The growth and development of plants is regulated by a number of chemical substances which together exert a complex interaction to meet the needs of the plant. Five groups of plant hormones are well established; they are the auxins, gibberellins, cytokinins, abscisic acid and its derivatives, and ethylene. These substances are of wide distribution and may, in fact, occur in all higher plants. They are specific in their action, are active in very low concentrations, and regulate cell enlargement, cell division, cell differentiation, organogenesis, senescence and dormancy. Their action is probably sequential. Other hormones concerned with flower formation and reproduction, but as yet uncharacterized, have also been envisaged. The essential role of these substances is illustrated by cell and tissue cultures; without the addition of suitable hormones no development or cell division occurs. The effects of these very active substances on the production of secondary metabolites, particularly with a view to producing plants containing an enhanced proportion of active constituent, are of interest to pharmacognosists. In such studies the manner in which the results are recorded is all-important, particularly as the treatment may also influence the size of the test plant compared with the controls. For commercial purposes yield per hectare is an obvious criterion, whereas for biosynthetic studies yield per plant or per cent fresh weight may be of more significance. For final drug evaluation per cent dry weight is the most likely requirement.

1. HORMONE AUXIN GIBBERELLINS CYTOKININS ETHYLENE ABSCISIC ACID (ABA)
INTRO
Term indicate
substance that
promote elongation of
coleoptile tissue.
Class of endogenous
plant regulators.
Discovered from
Gibberella fujikuroi
(fungus)
These are either natural
or syntheticcompounds
with growth regulatory
activity.
Simple organic molecule
presents in the form of
volatile gas and shows
profound physiological
effects.
It is an
accelerating substance
for retainingorshredding
of different organs.
NATURAL
Indole aceticacid(IAA),
indole-3-acetonitrile
(IAN), phenyl acetic
acid
GibberellinA (gibberellic
acid)
Zeatin, N6 dimethyl
amino purine.
Ethylene, ethephon,
glyoxime.
Abscisin I and abscisin II
SYNTHETIC
Indole-3-butyric acid
(IBA), 2-
napthyloxyacetic acid
(NOA), α-naphthyl
acetic acid (NAA), 1-
napthyl acetamide
(NAD), 2 4-D, 2 4 5-T.
Notyet beensynthesised
Kinetin isolated from
autoclaved herring
sperm DNA. Adenine,
diphenyl urea.
Maleic hydrazide,
daminozide, glyphosine,
chromequat chloride,
morphactins
FUNCTION
Internode elongation,
leaf growth, initiation
of vascular tissues,
cambial activity, fruit
growth (NOA), apical
dominance, inhibition
of root growth and
lateral buds,IBA induce
rooting in cutting.
Rapidexpansionof plant
cells,stimulationof seed
germination, breaking
dormancy,increase stem
elongation and size of
leaves and induction of
panthenocarpic fruit
leading to seedless fruit
sets.
Promote cell division,
play role in nucleic acid
metabolismandprotein
synthesis. Promote
lateral bud
development and
inhibition of
senescence.
Ripening, leaf abscission,
stem swelling, leaf
bending, flower petal
discoloration, and
inhibition of stem and root
growth. Breaking
dormancy.
Helps in seed dormancy,
enhanced in stress
condition. Potential
antitanspirant, inhibit GA
actions. Morphactins
potential inhibition of
auxin.
PLANT HORMONES