Endosperm-specific demethylation and activation of specific alleles of α-tubulin genes of Zea mays L.

We have investigated the methylation status of the -tubulin genes, and the degree of accumulation of their mRNAs in endosperm, embryo and seedling tissues of Zea mays L. We have found that many of the -tubulin genes are differentially demethylated in the endosperm relative to the embryo and seedling. However, only for tub2 and tub4 could a correlation between DNA demethylation and increased RNA accumulation be detected. By analyzing the inbred lines W64A and A69Y and their reciprocal crosses, we have also identified in the endosperm two -tubulin genes, tub3 and tub4, that are differentially demethylated if transmitted by the maternal germline, but that remain hypermethylated when transmitted by the paternal germline.     

Mutations of the 22- and 27-kD zein promoters affect transactivation by the Opaque-2 protein.

By utilizing a homologous transient expression system, we have demonstrated that the Opaque-2 (O2) gene product O2 confers positive trans-regulation on a 22-kD zein promoter. This trans-acting function of the O2 protein is mediated by its sequence-specific binding to a cis element (the O2 target site) present in the 22-kD zein promoter. A multimer of a 32-bp promoter fragment containing this O2 target site confers transactivation by O2. A single nucleotide substitution in the O2 target sequence not only abolishes O2 binding in vitro, but also its response to transactivation by O2 in vivo. We have also demonstrated that an amino acid domain including the contiguous basic region and the heptameric leucine repeat is essential for the trans-acting function of the O2 protein. Similar but not identical O2 target sequence motifs can be found in the promoters of zein genes of different molecular weight classes. Conversion of such a motif in the 27-kD zein promoter to an exact O2 target sequence by site-directed mutagenesis was sufficient to increase the binding affinity of the O2 protein in vitro and to confer transactivation by O2 in vivo.     

Pore dimensions for accumulating biomass. I. Microbes that reproduce by fission or by budding

The relationship between the dimensions of a microbe and the accumulation of that microbe in porous, inorganic structures has been determined. That relationship is dependent upon the cell dimensions, the mode of reproduction, and the pore diameter of the material. In order to achieve high accumulation of microbes that reproduce by fission, at least 70% of the pores of an inorganic carrier should have pore diameters in the range of one times the smallest major dimension through five times the largest major dimension of the cell. To achieve the highest accumulation of microbes that reproduce by budding, at least 70% of the pores should have pore diameters in the range of one times the smallest dimension of the cell and less than four times the largest cell dimension. These relationships were established by varying the physical parameters of the carriers as well as their chemical composition.     

Response of the melon fly parasitoidPysttalia fletcheri (Hymenoptera: Braconidae) to host-habitat stimuli

Cohorts of mass-reared adult femalePysttalia fletcheri, parasitoids of the melon fly (Bactrocera cucurbitae), were exposed to host-plant stimuli in a laminar airflow wind tunnel to analyze the cues used in host-habitat finding. Parasitoids hovered twice as frequently around plastic zucchini models emitting fresh cucumber odor as around models emitting clean air. The odor of decaying pumpkin was even more attractive, resulting in over a 10-fold increase in hovering, a 50-fold increase in landing, and a 150-fold increase in host-searching and probing behaviors compared to clean air. Fresh cucumber leaf odors were not attractive to the parasitoids, but decomposing leaves elicited a strong increase in hovering, landing, and searching behaviors. Plastic leaves which visually simulated cucurbit foliage did not in themselves significantly alter orientation behaviors, but the combination of leaf visual stimuli plus decaying leaf odors caused strong increases in hovering, landing, and searching. Fresh pumpkin odor and the odor of yeast-inoculated pumpkin were not as attractive to parasitoids as decaying leaf odors. Yeast isolated from decaying pumpkin and cultured on various sterile media were not substantially more attractive than clean air.