GTR-Mediated Radial Import Directs Accumulation of Defensive Glucosinolates to Sulfur-Rich Cells in the Phloem Cap of Arabidopsis Inflorescence Stem

In the phloem cap region o i Arabidopsis plants,sulfur-rich cells(S-cells)accumulate>100 mM glucosinolates(GLS),but are biosynthetically inactive.The source and route of S-cell-bound GLS remain elusive.In this study,using single-cell sampling and scanning electron microscopy with energy-dispersive X-ray analysis we show that two GLS importers,NPF2.10/GTR1 and NPF2.11/GTR2,are critical for GLS accumulation in S-cells,although they are not localized in the S-cells.Comparison of GLS levels in S-cells in multiple combinations of homo-and heterografts o lg t r l gtr2,biosynthetic null mutant and wild-type plants indicate that S-cells accumulate GLS via symplasmic connections either directly from neighboring biosynthetic cells or indirectly to non-neighboring cells expressing GTR1/2.Distinct sources and transport routes exist for different types of GLS,and vary depending on the position of S-cells in the inflorescence stem.Based on these findings,we propose a model illustrating the GLS transport routes either directly from biosynthetic cells or via GTR-mediated import from apoplastic space radially into a symplasmic domain,wherein the S-cells are the ultimate sink.Similarly,we observed accumulation of the cyanogenic glucoside defensive compounds in high-turgor cells in the phloem cap of Lotus japonicus,suggesting that storage of defensive compounds in high-turgor cells may be a general mechanism for chemical protection of the phloem cap.

A Single Amino-Acid Substitution at Lysine 40 of an Arabidopsis thaliana α-tubulin Causes Extensive Cell Proliferation and Expansion Defects

Microtubules are highly dynamic cytoskeletal polymers of α/β-tubulin heterodimers that undergo multiple post-translational modifications essential for various cellular functions in eukaryotes. The lysine 40 （K40） is largely conserved in α-tubulins in many eukaryote species, and the post-translational modification by acetylation at K40 is critical for neuronal development in vertebrates. However, the biological function of K40 of α-tubulins in plants remains unexplored. In this study, we show in Arabidopsis thaliana that constitutive expression of mutated forms of α-tubulin6 （TUA6） at K40 （TUA6K40A or TUA6K40Q ）, in which K40 is replaced by alanine or glutamine, result in severely reduced plant size. Phenotypic characterization of the 35S：TUA6K40A transgenic plants revealed that both cell proliferation and cell expansion were affected. Cytological and biochemical analyses showed that the accumulation of α- and β-tubulin proteins was significantly reduced in the transgenic plants, and the cortical microtubule arrays were severely disrupted, indicating that K40 of the plant α-tubulin is critical in maintaining microtubule stability. We also constructed 35S：TUA6K40R transgenic plants in which K40 of the engineered TUA6 protein is replaced by an arginine, and found that the 35S：TUA6K40R plants were phenotypically indistinguishable from the wild-type. Since lysine and arginine are similar in biochemical nature but arginine cannot be acetylated, these results suggest a structural importance for K40 of α-tubulins in cell division and expansion.

A minimum volume prediction of spacer based on turbulent dispersion theory: Model and example

During cementing operations involving cement slurry contamination,problems often occur due to the inaccurate calculation of the space fluid volume.This study,based on the turbulent dispersion theory,developed a minimum volume calculation model of spacer fluid to prevent cement slurry contamination.This model was used to analyze influence factors and practical calculations.The results indicated that the minimum volume of spacer fluid increase with the eccentricity of casing and injection rate and decrease with the density of cement slurry.Additionally,the better rheological properties of the cement slurry and spacer fluid would increase the volume of the spacer fluid.Furthermore,this model fitted actual field data better than other heat calculation models.