Apyrase (ATP diphosphohydrolase, EC 3.6.1.5) catalyzes hydrolysis of nucleoside tri- and di-phosphates to nucleoside monophosphates and orthophosphates. In the present study, the spatio-temporal expression of an apyrase gene (PsAPY1) in pea (Pisum sativum L. var. Alaska), was investigated during early stages of apical hook development using nonradioactive mRNA in-situ hybridization. During the formation of apical hook; at 45 hours after sowing (HAS), expression of PsAPY1 was obvious in epidermis and vascular bundle. By 60 HAS, the apical hook was completely formed. At this stage, transcript accumulation became higher than at the previous stage and expression was also visible in the cortex tissues of the developing hook. However, at 78 HAS, the curvature of the hook was reduced and hook was in the process of opening. At this time, expression of PsAPY1 was visible in all the above-mentioned tissues although the level of expression was slightly lower than at the previous stage (60 HAS). Apical hook formation provides a unique mechanism of protection for delicate shoot meristem in dicot plants. Its establishment is orchestrated by differential elongation rates of cells within the structure. The expression pattern of a gene provides essential information concerning the likely appearance and localization of its encoded protein and this helps to understand the mechanism of development of plant cells and tissues. Higher expression of PsAPY1 during the process of hook development indicates its essential role in the process of formation and maintenance of hook curvature and thus aids in protection of delicate shoot meristem.