Mj. Hutchinson et Pk. Saxena, ROLE OF PURINE METABOLISM IN THIDIAZURON-INDUCED SOMATIC EMBRYOGENESIS OF GERANIUM (PELARGONIUM X HORTORUM) HYPOCOTYL CULTURES, Physiologia Plantarum, 98(3), 1996, pp. 517-522
Somatic embryogenesis in geranium (Pelargonium x hortorum Bailey cv. S
carlet Orbit Improved) was achieved by culturing hypocotyl sections on
Murashige and Skoog (1962) (MS) medium containing 10 mu M thidiazuron
(TDZ) (induction medium) for 3 days and subsequently transferring the
sections onto a basal medium lacking any plant growth regulators (exp
ression medium). Addition of the purine analogue 2,6-diaminopurine (DA
P) to the somatic embryo induction medium completely inhibited the emb
ryogenic response as well as chlorophyll accumulation without affectin
g enlargement of the treated tissues. Addition of 20 mu M adenine sulp
hate to the expression medium, i.e during embryo growth and developmen
t phase, completely reversed the DAP-induced inhibition of the embryog
enic response while addition during the induction phase caused only a
50% reversal of the inhibition. Analysis of endogenous levels of plant
growth substances indicated that TDZ alone elevated the levels of aux
ins, cytokinins and abscisic acid while the presence of DAP during the
induction phase caused a further increase in the levels of adenine an
d adenosine. These findings indicate a possible critical role for puri
nes in embryogenesis from geranium hypocotyl tissues. However, the con
version of cytokinin bases to their corresponding nucleotide forms was
not evident as the levels of isopentenyl adenine and zeatin increased
during the second day of culture.