Aspects of the role of cytokinins in adventitious root formation.
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Date
1996
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Abstract
The initiation and development of adventitious roots in cuttings are highly
complex processes, influenced by both endogenous and exogenous factors.
These vary from the environmental factors prior to the striking of the cutting,
to the anatomical and physiological factors, within the stem. Encompassed are
the nutrient status, physiological age and degree of differentiation of the
tissues, and the balance of endogenous rooting inhibitors and/or promoters
(including hormones).
The role of cytokinins in root initiation and development has been perceived
as that of an inhibitor. This investigation considered several aspects of the
role played by cytokinins in the process of root development.
A qualitative/quantitative analysis of the cytokinin-like activity in stem
cuttings of several plants, including both easy- and difficult-to-root species
was conducted on a comparative basis. There was no clear correlation
between the type / level of cytokinins detected in the cuttings and the relative
ease of root formation. Both qualitative and quantitative changes in the
compounds exhibiting activity in the soybean callus bioassay were observed
over the period of root formation in Impatiens stem cuttings.
The effects on root formation in cuttings of exogenously applied auxins and
cytokinins were investigated. Auxins generally promoted root number and
elongation at relatively high concentrations (10[-4] M), but showed less effect
on lateral root initiation and development. At high concentrations, cytokinins
strongly inhibited root development, but did promote lateral root growth. In
suspension culture, the effect of these hormones differed slightly, with IAA
and IBA having no significant effect on root development, but NAA strongly
stimulating lateral root initiation. Zeatin (10¯¹¹ M) significantly increased root
length and the number of lateral roots produced. The effect of treatment of the stem cuttings with potassium permanganate
and centrifugation was examined. While both these treatments have been
perceived to increase root production in cuttings, no significant improvement
in rooting ability following centrifugation (relative to the control) was
observed. Impatiens cuttings centrifuged in the presence of distilled water
showed a significantly reduced rooting ability relative to those centrifuged in
the dry state. Treatment with an 8-hour pulse in 0.05 % potassium
permanganate significantly increased the average root length.
These treatments had an effect on the cytokinin levels and distribution in the
stem cuttings. Slightly higher levels of cytokinins were associated with the
increase in root number and length in both experiments.
Description
Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1996.
Keywords
Roots (Botany), Cytokinins., Plant cuttings., Theses--Botany.