introduction anther wall sporogenous tissues microsporogenesis

1. Presented by:-
Gosai Rajeshwariben v.
M.sc sem-2 (BOTANY)
Paper –CBO 404
Roll no : 6
Department of life sciences,
HNGU Patan.

2. ● Introduction.
●Anther Wall
● Sporogenous tissues
● microsporogenesis

3. → In considering the course of events leadi
-ng to the origin of the embryo,we must
first deal with the development of the
micro and megasporangia.
→ It is the microsporangium which produces
the microspores and eventually the male
gametophyte.

4. → Microsporangium gives rise to male game
-tophytes.
→ Microsporangia are notable in spikemosse
-s and minority of ferns.
→ In gymnosperms and angiosperms , the
microsporangia produce the microsporo
-cyte, also known as the microspore mother
cell, which then creates four microspores
divide through mitosis to create pollen grains.
→ The term is not used for bryophytes.

5. → A mature anther wall consists of four layer
(a) Epidermis
(b)Endothecium
(c) Middle layer
(d)Tapetum
(a) Epidermis
-outer layer
-it undergoes anticlinal divisions only to keep pace
with the rapidaly enlarging internal tissues.
-protection.

6. Fig: stages in the development of anther
(b) Endothecium:
-just below the epidermis.
- usually single layer , multilayer (Nicotiana tabacum.)

7. - The cells of the endothecium become radially elongated
and form their inner tangential wall fibres run upwards
ending near the outer Wall of each cell.
-High content of cellulose material.
-The endothecial layer is responsible for the dehiscence of
the anther due to differential hygroscopic expansion of
the outer and the inner tangential wall.
(c) Middle layer :
-Next to the endothecium.
-1-3 layers of cells constituting middle layer or there
may be several as in Lilium.
-As a rule, all of them become flattened and crushed
at the time of meiotic division in the microspore

8. mother cell, however , there are a few exceptions where
outermost layer persists for a long time.
-The cells are generally rich in reserve foods such as starch
, thus suggesting its nutritive role in pollen development.
(d) Tapetum:
-The innermost layer.
-Its considerable physiological importance because all
the food materials entering into the sporogenous
tissues pass through it.
-composed single layer , which shows dese cytoplasm
and distinct nucleus.
→NUCLEAR DIVISION OF THE TAPETUM
1. Endomitosis 2. Retitution nuclei 3.Polytenu

9. → TYPES OF TAPETUM
1. Amoeboidal tapetum.
2.Secretary or glandular.

10. → The primary sporogenous layer cells give rise to the
microspore mother cells or the pollen mother cells.
→ The sporogenous cells in normal way divide several
times mitotically before functioning as pollen mother
cells.
→ In certain cases the primary sporogenous cells may
either show only few division or no division at all ,
thus giving rise to a very small group of sporogenous
cells or the primary sporogenous cells themselves
function directly as the microspore mother cells.

11. In the beginning of their formation the microspore mother
cells or the pollen mother cells remain closely packed but
as the anther enlarges in size, the pollen sac also increases
in size , the microspore mother cells also enlarge in size,
become spherical in shape and get loosely arranged.
→ some of sporogenous cells are nonfunctional and serve
as the food material for the functional m.m cells .
Fig: sporogenous tisses

12. →The microspore mother cells which are at first polygonal
and closely packed gradually become rounded and
loosely arranged in the rapidly enlarging microsporangium.
→ Although all of the mother cells in an anther are capebale
of giving rise to pollen grains but some of them may
degeneratre and serve as food material for the remain
-ing cells which give rise to pollen grains.
→ Each functional spore mother cell produces four micro
-spores or pollen grains.

13. Fig: Microsporogenesis

14. → Cytomixis:
- while studying oenothera gigas and O.blennis ,gates
for the first time observed a frequent migrastion
of chromatic material from one microspore mother
cell into another, and called it cytomixis.
- This phenomenon has also been reported in several
other plants.
- In coreopsis tripteris, cytomixis occurs at the end of
the meiotic divisions but the multi nuleate cells
formed in this way again break up into smaller units
of one or two nuclei.

15. → Cytokinesis:
Fig: Formation of megaspores from a megaspore mother cell

16. - This division of the microspore mother cells may be of
the successive and simultaneous type.
-In the successive type, a cell plate is developed immedi
-ately after the first meiotic division and another in
each of the two daughter cells after he second meiotic
division.
-However, in the simultaneous type, no wall is formed
after the first division and the mother cell becomes
separated into four parts when the meiotic divisions
are over.

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