Cultivo in vitro de Brosimum gaudichaudii Tréc. (Moraceae) / In vitro cultivation of Brosimum gaudichaudii Tréc. (Moraceae)

O objetivo desta pesquisa foi avaliar o potencial organogenético de entrenós, discos foliares, e raízes de Brosimum gaudichaudii utilizando 12 diferentes combinações dos fitorreguladores 6-benzilaminopurina e ácido naftaleno acético, em meio MS (diluído à metade), sólido (6,5 g de ágar), e com 20 g.L-1 de sacarose. Independentemente das combinações hormonais testadas verificou-se a formação de calos friáveis (2 a 20 mm de diâmetro) em 90% dos entrenós usados como explantes. No entanto, os tratamentos testados não foram capazes induzir calos ou gemas em raízes e em discos foliares. O estudo anatômico revelou a formação de meristemóides nas regiões mais externa e mais interna dos calos. Os resultados obtidos poderão servir de base para novos testes de indução de calos na espécie.

The objective of this research was to evaluate the organogenic potential of internodes, leaf discs and roots of Brosimum gaudichaudii using 12 different combinations of the plant growth regulators 6-benzylaminopurine and naphthalene acetic acid in MS medium (half strength), solid medium (6.5 g agar) and sucrose medium (20 g.L-1). Regardless the hormonal combination tested, we observed the formation of friable calluses (2 - 20 mm wide) in 90% of the internode explants. However, the treatments were not able to induce callus or buds on roots and leaf discs. The anatomical analysis revealed meristemoid formation in the outer and inner regions of the calluses. The results may serve as the basis for further testing of callus induction in this species.

Methyl recycling activities are co-ordinately regulated during plant development.

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.

Deficiency of adenosine kinase activity affects the degree of pectin methyl-esterification in cell walls of Arabidopsis thaliana.

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.