The document discusses the types and structures of pits in plant cell walls, which facilitate communication and transport between adjacent cells. It describes various types of pits, including simple, bordered, half-bordered, blind, compound, and vestured pits, along with their characteristics and functions. It also highlights the similarities between pits and plasmodesmata in enabling substance exchange within plant cells.

1. PITS AND ITS
TYPES

2. PRESENTED BY:
Muhammad Sohail Riaz
PRESENTED TO:
Miss Iqra Munir

3. Pits
 Pits are thin portions of the cell wall that adjacent
cells can communicate or exchange fluid through
 Also known as the opening present in primary cell
wall
 Also known as primary pit field or primodial pits

4. Cont…..
 It is the portions of the cell wall that remained thin
even as secondary wall is formed
 Pits are un-thickened areas in the secondary walls of
plant cells
 They act as the channels for the transport
of water and minerals between adjacent cell
 Plasmodesmata are abundant in pits

6. Pit pair
 Generally each pit has a complementary pit
opposite of it in the neighboring cell
 These complementary pits are called pit pair

8. STRUCTURE OF PITS
 Pit chamber
 Pit aperture
 Pit membrane

9. CONT…….
Pit chamber:
 The pit chamber is the hollow area where the
secondary layers of the cell wall are absent
Pit aperture:
 The pit aperture is the opening at either end of the
pit chamber
 They are of round, elliptic, linear shape

10. CONT……
Pit membrane:
 The pit membrane is the primary cell wall and
middle lamella, or the membrane between adjacent
cell walls, at the middle of the pit chamber
 The pit membrane is common to both pits of a pit
pair and consists of two primary walls and a middle
lamella

12. Types of pits
 Simple pits
 Bordered pits
 Half bordered pits
 Blind pits
 Compound pits
 Vestured pits:

13. CONT…….
Simple pits:
 A pit pair in which the diameter of the pit chamber
and the diameter of the pit aperture are equal
 Parenchyma cells, phloem fibers, companion cells,
and trachieds of several flowering plants have
simple pits
 Two simple pits form a simple pit pair

14. CONT…….
 The simple pit may be circular, oval, polygonal,
elongated
 The main function of diffusion of protoplasm takes
place through these pits

15. CONT……..
Bordered pit:
 A pit pair in which the pit chamber is over-arched
by the cell wall, creating a larger pit chamber and
smaller pit aperture
 Vessels of many angiosperms and tracheids of many
conifers have bordered pits abundantly
 Two bordered pits make up a bordered pit pair
 They are more complex and variable in their
structure than simple pits

16. Structure of Bordered pits
 The overarching secondary wall which encloses a
part of the pit cavity is called, the pit border, which
opens outside by a small rounded mouth known as
pit aperture
 The overarching rim forms a border around the
aperture and thus named ‘bordered pits’
 The pit aperture may be circular, lenticular, linear or
oval

17. CONT……..
 The space between the closing membrane and the
pit aperture may be called the pit chamber
 The pit canal opens in the pit chamber by an outer
aperture and at the same time it opens in the lumen
of the cell by an inner aperture

19. Patterns of bordered pits
 The bordered pits in vessel walls of angiosperms
show three main types of arrangement:
 Scalariform
 Opposite and
 Alternate

20. CONT……
Scalariform
 If the pits are elongated or linear and make ladder-
like arrangement, it is called scalariform pitting
 The scalariform pitting is highly efficient in
conducting water
Opposite
 When the pits are arranged in horizontal pairs, it is
called opposite pitting

21. CONT……
Alternate
 When the pits occur in diagonal rows, the
arrangement is called alternate pitting

23. CONT…..
Half bordered pits:
 A pit pair in which a bordered pit has a
complementary simple pit
 Such a pit pair is called half bordered pit pair
Blind pits:
 A pit pair in which a simple pit has no
complementary pit

25. CONT……
Compound pits:
 A pit pair in which one cell wall has a large pit and
the adjacent cell wall has numerous, small pits
Vestured pits:
 In some dicotyledons, thin, simple or branched
sculpturings are present on the secondary wall that
forms the pit chamber or around the pit aperture
 Such pits are called vestured pits

27. Difference between simple and
bordered pits
 The bordered pit differentiates from a simple pit in
having a secondary wall arching over the pit cavity,
which constitutes the actual border and becomes
narrow like a funnel towards the lumen of the cell
 In the simple pit, no such arching of the secondary
wall and narrowing of the pit towards the lumen of
the cell occurs

28. Combinations in bordered pits
 The torus and margo are characteristic features of
bordered pit-pairs in gymnosperms, such as
Coniferales, Ginkgo, and Gnetales
 In other vascular plants, the torus is rare
The pit membrane is separated into two parts:
 A thick impermeable torus at the center of the pit
membrane, and the permeable margo surrounding
it

29. CONT…….
 The torus regulates the functions of the bordered
pit, and the margo is a cell wall-derived porous
membrane that supports the torus
 The margo is composed of bundles of microfibrils
that radiate from the torus
 The margo is flexible and can move towards either
side of the pit while under stress
 This allows the thick, impermeable torus to block the
pit aperture

30. CONT……
 When the torus is displaced so that it blocks the pit
aperture, the pit is said to be aspirated

31. Similarities Between Pits and
Plasmodesmata
 Both pits and plasmodesmata are present in
plant cells
 Plasmodesmata are abundant in pit
membranes
 Pits and plasmodesmata help plant cells to
communicate with each other and transport
substances between them