Journal of Experimental Botany, Vol. 53, No. 378, pp. 2143-2149,
November 1, 2002
© 2002 Oxford University Press
KNAP2, a class I KN1-like gene is a negative marker of bud growth potential in apple trees (Malus domestica [L.] Borkh.)
Received 7 June 2002; Accepted 21 June 2002
1 INH, UMR SAGAH A462, 2, rue Le Nôtre, F-49045 Angers Cedex 01, France
2 UFR Sciences, UMR SAGAH A462, Laboratoire ‘Morphogenèse des Ligneux’, 2, boulevard Lavoisier, F-49045 Angers Cedex 01, France
3 UFR Sciences, UMR PAVE A77, Laboratoire de Microbiologie Végétale, 2, boulevard Lavoisier, F-49045 Angers Cedex 01, France
Abbreviations: DIG, digoxigenin; FAA, formaldehyde alcohol acetic acid; PFA, paraformaldehyde; RT-PCR, reverse transcription-polymerase chain reaction.
The determinism of bud bursting pattern along the 1-year-old shoot was studied at the molecular and morphological levels in the apple tree variety ‘Lodi’ which shows an acrotonic tendency. At the molecular level, the expression of KNAP2, which belongs to the class I KN1-like gene family, was studied. Measurements were carried out during dormancy (October), breaking dormancy (January) and just before bud bursting (March). The results showed that KNAP2 is more highly expressed in buds that will remain at rest in the spring. Expression of KNAP2 was found in the meristem and in the marginal meristem of the two latest shaped primordia. In the January and March buds, this gene is also expressed in the procambial zone underneath the apical meristem. This study therefore suggests that KNAP2 may be considered as a negative marker of bud growth potential and that the growth inhibition in proximal buds could partially result from differential gene activity. At the morphological level, it was shown that no organogenetic activity took place between October and March as revealed by the constant number of leaf primordia in buds. Nevertheless, those buds likely to grow the following spring had a larger size and fewer hard scales than other buds. This suggests that genetic control may act together with other mechanisms, possibly physical (number of scales) or biochemical, to control bud inhibition.
Key words: Key words: In situ hybridization, KN1-like genes, Malus domestica [L.] Borkh., morphogenesis, vegetative bud.
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