SPR3 is one of at least nine genes which are expressed in sporulating Saccharomyces cerevisiae cells at the time of meiosis I. We show below that strains homozygous for null alleles of SPR3 are capable of normal meiosis and the production of viable ascospores. We have also monitored SPR3 expression in a series of strains that are defective in meiotic development, using an SPR3:lacZ fusion carried on a single copy plasmid. beta-Galactosidase activity occurred at wild-type levels in diploid strains homozygous for mutations in spo13, rad50, rad57 and cdc9, but was greatly reduced in strains carrying cdc8 or spo7 defects. We conclude that SPR3 expression is a valid monitor of early meiotic development, even though the gene is inessential for the sporulation process.

The relative transcription rates of three sporulation-regulated genes of yeast (SPR1, SPR2 and SPR3) were determined at intervals during sporulation, using a filter binding assay. The binding of in vivo labeled RNA to the corresponding DNAs increased 3- to 12-fold at the time of meiosis I, in parallel with the accumulation of the SPR transcripts. SPR1 and SPR3 mRNA abundance increased from less than 0.7 to 130 and 90 copies per cell, respectively, between the time of shift to sporulation medium and the initiation of spore formation. This represented a 150-to 200-fold increase in the steady-state levels of these RNAs. Similarly, the levels of beta-galactosidase present in sporulating cells harboring fusions between SPR3 and Escherichia coli lacZ increased at least 700-fold. We conclude that SPR1, SPR2 and SPR3 transcription is modulated during sporulation, possibly in response to earlier events in the process.

We have isolated a series of monoclonal antibodies that react to antigens in flowers of Nicotiana tabacum L. (tobacco) displaying specificity or preferentiality in their cell and tissue distributions. We immunized mice with extracts from tobacco flowers and then screened the hybridomas by enzyme-linked immunosorbent assay (ELISA) against extracts from leaves, sepals, petals, stamens and pistils; twenty five were chosen from the total screened. The antigens detected by about half of the antibodies were periodate-sensitive, implying that the epitopes were carbohydrate. Competition ELISA assays were used to determine if any antibodies were reacting to the same epitopes. Western blot analysis showed that while some antibodies reacted to specific bands, the bulk either failed to react or reacted to multiple bands, consistent with a glyco-conjugate nature for many of the antigens. Analysis of the spatial pattern of antigen distribution within tobacco flowers by immunolocalization showed that some antibodies recognized epitopes that were limited to very specific cells and tissues. We used the immunolocalization technique to analyze a mutant with stigmoid anthers: an antibody recognizing a pistil transmitting-tract antigen also reacted to cells in stigmoid anthers. Our results with this antibody set imply that biochemical differentiation within the tobacco flower includes cell-and tissue-specific glyco-moeities, and also that similarities, at the biochemical level, exist between a normal floral organ and the abnormal organ in a phenotype with a developmental switch.

We have found and characterized an antigen associated with crystal-containing cells in the stomium and connective tissue of the anthers of Nicotiana tabacum L. (tobacco). The antigen, defined by the monoclonal antibody NtF-8B1, localizes to subcellular regions surrounding the crystals. At the light-microscope level, the antigen is detectable just after the first appearance of crystals in the connective tissue of the anther, and at approximately the same time as the appearance of crystals in the stomium. The antigen is not detectable on a Western blot, and gave inconclusive results on a test of periodate sensitivity. It is not the crystals themselves, nor is the presence of the crystals required for antibody recognition. The antigen is sensitive to heat and protease treatment, indicating that it is a protein. The antigen is not tightly membrane-bound, in spite of its localization closely surrounding the crystals. Chemical tests indicate that the druse crystals in the stomium are calcium oxalate.

We characterized the development of a tobacco floral mutant, Mgr27, previously obtained by selecting for resistance to an inhibitor of an enzyme in the polyamine biosynthetic pathway. Mgr27 plants are shorter than the wild type with smaller leaves and a compact inflorescence. The plants have a regular leaf plastochron and a vegetative shoot apex similar to the wild-type vegetative shoot apex. There are frequently more than five floral organs in the first three whorls, and the anthers produce stigmatoids. At the scanning electron microscope level, the stigmatoids appear concurrently on all of the anthers and at approximately the same time that the stigma appears on the pistil. The stigmatoids contain tissue histologically and biochemically similar to transmitting tissue and they permit the germination and growth of pollen tubes. The mutant line has significantly lower levels of free and conjugated spermidine as well as significantly lower levels of conjugated putrescine. Key words: floral development, mutant, Nicotiana tabacum (tobaccco), polyamines, stigmatoid anthers.