OFF-TYPE MICROPROPAGATED BANANA PLANTS: ENDOGENOUS LEVELS OF AUXIN, CYTOKININS AND IAA-OXIDASE

The occurrence of dwarfism and variegation is an extensive and severe limitation for banana (Musa spp.
AAA) micropropagation.
Dwarf and normal plants were cultured (30 days) in vitro on MS-media with addition of gibberellic acid (GA₃), indoleacetic acid (IAA), L- tryptophan or D-tryptophan (Trp), and variegated plants were grown in the greenhouse.
The endogenous levels of cytokinins (CKs), indoleacetic acid (IAA) and IAA-oxidase were studied in dwarf and normal banana plants and in variegated leaves.
Extracts were fractionated by HPLC and IAA and CKs were quantified by ELISA.

GA₃ was the most stimulating substance on growth of both normal and dwarf plants.
IAA levels were significantly enhanced with L-Trp and GA₃. It is interesting to highlight the fact that the amount of IAA found in the dwarf material was significantly higher than in material from normal plants.
These results seem to be indirectly reinforced by the high levels of IAA-conjugate measured in normal plants and its low amount in dwarf plants.
In the variegated leaves, a significantly higher activity of IAA-oxidase was detected in green and yellow sectors as compared to normal and dwarf green leaves.
Total CK level (zeatin, Z; zeatin riboside, [9R]Z; isopentenyl-adenine, iP; and isopentenyladenosine, [9R]iP) in the variegated leaves was about 2 times lower than in normal leaves, diminishing to a value of 10 times when only yellow sectors were took into account.
These results indicate that in the variegated material IAA-cytokinin ratio is mainly affected by IAA oxidation rather then by conjugation processes.

XXV International Horticultural Congress, Part 10: Application of Biotechnology and Molecular Biology and Breeding – In Vitro Culture.

G.R. Zaffari, L.E.P. Peres, R.M. Suzuki, G.B. Kerbauy

banana, dwarfism, growth regulators, variegation, somaclonal variation

https://doi.org/10.17660/ActaHortic.2000.520.23