Nucleic Acid Metabolism during Greening and Unrolling of Barley Leaf Segments

Barley (Hordeum vulgare) leaf segments unroll and green when illuminated. Illuminated segments also have an increased capacity for RNA synthesis. Part of this increased RNA synthesis may be attributed to an increased RNA polymerase activity. In addition, following illumination there is an increased formation of polysomes.     

Chloroplast Protein Synthesis During Barley Leaf Growth and Senescence: Effect of Leaf Excision

Chloroplast protein synthesis was measured during the expansion,maturity and senescence of the oldest leaf of barley, Hordeumvulgare L., var. Hassan. A maximum rate of protein synthesisoccurred near the end of the expansion stage 9 d after sowing.Protein synthesis increased again at the beginning of senescenceand reached a new maximum at day 14 after sowing. Detachmentand incubation of leaves in the dark stimulated chioroplastprotein synthesis by fully expanded or by senescent leaves butnot by expanding leaves. If the detached leaves were kept inthe light, chloroplast protein synthesis was stimulated in fullyexpanded but not in senescent leaves. Short treatments (18 h)of leaf segments with growth substances in either light or indarkness, significantly changed the rate of protein synthesisshown by chloroplasts. The relationship between chloroplastprotein synthesis and leaf senescence is discussed. Key words: Hormones, light, maturity     

Uzu Mutation in Barley (Hordeum vulgare L.) Reduces the Leaf Unrolling Response to Brassinolide

A sensitive method to examine the brassinolide (BL) response of barley (Hordeum vulgare L.) using dark-grown leaf segments was established based on the known method for wheat. BL responses of 53 dwarf isogenic lines of barley were examined, and two lines were found having a uzu gene that doesn't respond significantly. These results indicate that uzu dwarfism may be caused by the non-responding character to BL.     

Incorporation of C-Leucine into Apple Leaf Protein and Its Inhibition by Protein Synthesis Inhibitors during Growth and Senescence

Of the total ¹⁴C-leucine taken up by intact apple (Pyrus malus L., Golden Delicious) leaf discs, 44 to 62% is incorporated into protein from June to early October. Of this amount, an average of 35% is released by mild, room temperature acid hydrolysis. Prior to mid-August when leaf protein begins to decline, 15 to 20% of the ¹⁴C-leucine incorporated into protein occurs in water-(buffer) soluble protein, of which only 3% is released by mild acid hydrolysis. After mid-August, 40% of the label in protein occurs in soluble protein. The specific radio-activity of the soluble protein increases by 4- to 5-fold after mid-August, while that of total protein increases by less than 2-fold. In presenescent leaves (before the decline of protein in August) 20 micrograms per milliliter cycloheximide inhibits the incorporation of ¹⁴C-leucine into protein by 71%, and 20 micrograms per milliliter chloramphenicol inhibits it by 30%. In senescing leaves, cycloheximide inhibits ¹⁴C-leucine by 85% or more, while chloramphenicol inhibits it by less than 15%. Coincident to the initial decline of leaf protein, chloramphenicol greatly loses its ability to inhibit the incorporation of ¹⁴C-leucine into apple leaf protein. At all leaf ages, chloramphenicol increases the loss of chlorophyll from apple leaf discs. The effect of cycloheximide on leaf disc senescence changes with leaf age: in early season samples, it increases the loss of chlorophyll; in mid-season samples, it has no effect; and in late season samples, it retards the loss of chlorophyll.     

Cell Morphogenesis and Macromolecule Synthesis during Phytochrome-controlled Germination of Spores of the Fern, Pteris vittata

The object of this study was to characterize the pattern ofcell morphogenesis and synthesis of nucleic acids and proteinsduring phytochrome-controlled germination of spores of the fern,Pteris vittata. Phytochrome activation and germination wereinitiated in fully imbibed spores by exposure to a saturatingdose of red light. At timed intervals thereafter, spores werefixed in acrolein and embedded in glycol methacrylate for examinationin the light microscope. The first sign of germination, visiblein sections of the spore 12 h after irradiation, was the hydrolysisof storage protein granules. This was followed by a migrationof the nucleus from its central location to one side of thespore. Subsequently, the protoplast enlarged at the site ofthe nucleus and appeared outside the exine as a papillate structure.An asymmetrical division of the protoplast gave rise to a smallcolourless rhizoid cell and a large, chloroplast-containingprotonemal cell. During the early phase of germination, DNAwas synthesized both in the nucleus and cytoplasm as judgedby autoradiography of [³H]thymidine incorporation. [³H]Uridine,a precursor of RNA synthesis, was incorporated into the nucleolusand the rest of the nuclear material of germinating spores.Protein synthesis monitored by [³H]leucine incorporation occurredboth in the nucleus and cytoplasm during the early stage ofgermination, although a strictly cytoplasmic protein synthesiswas observed later. Addition of cycloheximide completely inhibitedgermination of photoinduced spores and incorporation of labelledprecursors of macromolecule synthesis into cellular components.Actinomycin D was much less effective as an inhibitor of germinationand, even in high concentrations of the drug which effectivelyinhibited DNA and RNA synthesis in spores, proteolysis and proteinsynthesis appeared normal. These findings are discussed withrespect to the regulation of nucleic acid and protein synthesisduring spore germination and the role of phytochrome in theprocess.     

Phytochrome-controlled ethylene biosynthesis of intact etiolated bean seedlings

Intact etiolated bean (Phaseolus vulgaris L. cv. Limburgse vroege) seedlings were illuminated with red light (10.5 W·m^-2) for 10 min. After different time intervals ethylene production, and contents of 1-aminocyclopropane-1-carboxylic acid (ACC) and 1-(malonylamino)cyclopropane-1-carboxylic acid were measured. The red-light-induced decrease of ethylene production in 8-d-old intact etiolated bean seedlings was fast, strong and long-lasting ad was mediated through the phytochrome system. This effect appeared to be strictly age-dependent, as it could not be detected in plants younger than 6 d or older than 11 d.The capacity for the conversion of ACC to ethylene was not affected by red light. The inhibitory effect of the light treatment on ethylene production could be related to a reduced free-ACC content. This reduction was a consequence of a temporary non-reversible increase of ACC malonylation and a long-lasting, for a certain time reversible, inhibition of ACC synthesis. The effect of a brief irradiation with red light on the decrease of ethylene production and free-ACC content was completed after about 2 h. Reversibility by far-red, however, persisted for at least 3 h, and was lost between 3 and 6 h.Abbrevation ACC 1-aminocyclopropane-1-carboxylic acid - M-ACC 1-(malonylamino)cyclopropane-1-carboxylic acid     

Phytochrome-controlled Hydrogen Ion Excretion by Avena Coleoptiles

A red light-induced, far red reversible stimulation of proton efflux from apical segments of etiolated Avena sativa L. cv. Victory coleoptiles was observed. The acidification responses to red light and also to auxin were not the consequence of respired CO(2). The response to red light was strongly inhibited by cycloheximide and carbonyl cyanide, m-chlorophenyl hydrazone, but mannitol had a stimulatory effect. Red light and auxin applied together yielded a greater than additive response, in comparison to the effects of the two stimuli applied separately.     

叶蛋白食用研究与开发应用

随着世界人口的剧增和人民生活水平的提高,人类对优质蛋白的需求越来越大,开发新的蛋白质势在必行。植物叶蛋白因具有来源广泛、营养丰富、不含动物性胆固醇等特点而备受关注。从叶蛋白的组成特点、食用研究、研究进展及应用现状出发,论述了叶蛋白的食用研究状况和开发价值。最后提出其在食品应用中的局限性以及一些改进措施。     

Regulation of Corn Leaf Nitrate Reductase : II. Synthesis and Turnover of the Enzyme's Activity and Protein

The appearance and disappearance of NADH:nitrate reductase (NR) in the leaves of corn (Zea mays L. W64A × W182E) were studied using activity assays, an enzyme-linked immunosorbent assay (ELISA) and western blotting. N-starved, etiolated corn plants were treated with nutrients containing either 35 millimolar NH₄-nitrate or K-nitrate and immediately thereafter given light. The curve for enhancement of NR activity had three phases: 1 hour lag, 5 hour rapid increase, and steady state. The pattern for NR protein, as measured with the ELISA, also had three phases, but the increase was more rapid and the steady state was established earlier. To differentiate the effects of N nutrition from those of light, N-starved etiolated plants were given N nutrients 4 hours before light. During the dark pretreatment, NR activity and protein increased. When the light was turned on the NR activity and protein increased very rapidly without a lag. Western blots of polyacrylamide gels of native and denatured crude extracts showed that NADH:NR polypeptide was absent prior to treatment with N nutrients, but appeared after nitrate was given in dark or light. A low level of NR activity was found in N-starved, etiolated plants and it was shown by western blotting to be an NR form with a different electrophoretic mobility in nondenaturing gels. Since this minor NR form was not influenced by either nitrate or light, it was designated a constitutive NR. Dark decay of NR activity and protein was also studied. After the plants which had been in light with N nutrients for 24 hours were transferred to dark, the NR activity dropped by 30% within 1 hour, but the NR protein did not decrease. This inactivation of NR was further supported by returning the plants to the light after 1.5 hours of dark and finding the activity restored without change in NR protein. After the initial activity drop, a parallel decrease in NR activity and protein was observed, which was likely due to irreversible degradation by proteolysis.     

Phytochrome-controlled extension growth of Avena sativa L. seedlings

The effects of continuous red and far-red light and of brief light pulses on the growth kinetics of the mesocotyl, coleoptile, and primary leaf of intact oat (Avena sativa L.) seedlings were investigated. Mesocotyl lengthening is strongly inhibited, even by very small amounts of P_fr, the far-red light absorbing form of phytochrome (e.g., by [P_fr]0.1% of total phytochrome, established by a 756-nm light pulse). Coleoptile growth is at first promoted by P_fr, but apparently inhibited later. This inhibition is correlated in time with the rupturing of the coleoptile tip by the primary leaf, the growth of which is also promoted by phytochrome. The growth responses of all three seedling organs are fully reversible by far-red light. The apparent lack of photoreversibility observed by some previous investigators of the mesocotyl inhibition can be explained by an extremely high sensitivity to P_fr. Experiments with different seedling parts failed to demonstrate any further obvious interorgan relationship in the light-mediated growth responses of the mesocotyl and coleoptile. The organspecific growth kinetics, don't appear to be influenced by P_fr destruction. Following an irradiation, the growth responses are quantitatively determined by the level of P_fr established at the onset of darkness rather than by the actual P_fr level present during the growth period.Abbreviation P_fr far-red light absorbing form of phytochrome     

Ligand Specificity of Bean Leaf Soluble Auxin-binding Protein

The soluble bean leaf auxin-binding protein (ABP) has a high affinity for a range of auxins including indole-3-acetic acid (IAA), α-napthaleneacetic acid, phenylacetic acid, 2,4,5-trichlorophenoxyacetic acid, and structurally related auxins. A large number of nonauxin compounds that are nevertheless structurally related to auxins do not displace IAA from bean ABP. Bean ABP has a high affinity for auxin transport inhibitors and antiauxins. The specificity of pea ABP for representative auxins is similar to that found for bean ABP. The bean ABP auxin binding site is similar to the corn endoplasmic reticulum auxin-binding sites in specificity for auxins and sensitivity to thiol reagents and azide. Qualitative similarities between the ligand specificity of bean ABP and the specificity of auxin-induced bean leaf hyponasty provide further evidence, albeit circumstantial, that ABP (ribulose 1,5-bisphosphate carboxylase) can bind auxins in vivo. The high incidence of ABP in bean leaves and the high affinity of this protein for auxins and auxin transport inhibitors suggest possible functions for ABP in auxin transport and/or auxin sequestration.     

Relationship Between Protein Synthesis and Viral Deoxyribonucleic Acid Synthesis

Evidence is presented that poxvirus deoxyribonucleic acid (DNA) synthesis required concurrent protein synthesis. The protein requirement in question can be distinguished from viral-induced thymidine kinase and DNA polymerase by virture of the instability of its messenger ribonucleic acid and its stoichiometric rather than catalytic relation to DNA synthesis. The protein(s) required did accumulate in the presence of fluorodeoxyuridine, an inhibitor of DNA synthesis, and, thus, appeared to be an "early" poxvirus function. The protein(s) was stable since it did function several hours after its synthesis had been terminated by puromycin. Two possible roles for such a protein requirement are discussed.     

Regulation of Maize Leaf Sucrose-Phosphate Synthase by Protein Phosphorylation

Studies were conducted to determine the potential for regulationof maize leaf sucrose-phosphate synthase (SPS) by protein phosphorylation.Highly activated enzyme, in desalted crude leaf extracts preparedfrom illuminated leaves, was inactivated in vitro in a time-and ATP-de-pendent manner. Partial purification of SPS by polyethyleneglycol fractionation and Mono Q chromatography yielded enzymethat was not ATP-inactivated, possibly due to elimination ofcontaminating protein kinase. We used the partially purifiedSPS as substrate to identify an endogenous protein kinase. Theprotein kinase catalyzed the time- and ATP-dependent inacti-vationof SPS, and the apparent K_m for Mg-ATP was estimated to be approximately10µM. The partially purified maize SPS protein was phosphorylatedin vitro using [y-³²P]ATP and either the endogenous proteinkinase or the catalytic subunit of cAMP-dependent protein kinase.The incorporation of radiolabel was closely paralleled by inactivationof the enzyme. These results provide the first evidence forregulation of maize leaf SPS by protein phosphorylation, whichwe postulate is the mechanism of light-dark regulation in vivo. (Received October 23, 1990; Accepted January 7, 1991)     

Ribulose-1,5-Diphosphate Carboxylase Protein during Flag Leaf Senescence

Ribulose-l,5-diphosphate (RuDP) carboxylase protein and activitywere determined in relation to net photosynthetic rate duringthe senescence of intact flag leaves of wheat on the plant.Initially the decrease in RuDP carboxylase activity was greaterthan the decline in net photosynthesis. The major decrease inRuDP carboxylase activity over this period resulted from a decreasein enzyme specific activity from 11 to 2 µmol CO₂ fixedh^–1 mg^–1 protein. Loss of RuDP carboxylase proteindid not occur until late in senescence by which time chlorophyllconcentration had decreased by more than 50%. Treatment of flagleaves at weekly intervals with either 1000 parts 10^–62-chloro-ethyltrimethylammonium chloride or 100 parts 10^–6gibberellic acid with 1 part 10^–6 kinetin did not significantlyaffect net photosynthetic rate, RuDP carboxylase protein oractivity during senescence.     

蛋白核酸合成抑制剂和蛋白磷酸化对基因表达的调节

环己酰亚胺和放线菌素D明显降低小麦幼苗中BADH基因的表达,表明BADH基因表达在转录和转译水平上受到调控。氯霉素则有增加表达的效应。线粒体可能形成阻遏蛋白参与调节。H7和甘露糖降低BADH基因表达,相应地冈田酸(Okadaic acid)明显增加表达,说明蛋白磷酸化积极参与小麦幼苗中BADH基因表达的调节。