There are two main types of self-incompatibility in plants: gametophytic self-incompatibility (GSI) and sporophytic self-incompatibility (SSI). In GSI, compatibility is determined by the genotype of the pollen grain itself, while in SSI it is determined by the genotype of the plant tissue that produced the pollen. Additionally, GSI typically occurs in plants with two-celled pollen that is easy to germinate in vitro, while SSI occurs in plants with three-celled pollen that is more difficult to germinate in vitro. The main mechanisms of rejection also differ between the two types.

1. DIFFERENCES BETWEEN GAMETOPHYTIC SELF
INCOMPATIBILITY AND SPOROPHYTIC SELF
INCOMPATIBILITY
( GSI vs SSI )

2. Differences between GSI and SSI
Gametophytic self incompatibility
• The incompatibility process
is determined by the
genotype of male
gametophyte(pollen) itself.
• Common in 2 celled pollen.
• Invitro germination is easy.
Sporophytic self incompatibility
• The incompatibility process is
controlled by genotype of the
sporophytic tissue of the plant
from which the pollen is
derived.
• Common in 3 celled pollen.
• Invitro germination is difficult.

3. Gametophytic self incompatibility
• Viable for long period or
long lived.
• Respiration rate is low.
• Wet stigma
• Rejection of incompatible
male gametophyte occur in
the style.
Sporophytic self incompatibility
• Viable for short period or
short lived .
• Respiration rate is high.
• Dry stigma
• Rejection reaction occur on
the stigma surface.

5. Gametophytic self incompatibility
• SI response after pollen
germination on stigma surface
in Papaver rhoeas.
• Exhibit 2 mechanism,
i. Programmed cell death of
pollen tubes after
penetration into stigma
surface.
ii. Inhibitory by cytotoxic stylar
RNases and degradation of
pollen tube RNA in
Solanaceae .
Sporophytic self incompatibility
• SI response take place early
at level of interaction
between pollen grain and
stigma surface.
• Exhibit single mechanism,
i. Rejection of self pollen at
stigma surface mediated
by receptor ligand
interactions.

6. Gametophytic self incompatibility
• In Solanaceae and Rosaceae
male determinant is S Locus
F Box or SFB and female
determinant is S locus
Ribonuclease(S-RNase).
• Example- Liliaceae, poaceae
and Solanaceae.
Sporophytic self incompatibility
• In Brassicaceae male
determinant is S locus
cysteine rich/SP11 and
female determinant is S locus
receptor.
• Example- Asteraceae,
Brassicaceae.