The activity of 1-aminocyclopropane-1-carboxylate oxidase (ACO) was characterized in seeds of the tropical legume Townsville stylo (Stylosanthes humilis) both in vitro (desalted extract of non-dormant seeds) and in vivo (entire dormant seeds). Optimum conditions for maximum in vitro ACO activity in a Trizma-HCl 100 mM buffered medium were: pH 7.0, temperature 32ºC and cofactors and co-substrate at the following concentrations: NaHCO3 30 mM, sodium ascorbate 30 mM and FeSO4 50 µM. Rates of in vitro reaction catalyzed by ACO were shown to be constant within the interval 15-150 minutes from the onset of the reaction. The apparent Km for in vitro ACO, as determined from the non-linear curve fitting to the Michaelis-Menten equation, was 156±8.3 µM ACC with a Vmax 5.4±0.08 mmol (ET) g-1 h-1 on a fresh matter (FM) basis. In vivo (control basal medium: HCl-KOH 10 mM pH 7.0, 30ºC, reaction time 15 hours) apparent Km was 230±27 µM ACC and Vmax 11.9±0.38 mmol (ET) g-1.h-1 on a FM basis. These data suggest that the enzyme exhibits a relatively low affinity for the substrate. The well-known inhibitors of ACO activity, α-aminoisobutyric acid, salicylic and acetylsalicylic acids, n-propylgallate and cobaltous ions, were highly effective in inhibiting ACO activity of Townsville stylo seeds.

A possibilidade de se encontrar genótipos de arroz, gramínea C3, com características anatômico-foliares semelhantes às gramíneas C4 levou ao presente estudo. Genótipos com características C4 seriam superiores fotossinteticamente, mais adaptados ao estresse ambiental e mais produtivos. Nesta pesquisa foi observada a anatomia foliar de 483 exemplares de arroz, sendo 477 da espécie Oryza sativa L. e seis de outras espécies (Oryza glumaepatula, O. glaberrima, O. nivara, O. rufipogon, O. flotante e O. longistaminata). Na pesquisa, observou-se a presença de cloroplastos nas células da bainha vascular da cultivar CNA 6189. Em alguns outros genótipos, foram encontrados apenas vestígios de cloroplastos, e nenhum cloroplasto na maioria dos genótipos, como o IAC 25. Com base nos resultados encontrados, espera-se que por meio de técnicas de biologia molecular, características de plantas C4 venham a ser incorporadas a plantas, como o arroz, melhorando substancialmente as suas potencialidades de adaptação a ambientes menos favorecidos.

The objective of this study was search genotypes of rice, a C3 Gramineae, with characteristics of leaf anatomy similar to C4 Gramineae. Genotypes with C4 characteristics would have higher photosynthetic rates, be better adapted to environmental stress and higher productivity. In these research was studied the leaf anatomy of 483 rice genotypes, 477 of which were Oryza sativa L. and six from other species (Oryza glumaepatula, O. glaberrima, O. nivara, O. rufipogon, O. flotante and O. longistaminata). The results showed that the cultivar CNA 6189 presented chloroplasts in the bundle sheath cells. Vestiges of chloroplasts were observed in some genotypes but no chloroplasts were found in other genotypes, such as IAC 25. It is expected that through molecular biology techniques, characteristics of C4 plants might be incorporated into C3 plants, such as rice, improving their potential to adapt to an adverse environment.