Plasma membrane H+ -ATPases-mediated cytosolic proton gradient regulates pollen tube growth.

The polar growth of pollen tubes is essential for the delivery of sperm cells during fertilization in angiosperms. How this polar growth is regulated has been a long-standing question. An in vitro pharmacological assay previously implicated proton flux in pollen tube growth, although genetic and cellular supporting evidence was lacking. Here, we report that protons form a gradient from the pollen tube tip to the shank region and this gradient is generated by three members of Arabidopsis H+ -ATPases (AHAs). Genetic analysis suggested that these AHAs are essential for pollen tube growth, thus providing new insight into the regulation of polar growth.

Novel mode of action of polybia-MPI, a novel antimicrobial peptide, in multi-drug resistant leukemic cells.

As the frequent emergency of resistant tumor cells during treatment, the development of new agents with new modes of action attracts a great deal of interest. Polybia-MPI was a short cationic alpha-helical amphiphilic peptide that has selective toxicity toward cancer cells but no hemolytic activity. Its target selectivity is based on the binding preference to membranes containing anionic phospholipids by electrostatic driving. Its ability to make PI and trypan blue permeate into tumor cells at the same rate (within minutes), suggests a killing mechanism that involves plasma membrane perturbation. SEM and confocal microscopy experiments verified that the cell died as a result of acute injury and bursting, suggesting necrosis. As compared to the conventional chemotherapy, polybia-MPI targets at the cell membrane rather than enters into the cell to exert its action. So it is difficult for tumor cells to develop resistance to polybia-MPI during treatment and its action is not affected by the common multi-drug resistant mechanism. Although this is an initial study that looked at its in vitro activity rather than the in vivo activity, with the increasing resistance of conventional chemotherapy, polybia-MPI may offer a novel therapeutic strategy in the treatment of multi-drug resistant cancer.