Annexin is a highly conserved protein family binding to phospholipids in a calcium-dependent manner,while different annexins harbore various gene expression patterns and protein subcellular localizations.Eight arnexins in Arabidopsis thaliana (AnnAt) have been identified.These annexins play important roles in growth,development and responses to stress.Annexin 2 in Arabidopsis thaliana (AnnAt2) is involved in root secretion and auxin-mediated geotropism growth of root cells.However,the molecular mechanism remains undefined.The subcellular localization of proteins is a crucial cue to explore their biological functions and molecular mechanisms.In the current study,the subcellular localization of AnnAt2 was investigated with fusion protein expression and colocalization with green fluorescent protein (GFP) of organelles or specific fluorescence dyes,respectively.Our results revealed that AnnAt2 was localized simultaneously in cytosol,nuclei,Golgi apparatus and endoplasmic reticulums.These data indicates that the translation and transportation of AnnAt2 are complex.AnnAt2 was colocalized with actin filaments marked by GFP in transgenic ArmAt2-mCherry Arabidopsis lines,suggesting that AnnAt2 might be involved in cell secretion via dynamic regulation of microfilaments and microfilament-mediated vesicles transport in Arabidopsis.These data provide the experimental evidence for further studies of protein translation,transport pathways and the functions of AnnAt2.

To elucidate the functional differences in how Arabidopsis stigmas regulate pollen hydration and germination, we analyzed receptivity of stigmas, epidermal surfaces (leaves, stems of inflorescence bolts, and floral organs), and an abiotic surface (cover glass) for pollen hydration and germination. Using 65% relative humidity (RH), we found that mature pollen grains were able to hydrate and germinate on stigmas at flower developmental stages 9–13, but not on the distal end of pistils at stage 8, epidermal surfaces, or glass. Furthermore, under 100% RH, pollen grains could hydrate on all tested surfaces, but pollen germination was observed only on the young floral organs (stages 9–12) and the stigmas at stages 9–13. The distal ends of pistils at stage 8, the epidermal surfaces, and the cover glass did not support pollen germination even under 100% RH. Our results indicate that pistil factors regulating pollen hydration and germination are synthesized at stage 9 when stigmatic papillar cells begin to develop. Although pistil factors involved in pollen hydration may only be present on the stigma, the factors involved in pollen germination may localize on both the stigma and surfaces of unopened floral organs.

The dynamic remodeling of actin filaments in guard cells functions in stomatal movement regulation. In our previous study, we found that the stochastic dynamics of guard cell actin filaments play a role in chloroplast movement during stomatal movement. In our present study, we further find that tubular actin filaments are present in tobacco guard cells that express GFP-mouse talin; approximately 2.3 tubular structures per cell with a diameter and height in the range of 1-3 µm and 3-5 µm, respectively. Most of the tubular structures were found to be localized in the cytoplasm near the inner walls of the guard cells. Moreover, the tubular actin filaments altered their localization slowly in the guard cells of static stoma, but showed obvious remodeling, such as breakdown and re-formation, in moving guard cells. Tubular actin filaments were further found to be colocalized with the chloroplasts in guard cells, but their roles in stomatal movement regulation requires further investigation.