Rapid response reactions of roots to boron deprivation

Upon B removal from the nutrient solution, several response reactions of ro ot cells can be measured within minutes. These include: reduction of cell w all elasticity modulus E, increase of hydraulic conductivity, reduced activ ity of plasmalemma-bound inducible (NADH) reductase, (smaller) changes of t he membrane potential, and liberation of Ca2+ (apoplastic and membrane-boun d). The B most demanding (root) tissues are epidermal and outer cortical ce lls of the extension zone, xylem vessels, and root hair tips. Deprivation o f B leads to morphological changes which can be noticed within hours to day s, including browning of tissues, growth inhibition, death of apical merist ems, and lack of root hairs. How the primary response reaction(s) lead to t he expression of visible symptoms, however, is not yet clear. The present r eview summarizes rapid responses to B deprivation and shows several possibi lities how primary might be linked to secondary reactions, including cytosk eleton-mediated responses.