Microgametogenesis Lecture Notes

MICROGAMETOGENESIS *It is the process of formation of male gametophyte & the male gamets. The process takes place inside a two-celled sac of pollen, and further developments take place when the pollen flies on the stigma of carpell aster poli—nation. The pollengrains becomes vaculated and expands on leads the movement of nucleus from centice to onside. * The pollen nucleus eat this stage undergoes asyme- tric, mitotic division to farm -Large vegetative cell -Smallere genercative cell *Larger Vegetative cell ~ The vegetective cell is bigger where cells grows continuasly. The nucleus in vegetative cell is spherical or irregular with thin chromatin material. It is morce and RNA. metabolically active with many preoteins * Smaller generative cell 2 ~ It is smallert in size The cytoplasm is highly reduced with mitochondria EP. The nuciens of the generative cell occupies. the most of the cell volume. + The cytoplasm separated by of these two cell are 2 plasma membrane. initiany - The generative cell's wall is formed between two cell membranes and adjoins in intine. The generative cell pinchs 099 & move to the centre of vegetative cell. The calose deposition disappears, and the shape of the genericetive cell becomes susiform, which facilitates its passage through the pollen tube. Pollen Gormation (Male gemet formation) Male gamets are formed inside anthert which Looks like a treicemelare naturre. At this stafe the pollen possess a nucleus with small amounts of cytoplasm... to The pollen also have own plasma membrane colth ouf a fid cell wall made up of pollysacpheurides. rigid MEGU (Male gamet unit) The male gerem unit is the association beth, Vegetative nucleus & sperem cells (genercative cell). * It was first observed by Jensen and fisherr in plumbago. * The terem was coined by Dumas so who consi -derced. The MGU as a sunctional unit of fertilizan in Angiosperm. to The MGU consist of two sperem cells out of which one is biggert called sc1 & smallere SC2. The larger scy is eassociated with vegetative nue- -reus with few plastids & mitochondrcia. The smaller sc₂ is not associated with vegetative nuciens & conterins more plastids & few mitochondria- The SC1 quses with polare nucleus cwhere as 3C2 Juses with egg... Inheriasy gets associated with vegetative...... nucleus itbrough cytoplasmic, prajection tis... ralled clueping groove. Role 01 MGU to The MGU is responsible for fertilization by the development of pollen tube. The pollen grains moves in growing pollen tube by the association of MGU. → In maize and Barcling syngamy and triple Jussion is reduced. Hence mau helps in meandinating condincating the development of embrego & endosperm The cytoplasmic connection helps fore smooth trea nster of sperm cell between vegetative cell and generative cell. 1159 NPC NPC is an artificial system of classification of pollen based on three features ay Number 1 d narby positionsIONA c) character It was proposed by ERDDMAN According & STRAKA 10 1961 ח. to this the pollen grain has Arithiem- atic caredial numbere consist of three digits The 1st digit revels apperaturce Coumber) the presence or absence of to The and digit explains the position of apperaturce Like distal, proximal, global ore, mescidional The thired digit explains the charactere like cir- cusar, oval, elongated or compound etc. * The term apperceturre is used fore preparing keys gor classification of pollien greains. (A)Classification based on number of apperature mm~~ Pollens are classified into I groups with 1 Sugging treme (Ni-NG). Ng = one appercature-monotreme N₂= Two cappercaturce- Ditrceme N= seven appercaturce-polytreme When pollen grains have an irregular spaced" apperaturce it is called Anoticeme (B) Classification based on position) (p) streands fore position where seven group are found (Po-Po) When pollen grains. have unknown position of apperature it is called 'Po'. * when polien greain have one apperaturce on provi- mal end it is (py) ortiu catatiremes OSRA when pollen grains have, apperrature on distal position t is (P3' which may be called Anatremeso →Py-zonotremes Ps - Dizonoticame Po-pantottremes →P₂-Anacatatiremesel c) Classification based on character of appercetune It is also seven groups (Co-(6) Co when apperrafurce of charactere is uncertain - Leptoma (2-Treichotomocolpate A Co-op colpate hy of - porcete 5 - colporcate Co Porcoreate Dalynology to the science which deals with the study of pollens is known as biology "Palynology oni pollen * The pollen biology involved the study of following *Dollen proteins noitizen the sorrorts 7) to These are the different proteins "gound in the form of enzyme in distercent layers. of pollen. These proteins where first. Identified by Barcanova in 1961 in Paeonia & Amaryllis ..... The proteins are distributed to ab Intine Layer: Id following manners!. * The proteins are the products of & gametophytic orcigin. cytoplasm to The proteins are found in the cellulosic layer in the forem of radially arranged tubules ord tagentially oreinted. These are formed when sporces are released gorom the tetravids. →The plasmalemma tubules sealed. aff from the cell surface and deposition occurrs... by Exine Layer to These are the proteins located in the cavities between baculae of the tectate grain ore, in the depression of the greains.. These are originated from sportophytic tapetum tissues. * The exine preoteins are divided into tevo layers one being sexine and othere nexine. to The proteins are distributed into diggercentiafe cavities depression cand inner layers of exines. cy Superficial Layer The proteins are located in diggerent re- -gion. Like tapetum and pollen kitt.. * Pollen kitt emits a particulare oredere to cattre- -act insects that some food tur *Pollen enzymes Dollen enzymes are found in disferrent which are in the forem, of. mucil 0f. mucllage pollen wall and glycoproteins The exine layer contain estercase enzyme while the intine contains acid phosphatase. *Lastry diggercent entymes like dehydrogenase...... oxydase, treanspercase, hydrolase, yase & ligase auce Hound. *protein viability *pollen viability is the ability of pollen greaing to pereforem, flis Junction of delivery mate geomets to the embryo sac. *paien viability is an index of quality and vigour of the pollens. The pollen viability is affected by pollen cytology humidity and temperrepelice of the environment. The best viability is observed at low. rueractive humidity (0-30%) and tempercafurce beth. (0-10°C). Desiccation Holercent pollens at the pollens which remains viability, aftere dehydration. pollen viability is lasted by two tastes ore, expe- -riment. 76 Tetrazolium taste Pollen grains are added to tetra- -zolium solution for 30 minutes gives reeddish colour due to the formation of formarone.wo fi Florochromatic rean. taste or, Pluroscein diacetate ~ teiste (FDA). ~ Plasma membrane of the pollen due to estarcase produce bright Huroscein *Pollen storage Do It is the process of keeping the poners grains of economically important plants for a continuous period, keeping in view their vigour and viability. 'Pollen stokage ta nequuticed govern conservahon 67 gorem plasma os the species like Arcutts, focage, споре and celceapg. go shoret terem storage is done by using sonystrcating agent like sillca gen, sulphuric acid which morgene humidity oreganic solvents like bencene eyelohorare, other alte used at ye to proserve the pollone sou 30-40 days bb Long terem storage Creyogente storage, involves. deep grceezing ent the pollens of unica low tempera ture (-1960) 24 тоstly plant pollens of pouceme gamily. Lyophilization is the vacuum drying that encourages the Firing of polliens out 80°c with gases like hellum and nitreogen. ex Pollen Germination It is the process by which physiological and developmental changes occur in a pollen grain with the formation of a pollen tube. (Germination occurs on the compactable stigma of the gemale Flower wnerce water is neccessary. The pollen tube grows towards the ovule underr sultable conditions like presence of borcon, calcium Anositol etce find me of boump, at t a pseudomonad This is a condition wherce tetrrades are gormed without partition walls between the four compartments of a pollens. This condition Looks Like a monad wherce out of the four nucleus one developes normaly & rest 3 disappearts masting for *It is also called cryptoterated. Ex: Cyperaceae by poryad The tetread cells upon cell division forms 8-64 cells, which forems a unit at This is called poryad. maturity. EX It is found in the family amonaceae cy Massulae These are the polyades contains 8-64. do Polynia It is a combined mass of pollen grains in a plant, which are the product of the one anther and transferred as a single unit durring pollination. A polynia is called corpusewum when attached by two arems called translater. It is found in the gamily asclepidacere, arcchidaceae & calotropis