Lachenalia is a perennial bulb, indigenous to South Africa, and has been developed as a flowering pot plant. Cultivars are propagated vegetatively by means of daughter bulbs, by in vitro adventitious bud formation on leaf segments (explants) or by bulbil formation on leaf cuttings. In this study, different anatomical and physiological aspects of adventitious bud formation on cultured Lachenalia leaf explants were studied. These included; bud formation at the microscopic level; the effects of the genotype, tissue age, and the growth regulators benzyladenine (BA) and naphthaleneacetic acid (NAA) on bud formation; possible relationships between endogenous cytokinin levels and adventitious bud formation; and the metabolism of BA in cultured leaf tissue.
Buds developed directly from adaxial epidermal cells near the proximal, transverse side of explants. The first divisions were transverse and were observed in epidermal cells about four to five days after culture initiation. Bud formation occurred mainly from the derivatives of primary stomatal mother cells. Although the majority of buds clearly had a single cell origin, observations suggest that a multiple cell origin of buds is possible. The ability of leaf tissue of 16 Lachenalia species and hybrids (genotypes) to form buds varied from low (less than 10 buds per leaf explant) to high (more than 20 buds per explant). Young tissue from the proximal ends of leaves formed the most buds and old tissue from the distal end, the least. The effects of tissue age and genotype showed a significant interaction. Factorial combinations of BA and NAA affected bud formation and, in general the optimal response was obtained when a combination of 2 mg 1 -1 BA and 0.1 mg l-1 NAA were used. An interaction was found, however, between the effects of genotype and growth regulator combinations. Thus for optimal bud production the optimum growth regulator treatment for each genotype should be determined and used. The maximal BA concentration for the different hybrids, varied from 1 to 4 mg l-1, and the maximal NAA concentration from 0.01 to 2 mg l-1. The effects of the concentration of BA and NAA were not equally pronounced in the different genotypes used. The effect of tissue age also showed an interaction with the concentration of the growth regulators. No relationship appeared to exist between adventitious bud formation and the levels of endogenous cytokinins in Lachenalia leaves as affected by the genotype. Some relationship appeared to exist between tissue age, bud formation and endogenous cytokinin levels. The cytokinin-like activity in Lachenalia leaves co-chromatographed with zeatin and ribosylzeatin, and it was generally present in higher levels in young tissue than in intermediate or older tissue. The major form of BA metabolism in cultured leaf tissue was probably through ribosylation.
|Degree Type||Doctoral degree|