IN-SITU DETECTION OF ADPGLUCOSE PYROPHOSPHORYLASE EXPRESSION DURING MAIZE ENDOSPERM DEVELOPMENT

ADPglucose pyrophosphorylase is considered to play a pivotal role in p lant starch biosynthesis. During the grain-filling period in maize ker nels (Zea mays L.), starch accumulation and ADPglucose pyrophosphoryla se (EC 2.7.7.27) activity have been correlated. In an attempt to relat e the morphological processes occurring during kernel formation to the concurrent events of synthesis and storage of starch, the cellular an d subcellular localization of the two composite subunits of the enzyme , designated BT2 and SH2, and the corresponding mRNAs were determined in developing kernels by immunocytochemistry and in situ hybridization . Immunolabel was first observed associated to amyloplasts and the sur rounding cytosol exclusively in cells of the pericarp layer at 8 DAP ( Days after pollination). Later, immunolabel was associated to discrete amyloplasts of the inner endosperm cells at 14 DAP and 23 DAP. At 35 DAP, fused starch grains, which entirely fill endosperm cells, were im mune-positive. The visualization of the transcripts by in situ hybridi zation was detected as early as 14 DAP exclusively in the cytosol of i nner endosperm cells. A gradient of expression pattern was observed fr om the periphery of the kernel towards the central zone at both 14 and 23 DAP At 35 DAP, however, transcripts were no longer detectable by i n situ methods. In all cases, cells of the aleurone and sub-aleurone l ayers were negative for both the protein subunits and transcripts. The tissue/cell specific expression varies throughout the grain-filling p eriod as a function of the maturation of the endosperm tissue and the developmental state of the amyloplasts.