibility of the inhibiting effect. — Cells of the highest concentration range show marked ultrastructural changes. Besides an enormous accumulation of starch and oil bodies and a condensed appearance of the ground plasma, a reduction of mitochondria, ER and the Golgi-system is found. The most striking effect occurs on the vacuolar system which appears extremely reduced and condensed. The cell wall is thickened by the formation of an additional cell wall layer with a spongy electron microscopical appearance. Through the cell wall many droplets of a probably fat-like substance are excreted. — In summary, salt stress induces growth-inhibited akinete cells in the sense ofFritsch; these can be reactivated by decreasing the salt concentration. The salt-induced akinete state seems to be an ecological adaption to unfavourable conditions rather than a degeneration of the cells.Dedicated to Prof. DrLothar Geitler on the occasion of his 90th birthday.23. 12. 1988     

Correlation between loss of turgor and accumulation of abscisic acid in detached leaves

Mature leaves of Phaseolus vulgaris L. (red kidney bean), Xanthium strumarium L. (cocklebur), and Gossypium hirsutum L. (cotton) were used to study accumulation of abscisic acid (ABA) during water stress. The water status of individual, detached leaves was monitored while the leaves slowly wilted, and samples were cut from the leaves as they lost water. The leaf sections were incubated at their respecitive water contents to allow ABA to build up or not. At least 8 h were required for a new steady-state level of ABA to be established. The samples from any one leaf covered a range of known water potentials (), osmotic pressures (), and turgor pressures (p). The and p values were calculated from pressure-volume curves, using a pressure bomb to measure the water potentials. Decreasing water potential had little effect on ABA levels in leaves at high turgor. Sensitivity of the production of ABA to changes in progressively increased as turgor approached zero. At p=1 bar, ABA content averaged 4 times the level found in fully turgid samples. Below p=1 bar, ABA content increased sharply to as much as 40 times the level found in unstressed samples. ABA levels rose steeply at different water potentials for different leaves, according to the at which turgor became zero. These differences were caused by the different osmotic pressures of the leaves that were used; must cqual - for turgor to be zero. Leaves vary in , not only among species, but also between plants of one and the same species depending on the growing conditions. A difference of 6 bars (calculated at =0) was found between the osmotic pressures of leaves from two groups of G. hirsutum plants; one group had previously experienced periodic water stress, and the other group had never been stressed. When individual leaves were subsequently wilted, the leaves from stress-conditioned plants required a lower water potential in order to accumulate ABA than did leaves from previously unstressed plants. On the basis of these results we suggest that turgor is the critical parameter of plant water relations which controls ABA production in water-stressed leaves.Abbreviations ABA abscisic acid - me-ABA abscisic-acid methyl ester - leaf water potential - osmotic pressure - p volumeaveraged turgor - volumetric modulus of elasticity