The Initial Research Of Mechanism Of Transition Of Leaf Color In The Bolting Process Of Chinese Cabbage

Chinese cabbage (Brassic campesstris L ssp. pekinensis) are biennial vegetable crops,it needs to go through a cold stage to complete the transition of its development successfully. Brassica.rapa. belongs to the type of plant the seed of which needs vernalization, germimated seeds could response to the low-temperature to complete vernalization. Breed strong winter species which is appropriate to grow and bolting resistant, has become the urgent problems.Brassica.rapa. shows transition of leaf color during the period from vernalization to bolt, then it will appear bud and bloom. This phenomenon appears more frequent in easy bolting species. In present study, we use different winter Brassca.rapa. as materials, study the Physiological Basis of Transition of Leaf Color in the bolting process of Brassica.rapa. by the change of different hormones, pigment content and the composition of protein. At the same time, using homologous sequences of Arabidopsis we cloned the AP1 gene, and analyze the expression of AP1 gene in the process of transition of leaf color in different bolting resistant species by RT-PCR, dicuss the probably molecular mechanisms of leaf color change with a view to provide theoretical basis for selecting the strong winter species. Main results were as follows:1.Different winter species of Chinese Cabbage had a different change of pigment content in the process of bolting. The peaks of chlorophyll a, chlorophyll b, and carotenoids of anti-bolting species were found in the differentiation period stem, the minimum value was found in the differentiation period of bud. Moreover,the content of three pigment in the strongest winter species was significantly higher than the other two winter species from the beginning of differentiate period of stem. The ratio of chlorophyll a to chlorophyll b in the bolting process was highest in the period of leaf color change. We inferred that there was some relationship between the ratio and the color change.2.In the process of bolting, different winter varieties had two peaks of IAA which were in the differentiate period of bud and the period of leaf color change respectively. We also found that the stronger winter species, the lower Iaa,GA3 content in the period of color change, however, ABA was opposite. It indicated that there was a critical concerntration before the bolting of Brassica.rapa., it would promote bolt when the concerntration reached it. 3.The expression level of soluable protein was different in different winter varieties of Brassica.rapa. Among those proteins the one whose molecular weight was about 51KD had a highest expression level. It expressed in the same development period of differente winter materials, and the level was reduced gradually with the strengthening of its winter. In addition, the protein whose molecular weight was about 77KD was expressed in every period of easy bolting varieties, but it frist expressed in the differentiate period of neutral and anti-bolting varieties, then it disappeared in the differentiate period of stem. It appeared again in the period of leaf color change and had a higher expression level, then dispeared in the elongation period of stem.4.We cloned 10 Chinese cabbage AP1 gene sequence fragments whose length were all about 372bp based on the homologous gene sequences of Arabidopsis. Their exons encodes the same amimo acid sequence and encodes 31 AA, there is only some different in the length of their introns. Sequence analysis showed that the gained 10 AP1 gene sequences had a high homology with AP1 gene of other plants. AP1 gene is highly conserved was further confirmedl.5.AP1 gene had a same trend of expression in the bolting process of different winter varieties, its express level was very low in the vegetative period, and the level was increase gradually with the blooming period. It showed that: the elongation period of stem > the period of transition of leaf color > the differentiate period of bud > vegatative period, which futhur confirmed that AP1 gene contols the characteristic of inflorescence meristem and the transition of inflorescence meristem to flower meristem.