The Absence of the AtSYT1 Function Elevates the Adverse Effect of Salt Stress on Photosynthesis in Arabidopsis.

Arabidopsis thaliana SYNAPTOTAGMIN 1 (AtSYT1) was shown to be involved in responses to different environmental and biotic stresses. We investigated gas exchange and chlorophyll a fluorescence in Arabidopsis wild-type (WT, ecotype Col-0) and atsyt1 mutant plants irrigated for 48 h with 150 mM NaCl. We found that salt stress significantly decreases net photosynthetic assimilation, effective photochemical quantum yield of photosystem II (ΦPSII), stomatal conductance and transpiration rate in both genotypes. Salt stress has a more severe impact on atsyt1 plants with increasing effect at higher illumination. Dark respiration, photochemical quenching (qP), non-photochemical quenching and ΦPSII measured at 750 µmol m-2 s-1 photosynthetic photon flux density were significantly affected by salt in both genotypes. However, differences between mutant and WT plants were recorded only for qP and ΦPSII. Decreased photosynthetic efficiency in atsyt1 under salt stress was accompanied by reduced chlorophyll and carotenoid and increased flavonol content in atsyt1 leaves. No differences in the abundance of key proteins participating in photosynthesis (except PsaC and PsbQ) and chlorophyll biosynthesis were found regardless of genotype or salt treatment. Microscopic analysis showed that irrigating plants with salt caused a partial closure of the stomata, and this effect was more pronounced in the mutant than in WT plants. The localization pattern of AtSYT1 was also altered by salt stress.

Specific expression of AtIRT1 in phloem companion cells suggests its role in iron translocation in aboveground plant organs.

IRON-REGULATED TRANSPORTER 1 (IRT1) is a central iron transporter responsible for the uptake of iron from the rhizosphere to root epidermal cells. This study uses immunohistochemistry, histochemistry, and fluorometry to show that this gene's promoter is also active in the aboveground parts, specifically in phloem companied cells. Promoter activity here was regulated by iron as it was in the roots. The promoter of the close IRT2 homolog was root-specific and only weakly active in the stem pits. RT-PCR showed the presence of a long splicing form exclusively in iron-deficient roots. The short splicing form was present in all organs regardless of the presence of iron. Immunohistology exhibited labeling on the periphery of the epidermal cells in matured root zone and intracellular patches in the meristematic cells. In the aboveground organs, the protein was seen in the whole volume of companion cells and in neighboring sieve elements as bodies. The fluorescent protein technique revealed the short IRT1 form to be present in the patches accumulated mainly around the nucleus and the long form as a continuous layer along the cells periphery. These results suggest that IRT1 has a role also in the aboveground organs.

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.

The Photoconvertible Fluorescent Protein Dendra2 Tag as a Tool to Investigate Intracellular Protein Dynamics.

Fluorescence proteins changing spectral properties after exposure to light with a specific wavelength have recently become outstanding aids in the study of intracellular protein dynamics. Herein we show using Arabidopsis SYNAPTOTAGMIN 1 as a model protein that the Dendra2 green to red photoconvertible protein tag in combination with confocal scanning laser microscopy is a useful tool to study membrane protein intracellular dynamics.

Changes in expression of BetV1 allergen of silver birch pollen in urbanized area of Ukraine.

The aim of the study was to determinate the level of expression of silver birch allergen Betv1 in pollen samples from different Ukraine areas by RT-qPCR SYBR Green assay. Protocol for quantifying the expression of Betv1 allergen was developed when testing of three housekeeping genes-cyclophylin, alpha-tubulin and transcription factor CBF1. Samples from urbanized area was analysed by real-time PCR when a sample from forest growth conditions was used as a calibrator. Real-time PCR based quantifying of Betv1 provides a useful method for rapid and sensitive analyses of this silver birch allergen. Our results show higher expression levels in samples from central parts of urbanized area as housing estates when compared to the samples from borders of the urbanized area.