Magnesium

Question 1

What can you say about magnesium?

Answer 1

1. Mg accounts to 0.2-0.4% of the plants dryweight
2. Ionic radius of Mg is substantially smaller and its hydrated radius substantially larger than that of K and Ca (Hydrated Mg ion is about 400 times larger than the dehydrated ion)
3. Mg₂₊ transport proteins are channels facilitating the transport of Mg through membranes along the gradient in electro-chemical potential
4. The uptake of Mg can be strongly depressed by other cations (K, NH₄₊, Ca²⁺, Mn²⁺, as well as by H⁺

Question 2

What are the main functions of magnesium in the plant?

Answer 2

• The functions of Mg in plants are mainly related to its capacity to interact with strongly nucleophilic ligands

Mg interactions with proteins:

1. Mg may bind directly to a protein/enzyme and determines its structure and/or serves a catalytic role (central atom of the chlorophyll molecul)
2. Mg may bind the substrate of an enzyme thus in increasing the efficiency of the catalytic reaction
3. Mg forms ternary complexes with enzymes in which bridging cations are required for establishing a precise geometry between enzyme and substrate (for example in RuBP-Carboxylase)
4. a substantial proportion of the total Mg in the cell is involved in the regulation of cellular pH and the cation-anion balance

Question 3

What are the main binding forms of magnesium?

Answer 3

Depending on the Mg nutritional status:

1. between 6 and 25% of total Mg is bound to chlorophyll
2. another 5-10% of total Mg in leaves and needles is firmly bound to pectin in cell walls or precipitated as sparingly soluble salts in the vacuole
3. and the remaining 60-90% are extractable with water

Question 4

Is foliar application commonly used for Mg-fertilizaztion?

Answer 4

1. Foliar sprays of MgSO4 7H2O (Epsom salts) are an effective temporary means of supplying magnesium to many fruit crops
2. These sprays supply enough Mg to prevent deficiency symptoms if used at the appropriate rate and time, but they should be considered as a supplement to, rather than a substitute for, adequate soil applications of magnesium

Question 5

When do