[Sedimentable amyloplasts in Japanese weeping cherry].

Area of Science:

• Plant Biology
• Gravitropism Research
• Tree Physiology

Background:

• Upright Japanese cherry branches form tension wood via gibberellin, enabling negative gravitropism.
• Weeping cherry branches exhibit downward growth due to gibberellin's role in tip elongation, leading to insufficient tension wood.
• Both cherry types possess sedimentable amyloplasts in endodermal starch sheath cells, key for gravity perception.

Purpose of the Study:

• Investigate the cause of abnormal gravi-response in weeping Japanese cherry branches.
• Examine the function and structure of endodermal starch sheath cells in weeping vs. upright cherry types.
• Determine if gravity sensor development is responsible for the weeping phenotype.

Main Methods:

• Collected and analyzed current-year branches from upright and weeping *Prunus spachiana*.
• Observed amyloplast sedimentation patterns in response to gravity and mechanical repositioning.
• Utilized electron microscopy to examine the fine structure of endodermal starch sheath cells.

Main Results:

• Amyloplasts in weeping cherry branches sedimented correctly towards the gravity vector, regardless of branch orientation.
• Mechanical repositioning of weeping branches induced normal amyloplast re-sedimentation, similar to upright types.
• Electron microscopy revealed similar fine structures, including lamellar amyloplasts and peripheral endoplasmic reticulum, in both cherry types, with no observed cell polarity.

Conclusions:

• The abnormal gravi-response in weeping *Prunus* trees is not caused by defects in the gravity-sensing apparatus (amyloplasts or associated cell structures).
• The observed phenotype is likely due to altered gibberellin distribution affecting tension wood formation rather than a faulty gravi-sensor.