Abstract: Plants of a rice mutant (Hubei photoperiod-sensitive genic male-sterile rice, Oryza sativa L. Nongken 58S) and its wild type cv. Nongken 58 were cultured in natural summer conditions in Beijing. After induction of proper photoperiods small panicle at the stem tip emerged and developed to the stage of secondary rachis-branch and spikelet primordium formation. Subsequently, part of the rice plants received long day (LD), i.e. 10 h of day-light treatment followed by 5 h of white fluorescent illumination with 1～2 Wm-2) . The others were exposed to daylight for 10 h alternating with a 14 h of dark period as short day (SD) treatment. After 10 days of the photoperiodic treatments, the chloroplast ultrastructure of the first leave below the flag leaf was examined by freeze-fracture rotary and unidirectionally shadowed electron microscopy. At anthesis stage, Nongken 58S plants with LD treatment showed complete pollen sterility, while the same plants with SD treatment exhibited normal fertility. And fertility of Nongken 58 was not affected by photoperiod treatments. The results from electron microscopic observation showed no significant effects of either SD or LD treatment on the freeze-fractured uhrastructure of thylakoid membranes in Nongken 58. No significant difference in particle density and size distribution was found on stacked and unstacked thylakoid membrane regions of the Nongken 58S-SD and those of Nongken 58 rice. However, the particle density of the endoplasmic fracture face in the staked region (EFs) and protoplasmic fracture face in the staked region (PFs) faces detected from the leaf thylakoid membranes of Nongken 58S-SD rice was significantly higher than that of the corresponding faces from Nongken 58S-LD. In some cases much more particles on EFs faces of thylakoid membranes isolated from Nongken 58S-SD rice appeared as paracrystalline particle array, indicating increases in the number of PS Ⅱ reaction centres, LHC I and Cyt b6/f per unit area of thylakoid membrane. The particle density of the endoplasmic fracture face in the unstaked region (EFu) and protoplasmic fracture face in the unstaked region (PFu) faces from unstacked thylakoid membranes of Nongken 58S-LD was less than that of the corresponding faces from Nongken 58S-SD. And the particle density of PFu faces from margin and end of the membranes of the grana thylakoids of LD-treated Nongken 58S leaves was also less than that of unstacked thylakoid membranes from SDtreated rice. In severe cases, most of the particles on endoplasmic fracture face in the unstaked region (EFu) and protoplasmic fracture face in the unstaked region (PFu) faces were even missing, indicating a decrease in the numbers of photosystem Ⅰ , LHCⅠ , Cyt b6/f and ATPase per unit area of' thylakoid membrane. The above results could further provide an augmentation for explaning the photoperiod-sensitive genic male-sterility.

Key words: Photoperiod, Male sterility: Rice: Thylakoid membrane: Supramolecular Architecture