| Songfengben Longan (Dimocrupus longan lour. cv. Songfengben) (late-maturing species) of field experiments and Fenglisui Longan (Dimocrupus longan lour. cv. Fenglisui) (mid-variety) of pot experiments were treated with potassium chlorate in August 2008 and September 2009 to study the relationship between the effects of the off-season flower-bud induction of Longan and the changes of the plant's endogenous hormones,polyamines,salicylic acid and other growth substances and the activity of a series of enzyme and its related substances for further exploring the mechanism of off-season flower-bud induction of Longan. The results are as follows:1. In the process of potassium chlorate induced off-season flowering of longan, the biological observation shown that off-season flower-bud induction of Longan need about 43 days. Anatomical observations of flower-bud shown that the first 33 days after application is the physiological differentiation period. The study of endogenous hormones shown that:ETH and ZT change significantly in the first 15 days of flower-bud physiological differentiation. Therefore, the first 15 days of flower-bud physiological differentiation is the critical period of off-season flower induction. This is valuable for practical applications and provides an important time basis for the development of control technology in off-season longan production.2. The study of endogenous hormone content and the ratios between hormone shown that:(1) In the flower-bud physiological differentiation, ETH increased significantly; ZT was much more higher than the control; GA3 was decreased significantly; ABA and IAA decreased slightly; that indicates that high levels of ETH and ZT, low levels of GA3,ABA and IAA is availed to floral-bud formation. (2) In the flower-bud physiological differentiation, ZT/GA3, ZT/IAA and ZT/ABA increased significantly, ABA/GA3 and IAA/GA3 are relatively higher, ABA/IAA decreased , those are availed to floral-bud formation.So high content of ETH,ZT and high ratio of ZT/GA3,ZT/IAA,ZT/ABA are important for hormone homeostasis.3. The study of the ETH content and the synthesis of related substances (polyamines and SA, etc.) shown that the content of ETH were significantly increased after treatment and always higher than the control, and come up to a peak in critical period of flower-bud physiological differentiation , which was 2.34 times higher than the control , and the content of ETH increased positively related with the potassium chlorate concentration. In addition, SA content increased positively related with the concentration of potassium chlorate, Spm content was lower than the control. As SAM is the common precursor of Spm and ETH, the process of ACC to ETH can be inhibited by SA , so the content of Spm and SA could be regulated by potassium chlorate to promote ETH synthesis, thus promoting flowering. Thus, high content of ETH is an important physiological index in flower-bud physiological differentiation .4. The study of the ZT content and its ratio with other endogenous hormones shown that in the critical period of flower-bud physiological differentiation, ZT were significantly increased and came up to the peak, which is 2.79 times higher than the control; the ratio of ZT/GA3,ZT/IAA and ZT/ABA is about 3.38 times,4.07 times and 3.16 times to the control at the peak in the critical period of flower-bud differentiation. This shows that high content of ZT and high ZT/GA3,ZT/IAA,ZT/ABA ratio in the critical period of flower bud differentiation play an important role on the flower-bud formation on off-season of longan .5. The activity of key enzymes in the biosynthesis of endogenous hormone was studied, the results show that the activity of cytokinin oxidase decreased, which is significant negative correlated with the content of ZT (r =- 0.81); the activity of IAA oxidase enhanced, which is significantly negative correlated with the content of IAA (r =- 0.66). This shows that the content of endogenous hormones can be regulated through regulating the activity of related enzymes by potassium chlorate. In summary, high content of ETH and ZT, low level of GA3,IAA and ABA content , and high ratio of ZT/GA3,ZT/IAA and ZT/ABA in the critical period of flower-bud physiological differentiation is availed for the physiological differentiation of flower-bud , and it is the key of flowering inducing, this provide an important theoretical basis for the regulation of technology development in off-season longan production .
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