ABSTRACT
Hybrids between the C(4)-like species, Flaveria brownii, A. M. Powell and the C(3)-C(4) intermediate species Flaveria linearis Lag., Flaveria floridana Johnston, and Flaveria oppositifolia (DC.) Rydb. exhibited bivalent chromosome pairing during meiosis and stainability of pollen was high, ranging from 51 to 95%. An F(2) population produced from an F. brownii x F. linearis F(1) hybrid, exhibited bivalent chromosome pairing and high pollen stainability indicating a high degree of fertility in the hybrid. Oxygen inhibition of apparent photosynthesis averaged 6.8% for F. brownii and 22.2% for the C(3)-C(4) species (in two experiments), and F(1) hybrids exhibited inhibitions which were intermediate to their parents. Values of carbon dioxide compensation concentration determined at low irradiance were 4.0, 34.0, and 6.5 microliters per liter for F. brownii, F. linearis and their F(1) hybrid, respectively. The mean value at low irradiance for 33 F(1) plants was 6.8 microliters per liter, and individual values ranged only from 3.7 to 11.7 microliters per liter. Anatomical characteristics for the F(1) hybrid leaves were intermediate to those of the parents, and there was considerable variation among F(2) plants derived from F. brownii x F. linearis. In the F(2) population delta(13)C values ranged from -27 per thousand to -20 per thousand. The expression of more C(4)-like characteristics by the F(1) hybrids in this study and their apparent high fertility make them promising specimens for producing segregating populations for use in C(4) inheritance studies.
ABSTRACT
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.
ABSTRACT
Physiological and isotopic aspects of several Peperomia species were investigated. All but one species had C(3)-like stomatal behavior, in that stomata were open during the day and closed during the night. In these species, most atmospheric CO(2) uptake occurred during the day. Concurrent with this stomatal behavior, there were Crassulacean acid metabolism-like acid fluctuations in most species. Carbon and hydrogen isotope ratios of cellulose nitrate from Peperomia reflect their physiological behavior. The delta(13)C values of cellulose nitrate from Peperomia species were similar to values observed in C(3) plants and consistent with the daytime uptake of exogeneous CO(2) via the C(3) photosynthetic pathway. The deltaD values of cellulose nitrate from Peperomia species approach those of Crassulacean acid metabolism plants. These elevated deltaD values are caused by fractionations occurring during biochemical reactions and not as a consequence of water relations.
ABSTRACT
Hydrogen and carbon isotope ratios of cellulose nitrate and oxygen isotope ratios of cellulose from C(3), C(4), and Crassulacean acid metabolism (CAM) plants were determined for plants growing within a small area in Val Verde County, Texas. Plants having CAM had distinctly higher deuterium/hydrogen (D/H) ratios than plants having C(3) and C(4) metabolism. When hydrogen isotope ratios are plotted against carbon isotope ratios, each photosynthetic mode separates into a distinct cluster of points. C(4) plants had many D/H ratios similar to those of C(3) plants, so that hydrogen isotope ratios cannot be used to distinguish between these two photosynthetic modes. Portulaca mundula, which may have a modified photosynthetic mode between C(4) and CAM, had a hydrogen isotope ratio between those of the C(4) and CAM plants. When oxygen isotope ratios are plotted against carbon isotope ratios, no distinct clustering of the C(4) and CAM plants occurs. Thus, oxygen isotope ratios are not useful in distinguishing between these metabolic modes. A plot of hydrogen isotope ratios versus oxygen isotope ratios for this sample set shows considerable overlap between oxygen isotope ratios of the different photosynthetic modes without a concomitant overlap in the hydrogen isotope ratios of CAM and the other two photosynthetic modes. This observation is consistent with the hypothesis that higher D/H ratios in CAM plants relative to C(3) and C(4) plants are due to isotopic fractionations occurring during biochemical reactions.
ABSTRACT
Carbon and hydrogen isotope ratios of cellulose nitrate and oxygen isotope ratios of cellulose from species of greenhouse plants having different photosynthetic modes were determined. When hydrogen isotope ratios are plotted against carbon isotope ratios, four clusters of points are discernible, each representing different photosynthetic modes: C(3) plants, C(4) plants, CAM plants, and C(3) plants that can shift to CAM or show the phenomenon referred to as CAM-cycling. The combination of oxygen and carbon isotope ratios does not distinguish among the different photosynthetic modes. Analysis of the carbon and hydrogen isotope ratios of cellulose nitrate should prove useful for screening different photosynthetic modes in field specimens that grew near one another. This method will be particularly useful for detection of plants which show CAM-cycling.
ABSTRACT
By measuring titratable acidity, gas exchange parameters, mesophyll succulence, and (13)C/(12)C ratios, we have shown that Cissus quadrangularis L. has C(3)-like leaves and stems with Crassulacean acid metabolism (CAM). In addition, the nonsucculent leaves show the diurnal fluctuations in organic acids termed recycling despite the fact that all CO(2) uptake and stomatal opening occurs during the day. Young succulent stems have more C(3) photosynthesis than older stems, but both have characteristics of CAM. The genus Cissus will be a fruitful group to study the physiology, ecology, and evolution of C(3) and CAM since species occur that exhibit characteristics of both photosynthetic pathways.
