In present paper, one of the T-DNA insertional embryonic lethal mutant of Arabidopsis is identified and designated as acd mutant. The embryo development of this mutant is arrested in globular stage. The cell division pattern is abnormal during early embryogenesis and results in disturbed cellular differentiation. Most of mutant embryos are finally degenerated and aborted in globular stage. However, a few of them still can germinate in agar plate and produce seedlings with shorter hypocotyl and distorted shoot meristem. To understand the molecular basis of the phenotype of this mutant, the joint fragment of T-DNA/plant DNA is isolated by plasmid rescue and Dig-labeled as probe for cDNA library screening. According to the sequence analysis and similarity searching, a 936 bp cDNA sequence (EMBL accession #: Y12555) from selected positive clone shows a 99.8% (923/925bp) sequence homology with Alanyl-tRNA Synthetase (AlaRS) gene of Arabidopsis thaliana. Furthermore, the data of in situ hybridization experiment indicate that the expression of AlaRS gene is weak in early embryogenesis and declines along with globular embryo 'development' in this mutant. Accordingly, the reduced expression of AlaRS gene may be closely related to the morphological changes in early embryogenesis of this lethal mutant.