Evaporating brine from frost flowers with electron microscopy, and implications for atmospheric chemistry and sea-salt aerosol formation

An environmental scanning electron microscope was used for the first time to obtain well-resolved images, in both temporal and spatial dimensions, of lab-prepared frost flowers (FFs) under evaporation within the chamber temperature range from −5 °C to −18 °C and pressures above 500 Pa. Our scanning shows temperature-dependent NaCl speciation: the brine covering the ice was observed at all conditions, whereas the NaCl crystals were formed at temperatures below −10 °C as the brine oversaturation was achieved. Finger-like ice structures covered by the brine, with a diameter of several micrometres and length of tens to one hundred micrometres, are exposed to the ambient air. The brine-covered fingers are highly flexible and cohesive. The exposure of the liquid brine on the micrometric fingers indicates a significant increase in the brine surface area compared to that of the flat ice surface at high temperatures, whereas the NaCl crystals can become sites of heterogeneous reactivity at lower temperatures. There is no evidence that, without external forces, salty FFs could automatically fall apart to create a number of sub-particles at the scale of micrometres as the exposed brine fingers seem cohesive and hard to break in the middle. The fingers tend to combine together to form large spheres and then join back to the mother body, eventually forming a large chunk of salt after complete dehydration. A present microscopic observation rationalizes several previously unexplained observations, namely, that FFs are not a direct source of sea salt aerosols and that saline ice crystals under evaporation could accelerate the heterogeneous reactions of bromine liberation

Endosidin 2 accelerates PIN2 endocytosis and disturbs intracellular trafficking of PIN2, PIN3, and PIN4 but not of SYT1.

We established that Endosidin2 (ES2) affected the trafficking routes of both newly synthesized and endocytic pools of PIN-FORMED2 (PIN2) in Arabidopsis root epidermal cells. PIN2 populations accumulated in separated patches, which gradually merged into large and compact ES2 aggregates (ES2As). FM4-64 endocytic tracer labeled ES2As as well. Both PIN2 pools also appeared in vacuoles. Accelerated endocytosis of PIN2, its aggregation in the cytoplasm, and redirection of PIN2 flows to vacuoles led to a substantial reduction of the abundance of this protein in the plasma membrane. Whereas PIN-FORMED3 and PIN-FORMED4 also aggregated in the cytoplasm, SYT1 was not sensitive to ES2 treatment and did not appear either in the cytoplasmic aggregates or vacuoles. Ultrastructural analysis revealed that ES2 affects the Golgi apparatus so that stacks acquired cup-shape and even circular shape surrounded by several vesicles. Abnormally shaped Golgi stacks, stack remnants, multi-lamellar structures, separated Golgi cisterna rings, tubular structures, and vesicles formed discrete clusters