Source pool kinetics for C-photosynthate translocation in morning glory and soybean

The kinetic behavior of translocation profiles indicates that their shape is determined largely by the rate at which tracer enters the sieve tubes in the source leaf. Confirmation of this relationship was sought by investigating the kinetics of ¹⁴C in the immediate source pool for translocated sucrose in soybean (Glycine max L., cv. Bragg) and morning glory (Ipomea nil Roth, cv. Scarlet O'Hara) leaves. Quantitative microautoradiography was used to follow the water-soluble ¹⁴C contents of the companion cells in minor veins after pulse-labeling with ¹⁴CO₂. In both morning glory and soybean, the observed kinetics in the companion cells matched reasonably well those expected from the shape of the translocation profiles.

Marked compartmentation of sucrose was evident in soybean leaves in that the specific radioactivity of total leaf sucrose was greatest immediately after labeling and quickly declined, whereas labeling in the companion cells was low at first and did not reach a maximum for about 35 minutes. In morning glory leaves, the kinetics of sucrose specific radioactivity and of companion cell-labeling more closely paralleled one another.

     

Floral-specific polypeptides of the Japanese morning glory

Polypeptides from stems, leaves, sepals, corollas, stamens and pistils of the Japanese morning glory (Ipomoea nil Roth (Pharbitis nil Chois.)) were separated by one- and two-dimensional gel electrophoresis and visualized by silver staining. The majority of polypeptides were expressed in two or more organs, while those specific to only one organ were comparatively rate. Among the polypeptides of the former class were two which appeared to be floral-specific. A 46-kDa (kilodalton) polypeptide was expressed in corollas, stamens and pistils, whereas a 32-kDa polypeptide was observed only in extracts prepared from reproductive organs. Polypeptide spots from the various organs were compared with those from leaves, and it was found that sepals and stems shared 40–50% of their polypeptides with leaves, whereas corollas, stamens and pistils shared 20% or less. The latter organs shared 120 polypeptides or roughly 15% of those identified in the floral extracts. Floralorgan-specific polypeptides comprised nearly 10% of the total floral polypeptides identified.Abbreviations kDa kilodalton - PAGE polyacrylamide gel electrophoresis - SDS sodium dodecylsulfate     

Kinetics of C-photosynthate uptake by developing soybean fruit

By pulse-labeling field-grown soybean leaves for 60 seconds at midday with ¹⁴CO₂ and then sequentially harvesting, dissecting, and extracting the radioactive fruit tissues (of pod and seeds), the route, uptake kinetics, and metabolic fate of ¹⁴C-photosynthate as it was imported by 35- to 40-day-old pods were determined. As the [¹⁴C]sucrose pulse entered the pods, the seeds became radioactive immediately but a lag of nearly 30 minutes occurred before label could be detected in the pod wall pericarp.     

Phytotoxic components produced by pathogenic Fusarium against morning glory

A pathogenic isolate of Fusarium, F. oxysporum f. sp. batatas O-17 (PF), causes wilt disease in leaf etiolation in sweet potato (Ipomoea batatas) and morning glory (Ipomoea tricolor). Extracts from PF cultures were screened for phytotoxic components using a growth inhibition assay with morning glory seedlings. The extracts were fractionated using differential solvent extraction and two active compounds, ergosterol and fusalanipyrone, were isolated from the less-polar fraction. Growth inhibition of morning glory seedlings showed a sigmoidal dose-response relationship, with fusalanipyrone exhibiting a two order of magnitude higher EC50 value than ergosterol (18 nM and 1.6 microM, respectively). Both compounds showed lower growth inhibition activity towards lettuce seedlings (Lactuca sativa). This study provides information on the phytotoxic components of PF and discusses the mechanism behind PFf-induced phytotoxicity.     

Fitness consequences of cotyledon and mature-leaf damage in the ivyleaf morning glory

To understand the evolutionary and ecological consequences of natural enemy damage to plants, it is essential to determine how the fitness effects of damage differ depending on the tissues damaged and the subsequent pattern of damage. In a field experiment with the ivyleaf morning glory, the direct and indirect effects on fitness of herbivore damage to cotyledons and mature leaves was evaluated. Damage to mature leaves had negligible direct effects on fitness and no indirect effects on fitness through other correlated traits. Damage to cotyledons also did not directly affect fitness, but did so indirectly through its effects on plant size. These findings suggest that increased resistance to cotyledon damage or increased compensatory growth following cotyledon damage could be effective strategies for plants of this species to counteract the negative effects of herbivory.     

Ethylene binding changes in apple and morning glory during ripening and senescence

Ethylene binding sites were measured during fruit ripening and morning glory flower senescence. Little change in ethylene binding was noted during these developmental stages, except a slight decline during the later stages of fruit ripening or flower senescence. The concentration of ethylene required to achieve 50% saturation of the binding sites was 0.14 l/liter for both apple pulp and morning glory flowers. Ethylene binding sites were calculated to be 3.2×10^–11 moles/kg and 3.8×10^–9 moles/kg in apple and morning glory, respectively. It does not appear that changes seen in ethylene sensitivity during fruit ripening can be readily ascribed to changes in the number of ethylene binding sites in the tissue.Paper No. 11398 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, NC 27695-7601, USA.     

Experimental evidence that selection favors character displacement in the ivyleaf morning glory

While there is abundant evidence to suggest that pollinators influence the evolution of plant floral traits, there is little direct evidence that interactions between plant species shape the evolution of such characteristics. The purpose of this study was to determine whether the presence of the morning glory Ipomoea purpurea alters patterns of selection on floral traits of its congener, Ipomoea hederacea. We show that while selection on I. hederacea floral traits is effectively neutral when I. purpurea flowers are absent, selection acts to increase clustering of anthers about the stigma when I. purpurea flowers are present. Our results provide direct experimental evidence that the presence of flowers of a co-occurring congener can influence patterns of natural selection on floral traits that influence the mating system and contribute to prezygotic isolation. To the extent that this result is general, it also lends support to the claim that distributional patterns interpreted as ecological and reproductive character displacement in other plant species have been caused by natural selection generated by interactions among plant species.     

Immunohistochemistry of active gibberellins and gibberellin-inducible alpha-amylase in developing seeds of morning glory

Gibberellins (GAs) in developing seeds of morning glory (Pharbitis nil) were quantified and localized by immunostaining. The starch grains began to be digested after the GA contents had increased and reached a plateau. Immunohistochemical staining with the antigibberellin A(1)-methyl ester-antiserum, which has high affinity to biologically active GAs, showed that GA(1) and/or GA(3) were localized around starch grains in the integument of developing young seeds, suggesting the participation of GA-inducible alpha-amylase in this digestion. We isolated an alpha-amylase cDNA (PnAmy1) that was expressed in the immature seeds, and using an antibody raised against recombinant protein, it was shown that PnAmy1 was expressed in the immature seeds. GA responsiveness of PnAmy1 was shown by treating the young fruits 9 d after anthesis with GA(3). RNA-blot and immunoblot analyses showed that PnAmy1 emerged soon after the rapid increase of GA(1/3). An immunohistochemical analysis of PnAmy1 showed that it, like the seed GA(1/3), was also localized around starch grains in the integument of developing young seeds. The localization of GA(1/3) in the integument coincident with the expression of PnAmy1 suggests that both function as part of a process to release sugars for translocation or for the further development of the seeds.     

Molecular evolution of the chalcone synthase multigene family in the morning glory genome

Plant genomes appear to exploit the process of gene duplication as a primary means of acquiring biochemical and developmental flexibility. Thus, for example, most of the enzymatic components of plant secondary metabolism are encoded by small families of genes that originated through duplication over evolutionary time. The dynamics of gene family evolution are well illustrated by the genes that encode chalcone synthase (CHS), the first committed step in flavonoid biosynthesis. We review pertinent facts about CHS evolution in flowering plants with special reference to the morning glory genus, Ipomoea. Our review shows that new CHS genes are recruited recurrently in flowering plant evolution. Rates of nucleotide substitution are frequently accelerated in new duplicate genes, and there is clear evidence for repeated shifts in enzymatic function among duplicate copies of CHS genes. In addition, we present new data on expression patterns of CHS genes as a function of tissue and developmental stage in the common morning glory (I. purpurea). These data show extensive differentiation in gene expression among duplicate copies of CHS genes. We also show that a single mutation which blocks anthocyanin biosynthesis in the floral limb is correlated with a loss of expression of one of the six duplicate CHS genes present in the morning glory genome. This suggests that different duplicate copies of CHS have acquired specialized functional roles over the course of evolution. We conclude that recurrent gene duplication and subsequent differentiation is a major adaptive strategy in plant genome evolution.     

Ribonuclease in senescing morning glory: purification and demonstration of de novo synthesis

Isolated flower buds and flowers of Ipomoea tricolor went through the same stages of development as those attached to the plant. Ribonuclease activity increased sharply in both cases during the time of flower fading and aging. Affinity chromatography using guanosine diphosphate-Sepharose was employed for fast and efficient purification of ribonuclease. Flowers which were kept on D₂O during the senescence phase incorporated deuterium into ribonuclease as shown by isopycnic density gradient centrifugation in CsCl, suggesting that ribonuclease was de novo synthesized during aging of the flower.     

C(2)H(4) metabolism in morning glory flowers

Flowers of Ipomoea tricolor Cav. (cv. Heavenly Blue) were cut at various stages of development and evaluated for their ability to metabolize ethylene. Freshly cut buds or flowers were treated in glass containers for 8 hours with 6 μl/liter of highly purified ¹⁴C₂H₄. Following removal of dissolved ¹⁴C₂H₄, radioactivity was determined for the different flower tissues and trappd CO₂. ¹⁴C₂H₄ oxidation to ¹⁴CO₂ and tissue incorporation occurred at very low to nondetectable levels 2 to 3 days prior to flower opening. About 1 day prior to full bloom, just at the time when mature buds become responsive to ethylene (Kende and Hanson, Plant Physiol 1976, 57: 523-527), there was a dramatic increase in the capacity of the buds to oxidize ¹⁴C₂H₄ to ¹⁴CO₂. This activity continued to increase until the flower was fully opened reaching a peak activity of 2,500 dpm per three flowers per 8 hours. It then declined as the flower closed and rapidly senesced. A similar but smaller peak occurred in tissue incorporation and it was followed by a second peak during late flower senescence. This first peak in tissue incorporation and the dramatic peak in ethylene oxidation slightly preceded a large peak of natural ethylene production which accompanied flower senescence. The ethylene metabolism observed was clearly dependent on cellular metabolism and did not involve microorganisms since heat killing destroyed this activity and badly contaminated heat-killed flowers were unable to metabolize ethylene.     

An examination of the monophyly of morning glory taxa using Bayesian phylogenetic inference

The objective of this study was to obtain a quantitative assessment of the monophyly of morning glory taxa, specifically the genus Ipomoea and the tribe Argyreieae. Previous systematic studies of morning glories intimated the paraphyly of Ipomoea by suggesting that the genera within the tribe Argyreieae are derived from within Ipomoea; however, no quantitative estimates of statistical support were developed to address these questions. We applied a Bayesian analysis to provide quantitative estimates of monophyly in an investigation of morning glory relationships using DNA sequence data. We also explored various approaches for examining convergence of the Markov chain Monte Carlo (MCMC) simulation of the Bayesian analysis by running 18 separate analyses varying in length. We found convergence of the important components of the phylogenetic model (the tree with the maximum posterior probability, branch lengths, the parameter values from the DNA substitution model, and the posterior probabilities for clade support) for these data after one million generations of the MCMC simulations. In the process, we identified a run where the parameter values obtained were often outside the range of values obtained from the other runs, suggesting an aberrant result. In addition, we compared the Bayesian method of phylogenetic analysis to maximum likelihood and maximum parsimony. The results from the Bayesian analysis and the maximum likelihood analysis were similar for topology, branch lengths, and parameters of the DNA substitution model. Topologies also were similar in the comparison between the Bayesian analysis and maximum parsimony, although the posterior probabilities and the bootstrap proportions exhibited some striking differences. In a Bayesian analysis of three data sets (ITS sequences, waxy sequences, and ITS + waxy sequences) no supoort for the monophyly of the genus Ipomoea, or for the tribe Argyreieae, was observed, with the estimate of the probability of the monophyly of these taxa being less than 3.4 x 10(-7).