Q. Plant deficient in element zinc, shows its effect on the biosynthesis of plant growth hormone
NTA AbhyasNTA Abhyas 2020
Solution:
Auxins (means 'to grow') are a class of plant growth regulators with the following properties:
1. They are acidic in nature, either Acetic acid (2,4-Dichlorophenoxy Acetic acid or 2,4-D) or Indole (Indole Pyruvic acid or IPA) derivatives.
2. Indole Acetic acid is a natural auxin, while 2,4-D is a synthetic auxin.
3. Auxins are synthesised from Tryptophan for which Zinc is absolutely necessary.
4. Auxins are synthesised in the apices of the shoot (more than apices of the roots) and are transported in the downward directions.
5. Bioassay for auxins includes the Avena coleoptile curvature test.
6. Several physiological effects are shown by auxins, like:
a. They induce parthenocarpy in banana, lime, etc.
b. They maintain apical dominance.
c. They help in rhizogenesis (root formation) and xylem differentiation (xylogenesis).
d. They promote cell elongation and sometimes cell division.
e. Naphthalene Acetic acid (NAA) is effective in the inhibition of premature fruit drop in tomato plants.
f. At a very low concentration of 2,4-D, pre-harvesting fruit fall can be prevented.
g. Treatment of auxins can induce femaleness in many flowers when applied well before anthesis.
Zeatin (a type of cytokinin) and GA3 does not prevent premature fruit fall. Ethylene is helpful in the ripening of fruit.
1. They are acidic in nature, either Acetic acid (2,4-Dichlorophenoxy Acetic acid or 2,4-D) or Indole (Indole Pyruvic acid or IPA) derivatives.
2. Indole Acetic acid is a natural auxin, while 2,4-D is a synthetic auxin.
3. Auxins are synthesised from Tryptophan for which Zinc is absolutely necessary.
4. Auxins are synthesised in the apices of the shoot (more than apices of the roots) and are transported in the downward directions.
5. Bioassay for auxins includes the Avena coleoptile curvature test.
6. Several physiological effects are shown by auxins, like:
a. They induce parthenocarpy in banana, lime, etc.
b. They maintain apical dominance.
c. They help in rhizogenesis (root formation) and xylem differentiation (xylogenesis).
d. They promote cell elongation and sometimes cell division.
e. Naphthalene Acetic acid (NAA) is effective in the inhibition of premature fruit drop in tomato plants.
f. At a very low concentration of 2,4-D, pre-harvesting fruit fall can be prevented.
g. Treatment of auxins can induce femaleness in many flowers when applied well before anthesis.
Zeatin (a type of cytokinin) and GA3 does not prevent premature fruit fall. Ethylene is helpful in the ripening of fruit.