Water homeostasis is crucial to the growth and survival of plants under water-related stress. Plasma membrane intrinsic proteins (PIPs) have been shown to be primary channels mediating water uptake in plant cells. Here we report the water transport activity and mechanisms for the regulation of barley (Hordeum vulgare) PIP aquaporins. HvPIP2 but not HvPIP1 channels were found to show robust water transport activity when expressed alone in Xenopus laevis oocytes. However, the co-expression of HvPIP1 with HvPIP2 in oocytes resulted in significant increases in activity compared with the expression of HvPIP2 alone, suggesting the participation of HvPIP1 in water transport together with HvPIP2 presumably through heteromerization. Severe salinity stress (200 mM NaCl) significantly reduced root hydraulic conductivity (Lp(r)) and the accumulation of six of 10 HvPIP mRNAs. However, under relatively mild stress (100 mM NaCl), only a moderate reduction in Lp(r) with no significant difference in HvPIP mRNA levels was observed. Sorbitol-mediated osmotic stress equivalent to 100 and 200 mM NaCl induced nearly identical Lp(r) reductions in barley roots. Furthermore, the water transport activity in intact barley roots was suggested to require phosphorylation that is sensitive to a kinase inhibitor, staurosporine. HvPIP2s also showed water efflux activity in Xenopus oocytes, suggesting a potential ability to mediate water loss from cells under hypertonic conditions. Water transport via HvPIP aquaporins and the significance of reductions of Lp(r) in barley plants during salinity stress are discussed.

Members of class II of the HKT transporters, which have thus far only been isolated from grasses, were found to mediate Na + -K + cotransport and at high Na + concentrations preferred Na + -selective transport, depending on the ionic conditions. But the physiological functions of this K

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Interaction of allyl isothiocyanate (AITC) with proteins and the digestibility of a protein-AITC adduct were studied in detail as a model reaction of isothiocyanate and protein in crushed Brassica seeds. Insulin, bovine serum albumin (BSA), ovalbumin and lysozyme as model proteins reacted slowly with AITC to cleave the disulfide bond in their cystine moieties followed by polymer formation. Besides this action, AITC also attacked free amino groups of lysine and arginine residues in protein to form their thiourea-like derivatives, detected by amino acid analyses and determination of the free amino group. Proteolytic

The molecular basis for regulation of dendritic cell (DC) development and homeostasis remains unclear. Signal regulatory protein α (SIRPα), an immunoglobulin superfamily protein that is predominantly expressed in DCs, mediates cell-cell signaling by interacting with CD47, another immunoglobulin superfamily protein. We now show that the number of CD11c(high) DCs (conventional DCs, or cDCs), in particular, that of CD8-CD4+ (CD4+) cDCs, is selectively reduced in secondary lymphoid tissues of mice expressing a mutant form of SIRPα that lacks the cytoplasmic region. We also found that SIRPα is required intrinsically within cDCs or DC precursors for the homeostasis of splenic CD4+ cDCs. Differentiation of bone marrow cells from SIRPα mutant mice into DCs induced by either macrophage-granulocyte colony-stimulating factor or Flt3 ligand in vitro was not impaired. Although the accumulation of the immediate precursors of cDCs in the spleen was also not impaired, the half-life of newly generated splenic CD4+ cDCs was markedly reduced in SIRPα mutant mice. Both hematopoietic and nonhematopoietic CD47 was found to be required for the homeostasis of CD4+ cDCs and CD8-CD4- (double negative) cDCs in the spleen. SIRPα as well as its ligand, CD47, are thus important for the homeostasis of CD4+ cDCs or double negative cDCs in lymphoid tissues.