Proceedings of the XLVI Italian Society of Agricultural Genetics - SIGA Annual Congress

Giardini Naxos, Italy - 18/21 September, 2002

ISBN 88-900622-3-1

Poster Abstract - 2.20

NEW EVIDENCE OF SIMILARITY BETWEEN HUMAN AND PLANT STEROID METABOLISM: 5 ALPHA REDUCTASE ACTIVITY IN SOLANUM MALACOXYLON

ROSATI F.*, DANZA G.*, GUARNA A.**, CINI N.**, RACCHI M. L.***, SERIO M.*

*) Dipartimento di Fisiopatologia Clinica, Unità di Endocrinologia, Università di Firenze, Viale G. Pieraccini 6, I-50134 Firenze, Italy

**) Dipartimento di Chimica Organica "Ugo Schiff", Polo Scientifico, Università di Firenze, Via della Lastruccia 13, I-50019 Sesto Fiorentino, Italy

***) Dipartimento di Biotecnologie Agrarie, Laboratorio di Genetica, Piazzale delle Cascine 24, I-50144 Firenze, Italy

a-reductase, DET2, Solanum malacoxylon, brassinosteroids, inhibitors

The physiological role of steroid hormones in humans development is well known and their metabolic pathway and mechanism of action are almost completely elucidated. By contrast, the role of brassinosteroids, the plant steroid hormones, in plant development is less known, though an increasing amount of data on brassinosteroids biosynthesis is evidencing surprising similarities between human and plant steroid metabolic pathways. In the present study we focused our attention particularly on the enzyme 5 alpha reductase for which a plant ortholog of the mammalian system, DET2, was recently described in Arabidopsis thaliana. With the intention of better define the similarities with the human enzymes, Solanum malacoxylon, a calcinogenic plant with a very active biosynthetic system of vitamin D-like molecules and sterols, was chosen to study the 5a-reductase activity. We used the natural DET2 substrate, campestenone, to study the kinetic characteristics of plant 5aR and to directly demonstrate that the plant substrate is reduced by the human isozymes. Substrates and inhibitors of human 5a-reductases were also used to better characterise the plant enzyme.

We demonstrated that campestenone, is reduced to 5a-campestanone by both the human 5a-reductase isozymes with different affinity. Leaves and calli of Solanum malacoxylon were chosen as examples of differentiated and undifferentiated tissues respectively. Two different 5a-reductase activities were evidenced in calli and leaves of Solanum using campestenone as substrate. The use of progesterone allowed the detection of both the activities in calli. The hypothesis of the existence of two different 5a-reductase isozymes in Solanum malacoxylon was confirmed by the different activity of inhibitors of the human 5a-reductases, in calli and leaves. These data demonstrate for the first time the existence of a 5a-reductase activity in Solanum malacoxylon. The evidences of the presence of two isozymes in different plant tissues extend the analogies between plant and mammalian steroid metabolic pathway. The comparative study of steroid hormone biosynthesis in plants and human represents an important starting point for the comprehension of how dietary substances may interfere with human enzymatic systems.