The Effects of Proline and Coconut Water on Callus Induction of Cucumber (Cucumis sativus L.)

Callus was initiated from shoot tips and embryonic axes of cucumber (Cucumis sativus L.) in a Murashige and Skoog (MS) medium supplemented with 1 mg/L naphthalene acetic acid (NAA) and 0.5 mg/L kinetin in the presence of 0, 10 and 20 mM proline. Earlier callus induction was observed with embryonic axes (3 days after initiation), compared to shoot tips (7 days after initiation) with callusing frequency of 100%. Moreover, the average size of embryonic axis-derived calli was 1.3- to 1.9-fold larger than those derived from shoot tips at 2 weeks of culture. No effect of proline was found on percentage of callus induction of both explants. Addition of proline also did not affect the growth of callus from shoot tips. However, inhibitory effect was found on the growth of embryonic axis-derived calli (1.3-fold reduction in comparison with control (without proline)). When the effect of coconut water on callogenesis was evaluated on embryonic axes, callus formation was substantially retarded. However, coconut water significantly promoted hypocotyl elongation. Germination of seeds either in liquid MS medium supplemented with 0.1 mg/L thidiazuron (TDZ) or 0.1 mg/L kinetin prior to callus initiation slightly delayed callus induction but did not significantly affect callus size. However, at 2 weeks of culture kinetin significantly decreased the length of hypocotyls.