The Study Of The Effect Of The Leaves Maturity In Terminal Shoot On Flowering In Litchi(Litchi Chinensis Sonn.)

Floral-initiation of litchi is closely related to external and internal conditions such as low temperatures and terminal shoot leaves maturity. In the field study, ‘Gui Wei'litchi plants with different maturities of leaves in terminal shoot were subjected to different treatments, including bud-removing, leaf-removing and shoot cutting before exposure to low temperature in winter, the flowering situation were recorded. In the greenhouse, The litchi plants with the leaves stages of expanding, greening and mature in the terminal shoots were treated with low temperature. The flowering time was observed, and the molecular mechanism was studied. The main results were as follows:1. The field study results showed that, all the litchi branches with terminal buds removed flowered, and the control plants(maintaining the buds) had 65% of the rate of flowering branches, the treatment of GA has no effect on flowering. The ration of flowering branches of litchi plants treated with young leaf-cuting was 98.6%, which is slight higher than that of control(96.9%). And similar result was observed in the comparison between trees treated with shoot-cutting and control plants. These results indicated that the maturity of leaves in terminal shoots were associated with litchi flowering.2. In the greenhouse, the value of SPAD, length and width of leaves at expanding,greening and mature stages didn't significantly change under low temperature treatment.After 60-day treatment, the plants with mature and expanding leaves flowered except for the trees with greening leaves.3. The contents of sucrose, glucose, quebrachitol and fructose in the leaves of different maturities were measured, and sucrose showed the highest abundance, followed by quebrachitol, glucose, and fruticose. During the low temperature induction period, the content of quebrachitol in leaves tended to be stable, but rapidly increased at the onset of floral initiation.4. Through analysis the expression of mi R156 and mi R172 in different maturity leavesof terminal shoots, The results show that the expression levels of mi R156 increased with maturity of leaves in litchi, expression up-regulated under the low temperature induced,but the expression levels were equal and low in leaves of expanding and greening. As to mi R172, there have no much expression difference in different maturity leaves,and transcripts were steady in the stage of low temperature treatment.5. The expression of important flowering genes including SPL and FT were measured.The expression levels of SPL6, SPL9, SPL11, SPL16, SPL19 and SPL21 decreased gradually throughout the period of flower induction, but the expression of Lc SPL2, Lc SPL3,Lc SPL5 and Lc SPL14 accumulated gradually under low temperature treatment, Lc FT1 was induced by low temperature and mainly expressed in mature leaves. There was no apparent of expression of Lc FT2 among leaves of at different mature stages.