Uptake and transport of calcium in plants.

Recently, research on Ca(2+) transport in plants has been focused on cellular and molecular level. But the uptake, transport and distribution are also very important for calcium to accomplish its function at whole plant level. There are many cells along the way of transport of Ca(2+) from root to shoot, and Ca(2+) passes either through the cytoplasm of cells linked by plasmodesmata (the symplast) or through the spaces between cells (the apoplast), which include Ca(2+) uptake by root cells, Ca(2+) transport from root cortex to and through the xylem, and then out of it into leaves or fruits. Ca(2+) channels, Ca(2+)/H(+) antiporter and Ca(2+)-ATPase play roles in the uptake and transport of Ca(2+) in root cells. To be transported from root surface to xylem, Ca(2+) needs to traverse endodermal cells and xylem parenchyma cells. Endodermal Casparian band, the main barrier for the apoplastic movement of ions into the stele, compels some Ca(2+) to enter root symplast through Ca(2+) channels in endodermal cells and then reach xylem parenchyma. Ca(2+)-ATPase may drive Ca(2+) into the stelar apoplast from xylem parenchyma. Some Ca(2+) effuses from endodermal cell and then get to xylem through apoplastic pathway. Ca(2+) is transported in plant xylem vessel in chelate form and the speed of water flow is the key factor Ca(2+) transport via xylem in trunk. There are both apoplastic and symplastic pathways of Ca(2+) transport in fruit or leaf tissue too.