不同盐度预处理后Ⅰ龄暗纹东方鲀的摄食、生长和饲料利用

通过4周的生长实验,研究了Ⅰ龄暗纹东方(8235±297g)在不同盐度预处理后的摄食、生长和饲料利用情况。结果显示:35‰的预处理盐度对暗纹东方的生长有抑制作用,当这种盐度胁迫解除后,暗纹东方的生长表现出明显的补偿现象。本实验中摄食率随前处理盐度的升高而增加,变化范围为183%-251%,特定生长率亦随前处理盐度增加而增加,即由083%增加到128%,饵料系数则随前期盐度实验中盐度的增加而降低,由167降至147。在盐度预处理实验及淡化养殖条件下的特定生长率除8‰外有显著差异。       

Wood formation in rolC transgenic aspen trees

Wood formation and structure of 3-year-old 35S-rolC transgenic aspen (Populus tremula L. × tremuloides Michx.) were compared with the situation in non-transformed control aspen trees. The transgenics are characterized by reduced shoot growth and an earlier bud break. Their wood formation did not immediately follow bud break and leaf development but occurred after some delay, about the same time as wood formation was initiated in the control trees. Quantitatively, the wood structure of the transgenics and of the non-transformed controls was not significantly different; therefore the dwarfism of the transgenics is very likely due to a reduction in cell number. Atypical formation of latewood led to the assumption that the differentiation of cells is decelerated. Additionally, cells lacked both secondary walls and normal lignification, and discoloration of the wood and the formation of tyloses were conspicuous in all transgenics. In contrast, they did not occur in the non-transformed control aspen trees. The observations are discussed in relation to the widely accepted auxin hypothesis. It is suggested that 35S-rolC transgenic aspen trees may be a useful model to study the regulatory mechanisms of wood formation. Received: 17 August 1999 / Accepted: 9 December 1999     

Is pathogenicity of Ustilago maydis (huitlacoche) strains on maize related to in vitro production of indole-3-acetic acid?

Corn smut caused by Ustilago maydis (DC) Corda on maize (Zea mays L.) is characterized by gall (tumour) formation on aerial parts of the plant. Young galls on immature corn ears are called huitlacoche and are highly appreciated as a food delicacy. Several reports have suggested that production of the auxin indole-3-acetic acid (IAA) by U. maydis might be involved in tumour formation. Because strains showing defects in IAA biosynthesis (Iaa^– phenotype) would be valuable in elucidating the role of IAA in pathogenicity, in a previous study we isolated and analysed several such mutants. In the present work, we have crossed a null Iaa^– auxotrophic mutant with compatible wild-type strains. The main objective of the present work was to evaluate the pathogenicity of crosses involving wild-type and Iaa^– strains, in order to examine its relation to IAA production. Significant differences were found in growth, IAA production and ability to survive in water suspension among wild-type and mutant progeny strains. In general, high levels of pathogenicity were associated to high levels of IAA production by the strains, which supports the hypothesis that U. maydis strains require the ability to produce IAA in order to induce tumours in the host.     

白腐菌协同热水预处理对毛白杨化学组分和酶水解效果的影响

【目的】增强真菌预处理的效率和降低热水预处理对反应条件的要求。【方法】综合利用白腐菌和热水预处理毛白杨,分析此方法对毛白杨化学组分和酶水解效果的影响。【结果】白腐菌Lenzites betulinus C5617协同热水处理,损失率最高达70.70%。纤维素在2个预处理阶段都有损失,其中L.betulinus C5617达到29.62%。木质素的降解主要集中在白腐菌预处理阶段,其中L.betulinus C5617降解的酸不溶木素较多,达到了16.98%。综合预处理显著改善了毛白杨的酶水解效果。与只经热水预处理的样品相比较,L.betulinus C5617和P.sanguineus D9497协同热水处理分别引起还原糖得率上升了20.60%和12.23%。【结论】综合预处理降低了热水解对反应条件的要求,节约了预处理成本。     

An Auxin Transport Inhibitor Interferes With Unicellular Gravitropism in Protonemata of the Moss Ceratodon purpureus

Abstract: Gravitropism of the protonemata of the moss Ceratodon purpureus (Hedw.) Brid. was studied after treatment with auxin transport inhibitors and auxin-related substances. The phytotropins NPA (naphthylphthalamic acid) and PBA (pyrenoylbenzoic acid), known to block auxin efflux in higher plants, strongly inhibited gravitropic curvature of the apical protonemal cell. At 3 μM NPA or PBA, approximately 60 % inhibition of curvature was observed; growth rates were less affected. Tyrphostin A47, a known antagonist of NPA effects in higher plants, released the inhibition of moss protonemal gravitropism and restored the full curvature response. Exogenous IAA, even at high concentrations (40 μM), did not interfere with protonemal gravitropism. To account for the results, modified hypotheses for auxin transport and action are discussed.     

Endophytic fungus Falciphora oryzae promotes lateral root growth by producing indole derivatives after sensing plant signals

The endophytic fungus Falciphora oryzae was initially isolated from wild rice (Oryza granulata) and colonizes many crop species and promotes plant growth. However, the molecular mechanisms underlying F. oryzae-mediated growth promotion are still unknown. We found that F. oryzae was able to colonize Arabidopsis thaliana. The most dramatic change after F. oryzae inoculation was observed in the root architecture, as evidenced by increased lateral root growth but reduced primary root length, similar to the effect of auxin, a significant plant growth hormone. The expression of genes responsible for auxin biosynthesis, transport, and signalling was regulated in Arabidopsis roots after F. oryzae cocultivation. Indole derivatives were detected at significantly higher levels in liquid media after cocultivation compared with separate cultivation of Arabidopsis and F. oryzae. Consistently, the expression of indole biosynthetic genes was highly upregulated in F. oryzae upon treatment with Arabidopsis exudates. Global analysis of Arabidopsis gene expression at the early stage after F. oryzae cocultivation suggested that signals were exchanged to initiate Arabidopsis–F. oryzae interactions. All these results suggest that signalling molecules from Arabidopsis roots are perceived by F. oryzae and induce the biosynthesis of indole derivatives in F. oryzae, consequently stimulating Arabidopsis lateral root growth.     

The effects of podolactone-type inhibitors on fusicoccin-induced growth and proton efflux

Podolactones A and E and lycoritidinol inhibit growth induced by fusicoccin in dwarf pea ( Pisum sativum L.) hooks and tips; however the inhibition is reduced at the highest fusicoccin concentrations. In short term experiments (3 h) on pea stem tissues, growth and proton efflux induced by fusicoccin are only partially inhibited by podolactone A and lycoricidinol. Auxin-induced growth and proton efflux are completely suppressed by 10 μM lycoricidinol. The inhibitors do not affect ATP levels.     

L- and D-tryptophan aminotransferases from maize coleoptiles

Two forms of L-tryptophan aminotransferases (L-TAT-1 and L-TAT-2) and one D-tryptophan aminotransferase (D-TAT) were separated from maize coleoptiles by using L- and D-tryptophan as amino group donors. The enzymes were partially purlfied by hydrophobic and gel filtration column chromatographies. L-TAT-1 and L-TAT-2 had similar properties, showing optimum pH at 8–9 and a high optimum temperature of 50–60 C for catalytic activity. As the amino group acceptor for these two enzymes, α-keto glutaric acid was more effective than pyruvic, oxaloacetic and glyoxylic acids. The molecular masses of L-TAT-1 and L-TAT-2 estimated by gel filtration were approximately 80 kDa and 45 kDa, respectively. D-TAT had an optimum pH similar to those of L-TATs, but the optimum temperature was conslderably lower (30 C). Pyruvic acid was an effective amino group acceptor for D-TAT, whereas oxaloacetic and α-keto glutaric acids were not. D-Cycloserine completely inhibited the activity. The molecular mass of D-TAT was approximately 55 kDa. These three TATs required pyridoxal-5-phosphate for their catalytic activities.     

Wall extensibility during hypocotyl growth: A hypothesis to explain elastic-induced wall loosening

The physico-chemical nature of wall loosening of plants is still a matter of speculation. For a better understanding of the mechanistic principles in which polymer interactions may be affected during wall loosening, the rheological properties of sunflower ( Helianthus annuus L.) were investigated during white light (WL)- and auxin (IAA)induced growth changes. As rheological parameter, the capacity for elastic shrinkage of standard hypocotyl segments after release of turgor-mediated wall stress by freezing/thawing was studied (relative reversible length). Segment length remaining after shrinkage relative to turgid length has been designated as relative irreversible length. The following results were obtained: Temporary growth inhibition of in planta growing hypocotyls by WL is characterized by a temporary increase in relative irreversible length and a complementary decrease of relative reversible length. Analogously, but with opposite effect, IAA-induced growth of hypocotyl segments is characterized by a decrease in relative irreversible length and an increase in relative reversible length; i.e., an increased capacity to shrink elastically per standard length. The changes of the two wall-rheological parameters follow similar principles in hypocotyls grown in planta and ex planta and independent of whether the growth rate was changed by either WL conditions or IAA concentration. As suggested earlier (Edelmann 1994) the results indicate that growth may be regulated by wall loosening mechanisms which initially result in elastic (reversible) wall extension. To render this extension irreversible, it must be fixed subsequently. The finding that loosened walls also become shorter in irreversible length per standard length once tensional stress is released is new. It represents pivotal evidence for an initially elastic-induced wall loosening.     

Ecophysiology of fire-stimulated seed germination in Cistus incanus ssp. creticus (L.) Hey wood and C. salvifolius L.

Abstract. Seed germination characteristics were investigated in the most common Cistus species in Greece, namely C. incanus ssp. creticus and C. salvifolius. In addition to the soft seed subpopulation, both species produce a large fraction of hardcoated, water-impermeable seeds which can be softened and, thus, promoted to germinate by mechanical scarification and thermal pretreatment. Temperature and light control of seed germination are unimportant. In the ecological context of the Mediterranean ecosystems, the eventually advantageous, opportunistic strategy of germination is based on: (a) seed heterospermy (which allows the smaller, softcoated fraction to germinate promptly each year while the majority of the seeds, the hard ones, accumulate in the soil); (b) the seed population heterogeneity in relation to coat hardness (so that any heat conditions produced by fire induce the softening and germination of a certain seed fraction); (c) the notably low germination rate (which suppresses premature germination); (d) the wide, Mediterranean-type (relatively cool), temperature range of germination (while higher temperatures simply inhibit but do not induce any dormancy); and (c) the apparent lack of photo-sensitivity (enabling germination under every light regime). In non-fire years, the temporal distribution of field germination and seedling appearance might be partly determined by the seed dispersal strategy of the individual Cistus species. Nevertheless, the post-fire regeneration response is manifested in the form of a huge wave of germination (of practically all seeds softened by the fire heat), shortly after the onset of the rainy season.