Adenosine (Ado) kinase (ADK; ATP:Ado 5Ј phosphotransferase, EC 2.7.1.20) catalyzes the salvage synthesis of adenine monophosphate from Ado and ATP. In Arabidopsis, ADK is encoded by two cDNAs that share 89% nucleotide identity and are constitutively, yet differentially, expressed in leaves, stems, roots, and flowers. To investigate the role of ADK in plant metabolism, lines deficient in this enzyme activity have been created by sense and antisense expression of the ADK1 cDNA. The levels of ADK activity in these lines range from 7% to 70% of the activity found in wild-type Arabidopsis. Transgenic plants with 50% or more of the wild-type activity have a normal morphology. In contrast, plants with less than 10% ADK activity are small with rounded, wavy leaves and a compact, bushy appearance. Because of the lack of elongation of the primary shoot, the siliques extend in a cluster from the rosette. Fertility is decreased because the stamen filaments do not elongate normally; hypocotyl and root elongation are reduced also. The hydrolysis of S-adenosyl-l-homo-cysteine (SAH) produced from S-adenosyl-l-methionine (SAM)-dependent methylation reactions is a key source of Ado in plants. The lack of Ado salvage in the ADK-deficient lines leads to an increase in the SAH level and results in the inhibition of SAMdependent transmethylation. There is a direct correlation between ADK activity and the level of methylesterified pectin in seed mucilage, as monitored by staining with ruthenium red, immunofluorescence labeling, or direct assay. These results indicate that Ado must be steadily removed by ADK to prevent feedback inhibition of SAH hydrolase and maintain SAM utilization and recycling.

This study investigates the initial development of two Cerrado species, Eugenia dysenterica and Byrsonima basiloba. Both species have high ethnobotanical importance and are widely used as a food source as well as in folk medicine. Eugenia dysenterica presented hypogeous cryptocotylar germination and the cotyledons were rich in reserve material. This plant species showed quick root development and after the shoot had produced the first two pairs of eophyls, the seedling went into a latent state for at least 1 year. Byrsonima basiloba had a hard endocarp, which had to be broken to facilitate germination. This species showed epigeous phanerocotylar germination. Similarly to E. dysenterica, B. basiloba roots also developed rapidly; however, the aerial part grew continuously and did not show a latent period. Moreover, within the first 6 months of cultivation B. basiloba developed a xylopodium. The strategies for seed dispersal and breakage of seed dormancy were different between the species, but their initial growth showed several similarities.

A large number of compounds including lignin, phospholipids, pectin, DNA, mRNA, and proteins require methyl groups for their functionality. A detailed study of the expression and activities of two enzymes, adenosine kinase (ADK) and S-adenosylhomocysteine hydrolase (SAHH), which are both required for the maintenance and recycling of S-adenosylmethionine-dependent methylation in plants, was carried out. The abundance and tissue localization of ADK and SAHH transcripts and protein were monitored along with their enzyme activities in leaves, stems, buds, siliques, and roots of Arabidopsis. In all but roots and seed coats, the transcript abundance of ADK and SAHH fluctuated co-ordinately, matching changes in their protein and enzyme activities. To evaluate whether this expression pattern was associated with methyl recycling, the protein content and distribution of S-adenosylmethionine synthetase and phosphoethanolamine N-methyltransferase, a key methyltransferase involved in phospholipid synthesis, were investigated. These were found to accumulate in a pattern similar to ADK and SAHH. ADK and SAHH protein and transcript amounts were shown to fluctuate similarly in tissues accumulating lignin. Additionally, the amounts of ADK and SAHH mRNAs were also found at high levels in inflorescence meristems likely to support their higher rates of cell division. Thus, the results point to a co-ordinated and probably transcriptional regulation of these genes in most organs of Arabidopsis; SAHH abundance is distinctly higher in seeds and roots which suggests it may have a non-methyl-related role in these organs.

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Although Brosimum gaudichaudii Tréc. occurs in the Amazon and Atlantic forests, it is the only species of the genus Brosimum found in the Cerrado vegetation. Its roots contain high levels of psoralens. Compared with the wood of stems, the rootwood has more parenchyma and fibers with thinner walls. The stems and their respective piths were naturally 'grafted' into the xylopodium. Xylopodium wood has aberrant parenchyma zones and wood cells orientated in several directions. Xylopodium wood has a stem structure in the superior regions, but a root structure in the inferior parts. Furthermore, laticifers were found in xylopodium wood. Starch is present in the roots, but not in the stems, except for the two plants whose subterranean systems had signs of predatory attack

Pectin methyl-esterification is catalysed by S-adenosyl-L: -methionine (SAM)-dependent methyltransferases. As deficiency in adenosine kinase (ADK; EC 2.7.1.20) activity impairs SAM recycling and utilization, we investigated the relationship between ADK-deficiency and the degree of pectin methyl-esterification in cell walls of Arabidopsis thaliana. The distribution patterns of epitopes associated with methyl-esterified homogalacturonan in leaves and hypocotyls of wild-type (WT) and ADK-deficient plants were examined using immunolocalization and biochemical techniques. JIM5 and LM7 epitopes, characteristic of low esterified pectins, were more irregularly distributed along the cell wall in ADK-deficient plants than in WT cell walls. In addition, epitopes recognized by JIM7, characteristic of pectins with a higher degree of methyl-esterification, were less abundant in ADK-deficient leaves and hypocotyls. Since de-esterified pectins have enhanced adhesion properties, we propose that the higher abundance and the altered distribution of low methyl-esterified pectin in ADK-deficient cell walls lead to the leaf shape abnormalities observed in these plants.

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Brosimum gaudichaudii Tréc. occurs in the Atlantic and Amazon forests, and is the only species of Brosimum commonly found in Cerrado vegetation. It is of pharmaceutical interest due to the large accumulation of furocoumarins such as psoralens in the bark of roots and xylopodia. This work describes the bark anatomy of sterns, roots, and xylopodia. Although the external bark morphology of stern and subterranean system are different, anatomically they are similar, with both having wavy and fused rays at the outer region of the phloem and a gradual transition between pervious (non-collapsed) and collapsed phloem. Tbe stern and bark periderms have three to seven layers of cells. The bark of younger stern regions is different from the bark of older parts of the stern. Younger stern parts have higher abundance of laticifers in the phloem, and gelatinous fibers arranged in bundles. Compared with the younger regions, older sterns have fewer laticifers and the gelatinous fibers are scattered in the phloem. The root and the xylopodium bark are structurally similar to each other, with a higher abundance of laticifers than sterns. Starch was found in the roots, but not in sterns.