Quantitation of gibberellins A9, A1 and A3 in relation to flower bud differentiation in Picea abies

Endogenous gibberellin A1 (GA1) GA3, GA4 and GA9 were quantitated in elongating shoots of Norway spruce (Picea abies (L.) Karst.) grafts with a good or poor flowering history. The grafts were grown either in a natural environment outdoors, cool and wet (CW) treatment, or in a greenhouse with elevated temmperatures and controlled drought stress, hot and dry (HD) treatment. The GAs were quantitated by gas chromatography-mass spectrometry selected ion monitoring (GC-MS SIM) using deuterated GA1, GA3, GA4 and GA9 as internal standards. Terminal shoots from the second whorl of branches were harvested at 76%, 86% and 96% shoot elongation for the CW treated grafts and at 90% and 99% shoot elongation for the HD treated grafts. The content of GAs in the CW grafts was highest during most rapid shoot elongation, GA9 being the dominant GA. The levels decreased as shoot elongation ceased. This was also noted for GA-content in shoots of the HD treated grafts. A comparison of the GA-amounts at ca. 96% of total shoot elongation for the CW treated grafts and ca. 99% of total shoot elongation for the HD treated grafts revealed that shoots of the good flowering clone had a higher content of GA9 and a lower content of GA1 and GA3. When comparing the HD treated and CW treated grafts, the shoots of HD treated grafts contained higher concentrations of GA9 but lower concentrations of GA1 and GA3. Calculating the ratios between (GA9) and (GA1) resulted in a ratio of 12.5 and 36.6 for the good flowering clone grown outdoors and in greenhouse, respectively. The same ratios were for the poor flowering clone 1.45 and 3.8 when grown outdoors and in greenhouse, respectively. A higher ratio may indicate a higher capacity to synthesize the importance of flowering GA4 from GA9 and a lower conversion of GA4 to GA1, thereby favouring the differentiation to reproductive buds.