Androgenesis: Affecting the fate of the male gametophyte

Abstract

Embryogenesis can be initiated directly from microspores or pollen grains. This process is known as androgenesis and is dependent on elicitation of a stress response in microspores and pollen grains. The cell response to stress includes the synthesis of small molecular weight heat shock protein proteins (smHSPs), the predominant heat shock protein family in plants. smHSPs are synthesized in all microspores and pollen grains subjected to stress, whether or not they are potentially androgenic. smHSPs serve as a marker indicating that cells have responded to a stress stimulus. Apart from the need of the stress response, induction of androgenesis is also developmentally regulated. Thus, microspores and pollen grains that are predominantly at the late uninucleate to early bicellular stage of development, around the first pollen mitosis, can be induced to undergo androgenesis. Younger or older cells are unlikely to be induced to undergo this process. For example, once pollen maturation gene products begin to accumulate, bicellular pollen grains become fully committed to the pollen maturation process. Even under stress, such cells cannot be induced to undergo androgenesis. In early bicellular pollen, androgenesis is initiated from the vegetative cell (VC). In contrast to the situation during pollen maturation, the VC, when stressed, continues to synthesize DNA. This is one of the prerequisites for pollen‐derived embryogenesis. The generative cell does not contribute to this process. Reorganization of the cytoskeleton and its polar axis can be observed during androgenesis induction. The first division is usually symmetrical. Based on the time difference between the removal of stress, the first cellular division and the synthesis of the cell wall, the first microspore or pollen grain cell division in Brassica napus can already be termed androgenesis‐related.