Silver ions inhibit the ethylene-stimulated production of ripening-related mRNAs in tomato

Abstract. Silver ions effectively inhibited both the initiation and the continuation of tomato ( Lyeopersicon esculentum Mill) ripening. Studies of protein synthesis in vivo showed that application of 2 mol m⁻³ silver thiosulphate to mature green fruit prevented the appearance of several novel proteins associated with ripening, including the softening enzyme polygalacturonase. However, total protein synthesis, as judged by the incorporation of [³⁵S] methionine into proteins, continued unabated after silver treatment. Ripening was also arrested when silver was supplied after ripening had begun. The accumulation of several ripening-related mRNAs, including that for polygalacturonase, was studied by translation in vitro and using cDNA clones as hybridization probes. Silver was shown to prevent the appearance of polygalaturonase mRNA when supplied to mature green fruit and to cause a rapid reduction in the concentration of mRNA for polygalacturonase and other ripening-related proteins when supplied after ripening had begun. It is proposed that silver exerts its effects due to interaction with the ethylene perception mechanism. The results suggest that perception of ethylene is vital not only for the initiation of ripening but also for the continued expression of genes required for ripening.     

Removal of seeds from Neotropical frugivore droppings

In a Costa Rican rain forest, the majority of tree and shrub species have their seeds dispersed by vertebrates. Over a third of the species' seeds are of a size accessible to, and primarily carried away by, ants. Frugivorous bird droppings come in sizes from a few seeds to over a thousand, with number of seeds isometric with bird body mass. Dropping size decreases as seeds are scattered by rain. Larger droppings produced from fruits ofMiconia affinis (Melastomataceae) are discovered and recruited to more by ants, with a diverse guild of 22 ant species carrying away the seeds. Droppings with 64 and 16 seeds were used by a subset of the ant community exploiting 4-seed droppings, likely due to resource defense by aggressive species. Seeds in the smallest droppings stood the smallest chance of being removed. Although soil-nesting ants of the tribe Attini were the primary removers of seeds in this forest, a third of removal was by ants living in ephemeral litter nests. Seeds ofM. affinis were found in litter ant nests in 8 of 28 1-m² plots, suggesting that seed rain was not highly localized. Since litter nests are common, contain few seeds/nest and are often abandoned by their ants, litter ants may be the best candidates for ant-plant dispersal mutualisms.     

Activities of de-N-glycosylation are ubiquitously found in tomato plant

Activities of two de-N-glycosylation enzymes, PNGase (peptide N ⁴(N-acetyl-glucosaminyl)asparagine amidase) and ENGase (endo N-acetyl-β-D-glucosaminidase), involved in the release of N-glycans from N-glycoproteins, were monitored in several organs of tomato plants (Lycopersicon esculentum, Mill., cv. Dombito) with a fluorescence-HPLC procedure using a resofurin-labelled N-glycopeptide substrate. PNGase and ENGase activities were detected in every organ assayed but with quantitative differences. The highest activities were found in the youngest parts of the plant, i.e. apical buds, flowers and leaf blades. PNGase activities were consistently higher than ENGase activities (three-fold in average). Both de-N-glycosylation activities were associated with high levels of proteins and protease activities. During fruit growth and ripening, these three parameters decreased notably. The ubiquitous detection of these enzyme activities in the different organs is probably associated with the previously characterized unconjugated N-glycans in tomato. The possible role of PNGase and ENGase degradation products (i.e. unconjugated N-glycans) are discussed in relation with their biological functions in plant development.     

大野芋种子形成丛生芽的微繁殖

大野芋(Colocasiagigantea)的成熟种子(褐色)和未成熟的种子(淡黄色)在1/2MS培养基上均能萌发,种子萌发率最高达50%,种子没有休眠期。在室温下,种子在1/4MS 1%蔗糖培养基上,寿命约可达1年。种子在MS BA2mg·L-1 IAA0.25mg·L-1的培养基上,产生丛生芽。增值率1∶4/60d。生根培养基为MS NAA0.3mg·L-1,生根率达95%以上。通过诱导大野芋种子产生丛生芽,建成了快繁无性系,并成功地实现了种子的离体保存。本研究工作的完成,对于芋头的这一野生近缘种的保存和利用、芋头品种的改良,均具有较大意义。     

Isolation and characterization of a novel thermostable non-specific lipid transfer protein-like antimicrobial protein from motherwort (Leonurus japonicus Houtt) seeds

In screening for potent antimicrobial proteins from plant seeds, a novel heat-stable antimicrobial protein, designated LJAMP2, was purified from seeds of the motherwort (Leonurus japonicus Houtt), a medicine herb, with a procedure involving cation exchange chromatography on a CM FF column, and reverse phase HPLCs on C8 column and C18 column. LJAMP2 exhibited a molecular mass of 6.2 kDa determined. Automated Edman degradation determined the partial N-terminal sequence of LJAMP2 to be NH2-AIGCNTVASKMAPCLPYVTGKGPLGGCCGGVKGLIDAARTTPDRQAVCNCLKTLAKSYSG, which displays homology with plant non-specific lipid transfer proteins (nsLTPs). In vitro bioassays showed that LJAMP2 inhibits the growth of a variety of microbes, including filamentous fungi, bacteria and yeast. The growth of three phytopathogenic fungi, Alternaria brassicae, Botrytis maydis, and Rhizoctonia cerealis, are inhibited at 7.5 μM of LJAMP2, whereas Bacillus subtilis is about 15 μM. The IC₅₀ of LJAMP2 for Aspergillus niger, B. maydis, Fusarium oxysporum, Penicillium digitatum and Saccharomyces cerevisiae are 5.5, 6.1, 9.3, 40.0, and 76.0 μM, respectively.     

Somatic embryo and root regeneration from quince leaves cultured in ventilated vessels or under different oxygen and carbon dioxide levels

Summary The influence of the gaseous composition of the atmosphere inside culturing vessels on somatic embryogenesis and on adventitious root formation was investigated in the quince clone (Cydonia ablonga Mill.) BA29. Leaves taken from in vitro-grown shoots were cultured in glass Petri dishes and exposed to ventilation with atmospheric air (flow rate 25 ml min⁻¹) for 0, 5, 10, 20, and 40 d. Twenty days of ventilation reduced the frequency of embryogenic leaves and a further decrease was observed after 40d of treatment. Conversely, adventitious root formation in the ventilated dishes was never different from the untreated cultures. In a second test, leaves were incubated in atmospheres containing different levels of oxygen (0, 5.0, 10.0, and 21.0%) or carbon dioxide (0, 0.04, 0.15, 1.5, and 3.0%). Anoxia conditions almost completely inhibited somatic embryo and adventitious root formation, but without compromising callus formation and explant viability. In contrast, embryo and root regeneration occurred even in totally CO₂-free atmosphere. Oxygen seemed to influence somatic embryogenesis according to a quadratic response; a similar relationship was also observed for root regeneration. Instead, no clear trend could be inferred between embryo or root regeneration and CO₂ levels. Furthermore, in dishes flushed with gas mixtures containing oxygen or carbon dioxide somatic embryo formation was almost always lower than in confined dishes. A different result was observed for root regeneration, since the number of roots was never lower than in the control and increased appreciably with 3.0% CO₂. These results demonstrate that atmosphere composition of the culture head-space can influence somatic embryogenesis in quince. The finding that both vessel ventilation and atmosphere replacement with different gas mixtures reduced somatic embryo formation suggests that gaseous compounds, different from O₂ an CO₂, present in the gaseous environment may promote embryogenesis in this species.     

The Effects of Root Treatment with Various Stress Agents on Plant Cold- and Heat-Tolerance

The root systems of cucumber (Cucumis sativus L.), wheat (Triticum aestivum L.), and barley (Hordeum vulgare L.) plants were subjected to a short-term (6–7-h-long) treatment with low and high temperatures, sodium chloride, and lead nitrate, and the effect of these treatments on the changes in the cold- and heat-tolerance of leaf cells was determined. It was established that chilling of cucumber and wheat seedling roots at 10 and 2°C, respectively, or their heating at 38°C and 40°C, respectively, induced an increase in both cold- and heat-tolerance of leaf cells. An increase in the cold- and heat-tolerance was also observed in roots treated with sodium chloride at concentrations of 0.15 M (cucumber) and 0.2 M (wheat), as well as with lead nitrate at a concentration of 0.1 mM (barley, wheat). The tolerance increase induced by these stress agents was accompanied by a considerable increase in the ABA concentration in leaves. The effect of physical and chemical stress agents is suggested to induce the same nonspecific changes in the aboveground organs. These changes bring about, directly or indirectly, an increase in the cold- and heat-tolerance and are related to an increase in the ABA content.     

The effect of vitamin A on limb regeneration in Rana temporaria

Previous experiments in which vitamin A has been administered to developing or regenerating limbs have shown that different limb axes are affected. In regenerating axolotl limbs, serial reduplications in the proximodistal axis are produced. In the developing chick limb bud, mirror-imaged reduplications in the anteroposterior axis are produced. Results reported here on Rana temporaria limb buds reveal that vitamin A causes both effects to occur. That is, limbs are both serially reduplicated in the proximodistal axis and mirror imaged in the anteroposterior axis. Time and concentration effects are explored and the significance of these results for our current understanding of axial organisation in limbs is discussed.