The ribosomal gene intergenic region from Arabidopsis thaliana contains four clusters of mutually unrelated repeated sequences. By comparison with the respective regions in two other Brassicaceae, Raphanus and Sinapis, the putative promoter sequence for RNA polymerase I was located. The homologies suggest that the RNA polymerase I promoter in Brassicaceae ranges further upstream than in animals. Upstream duplications of at least a part of the promoter region were found to be located between individual blocks of the largest internal repeat family ("A" repeats), which is made up of multiple repeats of two closely related sequences 21 or 20 bp in length. Overall structural similarities of the A. thaliana rDNA intergenic region with those from wheat and from Xenopus laevis are discussed. We also present data on the range of intraspecific length heterogeneities found in the central FcoRI fragment of the intergenic region and on the frequencies with which specific length variants occur in the genome. To determine the nature of the length heterogeneities, we sequenced the central EcoRI fragments from four independently isolated genomic clones. Three levels of rearrangements were detected length variation can be caused by duplication of a whole A repeat block, or, most frequently, by insertion and/or deletion or one of a few A repeat units. Surprisingly, single base mutations are extremely rare, which hints at some mechanism of homogenization which might be acting on the intergenic region. A possible function of the described sequences in transcriptional regulation is discussed and will be the aim of further investigations.

Differential screening of a mature Brassica campestris pollen cDNA library has identified five cDNA clones that represent transcripts expressed exclusively, or at elevated levels, in pollen. We show here that the expression of one of these, clone Bcp1, is tissue specific and temporally regulated. The gene is activated during microspore development, as detected by in situ hybridization. Expression is enhanced at the time of pollen maturation and during pollen germination. In situ hybridization has also shown that Bcp1 is activated in the tapetal cells in early anther development and continues to be expressed until tapetal dissolution. Homologous transcripts are present in pollen of other taxa of Brassicaceae including Arabidopsis, but not in pollen of any other families tested.

Similarities among taxa of glucosinolate-producing plants and putative relatives were evaluated using numerical methods applied to a dataset of 93 characters. These include anatomical and morphological (vegetative and reproductive), chromosomal, palynological, phytochemical, and ultrastructural features. Principal components and coordinates analyses reveal considerable complexity, hence little redundancy in this dataset. Cluster analyses show that glucosinolate taxa as a whole are not phenetically coherent. With or without glucosinolate characters included in the analyses, a core capparalean group comprises Brassicaceae, Capparaceae, Resedaceae, and Tovariaceae, to which are linked the non-glucosinolate Koeberlinia and the families Bataceae, Gyrostemonaceae, and Salvadoraceae but not Moringaceae. Based on a sparser dataset, Drypetes clusters with Euphorbiaceae; Akania and Bretschneidera cluster together but not close to Sapindaceae; Pentadiplandra is too poorly known to be placed with confidence. Caricaceae, Limnanthaceae, Moringaceae, and Tropaeolaceae remain problematic.

A dataset of 90 putatively homologous characters was assembled to analyze phylogenetic relationships among the 15 taxa of glucosinolate-producing plants and 11 potential outgroups. The characters sample a broad range of anatomical, morphological, physiological, and phytochemical aspects of these plants. With or without glucosinolate characters included in the cladistic analysis, a lineage emerges consisting of core Capparales (Brassicaceae, Capparaceae, and Resedaceae) allied with Gyrostemonaceae and Tovariaceae and affiliated with Bataceae, Salvadoraceae, and the non-glucosinolate Koeberlinia. This clade is marked by vestured pitting, curved embryo in seed, vacuolar or utricular cisternae of the endoplasmic reticulum, myrosin cells, and a fundamentally tetramerous floral construction. Drypetes affiliates with Euphorbiaceae, and Limnanthaceae with Balsaminaceae, affirming the convergent nature of glucosinolate biosynthesis. Caricaceae, Moringaceae, and Tropaeolaceae remain problematic as do the poorly known genera Akania, Bretschneidera, and Pentadiplandra. Earlier serological comparisons corroborate some of these alignments, including displacement of Moringaceae from core Capparales.

Boll weevils, Anthonomus grandis grandis Boheman, were collected in 1978-1980 from grandlure-baited traps in the Lower Gulf Coast (LGC) and the Lower Rio Grande Valley (LRGV) of southern Texas, and in northeastern Mexico (NEM). The weevils were dissected, and the midgut was removed and examined for the presence of pollen grains. Pollen grains representing 12 families of plants were found in boll weevils from the LRGV, 9 families of plants from the LGC, and 6 families of plants from NEM. The most frequently encountered pollen grains were from plants in the families Poaceae (grasses), Brassicaceae (mustards), and Asteraceae (sunflowers and daisies). Some ingested pollen grains could not be identified. In a separate no-choice study, boll weevils were caged on 22 species of plants during blooming to document pollen feeding. Twenty to 100% of the boll weevils caged on a plant species consumed pollen from that species. These data suggest that adult boll weevils in the field may consume pollen from a wide range of plant species; however, further studies are required to confirm this.

We observed norms of reaction for life history and floral traits in Raphanus sativus L. (wild radish: Brassicaceae) among genotypes raised in three planting densities. In the greenhouse, we used a nested breeding design to produce F1 seed representing 60 maternal plants and 15 pollen donors grown from field-collected seed. Eighteen hundred-seeds were grown in three planting densities in an experimental garden. For each individual, we recorded survivorship, germination date, flowering date, petal area, ovule number, pollen production, and the mode of individual pollen grain volume/flower. Planting density had a strong effect on survivorship, but differential mortality among genotypes was not density-specific. Two-way ANOVAS (block and density as class variables) were conducted on each paternal sibship to detect significant differences among densities with respect to mean phenotype. Among the 15 paternal genotypes, 12 exhibited significantly faster germination in the high-density plots. Three paternal families exhibited significantly delayed flowering at high-density. Two paternal families exhibited significant effects of density on petal area, but in opposite directions. Two paternal families had significantly lower ovule production at high-density. No paternal families exhibited significant effects of density on pollen production or pollen-grain volume. Strong differences among genotypes with respect to the effects of density on phenotype indicate genetic variation in the plastic response to density for these traits. Three-way ANOVAS of each density treatment measured the effects of block, paternal family and maternal family on phenotype; significant paternal effects indicated the presence of significant additive genetic variance (VA) in the measured trait. The ability to detect VA and maternal effects nested within paternal genotypes in most of these traits was density-specific.

We have examined the organization of tRNA Tyr genes in three ecotypes of Arabidopsis thaliana, a plant with an extremely small genome of 7 X 10(7) bp. Three tRNA Tyr gene-containing EcoRI fragments of 1.5 kb and four fragments of 0.6, 1.7, 2.5 and 3.7 kb were cloned from A. thaliana cv. Columbia (Col-O) DNA and sequenced. All EcoRI fragments except those of 0.6 and 2.5 kb comprise an identical arrangement of two tRNA Tyr genes flanked by a tRNA Ser gene. The three tRNA genes have the same polarity and are separated by 250 and 370 bp, respectively. The tRNA Tyr genes encode the known cytoplasmic tRNA Try GpsiA. Both genes contain a 12 bp long intervening sequence. Densitometric evaluation of the genomic blot reveals the presence of at least 20 copies, including a few multimers, of the 1.5 kb fragment in Col-O DNA, indicating a multiple amplification of this unit. Southern blots of EcoRI-digested DNA from the other two ecotypes, cv. Landsberg (La-O) and cv. Niederzenz (Nd-O) also show 1.5 kb units as the major hybridizing bands. Several lines of evidence support the idea of a strict tandem arrangement of this 1.5 kb unit: (i) Sequence analysis of the EcoRI inserts of 2.5 and 0.6 kb reveals the loss of an EcoRI site between 1.5 kb units and the introduction of a new EcoRI site in a 1.5 kb dimer. (ii) Complete digestion of Col-O DNA with restriction enzymes which cleave only once within the 1.5 kb unit also produces predominantly 1.5 kb fragments. (iii) Partial digestion with EcoRI shows that the 1.5 kb fragments indeed arise from the regular spacing of the restriction sites. The high degree of sequence homology among the 1.5 kb units, ranging from 92% to 99%, suggests that the tRNA Ser/tRNA Tyr cluster evolved 1-5 million years ago, after the Brassicaceae diverged from the other flowering plants about 5-10 million years ago.