Ultrastructure and cytochemistry of Eucalyptus globulus(Myrtaceae) pollen grain

The morphology, ultrastructure and cytochemistry of Eucalyptus globulusmature pollen were investigated using light (LM), scanning electron (SEM) and transmission electron microscopy (TEM). The pollen morphology is typically myrtaceous with a suite of characters that allows its distinction from the pollen of other Eucalyptusspecies. The exine consists of a thick endexine and a massive ectexine with hardly distinguishable columellae. The endexine is 2-layered towards the apertural regions where the inner and spongy-granulate layer forms a continuous colpus membrane and a thinner pore membrane. Under the pores the intine is 3-layered forming complex onci. The spindle-shaped generative cell (GC) is deeply undulated and located in a cup-shaped depression of the vegetative cell (VC) nucleus. In the dense VC cytoplasm the main storage reserves are lipid bodies and insoluble carbohydrates in the cytosol, although proteins are also present. The most characteristic feature of the VC cytoplasm is the extremely well-developed rough endoplasmic reticulum (RER), which forms extensive stacks filling large areas of the central cytoplasm. Single RER cisternae are also scattered throughout the cytoplasm, most of them establishing an intimate association with lipid bodies, storage vacuoles, the VC plasmalemma and a few proplastids. The physiological significance of the RER stacks and of the RER cisternae association with other cell components, as well as the structure and function of an endomembrane compartment, found only in the freeze-fixed pollen, are discussed.http://www.informaworld.com/10.1080/0017313080192336

NanoSIMS analysis of arsenic and selenium in cereal grain.

*Cereals are an important source of selenium (Se) to humans and many people have inadequate intakes of this essential trace element. Conversely, arsenic (As) is toxic and may accumulate in rice grain at levels that pose a health risk. Knowledge of the localization of selenium and arsenic within the cereal grain will aid understanding of their deposition patterns and the impact of processes such as milling. *High-resolution secondary ion mass spectrometry (NanoSIMS) was used to determine the localization of Se in wheat (Triticum aestivum) and As in rice (Oryza sativa). Combined synchrotron X-ray fluorescence (S-XRF) and NanoSIMS analysis utilized the strengths of both techniques. *Selenium was concentrated in the protein surrounding the starch granules in the starchy endosperm cells and more homogeneously distributed in the aleurone cells but with Se-rich hotspots. Arsenic was concentrated in the subaleurone endosperm cells in association with the protein matrix rather than in the aleurone cells. NanoSIMS indicated that the high intensity of As identified in the S-XRF image was localized in micron-sized hotspots near the ovular vascular trace and nucellar projection. *This is the first study showing subcellular localization in grain samples containing parts per million concentrations of Se and As. There is good quantitative agreement between NanoSIMS and S-XRF