Poster: Reproductive development

Abs # 344: Nuclease and protease activities associated with pollen collapse in S male-sterile maize

Presenter:	Riggio, Lauren B., lriggio@ufl.edu
Authors	Riggio, Lauren B. (A)   Siripant, May N. (A)   Chase, Christine D. (A)
Affiliations:	(A): University Of Florida

In the S cytoplasmic male sterility (CMS-S) system of maize, expression of mitochondrial open reading frames (orf355-orf17) conditions collapse of developing haploid pollen following the microspore mitosis. Based upon the role of mitochondria in signaling programmed cell death (PCD), we examined pre-collapse CMS-S microspores and collapsed CMS-S pollen for molecular features of PCD. Normal (N) cytoplasm microspores and starch-filling pollen served as controls. The DNA of the normal starch-filling pollen was intact, and the DNA of the sterile collapsed pollen was degraded into 30 kb fragments and smaller. A DNase activity gel was used to identify the nuclease potentially responsible for the degradation seen in the collapsed pollen. Two nucleases, with apparent molecular weights of 12 kDa and 13 kDa, were upregulated in the collapsed pollen. The cellular locations of these activities are under investigation. In addition to DNA degradation, protease activity is a feature that has been associated with PCD in mammals, and proteolysis is evident in protein samples extracted from collapsed CMS-S pollen. Protease activity gels revealed that collapsed CMS pollen shared a major protease activity with normal and CMS-S microspores at the molecular weight of 55 kDa. However, fertile starch-filling pollen had the major protease activity at 64 kDa. The protease class of each activity band is currently under investigation.