文档介绍：Chapter 13
Plant secondary nutrients
Calcium
Calcium in physiology
Higher plants often contain appreciable amounts Ca and generally in the order of about 5-30 mg Ca/g dry matter
The high Ca2+ concentrations related with the high Ca2+ levels in media, not related with the Ca2+ uptake mechanism of the roots cells.
The uptake rate of Ca2+ is usually lower than that of K+.
Why ?
Uptake and translocation
Uptake and translocation
This low Ca2+ uptake potential occurs because Ca2+ can be absorbed only by young root tips in which the cell walls often are still unsuberized未木栓化.
The amount of absorbed by the plant depends on the concentration in the root medium and is also ically controlled.
The calcicole(钙生植物)>calcifuge(避钙植物)
Dicotyledons>monocotyledons
This is related with cation exchange capacities and oxalate content in the tissue.
Uptake and translocation
Calcium ions are not transported effectively by the symplast. The typical pathway for Ca2+ uptake of involves initial movement into the free space of the root apoplast and then further movement through apoplastic pathways.
The movement of Ca2+ in the xylem vessels can not be explained simply in terms of mass flow as Ca2+ is absorbed by adjacent cells and also absorbed to indiffusible anions in the xylem walls.
The cell wall is as reservoir for supply to acropetal (向顶的)growing centre.
Uptake and translocation
In growing plants, Ca2+ is translocated preferentially towards the shoot apex even though the transpiration rate here is much low lower than in the older leaves.
The rate of Ca2+ downward of plant is very low due to the fact that Ca2+ is transported in only very small concentration in the phloem, tissues supplied by the phloem sap (such as fruit) has less Ca2+ than leaves.
Once it is deposited in older leaves it cannot be mobilized to the growing tips.
The factors affecting calcium uptake
1. The other cations such as K+ and NH4+
2. Transpiration steam
Calcium transport controlled by humidity
B