Abstract: An early leaf senescence rice mutant R7954（els）， obtained by 60Co\|γ irradiation from rice variety R7954， was applied to investigate the changes in physiological properties and in the ultra\|structure of chloroplast in flag leaf during different developmental stages. Compared with wild type R7954， the mutant R7954（els） showed weaker growth potential， lower growth rate and symptoms of early senescence， i.e. the presence of rusty and withered leaves since the beginning of the tillering stage. Lower activity of superoxide dismutase （SOD）， deceased contents of vitamin C （VC）， vitamin E （VE） and glutathione （GSH）， and higher content of malonaldehyde （MDA） were observed， indicating a lower antioxidant system in the mutant. The mutant also showed lower content of chlorophyll a， chlorophyll b and chlorophyll （a+b）， resulting in photosynthetic decline. The ultra\|structure of chloroplast in flag leaves in the mutant showed an increasing amount of disintegrating thylakoids， osmiophilic plastoglobuli and lipoid with the process of senescence， and the whole chloroplast were degraded at the mature stage.

Key words: rice, early leaf senescence mutant, antioxidant system, photosynthetic properties, ultra\, structure