植物钙素吸收和运转

近年来,钙素在植物体内的吸收和运输研究主要集中在细胞和分子水平,但整株水平上的研究也同样重要.整株水平上的钙吸收和运输包括根细胞的钙吸收、钙离子横向穿过根系并进入木质部、在木质部运输、从木质部移出并进入叶片或果实及在叶片或果实中运转分配等环节,既经过质外体也穿越共质体.钙离子通道、Ca2 -ATP酶和Ca2 /H 反向转运器等参与根细胞的钙吸收.在钙离子横向穿根进入木质部的过程中,需要穿越内皮层和木质部薄壁细胞组织.根系内皮层凯氏带阻挡了Ca2 沿质外体途径由内皮层外侧向内侧的移动,部分Ca2 由此通过离子通道流进内皮层细胞而转入共质体并到达木质部薄壁细胞组织,而由木质部薄壁细胞组织进入中柱质外体可能需要Ca2 -ATP酶驱动;还有一些Ca2 由内皮层细胞运出,沿内皮层内侧的质外体途径进入木质部导管,并通过导管运向枝干.钙离子以螯合态的形式在枝干导管运输;水流速率是影响钙离子沿导管运输的关键因子.钙离子在果实和叶片中的运输和分配不仅通过质外体途径也通过共质体途径.

Uptake and Transport of Calcium in Plants

Recently, research on Ca2+ transport inplants has been focused on cellular and molecular level.But the uptake, transport and distribution are also veryimportant for calcium to accomplish its function atwhole plant level. There are many cells along the wayof transport of Ca2+ from root to shoot, and Ca2+ passeseither through the cytoplasm of cells linked by plas-modesmata (the symplast) or through the spaces be-tween cells (the apoplast), which include Ca2+ uptakeby root cells, Ca2+ transport from root cortex to andthrough the xylem, and then out of it into leaves orfruits. Ca2+ channels, Ca2+/H+ antiporter and Ca2+-AT-Pase play roles in the uptake and transport of Ca2+ inroot cells. To be transported from root surface to xylem,Ca2+ needs to traverse endodermal cells and xylemparenchyma cells. Endodermal Casparian band, themain barrier for the apoplastic movement of ions intothe stele, compels some Ca2+ to enter root symplastthrough Ca2+ channels in endodermal cells and thenreach xylem parenchyma. Ca2+-ATPase may drive Ca2+into the stelar apoplast from xylem parenchyma. SomeCa2+ effuses from endodermal cell and then get to xy-lem through apoplastic pathway. Ca2+ is transportedin plant xylem vessel in chelate form and the speed ofwater flow is the key factor Ca2+ transport via xylemin trunk. There are both apoplastic and symplastic path-ways of Ca2+ transport in fruit or leaf tissue too.