Primary roots of a starchless mutant of Arabidopsis thaliana L. are strongly graviresponsive despite lacking amyloplasts in their columella cells. The ultrastructures of calyptrogen and peripheral cells in wild-type as compared to mutant seedlings are not significantly different. The largest difference in cellular differentiation in caps of mutant and wild-type roots is the relative volume of plastids in columella cells. Plastids occupy 12.3% of the volume of columella cells in wild-type seedlings, but only 3.69% of columella cells in mutant seedlings. These results indicate that: (1) amyloplasts and starch are not necessary for root graviresponsiveness; (2) the increase in relative volume of plastids that usually accompanies differentiation of columella cells is not necessary for root graviresponsiveness; and (3) the absence of starch and amyloplasts does not affect the structure of calyptrogen (i.e. meristematic) and secretory (i.e. peripheral) cells in root caps. These results are discussed relative to proposed models for root gravitropism.
|Original language||English (US)|
|Number of pages||7|
|Journal||Annals of Botany|
|State||Published - Sep 1989|
Bibliographical noteFunding Information:
ACKNOWLEDGEMENTS I thank Timothy Caspar for graciously providing seeds and C. E. McClelen for his technical assistance. This work was supported by grant number NAGW-734 from the National Aeronautics and Space Administration.
- Arabidopsis thaliana
- Gravitropism (root)
- Root cap