Overview of Plant Developmental Biology

• THE ENDOSYMBIOSIS THEORY FOR MITOCHONDRIA AND CHLOROPLAST EVOLUTION

  A) anaerobic eukaryote

  B) aerobic bacterium

  C) eukaryotic cell surrounds and engulfs bacterium

  D) bacterium lives within eukaryotic cell

  E) protection

  F) carbon

  G) atp

  H) pyruvate and o2

  
• Each would have performed mutually benefiting functions from their symbiotic relationship. The aerobic bacteria would have handled the toxic oxygen for the anaerobic bacteria, and the anaerobic bacteria would utilize ingested food and protected the aerobic "symbiote".
• An endosymbiont is any organism that lives within the body or cells of another organism, i.e. forming an endosymbiosis (Greek: endon "within", syn "together" and biosis "living").
• Examples of endosymbiotic relationship:

  • nitrogen-fixing bacteria (called rhizobia) that live in root nodules on legume roots,
  • single-celled algae inside reef-building corals, and
  • bacterial endosymbionts that provide essential nutrients to about 10%–15% of insects.
• Andreas Schimper observed in 1883 that the division of chloroplasts in green plants closely resembled that of free-living cyanobacteria (blue-green algae) and tentatively proposed that green plants had arisen from a symbiotic union of two organisms.
• Margulis and Sagan (2001) "Life did not take over the globe by combat, but by networking"
• Secondary Endosymbiosis

  • Serial ingestion of photosynthetic bacteria by endosymbiotic prokaryotes or eukaryotes led to the ancestors of eukaryotic plants.
  • As the ingested photosynthetic bacteria adapted to the ingesting prokaryotic host cell, plastids, such as the chloroplast evolved. Primary plastids are found in some algae because their plastids are derived directly from a Cyanobacterium.

  
• All other lineages of plastids have arisen through secondary (or tertiary) endosymbiosis, in which a eukaryote already possessing plastids is engulfed by a second eukaryote. Considerable gene transfer has occurred among genomes and, at times, between organisms.
• Mitochondria and chloroplasts contain DNA

  • The most convincing evidence of the descent of these organelles from bacteria is the position of mitochondria and plastid DNA sequences in phylogenetic trees of bacteria.
• Mitochondria and chloroplasts contain DNA

  • Mitochondria have sequences that clearly indicate origin from a group of bacteria called the alpha-Proteobacteria.
  • Chloroplasts have DNA sequences that indicate origin from the cyanobacteria (blue-green algae).
• The Evolution of Plant

  • green algae (charophytes) are the ancestors of plants
• Plants adaptations for life on land

  • more than 500 mya, the algal ancestors of plants may have carpeted moist fringes of lakes and coastal salt marshes
• Plants adaptations for life on land

  • plants and green algae called charophytes
  • evolved from common ancestor
  • complex multicellular bodies
  • photosynthetic eukaryotes
  • algae do not have tissues like plants
• Opportunities in land for plants adaptations

  • unlimited sunlight
  • abundant CO2
  • initially, few pathogens for herbivores
• Disadvantages in land for plants

  • maintain moisture inside their cells (to not dry out)
  • support their body in a nonbuoyant medium
  • reproduce and disperse offspring without water
  • obtain resources from soil and air
• Unlike land plants, algae:

  • generally have no rigid tissues
  • supported by surrounding water
  • obtain CO2 and minerals directly from the water surrounding the entire algal body
  • receive light and perform photosynthesis over most of their body
  • use flagellated sperm that swim to fertilize an egg
  • disperse offspring by water
• Algae to Land Plants

  A) alga

  B) moss

  C) fern

  D) pine tree

  
• Origin of land plants

  • 475 mya
  • First evidence of land plants: cuticle, spores, sporangia
• Silurian-Devonian explosion

  • Most major morphological innovations: stomata, vascular tissue, roots, leaves

  A) Cooksonia pertoni

  
• Carboniferous: Lycophytes and horsetails abundant

  • 359 mya
  • Extensive coal-forming swamps

  
• Gymnosperms abundant

  • 299 to 145 mya
  • Both wet and dry environments blanketed with green plants for the first time

  A) Araucaria mirabilis

  
• Angiosperms abundant

  • present
  • Diversification of flowering plants

  A) Archaefructus

  
• History of evolution of major plant types on land

  A) origin of plants

  B) early vascular plants

  C) first seed plants

  D) radiation of flowering plants

  
• Land plants maintain moisture in their cells using

  • waxy cuticle
  • cells that regulate the open/close of stomata
• Land plants obtain

  • water and minerals from the roots in the soil
  • CO2 from the air and sunlight through leaves
• Growth producing regions of cell division, called apical meristems, are found near the tips of stems and roots.
• In many land plants, water and minerals move up from roots to stems and leaves using vascular tissues.

  • xylem
  • consists of dead cells and
  • conveys water and minerals
  • phloem
  • consists of living cells and
  • conveys sugars
• In all plants the

  • gametes and embryos must be kept moist
  • fertilized egg (zygote) develops into an embryo while attached to and nourished by a parent plant, and
  • life cycle involves an alternation of a
  • haploid generation, which produces eggs and sperm
  • diploid generation, which produces spores within protective structures called sporangia
  • pines and flowering plants have pollen grains, structures that contain the sperm producing cells.
• Plant diversity reflects the evolutionary history of the plant kingdom

  A) liverworts

  B) hornworts

  C) mosses

  D) lycophytes

  E) pterophytes

  F) gymnosperms

  G) angiosperms

  
• Growth is the irreversible change in size and weight, mass/volume of a plant or its parts

  • cell number
  • fresh weight
  • dry weight, length
  • width
  • area
  • volume
• types of growth

  • primary growth
  • mitotic division of meristematic cells present at the root and shoot apex increases the length of the plant body
  • secondary growth
  • secondary meristem increases the diameter of the plant body
  • unlimited / intermediate growth
  • root and shoot system of plants grow continuously from germination stage to the death of throughout the life span of the plant
  • limited / determinate growth
  • leaves, fruits, and flowers stop growing after attaining certain size
• Primary Growth

  Meristematic tissues

  • derived from Greek meristos - "divided"
  • unspecialized cells that can divide indefinitely to produce new cells
• • meristem is the region where meristematic cells dwell
  • meristematic tissues are usually found at the apex of root and shoot
• Location of Meristematic Tissues

  A) lateral bud

  B) leaf primordia

  C) lateral bud primordia

  D) cork cambium

  E) vascular cambium

  F) root apical meristem

  G) root hairs

  H) root apical meristem

  I) root cap

  
• Characteristic of Meristematic tissues

  • living, thin walled
  • spherical, oval, or polygonal shape
  • vacuoles - few and small in size
  • dense protoplasm and conspicuous nuclei

  
• • The meristematic tissue has the quality of self-renewal. Every time the cell divides, one cell remains identical to the parent cell, and the others form specialized structures.
  • They have very small and few vacuoles.
  • The protoplasm of the cells is very dense.
  • The meristematic tissues heal the wounds of an injured plant.
  • The cells of the meristematic tissue are young and immature.
  • They do not store food.
  • They exhibit a very high metabolic activity
• Classification of Meristem

  A) promeristem

  B) primary meristem

  C) secondary meristem

  D) apical meristem

  E) intercalary meristem

  F) lateral meristem

  
• Promeristem

  • early embryonic meristem from which other advanced meristems are derived
  • function: produce the cells of the primary meristems
  • made up of initials
  • divide further to form primary meristem
• Promeristem

  A) leaf primordium

  B) shoot apical meristem

  C) protoderm

  D) ground meristem

  E) procambium

  
• Primary Meristems

  • derived from promeristem
  • give rise to the primary tissue systems: protoderm, ground meristem, and procambium
  • these cells divide and form permanent tissues