features with CRKs found in other plants (Harper et al. 2004). Its plasma-membrane
localization is probably mediated by a myristoylation/plamitoylation modification
and is polar in statocytes, forming a U-shaped zone towards the root tip (Figs. 7.2
and 7.3). Absence of CRK5 in a T-DNA mutant did not affect the localization of
AUX1 or PIN1, PIN3, PIN4 or PIN7 in the root cap and gravisensing statocytes.
However, a PIN2-GFP reporter was depleted in the transition zone between root
cap and elongation zones. There was also a remarkable basal-to-apical shift of
Fig. 7.2 Expression of PIN3 and CRK5 in columella cells. Six days old Arabidopsis thaliana
seedlings expressing respectively, (a–b) and CRK5::CRK5-GFP (c-d). (a) PIN3::PIN3-GFP in
vertically grown plants. In columella cells PIN3-GFP localizes all around the cell whereas statoliths
(*) are distributed at the bottom of the cells. (b) PIN3::PIN3-GFP in gravistimulated (90
) roots for
1 h. Statoliths and PIN3 re-localize laterally in columella cells. (c) CRK5::CRK5-GFP localization
at the root tip. (d) Enlargement of the boxed area in (c) showing nuclei (blue) and the polar
localization of CRK5-GFP in columella and lateral root cap cells. White arrows in (a) and (c)
indicate the direction of the gravity vector
100
7 Gravitropism in Higher Plants: Molecular Aspects
localization is probably mediated by a myristoylation/plamitoylation modification
and is polar in statocytes, forming a U-shaped zone towards the root tip (Figs. 7.2
and 7.3). Absence of CRK5 in a T-DNA mutant did not affect the localization of
AUX1 or PIN1, PIN3, PIN4 or PIN7 in the root cap and gravisensing statocytes.
However, a PIN2-GFP reporter was depleted in the transition zone between root
cap and elongation zones. There was also a remarkable basal-to-apical shift of
Fig. 7.2 Expression of PIN3 and CRK5 in columella cells. Six days old Arabidopsis thaliana
seedlings expressing respectively, (a–b) and CRK5::CRK5-GFP (c-d). (a) PIN3::PIN3-GFP in
vertically grown plants. In columella cells PIN3-GFP localizes all around the cell whereas statoliths
(*) are distributed at the bottom of the cells. (b) PIN3::PIN3-GFP in gravistimulated (90
) roots for
1 h. Statoliths and PIN3 re-localize laterally in columella cells. (c) CRK5::CRK5-GFP localization
at the root tip. (d) Enlargement of the boxed area in (c) showing nuclei (blue) and the polar
localization of CRK5-GFP in columella and lateral root cap cells. White arrows in (a) and (c)
indicate the direction of the gravity vector
100
7 Gravitropism in Higher Plants: Molecular Aspects