|Smith, Marianne - IOWA STATE UNIVERSITY|
|Horner, Harry - IOWA STATE UNIVERSITY|
Submitted to: American Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 23, 2001
Publication Date: N/A
Interpretive Summary: Sterility in plants can affect both male and female reproductive function simultaneously or separately. Male-sterile, female-fertile plants are desired by plant breeders to use to produce hybrid seed. The resulting hybrid plants have increased yield, and more tolerance to pests, and environmental stresses. A male-sterile, female-fertile soybean was identified. Our objective was to determine where in the male-reproductive process does this abnormality occur that results in male sterility. Sexual reproduction proceeded normally until late in male development. Certain organs (called mitochondria) became disorganized. This resulted in abnormal starch accumulation in the developing male cells. Without starch as a food source the male cells failed to develop and died. The end result was male sterility. This research will provide growers with soybean lines with resistance to insects and disease resulting in increased yields.
Technical Abstract: Cytoplasmic male sterility (cms) has been described in soybean but no microscopic investigation has been published. The purpose of this microscopic study was to establish the developmental sequence leading to sterility in a cms soybean line found to be environmentally stable, and to demarcate the temporal and spatial parameters that result in degeneration of the male cells. Light microscopy showed an abnormal development and/or premature degeneration of the tapetum after meiosis II, but the microspores and pollen persisted until after microspore mitosis. The pollen grains never completely filled with reserves. A premature formation of the endothecium also was evident. Histochemical staining for water-insoluble carbohydrates revealed abnormal starch accumulation in the anther walls that coincided with the lack of filling of the pollen grains. Electron microscopy identified early degeneration of the inner membrane of the mitochondria in the tapetum as an initial change associated with abnormal organelle structure. Subsequently, the tapetal endoplasmic reticulum exhibited atypical concentric rings. Pollen grains displayed mitochondria with unusually enlarged inner mitochondrial spaces, degraded plastids, only a rudimentary intine, and no starch or lipid reserves. Results link mitochondrial degeneration, premature formation of the endothecium, and energy deprivation to male sterility.