Enhanced Sensitivity to Ethylene in Nitrogen- or Phosphate-Starved Roots of Zea mays L. during Aerenchyma Formation

Adventitious roots of maize (Zea mays L. cv TX 5855), grown in a well-oxygenated nutrient solution, were induced to form cortical gas spaces (aerenchyma) by temporarily omitting nitrate and ammonium (-N), or phosphate (-P), from the solution. Previously this response was shown (MC Drew, CJ He, PW Morgan [1989] Plant Physiology 91: 266-271) to be associated with a slower rate of ethylene biosynthesis, contrasting with the induction of aerenchyma by hypoxia during which ethylene production is strongly stimulated. In the present paper, we show that aerenchyma formation induced by nutrient starvation was blocked, under noninjurious conditions, by addition of low concentrations of Ag⁺, an inhibitor of ethylene action, or of aminoethoxyvinyl glycine, an inhibitor of ethylene biosynthesis. When extending roots were exposed to low concentrations of ethylene in air sparged through the nutrient solution, N or P starvation enhanced the sensitivity to exogenous ethylene at concentrations as low as 0.05 microliters ethylene per liter air, promoting a more rapid and extensive formation of aerenchyma than in unstarved roots. We conclude that temporary deprivation of N or P enhances the sensitivity of ethylene-responsive cells of the root cortex, leading to cell lysis and aerenchyma.     

Molecular cloning and mapping of phenol degradation genes from Bacillus stearothermophilus FDTP-3 and their expression in Escherichia coli.

Two genes of the meta pathway of phenol degradation were cloned from a phenol-utilizing strain of Bacillus stearothermophilus and were mapped by subcloning and by use of a Tn5 insertion mutation. They code for phenol hydroxylase and catechol 2,3-dioxygenase, respectively. The gene encoding catechol 2,3-dioxygenase, which is more thermostable than catechol 2,3-dioxygenase encoded by the other gene, shares rather limited homology with that from Pseudomonas putida.     

眶脊巨蜂属一新种记述(膜翅目:姬蜂总科, 巨蜂科)

巨蜂科 Megalyridae 是姬蜂总科 Ichneumonoidea 的一个小科,主要分布于大洋洲及南非。寄生于树木的穿孔性昆虫幼虫,我国尚未见报道。眶脊巨蜂属 EttchellsiaCameron(1909)过去仅知2种,分别产于加里曼丹岛和菲律宾。该属的主要特征是:沿复眼上颊眶有一明显的脊(汉名即据此而拟),前缘脉和亚前缘分开;中胸盾片有一明显     

Vibrational spectroscopy of bacteriorhodopsin mutants. Evidence for the interaction of aspartic acid 212 with tyrosine 185 and possible role in the proton pump mechanism

The role of Asp-212 in the proton pumping mechanism of bacteriorhodopsin (bR) has been studied by a combination of site-directed mutagenesis and Fourier transform infrared difference spectroscopy. Difference spectra were recorded at low temperature for the bR----K and bR----M photoreactions of the mutants Asp-212----Glu, Asp-212----Asn, and Asp-212----Ala. Despite an increased proportion of the 13-cis form of bR (normally associated with dark adaptation), all of the mutants exhibited a light-adapted form containing as a principal component the normal all-trans retinal chromophore. The absence of a shift in the retinal C = C stretching frequency in these mutants indicates that Asp-212 is not a major determinant of the visible absorption wavelength maximum in light-adapted bR. It is unlikely that Asp-212 is the acceptor group for the Schiff base proton since both the Asp-212----Glu and Asp-212----Ala mutants formed an M intermediate. All of the Asp-212 mutants were missing a Fourier transform infrared difference band that had been assigned previously to protonation changes of Tyr-185. These results are discussed in terms of a model in which Tyr-185 and Asp-212 form a polarizable hydrogen bond and are positioned near the C13-Schiff base portion of the chromophore. These 2 residues may be involved in stabilizing the relative orientation of the F and G helices and isomerizing the retinal in a regioselective manner about the C13 = C14 double bond.     

Ontogenetic trait variation and metacommunity effects influence species relative abundances during tree community assembly

Predicting species abundance is one of the most fundamental pursuits of ecology. Combining the information encoded in functional traits and metacommunities provides a new perspective to predict the abundance of species in communities. We applied a community assembly via trait selection model to predict quadrat-scale species abundances using functional trait variation on ontogenetic stages and metacommunity information for over 490 plant species in a subtropical forest and a lowland tropical forest in Yunnan, China. The relative importance of trait-based selection, mass effects, and stochasticity in shaping local species abundances is evaluated using different null models. We found both mass effects and trait selection contribute to local abundance patterns. Trait selection was detectable at all studied spatial scales (0.04–1 ha), with its strength stronger at larger scales and in the subtropical forest. In contrast, the importance of stochasticity decreased with spatial scale. A significant mass effect of the metacommunity was observed at small spatial scales. Our results indicate that tree community assembly is primarily driven by ontogenetic traits and metacommunity effects. Our findings also demonstrate that including ontogenetic trait variation into predictive frameworks allows ecologists to infer ecological mechanisms operating in community assembly at the individual level.