Pollen - Pistil Interaction Vocabulary

Definition: Pollen-pistil interaction represents the continuous dynamic dialogue and interaction occurring between pollen grains and the sporophytic tissue of the pistil, specifically the stigma.
Temporal Boundaries:
- Initiation: The interaction begins immediately upon pollination (the landing/deposition of pollen grains onto the stigmatic surface).
- Termination: The process concludes with fertilization.
Span of Events: It encompasses all physiological and molecular events ranging from the deposition of the pollen grain on the stigma to the ultimate entry of the pollen tube into the ovule (specifically into the synergid).

Selectivity of Pollination:
- Pollination is a physical transport process and does not guarantee the delivery of the correct or compatible pollen.
- Foreign or non-compatible pollen types frequently land on the stigmatic surface alongside compatible pollen.
Pistil Recognition Ability:
- The pistil possesses the specialized capacity to recognize and accept compatible pollen belonging to the same species (intraspecific pollen).
- Incompatible or wrong types of pollen are identified and discarded by the pistil.
Molecular Basis: Compatibility and incompatibility reactions during the interaction are governed and determined by specialized protein interactions between the pollen and the pistil tissue.
Bimodal Outcomes of Recognition:
- Promotion: Recognition of compatible pollen triggers biological responses that promote pollen germination and pollen tube growth.
- Inhibition: Recognition of incompatible pollen leads to inhibition, preventing germination or stopping pollen tube elongation.
Intraspecific Physiological Mechanism: A dedicated physiological mechanism operates at the stigmatic surface to refuse non-compatible pollen and ensure that only intraspecific pollen germinates successfully.

Nutritional Dependence:
- The pollen grain lacks essential prerequisites required for autonomous germination.
- The stigmatic surface supplies these necessary biological prerequisites.
Germination Sequence:
- The compatible pollen grain absorbs water and nutrients from the surface of the stigma.
- Upon absorption, the pollen grain germinates and produces a pollen tube.
Chemotropic Guidance: The directional growth of the pollen tube through the style tissue is mediated and determined by specific chemical signals.

Path of the Pollen Tube: The pollen tube is pushed through the ovule to reach the embryo sac.
Synergid Penetration and Rupture:
- The tip of the pollen tube enters into one of the synergids within the embryo sac.
- Upon entry, the tip ruptures to release its internal contents (male gametes) for fertilization.

Gametophytic Competition: The environment of pollen-pistil interaction fosters intense biological competition among compatible pollen grains (gametes), ensuring that the most vigorous pollen tubes successfully participate in fertilization.
Role in Sexual Reproduction: Pollen-pistil interaction plays a fundamental role in driving successful sexual reproduction, preserving genetic integrity, and ensuring proper seed formation.

In Vitro Germination Capability: Pollen grains can be induced to germinate outside the living plant within a synthetic medium.
Role of Sucrose: Sucrose added to a synthetic medium actively induces pollen germination and stimulates pollen tube growth.
Role of Boric Acid: Boric acid facilitates and accelerates the rate of pollen germination and pollen tube elongation.