Morphoanatomic changes in shoot and root apices of banana Williams (AAA, Musa sp.) cultured on different N6- benzyladenine concentrations

Abstract

Structural evidence about the in vitro growth of the shoot apex (SA) and root apex (RA) of banana is for the most part lacking.This paper presents an analysis of the morphoanatomic events that occur in the in vitro development of the SA, RA and explants of banana Williams cultured under different N⁶-benzyladenine (BA) concentrations. We examined the SA of explants (8 mm X 1.5 mm, shoot tip with part of rhizome) grown on 0, 2.5 and 5 mg /L of BA for 0, 3, 6, 9 and 12 d, and also the first emergent root (1 to 1.5 cm long) from these explants. Samples were sectioned (10 to 12 µm) and stained with safranin-fast green. The SA showed a dome shape with tunica-corpus organization (a single tunica layer). SA diameters were larger for explants growing in BA (93.75 to 142.05 µm) than in those growing without the cytokinin (73.87 to 85.83 µm), except for the diameter on the sixth day (127.84 µm). The noncultured initial explant without culture reached a diameter of 164.78 µm. The SA showed a cambium-like transitional zone in explants cultured with 2.5 mg/L of BA on the ninth day. This concentration also induced the highest number of shoots per explant (2.19) in 35 days. RA growing in media without BA showed protoderm, ground meristem, procambium, initial cells and root cap whereas with BA procambium, fundamental meristem and root cap (compressed) were distinguished. Benzyladenine decreased the number and length of the roots, inhibited the formation of lateral roots, increased the time for root emergence and caused distortion in their anatomic structure.