dehiscence

Dehiscence of the follicular fruit of Asclepias syriaca revealing seeds within.

Dehiscence is the opening at maturity of a plant structure, such as a fruit, anther, or sporangium, to release its contents.

Anther dehiscence

This is the final function of the anther that causes the release of pollen grains. The anther wall breaks at a specific site that runs the length of the anther. This site is observed as an indentation between the locules of each theca.

Before/During images of anther dehiscence in the common Milk Pea.

The stomium, and septum are two specialised cell types present at this site. The degeneration of the stomium and septum cells is part of a developmentally timed cell-death program. Initially the septum degenerates thereby establishing the stomium as the future site of anther wall breakage and pollen release. Expansion of the endothecial layer and lignification of the endothecial cell walls are required for dehiscence.

The process of anther dehiscence is coordinated precisely with pollen differentiation, floral development, and flower opening.

Fruit dehiscence

Typically a fruit develops from a gynoecium composed of fused carpels, which, upon fertilization, grow to become a silique that contains the developing seeds. After seed maturation, dehiscence takes place, and valves detach from the central septum freeing the seeds. This is also known as shattering and can be important as a seed dispersal mechanism.

This process is similar to anther dehiscence and the region that breaks (dehiscence zone) runs the entire length of the fruit between the valves and the replum (external septum).

At maturity, the dehiscence zone is effectively a non-lignified layer between a region of lignified cells in the valve and the replum. Shattering occurs due to the combination of cell wall loosening in the dehiscence zone and the tensions established by the differential mechanical properties of the drying cells in the silique.

Xerochasy is dehiscence that occurs upon drying; conversely, hygrochasy is dehiscence that occurs upon wetting.

Explosive dehiscence

Explosive dehiscence is a ballistic form of seed dispersal in which fruit dehiscence is violent and flings seeds far from the parent plant. This rapid plant movement can achieve limited dispersal without the assistance of animals. A notable example is the Sandbox Tree (Hura crepitans), which can fling seeds 100 meters (300 ft) and has been called the "Dynamite tree" due to the loud sound of its explosive dehiscence. Another example is Impatiens, whose explosive dehiscence is triggered by being touched, leading it to be called the "touch-me-not."

Association with crop breeding

Manipulation of dehiscence can improve crop yield since a trait that causes seed dispersal is a disadvantage for farmers whose goal is to collect the seed. Many of the agronomically important plants have been bred for reduced shattering.