Diagnostic dilemma.

In those issues in which our regular Case of the Month does not appear, The Green Journal will present a Diagnostic Dilemma-an electrocardiogram or radiograph, or both, with a brief case history-as a challenge for our readers to solve. The correct answer appears on page 742. If you would like to contribute a Diagnostic Dilemma, please submit a high-quality copy of the ECG or radiograph with a brief synopsis (<250 words) of the case to editorial office of the American Journal of Medicine.

Alternative pathways of tobacco placental development: time of commitment and analysis of a mutant.

Previous work from our lab identified mutants, Mgr3 and Mgr9, of tobacco (Nicotiana tabacum) that produced unusual elongated green outgrowths from placentae in vivo. Similarly appearing stigmatoid growths were described developing from some in vitro cultures of excised placentae of tobacco (Hicks and McHughen, 1974, 1977). Here we report a developmental analysis and comparison of the unusual stigmatoid outgrowths seen in in vitro cultures of wild-type and mutant placentae, as well as the green outgrowths seen in vivo in the mutants. The growths produced by wild-type and mutant placental cultures in vitro, and the growths produced by the mutants in vivo, are identified as abnormal stigmas and styles. Wild-type in vitro placental cultures also produce outgrowths identified as homologs of whole carpels. Carpel fusion is not required for differentiation of stigma, style, transmitting tract, vascular traces, ovary, and ovules in these structures. The type and extent of stigmatoid growth production depends upon the age of the explant at excision and culture initiation. Before ovule primordium initiation, few growths are seen in culture; for a short window of time afterward, the primordia are competent to give rise to stigmatoid and carpelloid growths when cultured. After commitment to ovule development occurs, the primordia produce only ovules when cultured. The behavior of the mutant placental cultures is dimorphic. Explants from early stages behave similarly to wild-type when cultured, but differences between wild-type and the mutant behaviors in culture arise at the time when the stigmatoid growths begin to appear in vivo in the mutants. These results imply that ovule primordia pass through stages of distinct sequential restrictions of fate, first to growth as gynoecia, and then second to growth as ovules. The mutant strains described here perturb the commitment to differentiation as ovules.

Biochemical differentiation in the tobacco flower probed with monoclonal antibodies.

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.

Photosynthesis of F(1) Hybrids between C(4) and C(3)-C(4) Species of Flaveria.

Photosynthetic characteristics were studied in several F(1) hybrids between C(4) and C(3)-C(4) species of Flaveria. Stable carbon isotope ratios, O(2) inhibition of apparent photosynthesis, and phosphoenolpyruvate carboxylase activities in the hybrids were similar to the means for the parents. Values of CO(2) compensation concentrations were nearer to those of the C(4) parent and apparent photosynthesis was below that of both parents, being only 60 and 74% of that of the lowest (C(3)-C(4)) parent in two experiments. Reductions of CO(2) compensation concentration and O(2) inhibition of apparent photosynthesis as well as increases in carbon isotope ratios and phosphoenolpyruvate carboxylase activities compared to values in C(3)-C(4) species suggest transfer of a limited degree of C(4) photosynthesis to the F(1) hybrids. However, the lower apparent photosynthesis of the hybrids suggests that transfer of C(4) characteristics to non-C(4) species is detrimental unless characteristics associated with C(4) photosynthesis are fully developed. There was a highly significant negative correlation (r = -0.90) between CO(2) compensation concentration and the logarithm of phosphoenolpyruvate carboxylase activity in the parents and hybrids, suggesting involvement of this enzyme in controlling the CO(2) compensation concentration. Although bundle-sheath cells were more developed in leaves of hybrids than in C(3)-C(4) parents, they appeared to contain lower quantities of organelles than those of the C(4) parent. Reduced quantities of organelles in bundle-sheath cells could indicate incomplete compartmentation of partial pathways of the C(4) cycle in the hybrids. This may mean that the reduction of CO(2) compensation and O(2) inhibition of apparent photosynthesis relative to the C(3)-C(4) parents is less dependent on fully developed Kranz anatomy than is increased apparent photosynthesis.

Oxygen Stimulation of Apparent Photosynthesis in Flaveria linearis.

A plant was found in the C(3)-C(4) intermediate species, Flaveria linearis, in which apparent photosynthesis is stimulated by atmospheric O(2) concentrations. A survey of 44 selfed progeny of the plant showed that the O(2) stimulation of apparent photosynthesis was passed on to the progeny. When leaves equilibrated at 210 milliliters per liter O(2) were transferred to 20 milliliters per liter O(2) apparent photosynthesis was initially stimulated, but gradually declined so that at 30 to 40 minutes the rate was only about 80 to 85% of that at 210 milliliters per liter O(2). Switching from 20 to 210 milliliters per liter caused the opposite transition in apparent photosynthesis. All other plants of F. linearis reached steady rates within 5 minutes after switching O(2) that were 20 to 24% lower in 210 than in 20 milliliters per liter O(2). At low intercellular CO(2) concentrations and low irradiances, O(2) inhibition of apparent photosynthesis of the aberrant plant was similar to that in normal plants, but at an irradiance of 2 millimoles quanta per square meter per second and near 300 microliters per liter CO(2) apparent photosynthesis was consistently higher at 210 than at 20 milliliters per liter O(2). In morphology and leaf anatomy, the aberrant plant is like the normal plants in F. linearis. The stimulation of apparent photosynthesis at air levels of O(2) in the aberrant plant is similar to other literature reports on observations with C(3) plants at high CO(2) concentrations, high irradiance and/or low temperatures, and may be related to limitation of photosynthesis by triose phosphate utilization.

Photosynthesis, Leaf Anatomy, and Morphology of Progeny from Hybrids between C(3) and C(3)/C(4)Panicum Species.

Species in the Laxa group of Panicum have C(3) or C(3)/C(4) photosynthesis based on leaf anatomical and CO(2) exchange characteristics. Hybrids were previously made between C(3)/C(4) and C(3) species in this group (RH Brown et al. 1985 Plant Physiol 77: 653-658). In this paper, CO(2) exchange, morphological, and leaf anatomical characteristics of F(2) or F(5) progeny from colchicine-induced amphiploids of C(3)/C(4) x C(3) hybrids (Panicum milioides Nees ex Trin. [C(3)/C(4)] x Panicum laxum Mez [C(3)] and Panicum spathellosum Doell [C(3)/C(4)] x Panicum boliviense Hack. [C(3)]) were studied.There were no differences found in morphology or physiology between the amphiploids and the F(1) hybrids from which they were produced. In the segregating progeny, CO(2) compensation concentration and photorespiration values typical of C(3), but not of C(3)/C(4) plants, were recovered. Progeny were found from both crosses which possessed O(2) inhibition of apparent photosynthesis typical of the parents, and in the case of the P. milioides x P. laxum cross, leaf anatomy and overall plant morphology typical of the parents were observed in some progeny. The progeny were found to possess recombinations of various traits associated with reduced photorespiration, so that no correlation existed among O(2) inhibition of apparent photosynthesis, CO(2) compensation concentration, and leaf anatomical traits. One plant was especially noteworthy in possessing leaf anatomy typical of C(3)/C(4) plants, but with CO(2) exchange characteristics of C(3) plants.

Photosynthesis, Morphology, Leaf Anatomy, and Cytogenetics of Hybrids between C(3) and C(3)/C(4)Panicum Species.

The Laxa group of the Panicum genus contains species which have CO(2) exchange and anatomical characteristics intermediate to C(3) and C(4) photosynthetic types (C(3)/C(4)), and also species characterized as C(3). Hybrids were made between two of the C(3)/C(4) species and two C(3) species. Carbon dioxide exchange and morphological, leaf anatomical, and cytogenetic characteristics of F(1) hybrids between Panicum milioides Nees. ex Trin (C(3)/C(4)) and P. laxum Mez. (C(3)), P. spathellosum Doell (C(3)/C(4)) and P. boliviense Hack. (C(3)), and P. spathellosum and P. laxum were studied. There were no consistent differences in apparent photosynthesis, although two of the three hybrids had higher net CO(2) uptake than the C(3) parent. Values of inhibition of apparent photosynthesis by 21% O(2), CO(2) loss in the light, and CO(2) compensation concentration for the hybrids were between those of the parents. All three hybrids showed leaf anatomical traits, especially organelle quantities in the bundle sheath cells, between those of their respective parents. Linear regression of CO(2) compensation concentration on the percentage of mitochondria and chloroplasts in vascular bundle sheaths of the parents and hybrids gave correlation coefficients of -0.94. This suggests that the reduction in CO(2) loss in the C(3)/C(4) species, and to a lesser degree in the F(1) hybrids, was due to development of organelles and perhaps a higher proportion of leaf photorespiration in bundle sheaths. The overall morphology of the hybrids was so different from the parents that they could be described as new taxonomic forms. The chromosomes in the hybrids were mainly unpaired or paired as bivalents indicating possible homology between some parental genomes.