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A Handbook of Biology

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Concentration of an essential element below which plant growth is

retarded is called critical concentration. The element is said to be

deficient when element shows value below the critical concentration.

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In older leaves, biomolecules containing these elements are broken

down. It makes these elements available for mobilising to younger

leaves.

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This aspect of mineral nutrition has great significance in agriculture and

horticulture.

ÇHLØRØSÏS

Loss of chlorophyll leading to yellowing in leaves. It is due to the

deficiency of elements N, K, Mg, S, Fe, Mn, Zn and Mo.

ÑËÇRØSÏS

It is the death of tissue, particularly leaf tissue. It is due to the

deficiency of Ca, Mg, Cu, and K.

ÏÑHÏBÏTÏØÑ ØF ÇËLL DÏVÏSÏØÑ

Lack or low level of N, K, S,

and Mo inhibits cell division.

Low concentration of N, S,

Mo, etc., delay flowering.

Deficiency of different

elements may cause

same symptoms. Hence,

to identify the deficient

element, all the symptoms

are studied. Also, different

plants respond differently

to the deficiency of the

same element.

TØXÏÇÏTÝ ØF MÏÇRØÑÜTRÏËÑTS

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A moderate increase in micronutrients causes toxicity.

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Any mineral ion concentration in tissues that reduces the dry weight of

tissues by about 10% is considered toxic. Such critical concentrations

vary widely among different micronutrients.