Application of Growth Regulators in Sustainable Agriculture
Author: Rakesh Sil Sarma

Plant growth requlators have most important role in different physiological and morphological processes related to growth and development of crops plants. It was obvious that dramatic changes in the level of endogenous hormones due to different environmental stress alter the crop growth and their productivity. Exogenous application of growth regulators would might help for improvement of yield and productivity . Plant growth hormones are organic protenious substances produced naturally in the higher plants, controlling growth development or other physiological and biochemical functions at a site remote from its place of production, and active in minute amounts. Mainly five major classes of plant hormones are listed: auxins, cytokinins, gibberellins, abscisic acid and ethylene. However as research progresses, more active molecules are being found and new families of regulators are emerging; one example being polyamines such as putrescine or spermidine,jasmonic acid, salisylic acids. This classification is based on the chemical structure and plant physiological effects that certain substances exhibit.

Auxin: Auxin is the most active ingredient in most rooting culture media mixtures. These products help the vegetative and morphological propagation of plants. On a cell level auxins influence cell elongation, cell division and the formation of adventitious roots. Typical auxin concentration ranges from 0.01 to 10 mg/L. Function of Auxin shows below:

  • Stimulates cell division in the cambium and, in combination with cytokinins in tissue culture
  • Delays leaf senescence
  • Can inhibit or promote (via ethylene stimulation) leaf and fruit abscission
  • Stimulates root initiation on stem cuttings and lateral root development in tissue culture
  • Stimulates cell elongation .
  • Delays fruit ripening Stimulates the production of ethylene at high concentrations
  • Involved in assimilate movement toward auxin possibly by an effect on phloem transport
  • Can induce fruit setting and growth in some plants

GIBBERELLINS: There are about 100 different gibberellins, but gibberellic acid (GA3) is the most commonly used form. Gibberellins are fundamental to plant development especially with respect to the growth of stems. Gibberellins are particularly effective at breaking seed dormancy and at speeding up germination. Function of GA is given below

  • Stimulates enzyme production (a-amylase) in germinating cereal grains for mobilization of seed reserves
  • Can delay senescence in leaves and citrus fruits
  • Stimulate stem elongation by stimulating cell division and elongation.
  • Stimulates bolting/flowering in response to long days.
  • Breaks seed dormancy in some plants which require stratification or light to induce germination. .
  • Induces maleness in dioecious flowers (sex expression)
  • Can cause parthenocarpic (seedless) fruit development.
CYTOKININS: Cytokinins promote cell division, stimulate shoot proliferation, activate gene expression and metabolic activity in general. Natural cytokinin or kinetin hormone levels are high during growth periods of mature plants. In addition, cytokinins reduce the aging process in plants. Concentrations of cytokinin used in crops vary between 0.1 and 10 mg/L.Function of cytokinin was given below:

  • Promotes the conversion of etioplasts into chloroplasts via stimulation of chlorophyll synthesis
  • May enhance stomatal opening in some species
  • Stimulates cell division.
  • Stimulates morphogenesis (shoot initiation/bud formation) in tissue culture.
  • Stimulates the growth of lateral buds-release of apical dominance.
  • Stimulates leaf expansion resulting from cell enlargement.

ETHYLENE: Ethylene is unique that it is found only in gaseous form. It induces ripening, causes leaves to abscess and promotes senescence. Plants often increase ethylene production in response to stress and before death. Ethylene concentrations fluctuate with the seasons while playing a role in ripening of fruits. Function of ethylene was given below:

  • Stimulates fruit ripening.
  • Stimulates the release of dormancy.
  • Stimulates shoot and root growth and differentiation (triple response)
  • May have a role in adventitious root formation.
  • Stimulates leaf and fruit abscission..
  • Induction of femaleness in dioecious flowers.
  • Stimulates flower opening.
  • Stimulates flower and leaf senescence.

About Author / Additional Info:
PhD Research Scholar(ICAR-SRF) ,Department of Plant Physiology,Institute of Agricultural Science,BHU,Varanasi.