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     

Development of Plastids in Pollen and Tapetum of Rye-grass, Lolium perenne L

Proplastids of both tapetal cells and microsporocytes were presentearly in anther development. Tapetal proplastids differentiated—probablyinto elaioplasts—at late microspore stage. The tapetalcytoplasm was completely resorbed by early tricellular pollenstage. Microspore proplastids differentiated into amyloplastsat early bicellular stage, and were present in both vegetativeand generative cells. In the generative cell, the amyloplastswere ephemeral and apparently degenerated within autophagicvacuoles. Plastids were absent from sperm cells. Vegetativecell amyloplasts increased in number apparently by fission suchthat one amyloplast produced one amyloplast and one proplastidper division. Mature pollen grains were estimated to containbetween 550 and 820 amyloplasts with only one starch granuleper plastid. Elaioplasts, amyloplasts, plastid division, plastid differentiation, starch granules, autophagy, Lolium perenne, Poaceae, rye-grass     

Subcellular Distribution and Developmental Expression of Cholesterol Ester Hydrolases in Fetal Rat Brain Cultures

Abstract: Cholesterol ester hydrolase activities previously have been identified in brain and linked to the production of myelin, which has very low levels of esterified cholesterol. We have studied two cholesterol ester hydrolase activities (termed the pH 6.0 and pH 7.2 activities) in cultures derived from 19- to 21-day-old dissociated fetal rat brains and in developing rat brain. In vivo the levels of both the pH 6.0 and pH 7.2 activities began to increase by about 10 postnatal days, reached maximal levels at 20 days (20 and 1.5 nmol/h/mg protein, respectively), and thereafter remained nearly constant (pH 6.0) or decreased somewhat before becoming constant (pH 7.2). In contrast, in the cultures the pH 6.0 cholesterol ester hydrolase activity was low until 21 days in culture (DIC; 20 nmol/h/mg protein), increased to a peak activity at 31 DIC (60 nmol/h/mg protein), remained high for 24 days, and finally decreased (18 nmol/h/mg protein at 63 DIC); the pH 7.2 cholesterol ester hydrolase activity was very low until 20 DIC, increased to a peak activity at 31 days (3 nmol/h/mg protein), and thereafter decreased to a lower level (2 nmol/h/mg protein) that was maintained for about 24 days before decreasing (0.7 nmol/h/mg protein at 63 DIC). Therefore, (a) the time courses of appearance of both cholesterol ester hydrolase activities were delayed by 10–14 days relative to that seen in vivo, and (b) the specific activities observed in the cultures were transiently two- to three-fold higher than in rat brain, but then declined to levels characteristic of whole brain homogenates. Subcellular fractionation of the cultures demonstrated that the pH 7.2 cholesterol ester hydrolase activity, along with myelin basic protein and 2′,3′-cyclic nucleotide-3′-phosphohydrolase activity, was enriched in a membrane fraction collected at an interface between 0.32 M and 0.9 M sucrose; the pH 6.0 cholesterol ester hydrolase activity, in contrast, was enriched in the microsomal fraction.     

Cell Wall Degrading Enzymes in Cuscuta reflexa and Its Hosts

Pectin degrading enzymes, hemicellulose degrading enzyme andcellulose degrading enzymes were studied in Cuscuta reflexaRoxb., its susceptible hosts, Brassica campestris L., Cocciniaindica W. & A. Datura innoxia Mill, Helianthus annuus L.,Holoptelea indica Planch, Lantana camara L., Medicago sativaL., Manihot utilissima Pohl, Petunia hybrida X Hort exvilm,Pisum sativum L., Phaseolus vulgaris L. and Solanum nigrum L.and non-susceptible plants Ipomoea batata Lam. and Solanum tuberosumL. Pectin esterase and polygalacturonase were present in higheramounts in Cuscuta parasitic on P. vulgaris and S. nigrum, whichneeded more time for haustorial establishment. Exo-l, 4-ß-D-glucosidaseactivity was found in Cuscuta but could not be detected in itshosts. Xylanase and cellulase activity of host plants increasedwhile cellobiase activity decreased as a result of infectionby the parasite. Higher pectin esterase, polygalacturonase,xylanase and exo-l, 4-ß-D-glucosidase activities inthe haustorial region of the parasite is likely to bring aboutthe lysis of the cell wall of the host plant and thus facilitatethe penetration of the parasite haustoria into the host sieveelement, which is necessary for the transport of nutrients betweenthe host and the parasite. Key words: Cell wall degrading enzymes, Cuscuta reflexa     

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.     

Studies on the Physiology of Host-parasite Relationship in Orobanche. I. Respiratory Metabolism of Host and Parasite

The respiratory rate of the roots of mustard (Brassica cam-pestris L.) and tomato (Lycopersicum esculentum Mill.) serving as hosts for the total root parasites Orobanche aegyptiaca Pers. and O.cernua Loefll. was measured using Warburg manometric technique. At the same time determinations were made of the respiration of the apical, basal and root regions of the parasites. The effects of sodium fluoride, malonic acid, sodium azide and DNP (2,4-dinitrophenol) on the rate of respiration of the host roots as well as of the parasites were studied. The Orobanche infection results in a marked increase in the respiratory rate near the host-parasite contact region. The damaging effect of infection seems to be due mainly to a continuous flow of water, minerals and metabolites from host to parasite. The haustorial invasion creates an obstruction in the translocation of metabolites. The respiration rate is lower in Orobanche than in the host, which might be related to its slower growth rate, inefficient oxidative processes and an escaping of certain energy-requiring interconversion processes. Roots of O. aegyptiaca are more well-developed and have higher rate of respiration. They can absorb more water and minerals from the soil. This fact might be connected with the specificity of the two species. NaF and malonic acid inhibit the respiration to a similar extent in healthy and infected roots. This indicates that the pathway of respiration does not change materially after infection. The EMP and Krebs cycle seem to operate at a lower intensity in Orobanche, which is proved by the lower inhibition of the respiration as compared to in the host. Azide causes a stronger reduction of the respiration in infected than in healthy roots. It would imply that the infection stimulates the activity of metal containing oxidases. The weaker inhibition of the respiration in Orobanche tissues indicates a mediation of other enzymes in the oxidation processes than in the host. The respiration is less stimulated by DNP in infected than in healthy roots. Contrary to the general effect of DNP, this substance decreases the O₂ uptake in the parasite tissues. This fact may be explained by the occurrence of exceptionally high amounts of endogenous phenolic compounds and an insufficient production of ATP in the parasite.