A preliminary study on the mechanism of fertilization and setting fruit of apple

The content of GA3, GA4+7, ABA, IAA, Z and ZR in the fruits and fruiting shoots treated with PP333, GA3 was measured by GC and that of 15N was measured by MS. The results showed that the number of fruits was increased, but the size of fruit and length of fruiting shoot were inhibited by PP333 treatment. Opposite results were observed with GA3 treatment although the number of fruits was higher than that in control. The content of CTK was consistent with the ability of setting fruit, but no relationship was found between the other hormones and setting fruit. Together with evidences of the high level of 15N and total N or IAA + CTK/GA4=7 in fruits and the low level of those in fruiting shoots after PP333 treatment allow us to conclude that the mechanism of PP333 on setting fruit probably is to inhibit biosynthesis of GAs, to increase the content of CTK, and to promote the ratio value of IAA + CTK/GA4+7, increasing and changing the status of nutrition. The distribution of 15N is changed from the order of king fruit>fruiting shoot>lateral fruit to king fruit>lateral fruit>fruiting shoot. Thus the competition between fruits and shoots growth was weaken, which resulted in the higher ability of setting fruit than that in the control and GA3 treatment