The gravity-regulated growth of axillary buds is mediated by a mechanism different from decapitation-induced release.
When the upper part of the main shoot of the Japanese morning glory (Pharbitis nil or Ipomoea nil) is bent down, the axillary bud situated on the uppermost node of the bending region is released from apical dominance and elongates. Here, we demonstrate that this release of axillary buds from apical dominance is gravity regulated. We utilized two agravitropic mutants of morning glory defective in gravisensing cell differentiation, weeping (we) and weeping2 (we2). Bending the main shoots of either we or we2 plants resulted in minimal elongation of their axillary buds. This aberration was genetically linked to the agravitropism phenotype of the mutants, which implied that shoot bending-induced release from apical dominance required gravisensing cells. Previous studies have shown that basipetal translocation of auxin from the apical bud inhibits axillary bud growth, whereas cytokinin promotes axillary bud outgrowth. We therefore compared the roles of auxin and cytokinin in bending- or decapitation-induced axillary bud growth. In the wild-type and we plants, decapitation increased cytokinin levels and reduced auxin response. In contrast, shoot bending did not cause significant changes in either cytokinin level or auxin response, suggesting that the mechanisms underlying gravity- and decapitation-regulated release from apical dominance are distinct and unique.
Kitazawa
Daisuke
D
Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577 Japan.
Miyazawa
Yutaka
Y
Fujii
Nobuharu
N
Hoshino
Atsushi
A
Iida
Shigeru
S
Nitasaka
Eiji
E
Takahashi
Hideyuki
H
D001483:Base Sequence; D003583:Cytokinins / Q000235:genetics / Q000494:pharmacology / Q000502:physiology; D018506:Gene Expression Regulation, Plant / Q000187:drug effects / Q000502:physiology; D017343:Genes, Plant; D017930:Genes, Reporter; D005819:Genetic Markers; D018522:Gravitropism / Q000187:drug effects / Q000235:genetics; D007210:Indoleacetic Acids / Q000494:pharmacology; D049915:Ipomoea nil / Q000187:drug effects / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D010937:Plant Growth Regulators / Q000235:genetics / Q000494:pharmacology / Q000502:physiology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018520:Plant Shoots / Q000254:growth & development
D003583:Cytokinins; D005819:Genetic Markers; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D010940:Plant Proteins