Plant Development

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Chapter 11

• Plant Development

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Embryos and Seeds

• Fertilization makes embryos in plants.
• Usually the embryo is dormant in a seed until
  suitable conditions.
• Plants also do asexual reproduction.
• As the embryo develops it is surrounded by a
  tissue called endosperm.
• The endosperm transfers nutrients from the mother
  plant to the embryo.

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Embryo and Seed
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• Differentiation starts as small bumps on the the
  embryo that become cotyledons.
• A cotyledon is a seed leaf. It is not a true
  leaf. These leaves do photosynthesis until the
  true leaves develop and take over.
• Rapid division occurs and cells begin to become
  specialized structures.

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Cotyledons
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• Plant cells do not migrate like animal cells
  because plant cells are attached to each other.
• They become specialized based on their location.
• Plant embryos differ from animal embryos in that
  they become dormant until germination.

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Germination

• Germination is the sprouting of a seed.
• This occurs when conditions are suitable for the
  growth and development of the plant.
• Conditions include temperature, oxygen, water,
  etc.

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Meristems

• Plants have several meristems.
• A meristem is a tissue that remains embryonic and
  is responsible for producing new cells.

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Meristem Locations
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Apical Meristems

• The central vertical structure is the shoot tip,
  which ends in the shoot apical meristem (the
  reddish structure with two horn-like leaf
  primordia).

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Primary Growth

• Primary Growth refers to the growth of roots and
  stems from the apical meristem.
• Primary Growth is responsible for Elongation in
  all parts of a Plant which include, Stems, Roots,
  Leaves Reproductive Structures.

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Root Cap

• As the plant puts roots into the soil a root cap
  forms and covers the apical meristem.

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Development

• As the plant grows it develops.
• The differentiated cells make up
• The epidermis that covers the plant (covered by a
  waxy coating called a cuticle.)
• The vascular tissues xylem and phloem (carry
  water and nutrients)
• Ground tissue that makes up the body of the plant.

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Secondary Growth

• Secondary Growth is when plants grow thicker in
  their roots and shoots.
• This develops from another type of meristem
  vascular cambium (located near outer surface of
  roots and stems.)

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Secondary Growth

• Have you ever seen the growth rings in a tree
  trunk? These are examples of secondary growth.

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Plant Growth and Development

• A hormone is any chemical produced in one part of
  the body that has a target elsewhere in the body.
  (Called PGRs, plant growth regulators.)
• Hormones and enzymes serve as control chemicals
  in multicellular organisms.

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• There are 5 classes of PGRs.
• Auxins promote stem elongation. They are produced
  in the stem, buds, and root tips.
• Gibberellins promote stem elongation. They are
  not produced in stem tip.
• Cytokinins promote cell division. They are
  produced in growing areas, such as meristems.
• Abscisic Acid promotes seed dormancy by
  inhibiting cell growth.
• Ethylene is a gas produced by ripe fruits.

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Plant Responses

• Plants move and change in their growth pattern
  depending on the environment.
• Growth toward or away from a stimilus is called a
  tropism.

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Phototropism

• Phototropism is a growth movement induced by a
  light stimulus. Growth towards a source of light
  is called positive phototropism, that away from
  the source is termed negative phototropism.

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Gravitropism

• Gravitropism is plant response to gravity. Roots
  of plants show positive geotropism, shoots show
  negative geotropism.
• Positive grows toward and negative grows away
  from gravity.

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Photoperiodism

• Photoperiodism is a plants response to the
  length of light and dark in a 24-hour period.
• Short-day plants flower during early spring or
  fall, when the nights are long and the days are
  short.
• Long-day plants flower mostly in summer, when the
  nights are short and the days are long.
• Day-neutral plants flower without respect for the
  day length.
• Phytochrome is a plant pigment in the leaves of
  plants that detects the day length and generates
  a response.