Root system architecture and gravity perception of a mangrove plant, Sonneratia alba J. Smith

We describe the features of the root system and the gravitropism of roots produced by Sonneratia alba. The root system consists of four root types with different growth directions: (a) Pneumatophores, which are negatively orthogravitropic and their statocytes are very large (922 mum(2)) and the statolith is located near the proximal wall, (b) Cable roots and (c) Feeding roots which are both diagravitropic and their statoliths are settled along the longitudinal wall, and (d) Anchor roots which are positively orthogravitropic. The statocyle cells are the smallest (420 mum(2)) and statoliths settled at the distal wall. We found that all roots with marked gravitropism have statoliths that settle along different walls of the statocyte. This implies that the statoliths sensing of gravity is done by gravity on mass, and that they are denser than surrounding cytoplasm and this position is related to root growth direction. This finding matches the statoliths sediment under the effect of gravity. Irrespective of statolith, position and direction of growth may be stable.