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Gladys M. Nazario and Carol Lovatt

A study was undertaken to identify the pathway(s) leading to the synthesis of caffeine and theobromine in leaves of Coffea arabica. The relative contribution of purine nucleosidcs and bases to the biosynthesis of these alkaloids was assessed by measuring the incorporation of radiolabeled inosine, adenosine, adenine, hypoxanthine, and xanthine into caffeine and theobromine.

The results of this investigation suggest that caffeine and theobromine are end products of two distinctively different pathways. The incorporation of radiolabeled formate, adenosine, and xanthine was significantly greater into caffeine than into theobromine. Furthermore, exogenously supplied theobromine did not dilute the incorporation of [14C]formate, [14C]inosine, or [14C]xanthine into caffeine. In contrast, radiolabeled adenine was incorporated into theobromine but not into caffeine, and exogenously supplied adenine diluted the incorporation of [14 C]adenosine into theobromine, but not into caffeine.

Taken together, these results provide strong evidence that theobromine is not a precursor of caffeine biosynthesis in leaves of C. arabica.

Supported by the Citrus Research Center and Agricultural Experimental Station of the University of California, Riverside,

Open access

Patricia Tolson Tomlinson and Carol J. Lovatt

Abstract

The capacity of ‘Washington’ navel orange fruit [Citrus sinensis (L.) Osbeck] to synthesize and catabolize purines and pyrimidines was assessed. De novo biosynthesis of purine nucleotide was demonstrated by [14C] bicarbonate incorporation into purine nucleotides, blockage of this process by four known inhibitors, and assimilation of radiolabeled carbon from formate, both carbons of glycine, and carbon-3 of serine into the adenine ring. De novo synthesis of pyrimidines via the orotate pathway in young fruit was demonstrated by incorporation of [14C] bicarbonate and [6-14C]orotic acid into uridine nucleotides, release of 14CO2 from [7-14C]orotic acid, and blockage of these processes by 6-azauridine. Synthesis of purine and pyrimidine nucleotides via salvage reactions was demonstrated by incorporation of radiolabeled bases and ribonucleosides into nucleotides and into nucleic acids. Release of 14CO2 from radiolabeled adenine, adenosine, hypoxanthine, and xanthine, uric acid, urea (purines), uracil, and uridine (pyrimidines) provided evidence the pathways for catabolism (degradation) of purines and pyrimidines in navel orange fruit are similar to those found in microorganisms and animal tissues. To the best of our knowledge, this report is the first to assess the capacity of anabolic and catabolic pathways of purine and pyrimidine nucleotide metabolism in fruit of any species. De novo synthetic activities in orange fruit permit increases in the pools of purine and pyrimidine nucleotides using simple precursors. Further, the patterns of salvage and catabolism suggest riboside pools are reused predominantly as nucleotides, while the majority of base pools are degraded to permit recycling of carbon and nitrogen into other metabolites.

Free access

Diana L. Lange and Adel A. Kader

Partially ripened avocado [Persea americana (Mill.) cv. Hass] fruit harvested in either June or Aug. 1994 were kept at 10 °C in air (21% O2), 20% CO2 (17% O2, balance N2), or 40% CO2 (13% O2, balance N2) for 7 to 12 days and then were transferred to air at 10 °C for 2 to 3 days. Mitochondrial respiration was stimulated in response to elevated CO2 treatments at 10 °C. A shift to alternative pathway (Alt) respiration occurred on day 4 in experiments using avocados from both harvest dates, with a return to initial levels in only the 20% CO2-treated fruit (June-harvested fruit after return to air). Elevated CO2 at 20 °C decreased the in vitro O2 consumption of isolated mitochondria compared to mitochondria kept in air. The Alt pathway contributed less to the total O2 uptake of CO2-treated mitochondria compared to mitochondria kept in air. The respiratory control ratios of the CO2-treated fruit and mitochondria were higher and lower, respectively, than the air controls. Induction of 33 to 37 kD proteins (corresponding to the size of the alternative oxidase proteins) occurred in avocados after 4 days in 40% CO2. These results indicate that elevated CO2 has various effects depending on concentration, duration and temperature of exposure, and mitochondrial function of avocado fruit, such as increased and altered respiratory oxidation and up-regulation of alternative oxidase proteins.

Open access

G. M. Glenn, B. W. Poovaiah, and H. P. Rasmussen

Abstract

Cuticles from ‘Golden Delicious’ apples (Malus domestica Borkh.) were isolated enzymatically. Changes in cuticles of developing fruit at various stages were studied using scanning electron (SEM) and light microscopy (LM). Structures allowing Ca penetration through the cuticle were studied by precipitating permeating Ca in agar as it passed through the cuticle. The importance of lenticels in the penetration of Ca at 2 stages of fruit development was studied under saturated conditions using a diffusion cell. The lenticels had a significant positive effect on Ca penetration. The development of a dense network of structures resembling cracks, as well as occasional surface discontinuities, were observed in cuticles isolated from fruit harvested in September. These structures seemed to provide pathways for cuticular Ca penetration. The importance of lenticels, cracks, or other surface irregularities, and the process of diffusion in the penetration of Ca into apple fruit is discussed.

Free access

Timothy W. Coolong and William M. Randle

To determine the extent to which sulfur (S) and nitrogen (N) fertility interact to influence the flavor biosynthetic pathway in onion (Allium cepa L.), `Granex 33' onions were grown in hydroponic solution culture with varying levels of S and N availability. Plants were grown at 5, 45, or 125 mg·L-1 sulfate (SO4 2-), and 10, 50, 90, or 130 mg·L-1 N, in a factorial combination. Total bulb S, total and individual flavor precursors and their peptide intermediates in intact onion tissue were measured. To measure the effect of S and N on alliinase activity, flavor precursors were also measured in onion macerates. Sulfur and N availability in the hydroponics solution interacted to influence all flavor compounds except S-methyl-L-cysteine sulfoxide. Levels of S-methyl-L-cysteine sulfoxide were influenced by N and S levels in the solutions; however, no interaction was present. At the lowest SO 4 2- or N levels, most precursors and peptides measured were present in very low concentrations. When SO 4 2- or N availability was adequate, differences among flavor compounds were small. Results indicated that S fertility had a greater influence on trans-S-1-propenyl-L-cysteine sulfoxide (1-PRENCSO) accumulation, while N availability had a greater influence on S-methyl-L-cysteine sulfoxide levels. Flavor precursors remaining in the onion macerates revealed that the percentage of intact precursors hydrolyzed by alliinase were not significantly influenced by either SO 4 2- or N levels in the solutions, except for 1-PRENCSO, which was affected by N levels. Nitrogen and S fertility interacted to influence the flavor biosynthetic pathway and may need to be considered together when manipulating onion flavor compounds.

Free access

Marilyn Rivera-Hernández, Linda Wessel-Beaver, and José X. Chaparro

Squash and pumpkins (Cucurbita sp.) are important contributors of beta-carotene to the diet. Consumers of tropical pumpkin and butternut squash (both C. moschata Duchesne) prefer a deep orange mesocarp color. Color intensity is related to carotene content. Among the five domesticated Cucurbita species, C. moschata and C. argyrosperma Huber have a close relationship. In crosses between these two species, fertile F1 plants can be easily obtained when using C. argyrosperma as the female parent. This research studied the relationship between and within C. moschata and C. argyrosperma by sequencing three genes in the carotenoid biosynthesis pathway and generating gene trees. Genotypes used in the study differed in flesh color from very pale yellow to dark orange. In some cases, haplotypes were associated with a particular mesocarp color. Further study of these types of associations may improve our understanding of color development in Cucurbita. The frequency of single nucleotide polymorphisms (SNPs) in the sequenced fragments was low. There were more SNPs and more heterozygotes among C. moschata accessions than among C. argyrosperma accessions. Haplotypes of the outgroups (C. ficifolia C.D. Bouché and C. maxima Duchesne) were always distinct from C. moschata and C. argyrosperma. These later species had both distinct haplotypes and shared haplotypes. Haplotypes shared among species tended to be maintained in the same branch of the phylogenetic tree, suggesting either gene flow between the species or a common ancestral gene. Both explanations suggest a close genetic and evolutionary relationship between C. moschata and C. argyrosperma.

Free access

Mercy A. Olmstead, N. Suzanne Lang, Gregory A. Lang, Frank W. Ewers, and Shirley A. Owens

Dye transport through vascular pathways was examined in tissues surrounding the graft union of second-leaf, field-grown trees of `Lapins'/Gisela 5 (`Gi 5') (dwarfing) and `Lapins'/'Colt' (nondwarfing). Excavated, intact trees were allowed to take up xylemmobile dye via transpiration for 6 h before sectioning the tree into scion, graft union, and rootstock tissue. `Lapins'/'Gi 5' had a significantly larger stem cross-sectional area in the central graft union than did `Lapins'/'Colt'. Per unit cross section, dye transport of both `Lapins'/'Gi 5' and `Lapins'/'Colt' was significantly less in the graft union than in rootstock sections, with still less transported to scion tissues in `Lapins'/'Gi 5'. `Lapins'/'Gi 5' had a tendency to produce vascular elements oriented obliquely to the longitudinal axis of the tree. Dye was distributed more uniformly axially and radially across the graft union in `Lapins'/'Colt' than in `Lapins'/'Gi 5', with an apparent accumulation of dye in `Lapins'/'Gi 5' graft union. Xylem vessel diameters and vessel hydraulic diameters (VDh) were smaller overall in `Lapins'/'Gi 5' than in `Lapins'/'Colt'; however, graft unions in both had smaller VDh than did rootstock sections. These observations suggest reduced transport efficiency of xylem vessels in the graft union in `Lapins'/'Gi 5' may be due to smaller vessels, vascular abnormalities and/or increased amounts of callus and parenchyma tissue.

Free access

Haejeen Bang, Sunggil Kim, Daniel I. Leskovar, Angela Davis, and Stephen R. King

Gene identification and characterization can be utilized for the identification of respective functions and their relationship to flesh color inheritance. Phytoene synthase (PSY), which converts two molecules of GGPP into phytoene, is the first committed step of the pathway. Previous phylogenetic analysis of PSY has indicated that PSY duplication is common in Poaceae, but rare in dicots. Degenerate PCR and RACE were used for PSY cloning. Three members of PSY gene family (PSY-A, PSY-B and PSY-C) were identified. PSY-A shared higher identity with PSY-C than PSY-B. PSYC shared 96% identity with melon PSY. PSY-C also showed a high homology with tomato PSY1, even higher than PSY-A and PSY-B. It showed a similar gene expression pattern, so we propose that PSY-C is a homologue to PSY1. RT-PCR analysis indicated that PSY-B has a different transcriptional behavior from PSY-A, similar to tomato PSY2. Therefore, PSY genes appear to be under different regulatory mechanisms. Deduced protein sequence of PSY1 or PSY2 between species has higher homology than between PSY1 and PSY2 within species. Phylogenetic analysis indicated that watermelon PSY gene family is very distantly related. Watermelon and carrot PSY gene families did not appear to cluster as closely as in Poaceae or tomato. This indicates that watermelon and carrot PSY genes are not conserved as much as PSY in tomato or Poaceae. There was no particular pattern in phylogenetic relationship of dicots. Poaceae PSY genes showed a clustering into a PSY1 group and PSY2 group. PSY duplication in watermelon provides additional evidence that PSY duplication may be a common phenomenon in dicots. They are likely to be duplicated evolutionarily a long time ago, possibly even prior to the evolution of monocot and dicot divergence.

Free access

Ahmad Khalighi, Manijeh Mohammadi Dehcheshmeh, Esmaeil Ebrahimie, Manoochehr Sardari, and Rohangiz Naderi

Fritillaria imperialis and Fritillaria persica are important medicinal and ornamental plants that are native to Iran. Wild populations of Fritillaria are at risk of extinction. For the first time, capability of developmental stages in respect to induction of different morphogenesis pathways from petal tissue was studied in detail. The developmental stages were green unopened flowers, colored unopened flowers, and open flowers. Direct bulblet regeneration and direct somatic embryogenesis were observed from green unopened flowers in both F. imperialis and F. persica. More bulblet regeneration was produced in F. imperialis in contrast with F. persica in colored unopened flowers. Somatic embryogenesis via callus was established in green unopened flowers of F. persica with cold pretreatment. The effect of light on induction of different morphogenesis pathways was nonsignificant except for green unopened flowers of F. persica with cold treatment. Our results showed that the developmental stages of petal explants play a significant role in micropropagation of Fritillaria and induction of different morphogenesis pathways.

Free access

John R. Stommel, Gordon J. Lightbourn, Brenda S. Winkel, and Robert J. Griesbach

Pigmentation of plant vegetative tissue, including leaves, stems, and roots and reproductive tissue in flowers and fruit, is attributed to anthocyanin and carotenoid pigments. These colored compounds are produced by independent metabolic pathways