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Plant Growth. Hormone Function and Tropisms. Primary Meristems. Whether they are involved in primary or secondary growth, all plant cells and tissues arise from three primary meristems *: • protoderm • ground meristem • procambium.

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Plant Growth

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Plant Growth

Hormone Function and

Tropisms


Primary Meristems

Whether they are involved in primary or secondary growth, all plant cells and tissues arise from three primary meristems*:

• protoderm

•ground meristem

•procambium

*Meristem: plant tissue that remains embryonic as long as the plant lives, allowing for indeterminate growth


Specialized Tissues in Plants

  • Plant Growth

    • Meristems – tissues responsible for growth

      • Undifferentiated cells

    • Apical Meristem

      • Produce growth increased length

    • Differentiation

      • Cells will assume roles in the plant

  • Flower Development

    • Starts in the meristem


Growth Hormones (Regulation)

  • Plants produce chemical substances called hormones that inhibit or promote growth.

  • Common plant hormones are….

    • Inhibitors

    • Cytokinins

    • Gibberellins

    • Auxins


Hormones that work with auxins to stimulate cell division.

Cytokinins


Gibberellins

  • Hormones that stimulate cell elongation, premature flowering, and breaking of dormancy.


Hormones that speed plant growth by stimulating cell enlargement.

Auxins


Tropisms

  • A tropism is a growth response involving bending or curving of a plant part toward or away from an external stimulus that determines the direction of movement

  • Response toward the stimulus is positive, and response away from the stimulus is negative


Phototropism

  • Phototropism is the growth of stems of plants toward light - it is probably the best known of the plant tropisms - phototropism is caused by elongation of the cells on the shaded part of the plant - so that entire plant bends or curves toward the light

  • This growth pattern is caused by the hormone auxin- auxin migrates to the shaded part of the plant and stimulates increased cell growth and elongation on the shaded part of the plant


Gravitropism

  • Gravitropism is a response to gravity - if a seedling is placed on its side, the root will curve to grow downward and the shoot will curve to grow upward

  • Auxin may play a role in the response of shoots


Gravitropism in plants


Thigmotropism

  • Thigmotropism is response to touch or contact with a solid object - this is most commonly seen in tendrils, modified leaves or stems depending on the species.

  • the tendrils wrap around any object they come in contact with and so enable the plant to cling and climb.


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