PLANT GROWTH SUBSTANCES AND
THEIR ROLES IN CROP PRODUCTION
•PPCP 202
•DR. AKINTOKUN P.O
• Growth is brought about by cell division,
expansion and assimilation.
• Any factor that directly or indirectly affects
those processes will influence growth.
• These are internal and external factors that
influence growth of plants.
• Protein form the structural foundation of the
body.
• Nitrogen for the building block of protein. Plants
growing in Nitrogen-deceit soils can’t
manufacture enough protein, thus show started
growth and development.
• Light play a major role in synthesis and action of
chlorophyll without which photosynthesis cannot
take place.
• Seedling growing in dark become etiolated: it is
yellow due to lack of chlorophyll, the leaves fail
and expand and the item is long and spindly.
• Oxygen those not generally affect the growths of the
above ground parts and plant, but it can have profound
influence on the growth of roots.
• Internal factor affecting growth include the genetic
constitution and the relative amount of hormones
prevent in the body thus these two are related.
• Hence, plant growth and development are
characterized by high degree of co-ordination and
phasing. The growth of one part is closely related with
the growth or activities in other parts of the plant.
• Such internal coordination system is maintained
by naturally occurring organic compounds
referred to as plant hormones or phytohormones
in the plant.
• This phyto-hormones influence the numerous
physiological processes culminating in plant
growth, development and death. Effects of
environment are largely influenced by either the
synthesis and or the general distribution of these
substances within the plant.
• Five basic classes of phyto-hormones have
been recognized:
• (1).AUXINS (2). GIBBERELLINS (3).CYTOKININS
• (4).ABSSCISIC ACID (5).ETHYLENE
• These are the most important agents involved
in coordinating the growth of the plant as a
whole. Depending on the plant, they act
either singly or in association.
• Phyto-hormones are organic compounds
which in small quantities promote, support,
maintain or inhibit various metabolic activities
within the plant system.
• Phyto-hormones are not carbohydrate in the
sense that carbohydrates are produced and
require by the plant in large quantities while
phyto-hormones are produced in small
quantities but their effect are pronounced.
• Regulation of growth by is actually based on
interaction and delicate balance amongst the
various groups of phyto-hormones.
• AUXINS
• The word auxin is actually a generic term which
applies to a group of compounds affecting the
plant in some way or manner. The word include
the internally occurring and the synthetic
members of the group called Auxins.
• The auxins are formed chiefly in the apical meristem of
the stem and root , buds, flower or inflorescene on
growing flower stalk- and transported from there to
another to produce a particular physiological effect
there.
• At low concentration, they stimulate growth while at
high concentration they retard growth. They are
characterized by causing cell enlargement and stem
elongation.
• They are also active in development of branches in
plants and are associated with apical dominance.
• CYTOKININS
• The word for cytokinins is a generic name for all
naturally occurring substances that are known to
promote cell division.
• They are also known to delay senescence. The
first naturally occurring cytokinin was found in
corn and is referred to as ZEATIN. The most
widely distributed cytokinins are the synthetic
benzyladenine and 6-sulfuryl aminopurine or
Kinetin
• Zeatin, a naturally occurring cytokinin was isolated
from Zea mays grains.
• Zeatin has since been found in other plants. Some
closely related compounds have also been found to
exhibit cytokinin activities. Such synthetic cytokinins
include Benzyl ammo-purine.
• The natural cytokinin appears to be made principally in
apical root meristem, inflorescences and developing
fruits. Certain cytokinins have been found to be the
constituent of certain transfer RNA molecules in a
number of different organisms.
• They are also involved in stimulation of organ
formation e.g. formation of leave, fruit, buds, and
branches.
• They tend to contract or overcome apical
dominance and break dormancy. They also
enhance seed germination and uniform
flowering. Cytokinins regulate the transportation
of metabolites in the phloem.
• Cytokinins are also useful in the preservation of
flowers, fruits and leafy vegetables.
• ABSCISIC ACID
• These were previously called Dormin or Abscisin
mainly because of their regulatory effect on
abscission and dormancy. This hormone is
widespread in higher plants and is found in many
different organs and tissues (both old and young)
of plants.
• ABA induces abscission of the leaves of a wide
variety of plants and fruits of some plant species.
IAA and ethylene interact with ABA in the control
of abscission.
• ABA appears to be an internal factor inducing
dormancy in the buds of at least some
temperature zone woody plants.
• ABA prevents or delays the germination of many
kinds of seeds. ABA retards the growth of a large
variety of plant tissues and organs including
leaves, colcoptiles, stems, hypocotyle and roots.
• It promotes senescence through leaf abscission,
degeneration of excised leaves and acceleration
of decomposition of chlorophyll. ABA inhibits
flower induction in some long day plants.
• ETHYLENE
• This is a simple gas that is produced in small
quantities by many plant tissues and they serve
as a very powerful regulator of growth and
development. They are found very prominently in
physiologically matured fruits undergoing
ripening. (Ethylene is a ripening agent).
• Ethylene operates as a fruit-ripening hormone.
Treatment of fruits such as banana, oranges
when mature, but not yet fully ripened, with
ethylene hasten their ripening.
• This treatment is of commercial importance.
Endogenously generated Ethylene plays a role
in normal abscission processes especially in
interaction with IAA and abscisic acid.
• The leaves of many species exhibit epinasty
(downward bending) when exposed to very
low concentration of ethylene.
• GIBBERELLIN
• It was originally discovered as a product of fungus
reffered to as GIBBERELLINFUJIKORA, which parasite
rice thereby causing rice plants to grow unusually tall.
Gibberellin promotes a wide variety of effects but it
particular eliminates dwarfism or shortness in plants.
• The gibberellins are structurally a distinctive and
closely-knit group of plant hormones. They are of wide
occurrence in vascular plants and they occur also in
very low concentration. The best known of gibberellins
is Gibberellic acid (i.e. A3)
• All know gibberellins have this basic structures
of four rings fixed together called gibberellane
ring. The gibberellins differ one from the other
in the side chain.
• Gibberellins are known to induce the
production of male flowers (in dioecious
flowers or plants).It reverses stunting caused
by virus.
• It encourages leaf expansion on and
acceleration of flowering especially in plants
that will require two or three years to mature.
• It can also be used to induce or eliminate the
need for cold treatment or photo-periodic
induction of plant in certain plants e.g.
horticultural crops.
• Excessive application can cause gigantism.