Intine

Intine is the inner layer of the pollen grain wall. It lies inside the outer exine and is in contact with the pollen cytoplasm. The exine is typically thick and resistant due to sporopollenin, while the intine is comparatively thin and more organic in composition. The intine is usually rich in cellulose and pectic substances, and may contain proteins and mucilage. It is formed during pollen development, primarily by material secreted by the pollen grain itself, with additional contributions from surrounding tapetal tissue in some species.

The intine plays a role in pollen hydration and germination. It often forms or thickens near apertures (germination pores) where the pollen tube will emerge. During germination, the intine ruptures or is degraded as the pollen tube grows, allowing the tube to emerge from the grain. In many species, the composition and structure of the intine influence pollen tube growth and the timing of germination, and it can vary considerably among plants. The intine is a useful feature in palynology for distinguishing taxa, though its details are species-specific.

See also: exine, pollen wall, pollen aperture, pollen tube.