1. Manganese:
Maganese exists in the soil in divalent, trivalent, and tetravalent forms, but it is absorbed largely as the divalent manganous cation (Mn2 ). Specific functions:
– Manganese is involved in oxidation-reduction processes tgether with decarboxylation and hydrolytic reactions.
– Photosystem II in chloroplast contains manganese protein.
ADVERTISEMENTS:
– RXA polymerase has an absolute requirement for manganese.
– Manganese is the predominant metal ion of Krebs cycle reactions. It acts as an activater for the enzymes nitrite reductase and hydroxyl amine reductase.
Deficiency symptoms:
– Manganese deficiency causes chlorotic and necrotic spots in the interveinal areas of the leaf.
ADVERTISEMENTS:
2. Boron:
Boron is absorbed by the plants form the soil as undissociated boric acid (H3B03). Specific functions:
It is evident that essentiality of boron for all green plants is not absolute.
– In higher plants, boron is essential for sugar transport.
ADVERTISEMENTS:
– Boron helps in germination and growth of pollen grains.
– Boron is concerned with the cell wall metabolism.
– Boron is essential for DXA synthesis.
Deficiency Symptons:
ADVERTISEMENTS:
– Root tip elongation is inhibited.
– Shoot apices die.
– Xodule formation in legumes is inhibited.
– The branches at the end of twig form a rosette.
ADVERTISEMENTS:
3. Molybdenum:
It is absorbed by the plants as molybdate ions.
Specific functions:
– Molybdenum is found to be essential in nitrogen fixation by legumes.
ADVERTISEMENTS:
– Molybdenum is a component of the enzyme nitrate reductase, nitrogenase etc.
Deficiency symptoms:
– Molybdenum deficiency causes chlorotic interveinal mottling of the leaves with marginal necrosis and infolding of leaves.
– Causes “White tail” disease in cauliflower.
– The flowers abscise before fruit setting.
4. Zinc:
Zinc is absorbed as divalent Zn2‘ ion
Specific functions:
– Zinc is associated with the biosynthesis of Indole-3-acetic acid (an auxin)
– Zn2” is required by the enzyme phosphodiesterase.
– Zn2T induces synthesis of cytochrome.
Deficiency symptoms:
– Growth is stunted in severe zinc deficiency.
– The leaves become smaller and the internodes shorten to give a rosette form.
5. Iron:
Iron is mainly absorbed by the plant in the ferrous form, but ferric ion may also be absorbed. Acid soil favours availability of soluble forms of iron.
Specific role:
– It functions both as a structural component and as a co-factor for enzymatic reactions.
– It is important constituent of iron-porphyrin proteins like cytochrome peroxidases, catalases etc.
– It is very important constituent of ferrodoxin which plays important role in Biological nitrogen fixation and primary photochemical reaction in photosynthesis.
Deficiency symptoms:
Iron deficiency causes rapid chlorosis of the leaves which is interveinal. The deficient symptom first appears in young leaves.
6. Copper:
It is absorbed as both monovalent and divalent cations.
Specific functions:
– Copper is a component of cytochrome.
– Copper is found in a group of enzymes in which oxygen is used directly in the oxidation of substrate.
Deficiency Symptoms:
– Copper deficiency results in exanthema, a disease of fruit trees.
– Blackening of potato is also caused by shortage of copper.
7. Chlorine:
Chlorine is absorb < as CI.
Specific function:
– Chlorine helps in the photoproduction of oxygen.
– It is required for the normal production of fruits.
Deficiency Symptoms:
– Leaves become wilted.
– Leaves develop bronze colour.
– Fruit formation is retarded. Absorption of mineral salts
Mineral salts are found in the soil usually in three forms- dissolved, adsorbed and combined. In the former two cases they occur as ions while in the third they are combined variously as ions, molecules or atoms.
The essential ions are absorbed in different amounts by the root hairs and are translocated through the xylem duct to the different parts of the plant body.