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Plant cell division:
•Plant cells are surrounded by walls (cellulose microfibrils
in matrix of pectins and hemicelluloses (1o) or lignin (2o))
•Lignin is hydrophobic and prevents cell expansion
•little cell migration (cell sliding possible)
•Cell expansion depends on orientation of microfibrils
•Molecules fixed in cell wall might fix cell fate (and
daughter cells’ fate)
Figure 2-1
Cellulose microfibrils are laid down in different directions to
increase strength
Raven, Fig 3-30
If microfibrils are laid down perpendicular to long edge of
cell, will cause increase in length as cell grows
Raven Fig 3.35
•Interconnected cell walls create an apoplastic channel for
cell-cell movement
•10kDa - 50 kDa exclusion
•Walls are negatively charged, therefore stop +ve
charged molecule movement
•Lignin (2o cell walls), Cutin (cuticle) or suberin
(endodermis) blocks apoplast
•Xylem is interconnected with apoplast - molecules secreted
into apoplast can be transported through the xylem
Vessel element (component of xylem) develops with ordered,
helical secondary wall thickenings and eventual apoptosis
Raven, fig 24-16, 17
A-c,
Vessel
elements
Raven, Fig 24-16
Dtracheid
Raven, Fig 24-13
Plasmodesmata:
•Connections between neighbouring cells
•Lined by plasma membrane, inner desmotubule (ER)
•Symplastic channel for cell-cell movement
•Movement of large nucleic acids and proteins may be facilitated
by movement proteins
Figure 2-2
Primary pit fields
parenchyma
sclerenchyma
Raven, 3-33
Developing sieve tube element - plasmodesmata develop
into pores = sieve plate
Raven 24-22
Sieve tube elements and companion cells
Raven, 24-19
Plant development is continuous, reiterative and plastic
determinate = restricted in time and space (e.g. flower, leaf)
indeterminate = unrestricted (e.g. shoot)
totipotent
Figure 2-3
Cell fate
•Division, growth, differentiation
Cell intrinsic, cell extrinsic control?