Dormancy in Light-sensitive Lettuce Seeds

Relatively brief treatment of imbibed seeds of positively photoblasticlettuce (Lactuca sativa L. cv. Cannington Forcing) with lowconcentrations of ethanol promotes germination. It is suggestedthat this effect is upon a cellular membrane, a view which issupported by the fact that a subsequent treatment with Ca²⁺markedly reduces the ethanol promotion. Data from experiments involving movement and transfer of seedsprovide no support for the involvement of a stable, leachable,endogenous inhibitor in the control of germination. It is concludedthat whether or not the seeds break dormancy is determined bythe interplay between forces generated in the developing embryoand the mechanical restraint provided by the tissues which envelopit.     

Red-Far Red Reversible Effect on Polysome Formation in the Embryos of Pinus thunbergii Seeds

Polysome formation in the embryos of Pinus thunbergii seeds was studied. Free ribosomes were dissociated to smaller subunits in a high salt buffer, but the complex ribosomes were not. The free ribosomes could be distinguished from monomer ribosomes derived from polysomes after RNase treatment. The monomer ribosomes present in the embryos of the dark-imbibed seeds were predominantly free ribosomes; very small quantities of polysomes could be detected in the embryos from dark-imbibed seeds. Such polysomes remained at a very low level during dark imbibition at least for a month. The level of polysomes increased 4 hours after a brief exposure to red light. The effect of red light on polysome formation was partially reversed when followed by far red light irradiation.     

Polysome Formation in Light-controlled Dormancy

Lettuce (Lactuca sativa) seeds var. Grand Rapids could be maintained many weeks in the dark without germination. Following illumination with white light, a gradual increase in polyribosome population up to the time of germination was demonstrated by sucrose gradient centrifugation. Polysomes could not be detected in imbibed seeds maintained continuously in the dark. Thus, polysome formation and therefore the capacity for a high rate of protein synthesis required for germination and growth, is not associated with the process of imbibition, but is dependent upon the seeds having received the dormancy-breaking stimulus of illumination.     

Ethylene, Nitrate and Nitrite Interactions in the Promotion of Dark Germination of Common Purslane Seeds

Ethylene (10 µ1^–1) caused about one-third of highlydark-dormant seeds of common purslane (Portulaca oleracea L.)to germinate in the dark. Attempts were made to increase germinationin the dark with nitrate and ethylene combinations. When applieddirectly to the seeds, KNO₃ did not stimulate germination andKNO₃ plus ethylene did not increase germination above that ofethylene alone. Pre-incubation of seeds in KNO₃ for 4 to 7 dbefore the ethylene applications significantly increased germination.The effects of the KNO₃ pre-incubation were additive at eachof four ethylene concentrations (0.1–100 µ11^–1).Potassium nitrate was effective only when ethylene followedthe KNO₃ pre-incubation period. Potassium nitrite stimulatedabout 25 per cent of the seeds to germinate without a pre-incubationperiod and without ethylene. Also, ethylene plus KNO₂ enhancedgermination above that achieved by either stimulus alone. Silvernitrate did not block the ethylene promotion of germination,but reversed the typical ethylene inhibition of seedling growthfollowing germination. The results support the views that nitrateexerted its effect via conversion to nitrite within the seedand that the rate of nitrate conversion may be a limiting factorin the dark germination of common purslane seeds. Ethylene mayfacilitate nitrite activity by increasing seed sensitivity tothe stimulus. Common purslane, Portulaca oleracea L., ethylene, nitrate, nitrite, germination, dormancy     

Protein Synthesis in Imbibed Seeds III. Kinetics of Amino Acid Incorporation Ribosome Activation, and Polysome Formation

The kinetics of development of protein-synthesizing capacity in the imbibing wheat embryo, were studied both in vivo and in vitro. During the first 30 minutes of imbibition protein-synthesizing capacity rises rapidly, lagging about 10 minutes behind water uptake. This rise in synthesizing capacity is accompanied by an increase in polysome content. As imbibition continues, both protein-synthesizing capacity and polysome content increase. With embryos from aged seed, the rate of protein synthesis is initially limited by another, presumably nonribosomal, reaction.     

Light-induced Polysome Formation in Etiolated Leaves: Kinetics of Inhibition by Antibiotics

Red light-induced, far red light-reversible increase in etiolated bean (Phaseolus vulgaris, var. Asgrow Valentine) leaf polyribosomes was shown to be sensitive to actinomycin D, cycloheximide, and rifampicin inhibition. Actinomycin prevented response to red light if administered simultaneously with a 10-minute illumination, had no immediate effect if given 2 hours after illumination, but was again rapidly inhibitory at 4 and 6 hours. The effects of actinomycin and far red light were more than additive.     

Induction of Polysome Formation in Sweet Potato Root Tissue in Response to Wounding

We determined the effects of yolk water-soluble protein (YSP) on bone resorption. YSP potently suppressed osteoclastogenesis from bone marrow-derived precursor cells driven by tumor necrosis factor-α (TNF-α). YSP (200 μg/ml) abolished the formation of tartarate-resistant acid phosphatase (TRAP)-positive osteoclasts. Furthermore, TNF-α induced TRAP activity was greatly inhibited by YSP (100 μg/ml) treatment. Our results suggest that YSP has therapeutic potential for bone-erosive diseases.     

Wounding Inhibits Protein Synthesis yet Stimulates Polysome Formation in Aged, Excised Pea Epicotyls

Wounding of aged, previously-excised pea epicotyl segments byremoval of the basal 1–2 mm resulted in a rapid (beginningwithin 15 min) recruitment of monosomes on to polysomes andan even more rapid (maximal between 6–12 min) inhibitionof protein synthesis in the remaining tissue. This inhibitionof protein synthesis in vivo did not appear to be an artefactcaused by the removal of highly active tissue (e.g., callus,contaminating bacteria), since wounds inflicted at a site distantfrom the region analyzed still elicited the response, and proteinsynthesis in the 1–2 mm slices (normally discarded) wasinhibited even more strongly than it was in the remaining tissue.The proportion of radioactive methionine in nascent chains (boundto polysomes) increased, while the production of completed polypeptidesdecreased, after wounding. Cycloheximide, a known inhibitorof the ribosome translocation/release process mimicked someof the effects of wounding. We interpret the results to indicatethat the initial effect of wounding is to inhibit translationby inhibiting the ribosome translocation/release process, whereasthe subsequent recovery in protein synthesis is brought aboutpartly by a recovery in ribosome translocation/release and partlyby enhanced initiation. ¹ Present address: Harvard-MIT Division of Health Science andTechnology, MIT, Cambridge, Massachusetts 02139, U.S.A. ² Present address: Institute of Agricultural Environment Control,College of Agriculture, Ehime University, 3-5-7 Tarumi, Matsuyama790, Japan. (Received May 26, 1986; Accepted August 4, 1986)     

Formation of Oleosomes in Maturing Safflower Seeds

The accumulation of oil in maturing safflower seeds was studied with an electron microscope. It was suggested that net-like clusters of proteinaceous particles in the cytoplasm are the site of triacylglycerol synthesis. No evidence was obtained to support the hypothesis that oleosomes originate in the. endoplasmic reticulum. A hypothesis has been proposed that triacylglycerols are initially synthesized by the net-like clusters in the cytoplasm to form a protein-oil complex, and the triacylglycerols are concentrated in the center of the cluster as their formation proceeds.     

Polysome Metabolism during Cold Acclimation in Wheat

The content, composition and biological activity of polysomesfrom three wheat genotypes were studied during cold acclimation.The structural integrity of the different polysome populationswas not affected by the hardening temperature. Polysomes werealso found to accumulate at higher level in cold hardened seedlingssuggesting a high protein synthesis capacity during the acclimationperiod. The in vitro translation of polysome-bound mRNAs inthe wheat germ cell-free system showed a high translation potentialof polysomes from cold hardened seedlings compared to that ofcontrol. The electrophoretic analysis of the translation productsby two-dimensional SDS-PAGE revealed the induction of severalnew mRNAs in cold hardened wheat seedlings. The presence ofthese new messengers in the polysomal fraction suggests thatnew messages have already been processed, transported and preferentiallyselected for translation by the ribosomes. The most importantchange was the induction and pronounced synthesis of four peptides[one high mol wt peptide of 200 kDa (pI 6.5) and three smallerones of 58 (pI 7.0), 48 (pI 7.1) and 48 (pI 7.2) kDa respectively]in the freezing tolerant cultivar Norstar. These specific polypeptideswere absent in the freezing sensitive cultivar Glenlea suggestingthat their induction and expression was associated with thefreezing tolerance capacity. (Received January 19, 1990; Accepted August 24, 1990)     

Polysome Turnover During Amino Acid Starvation in Escherichia coli

The experiments presented in this paper support earlier evidence that ribosomes are released from polysomes when they encounter a codon for which no charged transfer ribonucleic acid is available. However, it is further shown that these ribosomes then reinitiate and resume translation. The size and the level of polysomes during deprival of an amino acid is a function of the frequency with which that particular amino acid appears in cellular proteins. Polysomes from starved cells are more stable than those from growing cells, and, moreover, polysomes from starved relaxed strains are more stable than those from starved stringent strains.     

True Metabolizable Energy for Seeds of Common Moist-Soil Plant Species

Abstract: Understanding the true metabolizable energy (TME) value of food is important for constructing bioenergetic models. We estimated gross energy, nutrient composition, and TME values for the seeds of 3 native and 1 invasive exotic wetland plant that occur in the diet of waterfowl. True metabolizable energy values were 0.50 ± 0.080 kcal/g for spike rush (Eleocharis palustris), 0.65 ± 0.080 kcal/g for alkali bulrush (Schoenoplectus maritimus), 1.31 ± 0.090 kcal/g for perennial pepperweed (Lepidium latifolium), and 2.52 ± 0.080 kcal/g for lamb's quarters (Chenopodium album). The TME value for 3 of 4 species, including the invasive species, was low relative to the TME value of other seeds consumed by waterfowl.     

Abscisic Acid Inhibition of Kinetin Nucleotide Formation in Germinating Lettuce Seeds

Imbibing ‘Grand Rapids’ lettuce (Lactuca saliva L.) seeds take up ¹⁴C-kinetin, and metabolize this cytokinin to the 5′-nucleotide. The identity of the labeled nucleotide in seed extracts was verified by Sephadex LH-20 column chromatography, paper and thin layer chromatography, and high voltage paper electrophoresis. Incubations with kinetin in the presence of abscisic acid lead to an apparent specific inhibition of kinetin nucleotide formation. ABA has no effect on kinetin uptake, and does not inhibit kinetin nucleotide synthesis in vitro by a cell-free preparation from lettuce seeds. Additionally, ABA does not inhibit adenylate synthesis from exogenously supplied adenine. These results represent a specific cytokinin-ABA interaction, which might play a significant role in the hormonal regulation of lettuce seed germination.     

盐旱胁迫对3种新疆造林树木种子萌发的影响

以3种新疆常见造林树木白榆、大叶白蜡、梭梭种子为材料,通过测定不同土壤含盐量(0.1%～0.5%)和含水量(9%～23%)复合胁迫作用下种子的发芽率、发芽指数,以探讨3种种子萌发对盐分和干旱胁迫的响应特征.结果显示:(1)梭梭种子对盐和干旱胁迫的适应范围最广,大叶白蜡次之,然后是白榆.(2)在土壤含盐量不超过0.2%情况下,土壤含水量达到17%以后,3种树木种子发芽率都在50%以上;而当土壤含盐量为0.3%时,3树种种子仅在23%含水量下有较高发芽率;0.4%土壤含盐量条件下,只在含水量为23%时,梭梭、大叶白蜡萌发率能达到50%以上;0.5%土壤含盐量时,仅梭梭种子萌发率达到50%.(3)白榆、大叶白蜡、梭梭的耐旱临界值分别为15.1%、10.7%、9.6%,耐盐临界值分别为0.34%、0.41%、1.03%.研究表明,盐旱胁迫存在明显互作效应,盐旱复合胁迫对种子萌发的危害性明显强于单一的盐胁迫或旱胁迫.     

Proteomics Analysis of Embryo and Endosperm from Mature Common Buckwheat Seeds

We used proteomics analysis to generate the profiles of proteins in the endosperm and embryo of common buckwheat grains. These differentially expressed proteins are potentially involved in seed metabolism. Extractions were done by trichloroacetic acid (TCA) precipitation. The resulting proteins were separated using SDS-PAGE coupled to LC-ESI-Q/TOF-MS/MS. This allowed us to detect and identify 67 proteins with isoforms, making this the most inclusive protein profile. The proteins were determined to be functionally involved in the central metabolic pathway of the seed, with metabolic interest being reflected in the occurrence of a tissue-specific enzyme balance. For a case in point, we found a tissue-specific and subcellular compartment-specific isoform of granule-bound starch synthase 1 in the chloroplast/amyloplast. This provided proteomic verification of the presence of a distinct regulatory mechanism for the biosynthesis of glycan and starch, which produce amylase and amylopectin. Furthermore, several previously characterized allergenic proteins such as 11S and 13S globulin seed storage protein were acknowledged in our seed samples, thus representing the potential for proteomics techniques that survey food sources for any incidence of allergens. This protein profile of common buckwheat grain is a new avenue for understanding its seed physiology in dormant stage as well as suggesting commercial applications for the buckwheat industry as buckwheat flour.     

Failure of Chlorophyll Formation in the Cotyledons from Secondarily Dormant Cocklebur Seeds

The cotyledons of secondarily dormant cocklebur (Xanthium pennsylvankumWallr.) seeds lacked not only growing potential but also chlorophyll-formingability. These properties developed as the seeds establishedsecondary dormancy during a soaking period. The inability toform chlorophyll in cotyledonary segments was not improved inthe presence of S-amino levulinic acid. But this ability wasgreatly restored by benzyladenine or ethylene treatment, whichis effective in increasing cotyledonary growth. Similarly, theapplication of ethylene together with enriched oxygen and carbondioxide, or subsequent to a KCN treatment, which were the mosteffective means for breaking secondary dormancy, completelyrestored both chlorophyll formation and growing ability of thecotyledons. The depression of the greening-ability in cotyledonsmay be involved in development of secondary dormancy of cockleburseeds in concert with the decline of their growth pontential. (Received September 24, 1982; Accepted December 27, 1982)