Summary• PI-PLCs synthesise the calcium releasing second messenger IP 3 . We investigated the expression patterns of the Arabidopsis PI-PLC gene family and measured in vitro activity of encoded enzymes.• Gene specific RT-PCR and promoter-GUS fusions were used to analyse AtPLC gene expression patterns. The five available AtPLC cDNAs were expressed as fusion proteins in Escherichia coli .• All members of the AtPLC gene family were expressed in multiple organs of the plant. AtPLC1 , and AtPLC5 expression was localized to the vascular cells of roots and leaves with AtPLC5::GUS also detected in the guard cells. AtPLC4::GUS was detected in pollen and cells of the stigma surface. In seedlings, AtPLC2 and AtPLC3 were constitutively expressed, while AtPLCs 1 , 4 and 5 were induced by abiotic stresses. AtPLC1-5 were all shown to have phospholipase C activity in the presence of calcium ions.• AtPLC s showed limited tissue specific expression and expression of at least three genes was increased by abiotic stress. The differing calcium sensitivities of recombinant AtPLC protein activities may provide a mechanism for generating calcium signatures.

The effect of human recombinant tumor necrosis factor alpha (TNF-alpha) and interleukin 1 beta (IL-1 beta) on interleukin 2 receptor (IL-2R) expression on YT cells was examined. IL-2R expression was assessed by flow cytometric analysis with a monoclonal antibody to IL-2R (anti-TAC). TNF-alpha, like IL-1 beta, induced increased levels of IL-2R expression on YT cells with similar kinetics of induction. Maximum induction occurred at 20 to 30 hr. On a molar basis. TNF was less active than IL-1 beta. RNA isolated from TNF-alpha- or IL-1 beta-treated YT cells contained increased levels of IL-2R-specific mRNA as indicated by slot blot analysis by using an IL-2R-specific mRNA probe. Kinetic and IL-1 beta mRNA expression studies indicated that the TNF effect was a direct one. Because IL-2R expression is known to be associated with lymphocyte activation, the present results suggest that TNF-alpha may play a role in the regulation of immune responses.