F. P. de Araujo

Water relations and organic solutes production in four umbu tree (Spondias tuberosa) genotypes under intermittent drought

In order to evaluate changes in leaf water potential (ψw) and solute accumulation induced by intermittent drought, an research was performed under greenhouse conditions using four umbu tree genotypes (GBU 44, GBU 48, GBU 50 and GBU 68) and two water treatments (control and stressed by withholding water), with four replicates. The ψw was measured in four-hour intervals during a 24-hour period at the first stomatal closure and at the end of the experimental period. Carbohydrates, amino acids, protein and proline contents were also evaluated in leaves and roots. Significant differences were found in most of the studied parameters. The lower ψw hour was between 800 h and 1200 h. GBU 50 reduced significantly ψwin stressed plants at 800 h, while control plants reduced at 1200 h . GBU 68 presented the higher ψw. The extending of the stress induced reductions to carbohydrates in the leaves of all genotypes, increases in amino acids to GBU 44 and 48, and reductions of 40% and 43% to GBU 50 and 68, respectively; results also showed alterations in proline content. In the roots, increases in carbohydrates were observed only in GBU 48. Alterations in amino acids, protein, and proline were verified. Umbu trees presented isohydric behavior maintaining high leaf water potential and a great variability in organic solutes accumulation in response to drought with marked differences among the genotypes.

Purification and characterization of a peroxidase present in xilopodium exsudates of umbu plants ( Spondias tuberosa A.)

Umbu plants are drought resistant trees which are able to store water and several other substances intoxa0its adapted root, named xylopodium. The exsudate from xilopodium is a natural solution rich in salts,xa0sugars and a little concentration of proteins. In this work, we report the purification of a peroxidasexa0(POX) from umbu xilopodium exsudate by direct extraction from polyacrylamide electrophoresis gels.xa0Umbu POX showed optimum activity at pHs around 6.0 to 7.0 and high thermal resistance afterxa0incubation at 70°C for 6 min. POX activity present in crude extracts was more heat-resistant than in itsxa0purified form. When assayed with metal ions, umbu POX activity was shown to be inhibited by Mn 2+ andxa0stimulated by Ca 2+ and Mg 2+ ; it was also inhibited by sodium azide (concentrations higher then 1 mM)xa0and not inhibited by either EDTA or tropolone. POX Km values for guaiacol and methylcatecholxa0substrates were 6.83 and 22.25, respectively. The enzyme is proposed to be a guaiacol peroxidase andxa0was seen to be located at higher concentrations in the outermost layers of xylopodium tissue, such asxa0the endoderm. Key words: Root enzyme, tissue brownig, guaiacol peroxidase, oxidative metabolism.