西北农林科技大学：《植物营养学》课程教学资源（PPT课件讲稿，英文版）Chapter 13 Plant secondary nutrients

Chapter 13 Plant secondary nutrients

Chapter 13 Plant secondary nutrients

Calcium

Calcium

Calcium in physiology Uptake and translocation 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 Ca+ 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

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

RADIAL ROOT TRANSPORT Phloem Casparian Xylem with heat stri secondary walls Cellular pa (symplast and transmembrane) Cortex Root hair Epidermis Stel Apoplast pathway Endodermis Casparian stri 9 1998 Sinauer Associates, Inc

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 genetically 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 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 genetically 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 y the symplast. The typical pathway for b 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 Ca 2+ 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 ◼ 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 Ca+ than leaves Once it is deposited in older leaves it cannot be mobilized to the growing tips

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

1: 2nd Root segment. 3 cm 3rd Root segment. 4th Root 17 5th Root segment, 3 cm 6th Root segment, 3 cm ca-45 Treated segment, 3 cm 2nd Lower segment, 3 cm Fig. 11.4 Distribution of Ca-45 in a maize seedling following application to a specific of the root (after MARSCHNER and RICHTER [1974))

The factors affecting calcium uptake 1. The other cations such as K and NH4 2. Transpiration steam Calcium transport controlled by humidity Blossom end rot caused by drought water logged soil high salt concentration poor aeration low temperature

The factors affecting calcium uptake 1. The other cations such as K+ and NH4 + 2. Transpiration steam Calcium transport controlled by humidity Blossom end rot caused by drought, water logged soil, high salt concentration poor aeration low temperature

The forms of calcium in plant Free Ca2+ Absorbed ca 2+ by carboxylic phosphoryl(磷酰基) and pheno|ic hydroxyl groups Precipitated as Ca oxalate, carbonate and phosphate in vacuoles, or pectins n cell walls, or phytate in seed Calcium ions are also bound to membranes

The forms of calcium in plant ◼ Free Ca2+ ◼ Absorbed Ca2+ by carboxylic, phosphorylic(磷酰基) and phenolic hydroxyl groups. ◼ Precipitated as Ca oxalate, carbonate and phosphate in vacuoles, or pectins in cell walls, or phytate in seed. ◼ Calcium ions are also bound to membranes