Using 6 culture media (12, 12D, 12G, 11, A and B) made up of MS medium (Murashige-Skoog, 1962) supplemented or not with glycerine, with different cytokinins, and/or 2,4-D, the morphological characteristics and contents in total carbohydrates, reducing sugars, sucrose and starch were studied in calli induced from explants (cotyledon, petiole, hypocotyl and leaf) obtained from Medicago strasseri seedlings. Callus formation was induced under photoperiod (16h light/8h darkness) conditions or in the absence of light.Considerable variability in the calli was observed, depending on the explants and media used. Under photoperiod conditions, medium A with KIN (1 mg/1) and 2,4-D (3 rag/l) induced many calli with the highest contents in total carbohydrates (886.1-889.3 mg/g DW), sucrose (132.1-188.2 mg/g DW) and starch (125.2-247.6 mg/g DW) and the lowest contents in reducing sugars (118.4-173.3 mg/g DW). In media 11, A and B, under conditions of darkness, calli degenerated at the start of culture. Calli developed in darkness generally had dry weights and total carbohydrate and starch contents lower than those cultured under photoperiod conditions. However, sucrose contents were greater in calli formed in darkness.At these cultures times, differentiation, in the form of organogenesis, was only seen using medium B with cotyledons, petioles and leaves as explants. It was also observed when petioles were cultured in medium A but with a less pronounced organogenic response.

The different acid invertase activity (total, soluble, wall-bound and extracellular) in calli induced on explants (cotyledon, petiole, hypocotyl and leaf) originated from Medicago strasseri seedlings were evaluated. In cultures subjected to 16 h photoperiod, the highest total, soluble and extracellular activities were found in calli from leaves cultured in medium 12 (MS with 0.01 mg.dm -3 (0.045 ~tM) of TDZ), elevated amounts of total and wall-bound invertase being found in catli induced on 3 petioles in 12G medium (MS with 0.01 mg.dm-(0.045 ~M) TDZ and 3.104 mg.dm -3 glycerol). In cultures maintained in darkness, the activity detected was lower than that observed in cultures under light conditions. The highest amounts of enzyme was bound in calli cultured on medium 12 (total and extracellular invertase) -leaves-and medium 12D (MS with 0.001 rag.din -3 (0.0045 pM) TDZ) (soluble invertase) -using hypocotyls. In general, the different forms of invertase activity studied seem to appear in greatest amounts in calli induced under light conditions using leaves as explant and TDZ as growth regulator.