Agriculture Reference
In-Depth Information
w.
Plant Growth Regulators
Plant growth regulators (PGRs) are phytochemicals, which in minute
amounts alters the behavior and/or growth of plants, blossoms, or fruit.
These chemicals are regulated as pesticides, and besides being called PGRs,
they are referred to as plant hormones and plant-regulating substances.
1.
Auxins
Auxins are compounds that stimulate various growth processes. Auxins
occur naturally and can be manufactured.
Auxins are used to thin apples and pear, increase yields of vegetables, and
promote rooting in cuttings and fruit setting.
The mechanism of action is not completely clear, but auxins may act by
controlling the types of enzymes produced by the cell. In any event, auxins
induce cell enlargement, water uptake, and cell wall expansion.
Toxicity
Amid-Thin (naphthalene acetamide) is labeled “Danger” because of the po-
tential of severe irreversible eye damage, whereas Fruitone N, NAA 800, and
Tree-Hold Sprout Inhibitor (NAA) are relatively nontoxic (Category III). See
Table 5.28
for a listing of commercial products.
2. Gibberellic Acid (Gibberellin, GA
3
)
Toxicity and Mode of Action
Gibberellic acid is not a pesticide, but it is commonly used in agricultural
production as a growth-promoting agent. Gibberellins are compounds that
promote cell division and cell elongation. They are metabolic products of a
cultured fungus, formulated into tablets, granules, and liquid concentrates for
application to soil beneath growing plants and trees.
More than 50 gibberellins have been isolated and identified. They are
termed GA
1
, GA
2
, GA
3
, etc. The GA
3
is the most commonly used gibberel-
lin.
Experimental animals tolerate large oral doses without apparent adverse ef-
fect. No human poisonings have been reported. Sensitization has not been
reported, and irritant effects are not remarkable. See
Table 5.28
for a listing of
commercial products.
3.
Cytokinins
Mode of Action
The third type of plant hormone is known to control the induction of cell
division in plants, and these substances are known collectively as cytokinins.
