The Dosage Dependent Effect of KAuCl4 On Pollen Germination of Crotalaria Retusa.

Unique catalytic properties of gold nanoparticles (AuNPs) could be achieved by manipulating their geometries.  Recent studies have shown the in planta synthesis of AuNPs and manipulation of their geometries in the roots of plant species. However, due to the lignified cell wall of the plant tissue, isolation of biomatrix-embedded AuNPs have not been met with any success so far. On the contrary, in vitro germinated pollen tubes have been successfully used for the isolation of sperm nuclei by subjecting them to osmotic shock. Several studies have used pollen systems for dosage-dependent effect of various toxic heavy metals. However, the effect of KAuCl₄ on the in vitro germination and pollen tube length is not known. Crotalaria retusa pollen shows high percent germination and is amenable for long-term storage.  C. retusa pollen was used to decipher the dosage-dependent (0 - 1000 ppm) effects of KAuCl₄ on percent pollen germination and tube length.  Interestingly, compared with the control (0 ppm) there were significant increases in both percent germination and pollen tube length upon supplementing the germination medium (GM) with 10 ppm of KAuCl₄. When GM is supplemented with > 100 ppm of KAuCl₄ it induced significant reductions in percent germination and pollen tube length. This study clearly demonstrates the hormesis effect of gold treatment on pollen germination and tube length.  However, supplementation of GM with increasing concentrations of KAuCl4 resulted in a significant decline in the pH values ranging from 6.25 (0 ppm) to 2.56 (1000 ppm). To further determine whether the observed effect was due to KAuCl₄ or because of the resultant shift in the pH, KAuCl₄-supplemented GM was buffered to pH 6.0 with MES buffer.  Interestingly, the dosage–dependent effects of buffered KAuCl₄-supplemented GM on pollen germination and tube length was largely comparable with those of the non-buffered KAuCl₄-supplemented GM.  Efforts are now underway to use the mass pollen culture for the synthesis of AuNPs that would be confirmed by Transmission Electron Microscopy and Energy Dispersive X-ray Spectroscopy.  [This research was supported, in part, by a grant from NSF HBCU-UP (#HRD-0625289) awarded to Dr. Sarwan Dhir* Ph.D., Director for the Center for Biotechnology, Fort Valley State University, Fort Valley, GA 31030].