Nectar-carbohydrate production and composition were investigated by high-performance liquid chromatography and enzymology in nine species from five tribes of the Brassicaceae. In six species (Arabidopsis thaliana (L.) Heynh., Brassica napus L., B. rapa L., Lobularia maritima (L.) Desv., Raphanus sativus L., Sinapis arvensis L.) that produced nectar from both lateral nectaries (associated with the short stamens) and median nectaries (outside the long stamens), on average 95% of the total nectar carbohydrate was collected from the lateral ones. Nectar from these glands possessed a higher glucose/fructose ratio (usually 1.0-1.2) than that from the median nectaries (0.2-0.9) within the same flower. Comparatively little sucrose was detected in any nectar samples except from Matthiola bicornus (Sibth. et Sm.) DC., which possessed lateral nectaries only and produced a sucrose-dominant exudate. The anatomy of the nectarial tissue in nectar-secreting flowers of six species, Hesperis matronalis L., L. maritima, M. bicornus, R. sativus, S. arvensis, and Sisymbrium loeselii L., was studied by light and scanning-electron microscopy. Phloem alone supplied the nectaries. However, in accordance with their overall nectar-carbohydrate production, the lateral glands received relatively rich quantities of phloem that penetrated far into the glandular tissue, whereas median glands were supplied with phloem that often barely innervated them. All nectarial tissue possessed modified stomata (with the exception of the median glands of S. loeselii, which did not produce nectar); further evidence was gathered to indicate that these structures do not regulate nectar flow by guard-cell movements. The numbers of modified stomata per gland showed no relation to nectar-carbohydrate production. Taken together, the data on nectar biochemistry and nectary anatomy indicate the existence of two distinct nectary types in those Brassicacean species that possess both lateral and median nectaries, regardless of whether nectarial tissue is united around the entire receptacle or not. It is proposed that the term "nectarium" be used to represent collectively the multiple nectaries that can be found in individual flowers.

Various data mining techniques combined with sequence motif information in the promoter region of genes were applied to discover functional genes that are involved in the defense mechanism of systemic acquired resistance (SAR) in Arabidopsis thaliana. A series of K-Means clustering with difference-in-shape as distance measure was initially applied. A stability measure was used to validate this clustering process. A decision tree algorithm with the discover-and-mask technique was used to identify a group of most informative genes. Appearance and abundance of various transcription factor binding sites in the promoter region of the genes were studied. Through the combination of these techniques, we were able to identify 24 candidate genes involved in the SAR defense mechanism. The candidate genes fell into 2 highly resolved categories, each category showing significantly unique profiles of regulatory elements in their promoter regions. This study demonstrates the strength of such integration methods and suggests a broader application of this approach.

To date there have been few systematic studies comparing the results of transcript profiling from different microarray platform technologies. We evaluated in detail two different Arabidopsis thaliana microarray platforms: our own Genomic Amplicon arrays and the Qiagen long oligonucleotide arrays designed by Operon; furthermore, we cross-validated these arrays against the Affymetrix AG and ATH1 GeneChips. Data were obtained from all three platforms in each of two separate experiments; (1) at 2 h and (2) 8 h following a salicylic acid treatment applied to both wild-type and npr1-3 mutant plants. A total of 20 hybridizations were performed, analyzing the expression of 26,814 unique locus IDs. We demonstrate that intensity rank is a key variable that affects both inter-platform and cross-platform reproducibility. Although general agreement between platform technologies is low, data derived from high signal intensities (90th percentile) can correlate as well between differing platforms as replicates within the same platform (r=0.4-0.7). We also show that the identification of differentially expressed genes by significance analysis of microarrays is influenced by signal intensity and that overlap between significant gene lists from different platform technologies was as high as 67% when low intensity values were removed. Validation of 41 genes by Northern blot hybridization showed that all platform technologies performed well, qualitatively confirming 83-100% of differential gene expression. Our results suggest that the potential for the broad integration of microarray data from different platforms and laboratories is promising.

B-class floral homeotic genes are required for the proper formation and identity of petals and stamens in dicot flowers. A partial cDNA clone encoding a B-class gene, BnAP3 (Brassica napus APETALA3), was isolated from a B. napus cDNA library derived from young inflorescence meristems. The 5' region of the cDNA was retrieved by RACE. The deduced amino acid sequence of the full-length clone exhibited high similarity to APETALA3 of Arabidopsis thaliana and functionally homologous proteins from other species. 5' RACE and Southern analysis suggests that BnAP3 has multiple alleles in B. napus. Expression analysis assayed by RT-PCR shows that BnAP3 is expressed in floral tissues, as well as non-floral tissues such as root and bract. Transformation of wild-type A. thaliana and B. napus plants with BnAP3 under the control of a promoter specific to reproductive organs converts carpels to stamens, while the expression of this construct in A. thaliana plants mutant for AP3 restores the development of third-whorl stamens in addition to directing a carpel to stamen conversion in the fourth whorl.

To investigate the functional conservation of cis regulatory elements controlling AGAMOUS (AG) expression, we placed the promoter region of AG from Arabidopsis thaliana into a close relative, Brassica napus, and a distantly related species, Linum usitatissimum, and analyzed the subsequent expression patterns in each species. Spatially, the expression patterns in all three species were marginally similar, in that expression was confined primarily to the reproductive organs and nectarium. Within organs however, tissue-specific expression patterns were not conserved between species. Unlike Arabidopsis, the transgenic AG cis elements did not express in the ovules of B. napus and L. usitatissimum. Temporally, the pattern of AG cis-element expression in B. napus was identical to that of Arabidopsis during early development; however, the AG cis elements did not express at all during early flower development in L. usitatissimum. These results suggest that although regulatory factors controlling the generalized local expression of AG have been conserved between these species, those controlling temporal and tissue-specific expression have not.Key words: AGAMOUS, cis elements, regulation, Arabidopsis, Brassica napus, Linum usitatissimum.

flo10-1 (superman-2) is a floral mutant in Arabidopsis thaliana that normally produces female sterile flowers. This phenotypic aberration results from a combination of increased stamen number and reduced or abnormal carpels that are nonfunctional. The flowers of flo10-1 contain two lateral and four median stamens, as seen in wild-type plants; however, they also contain several additional stamens. All stamen types have been examined with respect to frequency and location within the flower. The amount of pollen produced from each of the three types of stamens of flo10-1 and the viability of this pollen were also examined and compared with wild-type (cv. Columbia) to determine the consequences of this mutation on male fertility. Both the lateral and median stamens of flo10-1 and wild-type plants produced similar amounts of pollen per stamen and demonstrated no significant difference in viability. Per stamen, the additionals of flo10-1 produced significantly less pollen than those of the laterals and medians. Furthermore, the pollen produced from these additional stamens was significantly less viable. Although less abundant and viable, pollen produced by additional stamens can effectively fertilize ovules, producing normal, healthy plants.Key words: pollen (viability, production), stamen, male fertility, flower development, Arabidopsis thaliana, flo10-1.

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