Multiple transcripts of a calcium‐binding protein gene from <i>Atriplex nummularia</i> are differentially regulated by developmental and environmental stimuli

H6 is an Atriplex nummularia gene having high sequence homology with the algal caltractin (a basal‐body‐associated calcium‐binding protein) gene. Recombinant H6 was expressed at high levels in Escherichia coli. The recombinant protein exhibited an ethylene glycol‐bis(β‐aminoethyl ether)‐ N,N,N′,N′ ‐tetraacetic acid‐induced mobility shift during sodium dodecyl sulfate‐polyacrylamide gel electrophoresis, and it was able to bind 45 Ca 2‐ . An H6 cDNA probe detected three RNA transcripts of 1.3, 2.2 and 2.4 kb, respectively. The levels of these transcripts were regulated by different environmental cues and during developmental stages. The steady state levels of the 1.3‐kb mRNA decreased after touch and heat treatments. Expression of the 2.2‐kb message correlated with cell proliferation activity. In cultured cells, the highest level of the 2.2‐kb message preceeded the peak of mitotic cell division activity. In plants, the 2.2‐kb message was detected only in shoot tips that contained meristematic tissues. The 2.4‐kb message was detected exclusively in heat‐shocked cells. The relationship among the three transcripts is discussed in the context of the possible role of H6 in mediating developmental and environmental signals.