A systematic cytological comparison of the anther development of photoperiod sensitive genic male sterile (PSGMS) rice with its normal fertility counterpart was conducted.The results showed that pollen abortion in PSGMS rice occurred first no later than the pollen mother cell (PMC) stage and continued during the entire process of pollen development till pollen degradation.This abortive process was closely associated with the abnormal behavior of tapetum.Although tapetum degeneration in the PSGMS rice initiated as early as at the PMC stage,it proceeded slowly and did not complete until the breakdown of the pollen,in sharp contrast to the rapid disintegration of the tapetal layer during the late microspore to the bicellular pollen stage in the fertile rice.Such cytological observation was supported by the results of the TUNEL (TdT2 mediated dU TP Nick End Labeling)assay that detects DNA fragmentation resulting from programmed cell death (PCD),indicating that the tapetum degeneration occurs in the process of PCD.