|dc.description.abstract||Background: Differentiation of long and short shoots is an important developmental trait in
several species of the Rosaceae family. However, the physiological mechanisms controlling this
differentiation are largely unknown. We have studied the role of gibberellin (GA) in regulation of
shoot differentiation in strawberry (Fragaria × ananassa Duch.) cv. Korona. In strawberry,
differentiation of axillary buds to runners (long shoot) or to crown branches (short shoot) is
promoted by long-day and short-day conditions, respectively. Formation of crown branches is a
prerequisite for satisfactory flowering because inflorescences are formed from the apical
meristems of the crown.
Results: We found that both prohexadione-calcium and short photoperiod inhibited runner
initiation and consequently led to induction of crown branching. In both cases, this correlated with
a similar decline in GA<sub>1</sub> level. Exogenous GA<sub>3</sub> completely reversed the effect of prohexadionecalcium
in a long photoperiod, but was only marginally effective in short-day grown plants.
However, transfer of GA<sub>3</sub>-treated plants from short days to long days restored the normal runner
formation. This did not occur in plants that were not treated with GA<sub>3</sub>. We also studied GA
signalling homeostasis and found that the expression levels of several GA biosynthetic, signalling
and target genes were similarly affected by prohexadione-calcium and short photoperiod in runner
tips and axillary buds, respectively.
Conclusion: GA is needed for runner initiation in strawberry, and the inhibition of GA
biosynthesis leads to the formation of crown branches. Our findings of similar changes in GA levels
and in GA signalling homeostasis after prohexadione-calcium and short-day treatments, and
photoperiod-dependent responsiveness of the axillary buds to GA indicate that GA plays a role
also in the photoperiod-regulated differentiation of axillary buds. We propose that tightly regulated
GA activity may control induction of cell division in subapical tissues of axillary buds, being one of
the signals determining bud fate.||en