Nutrients translocation in higher plants
How the growing parts of the plant are provided with sugar to synthesize new cells
A system of vascular tissue runs through all higher plants.
It evolved as a response to the increase in the size of plants, which caused a progressing separation of roots and leaves in space.
Two essential functions are performed by the vascular system, namely the delivery of resources (water, essential mineral nutrients, sugars, and amino acids) to the various plant organs.
Mobile nutrients such as nitrogen (N), potassium (K) and phosphorus (P), and magnesium (Mg) move from one place to another when there is any deficiency detected in plants. Even if there is deficiency like they are not absorbed at all, then the symptoms of deficiency are seen on older and lower leaves.
Water and sand culture experiments were carried out first in which particular mineral elements were omitted. These techniques made possible a more precise characterization of the essentiality of mineral elements and led to a better understanding of their role in plant metabolism. Progress in this research was closely related to the development of analytical chemistry, particularly in the purification of chemicals and methods of estimation. This relationship is reflected in the time scale of the discovery of the essentiality of micronutrients.
The beneficial effect of adding mineral elements (e.g., plant ash or lime) to soils to improve plant growth has been known in agriculture for more than 2000 years. Nevertheless, even 150 years ago it was still a matter of scientific controversy as to whether mineral elements function as nutrients for plant growth. It was mainly to the credit of Justus von Liebig (1803-1873) that the scattered information concerning the importance of mineral elements for plant growth was compiled and summarized and that the mineral nutrition of plants was established as a scientific discipline. These achievements led to a rapid increase in the use of mineral fertilizers.
By the end of the nineteenth century, especially in Europe, large amounts of potash, superphosphate, and, later, inorganic nitrogen were used in agriculture and horticulture to improve plant growth.
The above statement reflects a serious gap in our current knowledge and how to manage that is an urgent need.
Ion Uptake Mechanisms of Individual Cells and Roots: Short-Distance Transport:
1. Pathway of Solutes from the External Solution into the Cells:
1.1. Influx into the Apoplasm.
1.2. Passage into the Cytoplasm and the Vacuole.
2. Structure and Composition of membranes.
3. Solute Transport Across Membranes:
3.1 Transport and Energy Demand.
3.2 Active and Passive Transport: Electrogenic Pumps, Carriers, Ion Channels.
3.3 The Kinetics of Transport.
4. Characteristics of Ion Uptake by Roots:
4.1. Influx into the Apoplasm
4.2. Role of Physicochemical Properties of Ions and Root Metabolism
4.2.1 Ion Diameter.
4.2.2 Molecule versus Ion Uptake and the Role of Valency.
4.2.3 Metabolic Activity.
4.3 Interactions between Ions:
4.3.1 Competition:
4.3.1.1. Role of pH.
4.3.1.2. Ion Synergism and the Role of Ca2+
4.3.2. Cation-Anion Relationships.
4.3.3. External Concentrations.
4.3.4. Internal Concentrations and Nutritional Status.
4.3.5. Maintenance of Constant Internal Concentrations.
5. Uptake of Ions and Water Along the Root Axis.
6. Radial Transport of Ions and Water Across the Root.
7. Release of Ions into the Xylem.
8. Factors affecting Ion Release into the Xylem and Exudation Rate:
8.1. External and Internal Factors.
8.2. Xylem Exudate, Root Assimilation, and Cycling of Nutrients.