Fine Structure and Biomineralization of the Mucilage in Envelopes of Trachelomonas lefevrei (Euglenophyceae)1

Envelope development in Trachelomonas lefevrei (Deflandre) begins with the production of short, coarse mucilaginous strands, morphologically similar to the mucilage produced by non-enveloped euglenoids. These initial mucilaginous secretions subsequently become impregnated with manganese (Mn) and/or iron (Fe). Continued mucilage secretion and mineralization results in a mature envelope that is characteristic for the species. When these mature envelopes are treated with oxalic acid to remove the Mn and Fe, the envelopes collapse and are composed only of short, coarse mucilaginous strands similar to those present during early stages of development, prior to their mineralization. Brief treatment with 10 mM EDTA renders dark envelopes colorless, and our EM-EDS analyses show that this corresponds to a loss of Mn from the envelope; however, if Fe is present in the envelope, it is unaffected by the brief treatment. The mucilage present during early stages of envelope development and that remaining after complete demineralization is also morphologically similar to the mucilage in the plug at the anterior end of the envelope.     

Regulation of ACC-Dependent Ethylene Production by Excised Leaves from Normal and Albino Zea mays L. Seedlings

Dunlap, J. R. 1988. Regulation of ACC-dependent ethylene productionby excised leaves from normal and albino Zea mays L. seedlings.—J.exp. Bot. 39: 1079–1089. Albino corn (Zea mays L.) seedlings lacking natural leaf pigmentswere obtained by germinating seeds treated with fluridone, aninhibitor of carotenoid biosynthesis. Basal rates of ethyleneproduction were less than 2.0 nl g^–1 fr. wt h^–1in both treated (albino) and untreated (normal) leaves but increasedby 10- to 20-fold in the presence of added ACC. ACC-dependentethylene production (ADEP) was inhibited by cobalt or cyanideions and stimulated by NaHCO₃, CO₂ and light. ADEP in both tissueswas stimulated by glucose, fructose, galactose and sucrose.The accumulation of respiratory CO₂ did not account for thecarbohydrate response. The decline in the ADEP characteristicof albino leaf tissue was slowed by incubation in the presenceof sucrose. IAA and ABA stimulated ADEP in normal leaves butinhibited ADEP in albino leaves. Sucrose-stimulated ADEP wasinhibited in albino leaf tissue treated with IAA or ABA indicatinga possible role for the chloroplast in carbohydrate-facilitatedADEP. However, results from this study suggest that chloroplastsperform a function in the regulation of ethylene productionby leaf tissue that extends beyond merely influencing internallevels of CO₂. In the absence of detectable ACC, EFE was responsiblefor the entire series of responses expressed in regulation ofethylene biosynthesis by corn seedling leaf tissue. Key words: Corn, ethylene, sugars, phytohormones     

一株抑制黄曲霉毒素的深海微杆菌的分离与鉴定

从南大西洋深海海水中分离到一株放线菌菌株R104,该菌株的发酵无细胞上清液对黄曲霉毒素合成的抑制率高达96.2%,经16S rDNA序列分析,初步将该菌株鉴定为微杆菌（Microbacterium）,这是首次报道深海来源的微杆菌具有抑制黄曲霉毒素合成的能力。     

Effects of temperature and water potential on the germination of muskmelon cultivars

The rate and final germination of four muskmelon cultivars (Cucumis melo) were examined in response to incubation temperatures of 20, 26 and 32°C. Germination was also characterised at 26°C pr 32°C over a range of water potentials from 0 to - 1000 kPa achieved with solutions of polyethylene glycol. The germination of one cultivar, TAM-Uvalde, was consistently slower at 20°C than at 26°C or 32°C. The other three cultivars, Perlita, TAM-Dew and Greenflesh, were inhibited by incubation at 32°C. However, the germination responses of cvs Perlita, TAM-Dew and Greenflesh at 26°C or 32°C improved as water potentials were reduced from 0 to – 200 or – 400 kPa. Cv. TAM-Uvalde was extremely sensitive to water stress and failed to germinate at water potentials below – 600 kPa when incubated at 26°C. The inhibition of germination at low water potentials was partially reversed in all cultivars by increasing the incubation temperature from 26°C to 32°C. It is suggested that the inhibition of germination at 0 kPa (distilled water) was due to a seed coat-mediated barrier to oxygen that could be reversed by removal of the seed coat or exposure to an oxygen-enriched atmosphere.