SEXUAL Incompatibility. opa

SEXUAL INCOMPATIBILITY : 

SEXUAL INCOMPATIBILITY Introduction Types of incompatibility Genetic basis of Self-incompatibility Level of its occurrence Physiology and Biochemistry Biological significance Methods to overcome Incompatibility

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REFERENCES - JAIN, PANDEY, SINGH EMBRYOLOGY OF ANGIOSPERM

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PRESENTED BY LALAWMPUIA AND P.C LALREMRUATA

INTRODUCTION : 

INTRODUCTION Not all the pollen that reaches the stigma succeeded in effecting fertilization. Pistil is adequately equipped with sexual device to allow mating type to effect fertilization. What is Incompatibility? A Pistil carrying functional female gametes fail to set seeds pollination with viable and fertile Pollen capable of bringing fertilization in another pistil, the two are said to be incompatible. – The phenomenon is known as SEXUAL INCOMPATIBILITY .

1. INTERSPECIFIC – #Between individuals of different Species. # Heterogenic. Controlled by more than one gene. Linskens(1975) #Basis of new races & prevents free Cross-Pollination : 

TYPES OF SEXUAL INCOMPATIBILITY 1. INTERSPECIFIC – #Between individuals of different Species. # Heterogenic. Controlled by more than one gene. Linskens(1975) #Basis of new races & prevents free Cross-Pollination 2.SELF INCOMPATIBILITY – #Inability of a plant producing functional male and female gametes. #TWO TYPES- 1.Heteromorphic and 2.Homomorphic *Heteromorphic : - Characterised by occurrence of two (distyly) or three (tristyl) morphologically distinct mating type. -Due to inhibition of growth of pollen. -Features *Homomorphic :- Indistinguishable type. Categorized into:- (i)Gametophytic self-incompatibility(GSI): Determined by genotype of male gametophyte itself. Eg.Graminaceae, Liliaceae, Solanaceae &Trifolium. (ii)Sporophytic self-incompability(SSI): Controlled by genotype of the sporophytic tissue of the plant from which the pollen is derived. Eg,. Compositae & Cruciferae.

GENETIC BASIS OF SELF - INCOMPATIBILITY : 

GENETIC BASIS OF SELF - INCOMPATIBILITY Opposition S-alleles. East & Mangalsdorf(1925). Incompatible reaction are controlled by S-gene having several alleles. Pollen grain possessing S-alleles common to anyone of the two allele in the cells results in incompatibility. Pollen with S-alleles other than any two alleles in the pistil will effect Fertilization. Fig; Response of pollen on S1S2 plant showing gametophytic incompatibility. A- No Pollen from S1S2 plant is able to effect fertilization. B- Only S3 plant succeded in fertilizing ovules resulting into 50% fertilization.

LEVEL OF OCCURANCE OF INCOMPATIBILITY : 

LEVEL OF OCCURANCE OF INCOMPATIBILITY POLLINATION- Self-pollination is check in some plants through dichogamy, herkogamy&Unisexuality. Because of this, Self incompability occur in some plant. PROGAMIC PHASE- Inhibition occur at any stage from pollen germination to the discharge of male gamete in the incinity of the egg. (a)On the stigma- Pollen fail to germinate. eg,.Cruciferae & Graminae. (b)In the style- Pollen tube fail to grow through the full length of the style. SYNGAMY – In some plants like Gasteri, Hemerochallis, fusion of male and female gametes fail to occur.

PHYSIOLOGY AND BIOCHEMISTRY : 

PHYSIOLOGY AND BIOCHEMISTRY Two reactions are recognised as given below : 1.RECOGNITION REACTION- Occurs at the molecular level and by this the pistil recognises whether a particular grain is to be accepted(Compatible) or Rejected (Incompatible). In SSI system and certain GSI system the recognition reaction sets in almost immediately after the pollen comes in cintact with the stigma. Generally, in GSI systems, the recognition reaction occur inside the pistil. 2.REJECTION REACTION – It may occur in the stigma inhibiting pollen germination or preventing entry of pollen tubes into the stigma(SSI system) or it may occur in the style inhibiting pollen tube growth or leading to bursting of the tube into style(GSI system).

BIOLOGICAL SIGNIFICANCE OF INCOMPATIBILITY : 

BIOLOGICAL SIGNIFICANCE OF INCOMPATIBILITY A balance in breeding and outbreeding of plant is regulated by intraspecific and interspecific. Prevents extensive selfing of plant which leads to highly homozygous individual. Interspecific incompatibility brings about reproductive Isolation. Possess serious problem in order to maintain the homozygosity of a species. In several plants where the anther has failed to yield pollen, Self-Pollination is an important approach to achieve Homozygous individuals. Interspecific incompatibility also prevent distinct Hybridisation.

METHODS TO OVERCOME INCOMPATIBILITY : 

METHODS TO OVERCOME INCOMPATIBILITY MIXED POPULATION : In this method, the stigma is disguised from recognising the incompatible pollen by pollinating it with a mixture of live incompatible pollen, and killed(by chemical or radiation) compatible pollen(termed Mentor pollen or Recognition pollen). By employing recognisition pollens, self incompatibility has overcome in Cosmos (Howlett et al.,1975) andPetunia hybrida(Sastri and Shivanna.,1975) and interspecific incompability in genus Populus(Knox et al.,1972). BUD-POLLINATION : In some plants, pollination at an early bud stage has proceed very effective in overcoming intraspecific incompatibility. At the bud stage (before anthesis), the stigma lacks the exudate to inhibit pollens and by chance pollination at that stage may effect fertilization. STUB-POLLINATION : In some plants incompability may be restricted to the stigma or the style is too long and the pollen tube could not reach the ovary. In this case, removal of stigma and part of style before pollination may prove helpful in overcoming incompatibility. INTRA-OVARIAN POLLINATION : In this technique, the ovary surface is sterilised with ethanol and two punctures are made in the wall- one for introducing the pollen suspension and the other to permit the escape of of air in the ovarian cavity(Kanta et al.,1962). Variable seeds following intra-ovarian pollination have obtained in several members of Papaveraceae such as Argemone mexicana, A. ochroleuca, Papaver somniferum and P. rhoeas.

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HEAT TREATMENT OF STYLE : Moderately high temperature (up to 50 C) are known to reduce the self-incompability reaction in certain plants. e.g,. Lilium longiflorum (Hooper et al 1967). IRRADICATION : Induce temporary breakdown of incompatibility reaction (Pandey, 1963), or alteration of the inhibitory substances in the style(Kumar and Hecht,1965). Irradication helpful in those systems where process are controlled gametophytically. CHEMICAL TREATMENT :Application of certain chemicals may prolonged the life of flowers (Choudhury 1965). Oenothera species by the application of p-chloromercuribenzoate ..Hodgdon and Hetch(1975). PARASEXUAL HYBRIDISATION : In 1969 a new approach was proposed to raised such hybrid which could not be produced through the conventional method of hybridisation because of sexual incompatibility. This technique involves fusion of isolated protoplast of somatic cell and is described as parasexual hybridisation. This involves the following step :- (a)Isolation of protoplasts. (b)Fusion of isolated protoplasts. (c)Cultured of hybrid protoplasts to regenerate whole plant.

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