We have isolated two cDNA clones (Mshspl8-1; Mshspl8-2) from alfalfa (Medicago sativa L.) which encode for small heat shock proteins (HSPs) belonging to the hspl7 subfamily. The predicted amino acid sequences of the two alfalfa proteins are 92 ~o identical and a similar degree of homology (90 ~o) can be detected between Mshspl8-2 and the pea hspl7. In comparison to various members of small HSPs from soybean amino acid sequence similarities of 80-86~o were identified. The alfalfa HSPs share a homologous stretch of amino acids in the carboxy terminal region with hsp22, 23, 26 from Drosophila. This region contains the GVLTV motif which is characteristic of several members of small HSPs. At room temperature alfalfa hspl8 mRNAs were not detectable in root and leaf tissues but northern analysis showed a low level of expression in microcallus suspension (MCS). The transcription of Mshsp 18 genes is induced by elevated temperature, CdCI 2 treatment and osmotic shock in cultured cells. In alfalfa somatic embryos derived from MCS a considerable amount ofhspl8 mRNA can be detected during the early embryogenic stages under normal culture conditions. The differential expression of these genes during embryo development suggests a specific functional role for HSPs in plant cells at the time of the developmental switch in vitro.