Effect of culture medium and light conditions on the morphological characteristics and carbohydrate contents of Medicago strasseri calli

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/l) and 2,4-D (3 mg/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.