Source. The element is abundant in most soils and plants under natural conditions are seldom deficient in it. It is absorbed by the plants in the form of Ca2+ from calcium carbonate etc. It is one of the major exchange cation of fertile soils.
Regions. It is needed in meristematic and differentiating tissues. It accumulates in older leaves. The soil derived from stone or chalk rocks, contains sufficient quantity of calcium carbonate (carbonate of lime) as compared to sandy soils, which are deficient in calcium. Deficiency of calcium in sandy soils is met by adding lime or limestone.
Functions. Calcium is important in the synthesis of pectin in the middle lamella of cell well. It also plays a significant role in the metabolism of nucleus and mitochondria. It is involved in selective permeability of cell membranes. It activates certain enzymes like ATP-ase, some kinases and succinate, dehydrogenase. It is required for the development of stem and root apex. It is essential for fat metabolism, carbohydrate metabolism, nitrate assimilation, binding of nucleic acids with proteins and counteraction of metal toxicity.
Deficiency symptoms
(i) Death of meristematic regions.
(ii) Stunted growth.
(iii) Margins of leaves often appear irregular in form or leaf tip may become hooked causing the disease wither tip.
(iv) Formation of stunted and discolored roots.
(v) Potato tubers become small and malformed.
(vi) It may lead to abnormal cell division e.g., incomplete cell division or mitosis without the formation of cell walls (resulting in the formation of multinucleate cells).
(vii) In plants like flax and clovers, petioles and pedicels frequently collapse.
(viii) Thin chlorotic marginal bands develop.