Plant Growth & Development

Plant Growth and Development

      Plant growth is indeterminate and open.

Absolute Growth rate: Total growth that takes place in a given time. Eg. Initial size of leaf is 5cm². After time ‘t’ it is 10cm². Absolute growth rate is 10 – 5 = 5

Relative Growth: Growth per unit of dry mass.

Conditions for growth:

      Water, Oxygen and Nutrients are very essential for growth.

      Water is required for cell enlargement and as medium for enzymatic activity.

      Oxygen is needed for release of metabolic energy needed for growth activity.

      Macro and micro nutrients are needed for protoplasm formation and source of energy.

      Temperature, light and gravity also influence growth.

Differentiation, dedifferentiation and redifferentiation:

      Transformation of derivatives of primary meristems into permanent cells is differentiation.

      Regaining meristematic activity by permanent living cells is called as dedifferentiation.

      Tranformation of derivatives of secondary meristems into permanent cells is called as redifferentiation.

Development:

      All changes that tale place from seed germination to senescence is called as development. It includes growth and differentiation.

      Growth due to repeated divisions of formed cells is called as Plasmatic growth.

      Cell division, cell enlargement, cell differentiation, cell maturation and senescence are various stages of growth at cellular level.

      Ability of plants to follow different pathways to form different structures of it in response to environment and phases of growth is called as Plasticity. E.g. Heterophylly in Cotton, Larkspur, Coriander and Ranunculus. The shape of adult leaves is different from juvenile leaves.

Plant growth is under the control of both Intrinsic factors such as Intracellular factors known as genetic factors and Intercellular factors known as Phyto hormones and Extrinsic factors such as light, temperature, water, oxygen, nutrients etc.

Plant Growth Regulators

      Ethylene fits into growth promoters and growth inhibitors. It is more as a growth inhibitor.

      Cousins confirmed the existance of ethylene released from ripened oranges that promoted fruit ripening in bananas.

Auxins

      These were first isolated from human urine by Kogl and Hagensmidit.

      The term auxin was coined by Kogl.

      They promote flowering in Pineapple

      Prevent fall of young fruits and flowers.

      Promote abscission of senescent leaves and mature fruits.

      Control xylem differentiation.

      Removal of apical dominance by cutting the stem apices is called as topping. It applied in tea palntations and hedge making.

Gibberellins

      Increase the length of fruit stalks and improves fruit shape in Apple.

      Delay the senescence of fruits.

      Used in malting process in brewing industry.

      Increases sugarcane yield by 20 tonnes per acre.

      Promotes early seed production in conifers.

Cytokinins

      Promotes chloroplast formation.

      Adventitious shoot formation.

      Decreases apical dominance.

      Mobilizes nutrients to delay senescence.

Ethylene

      Promotes hook formation in dicot seedlings during seed germination.

      Causes respiratory climatric.

      Breaks seed dormancy in Peanuts and bud dormancy in potato.

      Promotes rapid internodal and Petiole elongation in flooded rice plants.

      Promotes root hair formation and lateral roots.

      Induces flowering in Mango.

      Ethephon is used for fruit ripening of Apple and Tomato and abscission of flowers in crops like Cotton, Cherry and Walnut.

Abscissic acid

      Inhibits Plant metabolism.

      Antagonistic to Gibberellins.

      It is stress hormone.