Early Development of the Plant Body

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Chapter 22

• Early Development of the Plant Body

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Introduction

• Structure and development of the angiosperm plant
  body (sporophyte)
• Embryogenesis-formation of the embryo consisting
  of two patterns
• 1-apical basal pattern on main axis
• 2-radial pattern of a concentrically arranged
  tissue system
• Accompained by seed development

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Formation of Embryo

• Early stages are the same in magnolids, dicots
  and monocots
• Zygote divides within embryo sac of ovule
• Polarity established-essential in the development
  of higher organisms
• Embryo differentiates into a spherical structure
  (embryo proper) and the suspensor
• Developing embryo is known as the proembryo

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Primary Meristems

• First, mass of undifferentiated cells
• Change in internal structure of embryo proper
  results in initial development of the tissue
  systems of plants
• Protoderm-future epidermis
• Ground meristem-ground tissue and surrounds
  procambium
• Procambium-xylem and phloem

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Developmental Stages

• Globular stage-preceeds cotyledon development
  embryo proper is spherical
• Heart stage-globular embryo in dicots takes on a
  heart shape form
• Globular embryo of monocots becomes cylindrical
  in shape
• Apical-basal pattern becomes noticeable, with the
  axis dividing into the shoot meristem,
  cotyledons, hypocotyl, embryonic root, and root
  meristem
• Torpedo stage-cotyledons, axis, and primary
  meristems grow and elongate
• Addition of new cells becomes restricted to the
  apical meristems of the shoot and root
• -magnoliids and dicots a.m. of shoot arises
  between 2 cotyledons
• -monocots a.m. shoot arises on one side of
  cotyledon and surrounded by sheathlike
  extension from the base of the cotyledon

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Suspensor

• Stalklike, anchors embryo at micropyle end
• Angiosperm suspensors metabolically active
• Support early development of embryo proper by
  providing nutrients and growth regulators
• Short-lived, apoptosis at torpedo stage
• Some evidence shows that the normally developing
  embryo proper limits the growth and
  differentiation of the suspensor

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Genes and Embryogenesis

• Over 50 different genes regulating embryonic
  pattern formation have been identified
• Affect apical-basal patterns of embryo and
  seedling
• -mutations delete different regions of
  apical-basal pattern
• Determine radial pattern of tissue
  differentiation
• -mutations prevent formation of protoderm
• Regulate changes in cell shape that give embryo
  and seedling an elongated shape

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