Abstract
BackgroundDifferentiation 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.ResultsWe 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 GA1 level. Exogenous GA3 completely reversed the effect of prohexadione-calcium in a long photoperiod, but was only marginally effective in short-day grown plants. However, transfer of GA3-treated plants from short days to long days restored the normal runner formation. This did not occur in plants that were not treated with GA3. 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.ConclusionGA 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.
Highlights
Differentiation of long and short shoots is an important developmental trait in several species of the Rosaceae family
We report the effects of daylength and GA biosynthesis inhibitor Pro-Ca on axillary bud differentiation, GA levels and GA signalling homeostasis
Photoperiod, prohexadione-calcium and GA3 affect the differentiation of strawberry axillary buds As shown in Table 1, 10, and 14-h photoperiods (SD) promoted crown branching whereas no branch crowns were found in plants grown under an 18-h photoperiod (LD)
Summary
Differentiation of long and short shoots is an important developmental trait in several species of the Rosaceae family. Differentiation of axillary buds to runners (long shoot) or to crown branches (short shoot) is promoted by long-day and short-day conditions, respectively. Long shoots have long internodes, whereas short shoots are lateral organs with very short internodes and leaf rosette-like appearance In these species, diverse flowering habits can be found and even the cultivars can differ from each other in this respect. Flowers are borne either on terminal (apple, pear) or lateral (cherry, apricot) buds of short shoots [1,2,3]. Both shoot types can be found in strawberry Strawberry axillary buds may form both short and long shoots; branch crowns and runners, respectively. Inflorescences are formed terminally in the short shoots, while the uppermost axillary bud(s) continue vegetative growth of the crown [4,5]
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