Systemic responses by definition involve a whole plant
body, though they are usually evoked by local signal(s). The signals spread through the plant body via
chemical, electrical, hydraulic and molecular pathways. Hydraulic signals are especially important in drought
stress and in wound reactions. However, turgor changes also drive rhythmic growth, leaf movements as well as
circumnutations and therefore seem to co-ordinate plant development. Hydraulic signals are probably perceived
as pressure changes both by mechano-transductive ion channels and as local deformations in cytoskeleton and
nucleoskeleton, with the possibility of influencing gene expression. Physical strain at the surface of the
apical meristem was previously suggested to play a key role in the patterning of organogenesis. We have
studied the influence of local water transport and turgor changes on organogenesis at the apical meristem of
Chenopodium plants. Specific changes in shape and size of the apical meristem were found to precede
reorganisation of organogenesis under photoperiodic flower induction. Optical properties of cell walls at the
surface of the apical meristem were changing during flower induction. Expression of the aquaporin
CrAQP increased at the apex during an early phase of flower induction and the application of an
inhibitor of aquaporin activity partially inhibited flowering. Changes in ion balance and carbohydrate levels
in the cells seem also to be involved in the process. Altogether, the results support a hypothesis about the
involvement of hydraulic signals in organogenesis at the apical meristem. It is anticipated that hydraulic
changes at the apex leading to flower initiation are mediated by a specific hydro-electrochemical
communication between (roots), leaves and the shoot apex. |