CONCEPTS OF GROWTH REGULATORS AND AGEING IN PLANTS

1. Concept of growth regulators and ageing in plants
Presentationby
Srihari katthi
Studentat LPU

2. CONCEPTS OF GROWTH REGULATORS AND AGEING IN PLANTS
 Growth regulators:
Plant growth regulators or phytohormones are organic substances produced naturally in
higher plants, controlling growth or other physiological functions at a site remote from
its place of production and active in minute amounts.
Or
Defined as organic compounds other than nutrients, that affects the physiological
processes of growth and development in plants when applied in low concentrations.
Or
Defined as either natural or synthetic compounds that are applied directly to a target
plant to alter its life processes or its structure to improve quality, increase yields, or
facilitate harvesting.
 Classes on basis of origin:
1. Endogenous
o a. Substance produced by a plant that affects the pattern of growth and
development.
o b. Production by the plant is regulated by the environment.
2. Exogenous
o a. Substance applied to the plant that alters growth and development in the
same way that endogenous substances do.
o b. May be the same or different chemically from the endogenous substance
3. Hormone
o a. Substance that acts in very low concentration (micro-molar or less)
o b. Produced in one part of plant and act in another ( translocatable )
o c. Has the same response in many different plant species
 Common Growth regulators
1. Auxins
2. Cytokinins
3. Gibberellins
4. Abscisic Acid
5. Ethylene

3. Growth stimulators
o Auxin - Substances generally resembles IAA and has the ability to stimulate the
elongation of coleoptiles.
o Gibberellins - are diterpenoids, which have the ability to elongate the stem of green
seedlings especially certain dwarf and rosette types. Cytokinin - Usually substituted
Adenines, which resembles zeatin (Naturally occurring cytokinin in Zea mays) and have
the ability to stimulate cytokinensis in cultures of tobacco cells.
o Cytokinin - Usually substituted Adenines, which resembles zeatin (Naturally occurring
cytokinin in Zea mays) and have the ability to stimulate cytokinensis in cultures of
tobacco cells
Inhibitors
Inhibitors are regulators of growth, which originally depress the Auxin
o Ethylene - Gaseous regulator that stimulate is diametric growth in the apices of dicot
seedlings (Ripening of fruits)
o Abscisic acid – Causes abscission OR senescence
Some few concepts of Growth regulators :
 To increase productivity
 To increase resistance and wide adaptation of crop plants
 To maintain selected growth and certain parameters
 To bring adequate flowering
 to maintain required number of fruits per plant
 Apical dominance
 Dormancy of seed to increase preservation period
 To break dormancy for off season cultivation
 Abscission or senescence to delay transpiration and translocation of nutrients in
inadequate conditions
 To induce parthenocarpy
 Internode elongation in use of stem crops like sugarcane

4. Role of growth regulators in AGING of plants :
 Like other organisms, also plants age as their development progresses. However,
depending on reproductive strategies and life form (whether annual, biennial or
perennial), plant life spans can vary from a few days to hundreds, and in some cases
even thousands of years
 The life cycle of flowering plants is a succession of distinct growth phases starting
with germination, followed by a juvenile and adult vegetative phase , flowering,
fruiting then resulting in senescence of the whole plant, which leads to its death
 In plants, in addition to age-dependent, developmental senescence, senescence can
also be induced by adverse environmental conditions such as darkness or drought
and not only with hormones
 During their life cycle, plants continuously produce new organs that are formed and
develop using nutrients, part of which are recycled and mobilized from senescing
organs
 A delay of flowering can delay senescence and thereby prolong the leaf and plant life
span
 Although senescence is a destructive process, it progresses orderly, in a highly
regulated manner, and importantly in plants it can be utilized for the benefit of the
organism
 In this review, we will briefly summarize our understanding of the role of different
classes of plant hormones in developmental and in aging of plants
Role of cytokinins :
o The idea for a function of CKs in senescence came from the observation that
endogenous CK levels declined during leaf senescence, while exogenous application
of CK delayed senescence in a large variety of monocotyledonous and dicotyledonous
species
o It is thought that CK targets in senescence are factors which regulate source to sink
nutrient transfer since inducing the expression of extracellular invertase
o Invertase an enzyme involved in the apoplastic phloem unloading pathway, was
sufficient to mediate CK-induced leaf longevity.
o Moreover, inhibition of this extracellular invertase repressed senescence in the
presence of Cytokinen, supporting the notion that CKs may act by modulating the
activity of this enzyme

5. Role of ethylene :
o In addition to CKs, also ethylene plays a prominent role in senescence.
o Ethylene is the smallest plant hormone known and the only one that is a gas under
ambient conditions.
o Ethylene regulates various developmental processes including seed germination, root
hair development, stress responses, flowering, fruit ripening and abscission
o In many plant species ethylene biosynthesis is induced in senescing leaves and in
ripening fruits
o Although the observation that ethylene-containing illumination gas induces leaf
abscission and yellowing of leaf and effects the growth of plants
Role of ABA:
o In addition to its important role in environmental stress responses, ABA also
regulates development processes including the induction of seed dormancyThe
synthesis of seed storage proteins and lipids and the inhibition of the transition from
embryonic to vegetative growth
o A promotive role of ABA in senescence , which have demonstrated that exogenous
application of ABA promotes leaf senescenc
o SAG113 is Enzyme induced by ABA in senescing leaves and is significantly reduced in
its expression in the ABA biosynthesis and signaling mutants aba2-1 and abi4-1
As all these plant growth regulators every growth promotor and growth inhibitors plays certain
important role in plants
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