Changes in Membrane Fluidity and Protein Composition during Release of Cucumber Seeds from Dormancy by a Higher Temperature Shift

Dormancy of seeds of cucumber (Cucumis sativus L.) was inducedby imbibing in -1.8 MPa polyethylene glycol 6000 (PEG) solutionand pulsing with far red light for 15 min prior to washing anddrying. When re-imbibed with water at 20 °C, dormancy wasbroken by raising the temperature to 30 °C for 6 h. Thistreatment was also effective when -0.9 MPa PEG was present duringre-imbibition and high temperature. Seeds with broken dormancywere found to germinate in water over a smaller temperaturerange than seeds in which dormancy had not been induced. Whenthe duration of the temperature shift to 30 °C was varied,germination percentage increased from 7 to 60% after 6 h, butlonger exposures up to 12 h had no further promoting effect.The time course of germination after transfer to water following6 h at 30 °C in PEG showed piercing of the perisperm-endospermenvelope after 9–12 h and radicle protusion after 12–15h. If PEG was retained after high temperature treatment no visiblegermination was observed. Thus, to study membrane fluidity andthe protein content associated with germination, seeds weresampled 9 h after high temperature treatment. To study the germinablebut not germinating state, seed held in PEG for 9 h rather thanin water was used. Dormant seed was sampled before the hightemperature treatment. Membrane fluidity was assessed usingfluorescence polarization of membrane fractions treated withDPH (1,6-diphenyl-1,3,5-hexatriene) or its derivatives. Membraneproteins were compared using one-dimensional SDS-PAGE electrophoresis.Intracellular membrane fluidity was not increased in the transitionfrom the dormant to germinable state, but did increase in thetransition to germination. There were no detected changes inintracellular membrane proteins during either transition. Inplasma membrane fractions, fluidity increased during both transitions,while a marked increase in 21, 18 and 17 kD proteins was observedin the transition from germinable to germinating state. Thusmodification of plasma membrane fluidity rather than changesin protein profile is associated with the high temperature releaseof cucumber seeds from dormancy. Copyright 2000 Annals of BotanyCompany     

On the degree of genetic divergence in Drosophila ananassae populations transferred to laboratory conditions

Twelve natural populations of Drosophila ananassae were sampled and laboratory populations were derived. All the populations were maintained in food bottles in the laboratory for ten generations by transferring fifty flies (females and males in equal number) in each generation. After ten generations they were analysed chromosomally to determine the frequency of different chromosome arrangements. The results show that there is significant variation in the frequencies of chromosome arrangements and in the level of inversion heterozygosity. Although some of the populations became mo-nomorphic for certain inversions, in general all populations remained polymorphic even after ten generations. The degree of genetic differentiation in the populations after they were transferred to laboratory conditions has been estimated by calculating genetic identity and distance between the initial and final populations based on the differences in chromosome arrangement frequencies. The estimates of I and D suggest that there is considerable variation in the degree of genetic divergence in D. ananassae populations. Some populations have remained unchanged while others have diverged to a considerable extent.     

Physiological and Biochemical Changes Associated with Cotton Fibre Development. IV. Glycosidases and {beta}-1,3-Glucanase Activities

Developing cotton fibre was analysed from 12 days post anthesis(DPA) till maturity for the activity of wall degrading enzymes,ß-galactosidase, ß-glucosidase, -mannosidaseand ß-1,3-glucanase. Each enzyme was estimated inthree different fractions namely cytoplasmic, ionically wall-boundand covalently wall-bound. There was a significant correlationbetween ß-galactosidase and ß-glucosidaseactivities in the covalently bound fraction, and the rate offibre elongation. Similarly, covalently bound ß-1,3-glucanaseactivity showed an increasing trend up to 18 DPA, i.e. aboutthe time when maximum rate of fibre elongation was achieved. The results presented here suggest that covalently wall-boundglycosidases may have an importafit role in cell wall loosening.Earlier reports providing evidence against the involvement ofthese enzymes in elongation growth in intact system, may perhapsbe due to scant attention paid to the subcellular distributionof these enzymes. Gossypium hirsutum, cotton fibre, glucanase, glycosidase, wall-loosening     

Ontogenetic interactions between photosynthesis and symbiotic nitrogen fixation in pigeonpea

Total nodule nitrogenase activity (TNA, μmols ethylene plant^-1 h^-1) in pigeonpea (Cajanus cajari) increased with plant growth to reach maximum at flowering (75 days after sowing), decreasing thereafter until maturity (120 days after sowing). However, specific nodule nitrogenase activity (SNA, μmols ethylene g^-1 nodule fresh wt h^-1) reached its maximum earlier (45 days after sowing). The rate of photosynthesis and shoot and nodule respiration followed a similar pattern to TNA. However, higest rates of root respiration were observed at flowering and again immediately before final harvest. ¹⁴CO₂ feeding studies showed that assimilates produced in leaves before flowering were retained in the vegetative parts. Assimilates produced after flowering were exported to the reproductive structure at the expense of the nodules. It is suggested that the decreased availability of photosynthate to nodules decreased nitrogen fixation.     

Control of pearl millet downy mildew by seed treatment with metalaxyl*

Three formulations of the systemic fungicide metalaxyl were tested in various seed treatments for the control of pearl millet downy mildew in three field experiments with downy mildew-susceptible pearl millet hybrid NHB-3. Uniform, high levels of sporangial inoculum of the causal fungus, Sclerospora graminicola, were provided throughout the growth of the test crops from inoculated infector rows of NHB-3, planted earlier between the test plots. Significant reductions in downy mildew were obtained with all fungicide treatments. Best control was obtained when seed was soaked in a 0.5% aqueous solution of a liquid formulation (mean infection index of 9.8% compared with 94.8% in the untreated check). The degree of control with the wettable powder formulations was directly related to fungicide dosage, and there were no significant effects of application method. Simple dusting of seed at 2 g a.i./kg, a rapid and simple operation requiring small quantities of fungicide and no special application equipment, gave a high level of control (infection index of 12.6% compared with 78.9% in the untreated check). In two experiments grain yields from all the treated plots were significantly greater than from the untreated plots (means of 1234 and 1534 kg/ha for treated plots compared with 485 and 743 kg/ha, respectively), and in the third, the treatment with the least downy mildew gave significantly more grain than the untreated check (1228 compared with 727 kg/ha).     

Floral development of Justicia gendarussa (Acanthaceae)

The sequence of primordial initiation is acropetal and the primordia develop in the same order in which they appear. The floral apex has a two-layered tunica in all stages of development. There is no significant difference in the initiation of any of the floral appendages and thus all floral organs are homologous with respect to their histogenetic origin. The short calyx tube is formed by ontogenetic fusion of the bases of sepals; but the corolla tube arises partly by ontogenetic union of originally free parts and partly by zonal or intercalary growth. Each primordium receives a single procambium strand shortly after its initiation, except those of the posterior pair of stamens, which do not receive any vascular supply. This provides another example which goes against the doctrine of "conservatism of vascular bundles". The placentation in Justicia is parietal ontogenetically as well as anatomically.     

The Role of ABA in the Control of Apple Seed Dormancy Re-appraised by Combined Gas Chromatography-Mass Spectrometry

Measured by GC—MS²—SIR³, endogenous ABA⁴ in embryonicaxes of seeds of Malus pumila L. cv. Golden Delicious decreased8-fold and cotyledon ABA by only 60%, during 10–50 d ofstratification at 5 ?C, after ABA leaching during an initial24 h soaking. During stratification, the percentage germinationof embryos transferred to 17?C showed a significant linear dependenceon log_e of ABA levels in the axes at transfer. Between 50 and70 d, ABA levels increased markedly in axes and testa both ofstratified seeds and seeds allowed to re-dry at 17 ?C afterinitial soaking. The ability of fully stratified axes with elevatedendogenous ABA to germinate indicated that stratification haddecreased their ABA sensitivity. Changes in cotyledon ABA couldnot account for the promotory effect of cotyledons on germinationduring the first 30 d of stratification. Loss of testa inhibitionof germination during stratification was not linked with changesin testa ABA. Stratification markedly increased the sequestrationin the axes of exogenous ABA supplied via the cotyledons. Changesboth in axis ABA levels and sensitivity were thus correlatedwith dormancy release, but subject to modifying control by thecotyledons and testa not involving ABA. Rehydration of driedseeds affected axis ABA later during storage via mechanismsunconnected with dormancy. Key words: ABA, seed dormancy, stratification     

An Apparatus for Automatic Recording of Losses of Water from Potted Plants, Soil, and Water Pans

An apparatus for automatic recording of losses of water frompotted plants, soil, &c., has been described. It is simple,and sufficiently robust for use in the open. Results on thedaily march of transpiration of wheat in the northern plainsof India have been given to demonstrate the working of the apparatus.