Transcript Basic Principle in Plant Physiology

Lignin
• Adds compressive strength
• Adds rigidity
• Found in cells having supporting (wood) or
mechanical function
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Lignin fills wall (yellow) e.g. in wood –
resists compression
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Plasmodesmata
• Connect adjacent cells
• Narrow channels that can be opened or closed
• Can transport:
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Ions
RNA
Proteins
Viruses
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Plasmodesmata Structure
• Desmotubule
– Specialized endoplasmic reticulum
– Not thought to be open
• Cytoplasmic sleeve
– Complex structure
– Believed to be site of transport
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Plasmodesmata cont.
• Types of transport
– Symplastic
• Through the plasmodesmata
– Apoplastic
• Through the cell wall
• Size exclusion limits
• Symplastic domains
– Although all cells connected by plasmodesmata, some
closed
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Cell Extensions
• Two types of cellular extensions are cilia and flagella.
• Cilia are small hairlike projections which beat to move
substances. The respiratory tract is lined with cilia which only
beat in one direction to move substances up from the lungs.
(then we swallow them)
• Flagella (flagellum is the singular) are cellular projections which
help the cell to move. A flagellum is found on sperm cells and
helps them to swim to fertilize the egg.
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Plant specific organelles
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Vacuole
Plastid
Cell wall
Plasmodesmata
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Plastid development
• Must arise from a pre-existing plastid
• Start out as a proplastid
– Small, undifferentiated plastids
– Found in meristems (dividing cells)
– Later differentiate
• Etioplasts
– Chloroplast precursors found in dark grown plants
– Have prolamellar bodies
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Mature types develop from undifferentiated young plastids
Types can
interconvert e.g
tomato ripening
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Evolution of plastids:
Endosymbiosis
• Plastids (like mitochondria) have own circular
genome, double membrane, ribosomes
• Originated as photosynthetic bacteria
(cyanobacteria)
• Engulfed by larger heterotropic cell
• Symbiosis
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