| Salicylic acid (SA) and Methyl Jasmonate (MJ) are important signal substances and also newly found plant hormones, which play a crucial role in regulation of physiological action and expression of genes in plants. Ripening and senescence occur dramatically during later stage of fruit development, which is closely associated with storage quality. It is helpful to further reveal the mechanism of fruit development so that the physiological and biochemical effects of SA and MJ on fruit ripening and senescence could be explained. Furthermore, the study on this respect could provide a theoretical basis for ripening control, quality improvement and extension of storage life.Two cultivars of apple, "Starkrimson" and "Red Fuji", and one variety of pear of "Yali" pear were used to examine the regulating effects of SA and MJ on fruit senescence and quality, as well as the relationship between SA and MJ by means of flesh discs culture. The main results were as follows:1. The external MJ greatly decreased the content of endogenous SA in fruit discs. SA content decreased gradually as MJ concentrations increased from 5X 10"7 mol ?L"1 to 5X 10~3 mol ?L"'. SA content in "Starkrimson" apple and "Yali" pear reached the lowest point when fruit discs were treated with MJ at 5X lO^mol ?L"1. SA content in "Red Fuji" fell to the lowest point when fruit discs were treated with MJ at 5 X 10~3 mol?L"'. These results indicated that MJ accelerated the process of fruit senescence by decreasing SA content.2. SA inhibited biosynthetic process of MJ because it remarkably inhibited LOX and AOS activities in fruit discs. LOX and AOS activities decreased gradually with increase of SA concentration and reached the lowest level when fruit discs were treated with SA at 2 mmol ?L"1. Furthermore, the degree of SA inhibition from AOS was higher than that of SA from LOX. This meant that inhibition of SA from AOS activity was responsible for the inhibition of SA from the biosynthesis process of MJ. It could be concluded that SA was able to delay fruit senescence by protecting cell membrane system; on the other hand, SA could control the biosynthetic process of MJ, thus delaying fruit ripening and senescence.453. The external MJ accelerated the biosynthetic process of endogenous MJ. MJ remarkably increased LOX and AOS activities in fruit discs. LOX activities in "Red Fuji", "Starkrimson" apple and "Yali" pear discs achieved the lowest level when fruit discs were treated with MJ at 5X 10"5mol ?I/1, 5X 10'7mol ?I/1 and 5X lO^mol ?L'1 respectively with corresponding reduction by 48.78%, 22.73% and 60.87% in contrast to that from CK. AOS activity in "Red Fuji", "Starkrimson" apples and "Yali" pear discs reached the lowest point when fruit discs were treated with MJ at 5 X 10~5 mol ?L"1, 5X 10"5 mol ?L"1 and 5X lO^mol ?L"1 respectively with corresponding reduction by 53.85%, 60.00% and 38.10% as compared with that from CK.4. The exotic MJ (5X 10"7~5X lO'Vol ?L"1) enhanced PG activity in fruit discs, which implied that MJ accelerated fruit senescence by increasing PG activity.5. The exotic MJ (5X 10~7~~5X lO^mol ?L"1) increased PPO activity in fruit discs. PPO activity in "Red Fuji", "Starkrimson" apples and "Yali" pear discs achieved the lowest level when the fruit discs were treated with MJ at 5X10"6 mol ?L"1, 5X 10"6 mol ?L'1 and 5X 10"7mol ?L"1 respectively. This showed that MJ could accelerate fruit browning and deteriorate fruit quality.6. The exotic MJ (5X 10"7~5X lO^mol ?L"1) increased PAL activity in "Red Fuji" apple and "Yali" pear discs. PAL activity in "Red Fuji" apple and "Yali" pear discs reached the highest point when fruit discs were treated with SA at 5X 10"4 mol ?L'1.7. The exotic MJ (5 X 10"7~5X lO^mol ?L"1) decreased POD activity in fruit discs. POD activity in "Red Fuji", "Starkrimson" apples and "Yali" pear discs decreased gradually with increase of MJ concentration.8. The exotic SA (0.002~0.2mmol ?L"1) decreased PG activity in fruit discs. This revealed that S...
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