Explain the characteristics and physiological effects of ethylene.

(N/A) Ethylene is a simple gaseous plant growth regulator.
$1$. Discovery: It was discovered by $H.H. Cousins$ from ripened oranges.
$2$. Physiological Effects:
- It promotes horizontal growth of seedlings,swelling of the axis,and apical hook formation in dicot seedlings.
- It promotes senescence and abscission of plant organs,especially leaves and flowers.
- It is highly effective in fruit ripening. It enhances the respiration rate during ripening,known as respiratory climacteric.
- It breaks seed and bud dormancy and initiates germination in peanut seeds and sprouting of potato tubers.
- It promotes rapid internode/petiole elongation in deep-water rice plants.
- It promotes root growth and root hair formation,thus helping the plants to increase their absorption surface.