Immunogold Localization of the L3 Protein of Maize Lipid Bodies during Germination and Seedling Growth

We have used antibodies directed against the 16.5 kilodalton protein L3, the most abundant integral protein of maize (Zea mays L. cv Mo 17) lipid bodies, to follow the fate of this protein in scutellar parenchyma cells of maize during germination and subsequent seedling growth. Using gel electrophoresis and immunoblotting as well as immunocytochemical electron microscopy, we found that the amount of L3 decreases gradually during the first 3 to 4 days of seedling growth and more rapidly over the course of the next several days. Immunogold localization of the protein on thin sections indicated that L3 is found exclusively in the surface phospholipid monolayer of lipid bodies. The density of L3 in the surface layer of individual lipid bodies does not change during seedling growth; therefore, the decrease in the amount of L3 can be attributed to a decrease in the number of lipid bodies rather than to selective removal of protein components from the surface of all lipid bodies. Thus, L3 is apparently degraded at the same time as the matrix lipid of each lipid body. Unlike lipase, L3 does not appear to be transferred to other cellular compartments such as vacuoles during late stages of seedling growth.     

Acid Lipase of Castor Bean Lipid Bodies : Isolation and Characterisation

The acid lipase of castor endosperm lipid bodies has been studied using colorimetric assay based on the measure of the hydrolytic activity of p-nitrophenyl ester of palmitate and other acyl derivatives. These substrates are compatible with the natural triacylglycerols for the measure of lipolytic activities. The subcellularly-surveyed acid lipolytic activity in the germinated castor bean endospermal tissue was found to be enhanced in the lipid bodies. The lipase, which is partially latent and tightly associated with lipid bodies, is an exceptionally stable enzyme with an optimum activity at pH 4.5 and displays an inverse relationship between its activity and the acyl chain length of its substrate. To facilitate isolation of the acid lipase, a procedure has been developed to solubilise the membrane-bound enzyme in an active form. The detergent-solubilised acid lipase after two chromatographic steps yielded an eight-fold active preparation which after gel permeation resolved as heterogeneous aggregate in excess of 500 kD. Lipase-enriched preparations showed consistent presence of 14 and 60 kD proteins which constituted the most abundant species of the lipid bodies. Although it has not been possible to obtain an active lipase preparation in a state free of either the 14 or 60 kD protein, the lipase activity in the detergent extracts of lipid bodies was immunoprecipitable with antibodies raised against the 60 kD component.     

Inhibition of Neutral Lipase from Castor Bean Lipid Bodies by Coenzyme A (CoA) and Oleoyl-CoA

The neutral lipase (EC 3.1.1.3) in lipid body membranes isolated from the endosperm of 4 day old castor (Ricinus communis L.) seedlings catalyzes the hydrolysis of [¹⁴C]trioleoylglycerol, releasing [¹⁴C]oleic acid for up to 4 hours. However, the addition of Mg-ATP and coenzyme A (CoA), which are present in the cytoplasm of plant cells, caused a progressive inhibition of the neutral lipase such that after 15 minutes, release of [¹⁴C]oleic acid was almost undetectable. A fatty acyl CoA synthetase was found in the lipid body membrane which converts [¹⁴C]oleic acid produced from the lipase reaction to [¹⁴C]oleoyl-CoA under these conditions. The concentration of free oleoyl-CoA in the reaction mixture when the lipase was inhibited by 50% was calculated to be about 21 micromolar. It was found that a mixture of exogenously added oleoyl-CoA and CoA was most effective in causing lipase inhibition. Little inhibition of lipase was detected in the presence of CoA alone. It is possible that this effect is important In vivo in coordinating lipase activity with fatty acid oxidation.     

Effect of Fluoride on Nucleic Acids and Growth in Germinating Corn Seedling Roots

Corn seeds were treated with 0.01 M sodium fluoride for various time periods. The treated seeds were germinated and grown until the seedling roots reached a standard size of 12±3 mm. Analyses were made for RNA and DNA contents of 3-mm seedling root tips. Determinations also were made for growth rate, rate of cell elongation, cell multiplication, and tissue maturity of 12-mm roots. RNA contents of 3-mm root tips were found to be directly proportional to the growth rates of the entire seedling root of corn seeds treated with sodium fluoride for various periods of time. The RNA content was reduced on a cell basis and was independent of the root tip cell number. The amount of DNA was not related to the growth rate of the intact seedling roots. Since fluoride reduced the number of mitotic figures, it was likely that fluoride inhibited DNA synthesis during the interphase of the mitotic cycle. Growth by cell multiplication was inhibited more than that by cell elongation in the sample treated with fluoride for a shorter period. The two types of growth, however, showed a similar level of growth reduction in the sample treated with fluoride for a longer period. Fluoride seemed to reduce the rates of cellular elongation and multiplication not more than about 40 per cent of the control value in these tissues under present experimental conditions. Fluoride also induced maturity in the seedling roots in proportion to the periods of fluoride treatment.     

焚烧秸秆不利于玉米幼苗和根际微生物的生长

焚烧秸秆对玉米幼苗生长具有明显抑制作用,苗高、苗鲜重、苗干重、苗体积、根干重、根体积、须根数、根系活力、胚乳有机物转化率均明显降低.根际微生物中的细菌、放线菌和真菌分别减少36.53%、16.20%和21.17%.     

NaCl胁迫对糯玉米种子发芽和幼苗生长的影响

采用InfoStat软件中DGC方差分析法,研究不同浓度NaCl对糯玉米种子发芽和幼苗生长影响的结果表明,随着NaCl浓度的增加,糯玉米的种子发芽势、发芽指数、活力指数、发芽速度以及苗高和根长均下降,而发芽时间延长,根苗比升高,活性氧清除能力显著降低,膜系统受损严重。     

Growth Interactions during Bacterial Colonization of Seedling Rootlets

Rootlet elongation and bacterial growth on rootlets were determined after inoculation of cucumber and spinach seedlings with Pseudomonas strains differing in production of siderophores and HCN. Siderophore producers grew more profusely than nonproducers on both species and promoted rootlet elongation on cucumber. Coinoculation of siderophore producers and nonproducers resulted in restricted growth of the latter. The total populations of nonproducers of HCN in the presence of HCN producers were not decreased, but the tenacity of their association with the rootlet surface was altered.     

Inoculation with Azospirillum lipoferum Affects Growth and Gibberellin Status of Corn Seedling Roots

Maize (Zea mays L., hybrid Cargill 147) seedlings, grown inaseptic conditions, were inoculated with three strains of Azospirillumlipoferum (Al op 33, Al iaa 320, and ATCC 29708) or culturedin different concentrations of indol-3-acetic acid (IAA) orgibberellin A₃ (GA₃). After 48 h, root length, root surfacearea, root dry weight, and shoot dry weight were measured inall treatments. Gibberellin content was evaluated in selectedroots of control and Azospirillum inoculated seedlings by gaschromatography-mass spectrometry-selected ion monitoring withthe use of deuterated gibberellins as internal standards. Thethree strains of A. lipoferum, IAA (2 ng ml^–1), and GA₃(40 to 400 pg ml^–1) significantly enhanced root growth.Improvement of root hair growth and density was obtained mainlywith A. lipoferum strain Al op 33 and GA₃ 40 pg ml^–1.GA₃ was identified by gas chromatography-mass spectrometry (byboth, full scan and selected ion monitoring) in a free acidfraction from roots of the seedlings inoculated with A. lipoferum.In the roots of the non inoculated seedlings GA₃ was found afterhydrolysis of a fraction expected to contain glucosyl conjugates. (Received April 26, 1993; Accepted September 27, 1993)     

Respiration and Alternative Oxidase in Corn Seedling Tissues during Germination at Different Temperatures

Respiration rates of Zea mays L. seedling tissues grown at 30 and 14°C were measured at 25°C at different stages of seedling growth. Accumulation of heat units was used to define the developmental stages to compare respiration between the two temperatures. At both temperatures, respiration rates of most tissues were highest at the youngest stages, then declined with age. Respiration rates of mesocotyl tissue were the most responsive to temperature, being nearly twofold higher when grown at 14 compared to 30°C. Alternative pathway respiration increased concomitantly with respiration and was higher in mesocotyls grown in the cold. When seedlings were started at 30 then transferred to 14°C, the increase in alternative pathway respiration due to cold was not observed unless the seedlings were transferred before 2 days of growth. Seedlings transferred to 14°C after growth at 30°C for 2 days had the same alternative oxidase capacity as seedlings grown at 30°C. Seedlings grown at 14°C for 10 to 12 days, then transferred to 30°C, lost alternative pathway respiratory capacity over a period of 2 to 3 days. Western blots of mitochondrial proteins indicated that this loss of capacity was due to a loss of the alternative oxidase protein. Some in vitro characteristics of mitochondria were determined. The temperature optimum for measurement of alternative oxidase capacity was 15 to 20°C. At 41°C, very little alternative oxidase was measured, i.e., the mitochondrial oxygen uptake was almost completely sensitive to cyanide. This inactivation at 41°C was reversible. After incubation at 41°C, the alternative oxidase capacity measured at 25°C was the similar to when it was measured at that temperature directly. Isolated mitochondria lost alternative oxidase capacity at the same rate when incubated at 41°C as they did when incubated at 25°C. Increasing the supply of electrons to isolated mitochondria increased the degree of engagement of the alternative pathway, whereas lower temperature decreased the degree of engagement. Lower temperatures did not increase the degree of engagement of the pathway in intact tissues. We interpret these observations to indicate that the greater capacity of alternative oxidase in cold-grown seedlings is a consequence of development at these low temperatures which results in elevated respiration rates. Low temperature itself does not cause greater capacity or engagement of the alternative oxidase in mitochondria that have developed under warm temperatures. Our hypothesis would be that the low growth temperatures require the seedlings to have a higher respiration rate for some reason, e.g., to prevent the accumulation of a toxic metabolite, and that the alternative pathway functions in that respiration.     

Demonstration of the Lipid Lipase Activators Produced by Candida paralipolytica

Lipase activators were extracted with ethyl ether from the culture medium of Candida paralipolytica at pH 2 and two kinds of activators were separated by silica gel column chromatography. The main component (activator A) was an oily liquid, and showed an Rf value different from that of oleic acid on thin-layer chromatograms. One mole of activator A seemed to be necessary to activate one active site of the lipase and it lowered the optimum pH of the lipase from 8.2 to 7.0. In relation to this, it was found that urea, ethanol and sodium chloride had the ability to lower the optimum pH.     

Lipid Requirement for the Lipase Production by Geotrichum candidum Link

The injection of live or heat-killed bacteria into larvae of the silkworm, Bombyx mori, induced antibacterial activity in the hemolymph. A wide variety of gram-negative and gram-positive bacteria were effective as inducing agents, but saline alone, yeast cells and fungal spores were not effective. The antibacterial activities were separated into six bands on native polyacrylamide gel electrophoresis, which were sensitive to trypsin. Some of these antibacterial proteins were partially purified by CM-cellulose column chromatography. The proteins were heat-stable and showed no lysozyme activity. The proteins repressed the growth of various gram-positive and gram-negative bacteria.     

Changes in Enzyme Regulation during Growth of Maize: I. Progressive Desensitization of Homoserine Dehydrogenase during Seedling Growth

The sensitivity of homoserine dehydrogenase (EC 1.1.1.3) to inhibition by the feed-back modifier, l-threonine, was examined in preparations derived from etiolated shoots, roots, and lightgrown tissues of Zea mays L. var. earliking. A progressive decrease in enzyme sensitivity was observed during seedling growth. Enzyme derived from internode tissue retained a greater sensitivity to the effector than enzyme derived from apical portions of etiolated shoots, whereas enzyme from root tips was characteristically more sensitive than that prepared from mature cells of the root. Enzyme desensitization occurred rapidly during culture of excised shoots and the activities of both homoserine dehydrogenase and aspartokinase (EC 2.7.2.4) declined during shoot culture under a variety of conditions. The initial enzyme levels and the characteristic sensitivity of homoserine dehydrogenase were preserved during culture at 5 to 7 C, but desensitization was not prevented by inclusion of cycloheximide in the culture medium.Results of control experiments provide evidence that desensitization occurs in vivo. No alteration of the enzyme properties was detected during extraction or concentration of sensitive or insensitive enzyme or during coextraction of enzyme from mixed populations of different age shoots; nor was a differential distribution of inhibitors or activators indicated during assay of mixed preparations. The change in enzyme sensitivity was apparent under a variety of assay conditions and was not accompanied by changes in the apparent affinity of the enzyme for the substrate, homoserine. It is suggested that systematic changes in the regulatory characteristics of certain enzymes could be an important level of metabolic regulation during cellular differentiation.Three forms of maize homoserine dehydrogenaase were detected after acrylamide gel electrophoresis of samples derived from 72-hr shoots. Similar analysis of samples from older shoots revealed a broad asymmetric band of enzyme activity, suggesting that changes in the relative distribution of specific forms of the enzyme could be related to the growth-dependent changes in the sensitivity of maize homoserine dehydrogenase.     

Selective Modulation of RNA Polymerase I Activity during Growth Transitions in the Soybean Seedling

RNA polymerase I and II activities were measured in tissues of the soybean (Glycina max, var. Wayne) hypocotyl where dramatic changes in the relative level of RNA synthesis are associated with normal and auxin-induced growth transitions. When assayed in isolated nuclei, the activity of RNA polymerase I changed much more than the activity of RNA polymerase II during these growth transitions. The activity of RNA polymerase I expressed in the nuclei generally showed a positive correlation with the relative level of RNA synthesis (i.e. accumulation) of that tissue. Following solubilization of the RNA polymerases from these isolated nuclei and fractionation of them on DEAE-cellulose, the activity of RNA polymerase I relative to that of RNA polymerase II showed smaller changes during these growth transitions than when assayed in the nuclei. Thus, these data indicate that the activity of RNA polymerase I is significantly modulated in the nucleus, up or down depending upon the growth state, during growth transitions in the soybean in addition to lesser changes which occur in the apparent level of the enzyme.     

麦秸覆盖夏玉米对其苗期生长发育的生化他感作用研究初报

麦秸覆盖夏玉米对其苗期生长发育的生化他感作用研究初报张玉铭,马永清（中国科学院石家在农业现代化研究所,０５００２１）ＡｌｌｅｌｏｐａｔｈｉｃＥｆｆｅｃｔｏｆＷｈｅａｔＳｔｒａｗＭｕｌｃｈｉｎｇｏｎＳｅｅｄｌｉｎｇＧｒｏｗｔｈａｎｄＤｅｖｅｌｏｐｍｅｎ...     

Effect of Lipid Materials on the Production of Lipase by Torulopsis ernobii

The yeast Torulopsis ernobii produced approximately 50 units of extracellular lipase (glycerol ester hydrolase, E.C. 3.1.1.3) per ml when grown in 30-liter fermentors at 33 C for 40 hr in a base medium at pH 5.0. The addition of fats, oils, triglycerides, or higher fatty acids to this medium at concentrations of 0.2 to 0.6% markedly increased production; twofold increases in yield were obtained when 0.2% olive oil or a mixture of 0.14% oleic acid and 0.04% palmitic acid was added. The production of lipase paralleled growth, and the role of lipid materials in augmenting lipase production appears to be related to cell growth.     

Lipid Bodies in Eremosphaera viridis De Bary (Chlorophyceae)

Under conditions of stress, e.g., nitrogen deficiency, Eremosphaeraviridis De Bary (Chlorophyceae, Chlorococcales) synthesizedsecondary carotenoids and large amounts of triacylglycerolsforming orange-red, cytosolic lipid bodies. Additionally, fourpolypeptides (28, 26, 25 and 23 kDa) as well as traces of chlorophylla and b, of violaxanthin, neoxanthin and zeaxanthin, and ofmembrane lipids could be demonstrated in isolated lipid bodies.No membrane could be shown around the lipid bodies by the useof electron microscopy. The formation of lipid bodies in Eremosphaerais discussed as a bulging of the chloroplast envelope membranes. (Received June 25, 1991; Accepted October 26, 1991)     

Nitrogen Fixation in Peanut Nodules during Dark Periods and Detopped Conditions with Special Reference to Lipid Bodies

The peanut plant (Arachis hypogaea L.), unlike other known legumes, can sustain nitrogen fixation when prolonged periods of darkness or detopping curtail the supply of photosynthate to the nodule. This ability to withstand photosynthate stress is attributed to the presence of lipid bodies in infected nodule cells. In both dark-treated and detopped plants, the lipid bodies show a gradual decrease in numbers, suggesting their utilization as a source of energy and carbon for nitrogen fixation. Lipolytic activity can be localized in the lipid bodies, and the existence of β-oxidation pathway and, glyoxylate cycle is shown by the release of ¹⁴CO₂ from ¹⁴C lineoleoyl coenzyme A by the nodule homogenate.     

The Role of Lipid Bodies in the Microglial Aging Process and Related Diseases

Lipid bodies (LBs) have long been considered to be organelles merely for the storage of neutral lipids. However, recent studies have shown the significance of LBs in signal transduction, especially in glial cells, including microglia. Microglial cells are the resident mononuclear phagocytes in the central nervous system and have a close relationship with the aging process and neurodegenerative diseases. Evidence suggests that LBs accumulate and are remodeled during the aging process and the development of neuroinflammatory conditions. However, the mechanisms underlying the formation of LBs under these conditions and the mechanism by which LB remodeling influences the progression of neurodegeneration remain to be clarified. In this review, we have summarized the findings from recent studies with the aim of further elucidating these issues.     

Seedling Growth in Controlled-Nutrient Conditions

An apparatus is described in which seedlings can be grown ona non-polar substrate in continuously flowing nutrient solutionsgiving a constant and defined root environment. The apparatus,which is simple to construct, allows seedling growth studiesto be begun as soon as the seeds have germinated. In an experiment in which seedlings were grown for 13 d in nutrientsolutions allowing normal growth or severely restricted growth,or were transferred from the latter to the former after 3 or6 d, root lengths and cotyledon areas differed significantlyafter only 3 d. After 13 d the transferred seedlings, althoughsmaller in absolute size than the normal seedlings, resembledthem in a number of over-all morphological features. Because of the rapid and substantial effects that nutrient treatmentscan have on seedling growth, it is suggested that seedling developmentstudies should be carried out under carefully controlled andaccurately defined nutrient conditions.