Analyzes of Micromorphology and Elemental Composition of Pollen of Three Types of Male Sterile Lines in Brassica napus L. by SEM-EDS

Abstract

To elucidate the characteristics of pollen abortion in male sterile lines, scanning electron microscopy combined with energy dispersive x-ray spectrometry technology analysis (SEM-EDS) was employed to compare and analyze the morphological structure and mineral element content of pollen of 219A cytoplasmic male sterile line and double haploid DH01A male sterile line, as well as those induced by chemical hybridization agent SQ-1 male sterility in Brassica napus. The results showed that the pollen grains of the three types of male sterile lines all exhibited distinct irregular abortions. Among these, the physiological male sterile pollen induced by SQ-1 was the smallest average size of 320.14 ± 59.63 μm², with severe pollen deformities and the highest pollen abortion rate. The pollen grains of the DH01A male sterile line were smaller with a size of 451.38 ± 9.70 μm² and exhibited a deformed elliptical shape. The pollen grains of the 219A male sterile line had an average size of 633.94 ± 16.82 μm², which showed a relatively small difference in size compared to the fertile line, but the pollen was deformed and twisted into a long spherical shape. Moreover, the pollen exine sculpturing of all three types of sterile lines showed different degrees of damage to the reticular structure, perforation disruption, deformity and reduction in the number of colpi, and accumulation of granules in the perforation. These phenomena may be the causes of male sterility and abortion in rapeseed. Meanwhile, the EDS analysis of mineral elements in three types of male sterile lines indicated that the content of calcium (Ca) was significantly higher than that in the normal fertile line, while potassium (K) levels were lower in all three types of male sterile lines than in the fertile line. Additionally, magnesium (Mg) enrichment was detected in the pollen of the SQ-1 induced male sterile line, whereas Mg was not detected on the outer wall of the pollen from the genetic male sterile lines 219A and DH01A. Notably, sulfur (S) was only present in the genetic male sterile lines 219A and DH01A. These results suggested that there were significant differences in the morphological characteristics, elemental composition and content of pollen grains among different types of male sterility. These findings provide a foundation for elucidating the mechanisms underlying pollen abortion in male sterile lines.