Žiauka, J. and Kuusienė, S. 2009. Plant Hormone Gibberellin Induces Decline of Viability in Isolated Larch Shoot Buds.  Baltic Forestry 15 (1): 13-22

The development of larch (Larix sp.) short shoots in vitro was investigated using isolated axillary buds. The explants were collected from two mature larch trees possessing different genotypes: 30-year old European larch (Larix decidua Mill.) and 42-year old hybrid larch (Larix kaempheri Carr. x Larix decidua Mill.) derived after crossing between Japanese larch and European larch. Isolated short shoot buds were planted onto MS nutrient medium supplied with distinct plant growth regulators. The negative effect of some kinds of plant hormones was noted. Gibberellins GA3 and, especially, GA4/7 caused strong decline of viability in isolated shoot primordia. Negative influence of auxin indole acetic acid was also noted, though in less extensive rate. The explants of the investigated hybrid larch tree were far more resistant to negative effect of these plant hormones than the explants collected from the European larch tree. The certain role of developing primordia of axial needles in stimulation of chlorophyll loss was confirmed in European larch explants. Cytokinin zeatin when supplied to the nutrient medium together with gibberellin significantly promoted the negative effect of gibberellin (but this effect of zeatin was noted only in European larch explants). It was also confirmed that in vitro developed larch shoots can act on new-planted explants from a distance if they share the same space for gas interchange (in vitro). Short shoots previously treated with auxin or gibberellin were significantly more sufficient for the induction of needle browning on newly developing shoots that shared the common space for gas interchange. The synergistic effect of gibberellin and other plant hormones, including gaseous plant growth regulator ethylene is under discussion.

Key words: axillary bud, explant development, in vitro culture, needle browning, plant hormones, short shoot