IN VITRO CULTURE OF SHOOT-TIP MERISTEMS IN SOME HIGHER PLANTS

Shoot-tip explants from Chrysanthemum morifolium, Antirrhinum majus and Solanum tuberosum were cultured on media with different hormonal concentrations and combinations. Large differences were found in the responses of the above species. However, two factors mainly determine the multiple shoots formation from the shoot-apices 1) size, of the explant used and 2) combination of growth hormones. The optimal size of the shoot-apex was 3–5 mm in lenght (meristem with 2 to 4 leaf primodia). Higher concentrations (above 5mg/l) of growth hormones used individually or in combinations gave usually callus with occasional abnormal shoot formation. For example with Chrysanthemum explants, frequently single shoot formations were found with vertually all combinations of auxin and cytokinin tested. However, the treatment with NAA (0.2mg/1) and kinetin (2mg/l) with or without GA₃ (0.2mg/1) gave multiple shoot formation. The well developped shoots (4–5cm) were then transferred to a root inducing medium (MS medium with only 1 % sucrose and only 0.1mg/1 of IAA). Optimum shoot proliferation in Antirrhinum explants was obtained with an auxin (NAA or IAA, 0.5–2mg/1) and a cytokinin (Kinetin or BAP : 1–3mg/1).

In Solanum tuberosum, the aptitude for multiple shoots formation from the cultured meristems (meristem with 2 leaf primordia of approximally 0,5 mm in size) of different genotypes (4N : Bintje, Brettor, Victor, Ostara and 2N : 4 genotypes) were tested.

The best results were obtained with all the 4 diploid genotypes. The meristems were first cultured on the initiating medium (MS + Kinetin (0.1mg/1) + GA₃ (0.1mg/1) + IAA (0.5mg/1). After 2 to 3 weeks these explants were transfered into the proliferating medium (MS + IAA 0.5mg/1) + BAP (1mg/1) + GA₃ (0.5 mg/1) + Calcium panthothenate (2mg/1). In the above medium, multiple shoots were formed which were then placed on a rooting medium (with 0.01mg/1 IAA and only 1 % of sucrose in the MS medium). At most 60 % of the total number of meristems isolated developed into plants. Regenerated plantlets transfered to soil developed normally. No or very rare chromosomal abberation was found in these plants. (MS : MURASHIGE and SKOOG).