Illumination-dependent effects of gibberellin on in vitro developing European larch shoots

Abstract

Some morphological differences were observed between European larch shoots eveloping from isolated axillary buds (buds were collected in the virst decade of April) on the nutrient medium enriched with 0.2 μM gibberellin GA3 and that developing on the medium without GA3. These differences were closely related with cultivation conditions, especially with the photoperiod and light intensity. Exogenous gibberellin had a slight negative effect on the development of needles under a long photoperiod but a more significant positive effect under a shorter photoperiod and slighter light intensity. On the medium without GA3 larch needles sprouted more intensively under a more intensive illumination, but light intensity had no effect on this developmental feature when explants were cultivated on the medium with gibberellin. Light intensity significantly increased the development of long axial needles if gibberellin was not applied to the nutrient medium. Exogenous gibberellin, by contrast, caused a more intensive development of axial needles under slighter illumination as compared to intensive illumination, but this development was generally reduced. A large part of larch explants on the medium without GA3 formed long-shoot primordia (instead of elongating axial needles) in the apical zone of sprouting buds under short-day conditions, but no increase in the formation of long-shoot primordia caused by a lower light intensity occurred in explants treated with gibberellin. A season can have a major influence on the response of larch buds to a certain gibberellin: the total mass of larch explants collected in the second decade of October and cultivated on the medium with gibberellin did not develop and kept browning. Keywords: gibberellin, larch, bud, explant, photoperiod