The agonist sensitivity of the calcium-sensing receptor (CaR) can be altered by protein kinase C (PKC), with CaR residue Thr 888 contributing significantly to this effect. To determine whether CaR T888 is a substrate for PKC and whether receptor activation modulates such phosphorylation, a phospho-specific antibody against this residue was raised (CaR pT888 mobilization rather than oscillations (9). Whereas this suggests that PKC-mediated CaR phosphorylation regulates CaR function, no reagents have existed previously for investigating CaR phosphorylation directly. Thus, we have developed a phospho-specific antibody that recognizes the phosphorylated form of CaR T888 , this residue being chosen because its mutation elicited the greatest effect on CaR function of the putative PKC sites. EXPERIMENTAL PROCEDURESMaterials-The calcimimetics NPS R-467 and S-467 and the calcilytic NPS-89636 were a kind gift of Dr. E. F. Nemeth and NPS Pharmaceuticals, Inc. (Toronto, Canada). Fura-2/AM was from Invitrogen and Gö6976, PKC␤-selective inhibitor (anilinomonoindolylmaleimide), and endothall thioanhydride (7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic acid) were from Calbiochem (EMD Biosciences, Inc., San Diego, CA). Horseradish peroxidase-conjugated anti-mouse and anti-rabbit secondary antibodies were from DakoCytomation (Ely, Cambridgeshire, UK). Unless stated otherwise, all other chemicals were purchased from Sigma.Cell Culture-HEK293 cells, stably transfected with human parathyroid CaR (6), were a gift from Dr. E. F. Nemeth (NPS Pharmaceuticals). Cells were grown in Dulbecco's modified Eagle's medium supplemented with 10% heat-inactivated fetal * This work was supported in part by Biotechnology and Biological Sciences Research Council Grant BBSB04986. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

SUMMARYThe depletion of cellular zinc (Zn) adversely affects plant growth. Plants have adaptation mechanisms for Zn‐deficient conditions, inhibiting growth through the action of transcription factors and metal transporters. We previously identified three defensin‐like (DEFL) proteins (DEFL203, DEFL206 and DEFL208) that were induced in Arabidopsis thaliana roots under Zn‐depleted conditions. DEFLs are small cysteine‐rich peptides involved in defense responses, development and excess metal stress in plants. However, the functions of DEFLs in the Zn‐deficiency response are largely unknown. Here, phylogenetic tree analysis revealed that seven DEFLs (DEFL202–DEFL208) were categorized into one subgroup. Among the seven DEFLs, the transcripts of five (not DEFL204 and DEFL205) were upregulated by Zn deficiency, consistent with the presence of cis‐elements for basic‐region leucine‐zipper 19 (bZIP19) or bZIP23 in their promoter regions. Microscopic observation of GFP‐tagged DEFL203 showed that DEFL203‐sGFP was localized to the apoplast and plasma membrane. Whereas a single mutation of the DEFL202 or DEFL203 genes only slightly affected root growth, defl202 defl203 double mutants showed enhanced root growth under all growth conditions. We also showed that the size of the root meristem was increased in the double mutants compared with the wild type. Our results suggest that DEFL202 and DEFL203 are redundantly involved in the inhibition of root growth under Zn‐deficient conditions through a reduction in root meristem length and cell number.