ABSTRACT
This chapter shifts the attention to leaves and analyzes their responses as part of the whole plant—a highly integrated system, with finely tuned communication loops between roots and shoot. This may be too ambitious. Indeed, although convincing evidence has been produced for a direct sensing of mechanical forces by roots, with profound physiological effects on leaves, information on the transduction pathway(s) is very thin and fragmented; mechanical impedance is not a special case. The reports that root impedance induced both reduced stomatal conductance and reduced leaf growth rate raised the questions of which of the two responses is elicited first and could it be that one derives from the other. However, more complex, true ontogenetic effects also modify the sensitivity of leaf development to root impedance. When examining long-term responses to root impedance, time-dependent adaptive processes will also cause apparent leaf position effects and changes in leaf sensitivity to high root impedance.
