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Plant Growth and Development

Seed

What is Growth?

  • It is a characteristic of living beings in which an irreversible permanent increase in size of an organ or its parts occur. In smaller living beings, an increase in the size of a cell can also be termed as growth.

Characteristics of Plant growth

  • Plant Growth is Indeterminate

    • Plants retain the capacity of unlimited growth throughout life.
    • Meristems are present in plants that have the ability to divide and self perpetuate.
    • Open form of growth − New cells are always being added to the plant by meristem.
    • Primary Growth − Occurs due to root apical meristems and shoot apical meristems
    • Secondary growth − Occurs due to the appearance of lateral meristems, vascular cambium, and cork cambium later in the life of certain dicots and gymnosperms
  • Plant Growth is Measurable

    • Growth is measured by measuring the parameters that are directly proportional to increase in protoplasm.
    • Increase in weight (fresh and dry weight both), length, area, volume, and cell number are some parameters.
    • Choice of parameters depends upon type of plant.
      Examples:
      For pollen tube − length is the parameter
      For water melon − cell size is used
      For dorsiventral leaf − surface area is used
In the above topics we have studied what is plant growth, but you must be aware that a plant can grow only after germination of seed.
This, means that seed germination is the first step in the growth of plants. Lets study more about seed germination.

Seed germination
  • It is the first step in the process of growth of plants.

  • Seed germination requires certain necessary conditions necessary like availability of water and oxygen. In the absence of these, the seeds may fail to germinate.

  • The steps of seed germination include -

    • absorption of water which causes swelling of seeds
    • swelling causes the rupture of seed coat
    • radicle emerges from one end of the embryonal axis and forms the root system
    • plumule emerges from the other end of the embryonal axis and forms the shoot system
  • Metabolic activities which take place during this process require oxygen for breaking down the food reserves.
  • Rate of respiration increases during germination process.

Certain plants such as Rhizophora and Sonneratia show vivipary. Vivipary is a special type of germination in which the seed germinates while it is still attached to the parent plant and is nourished by it. Germinating seed forms a seedling and as its weight increases, the seedling separates and falls down into the mud. Lateral roots then develop to help proper anchorage of the seedling.

Seed dormancy

It is not necessary that all the seeds may germinate even if favourable conditions are available. This condition where seeds are unable to germinate even in the presence of favourable conditions is called dormancy.

There are certain factors which can lead to seed dormancy -

  • impermeable or mechanically resistant seed coats
  • rudimentary or physiologically immature embryos
  • ​​​presence of germination inhibitors such as abscisic acid, phenolic acid, short chain fatty acids and coumarin

​There are two different ways by which dormancy of seeds can be broken:

  • Scarification - It involves scratching of seed coat to help break the dormancy caused by hard and impermeable seed coat.

  • Stratification - It involves subjecting the moist seeds to oxygen for variable periods of low or high temperatures.

Phases of Growth

  • Three Phases of growth − meristematic, elongation, and maturation
  • Meristematic Phase

    • Cells rich in protop…

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