Abstract:

The 12-day immature embryos of 2 maize (Zea mays L.) inbred lines with alternative phyllotaxy, 8701d and H4d, were cultured on media with different contents of 6-BA for 14 d to produce calluses, which were further subcultured twice on the same media. Type II calli were established on the differentiation mediums with 0–3 mg L^-1 of 6-BA content ladder to induce sprout formation. Sprouts in shoot tips were peeled off under a dissecting microscope and the images of the phyllotactic patterns of leaf primordium were taken by scanning electron microscope. The contents of 6-benzylaminopurine (6-BA), zeatin riboside group (ZRs), dehydro zeatin riboside group (DHZRs), isopentenyladenosine group (iPAs), napthalene acetic acid (NAA), and indole-3-acetic acid (IAA) in shoot apical meristem were measured by ELISA method. Three phyllotactic patterns, namely opposite, misshapen, and alternate were observed in the leaf primordium. In H4d plants, exogenous application of the cytokinin 6-BA induced a change in the phyllotaxy of shoot apical meristem (SAM) from alternate to opposite and misshapen. Higher 6-BA content and earlier treatment led to higher proportions of SAM with misshapen leaf primordia and opposite leaf primordia. The cytokinin/auxin (CTK/AUX) ratio in SAM with misshapen leaf primordia was higher than that with decussate leaf primordia, which in turn, was higher than that with alternate leaf primordia. The accumulation of cytokinin 6-BA increased the levels of cytokinin in SAM, but did not change the levels of endogenous cytokinins (ZRs, DHZRs, and iPAs). The comeback of CTK/AUX ratio in tissue cultured immature seedlings could induce the leaf primordium of them to come back to the original phyllotactic patterns. The CTK/AUX ratio is the determinative factor that regulates the differentiation of maize leaf primordium.

Key words: Maize, 6-BA, Differentiation of leaf primordium, Tissue culture