| Maize(Zea mays L.) mesocotyl is an important trait which is significantly correlated with drought resistance, deep sowing and seedling emergence rate, and its growth is an obvious light regulation process. Previous studies have indicated that the oxidase polyamine(PAO) gene expression is regulated by light in maize. The PAO activity and growth inhibition in the external tissues of the apical growth zone of the mesocotyl are enhanced by light. However, the mechanism of PAO in the inhibition of the growth inhibition of the light induced maize is still not clear so far. 54 maize inbred lines were used as materials, the mesocotyl and coleoptile length of maize seedlings grown in the dark for 3 days were investigated, and what is more, three agronomic traits such as plant height, ear height and length of the length of the plant were also measured in the field conditions. To further clarify the mechanism of PAO in the growth inhibition under light condition, two inbred lines, Zheng 58 and PH4 CV, which were significantly different in the mesocotyl length were selected as materials to study the effects of light on the elongation and related physiological characteristics in maize mesocotyl. The main results are as follows:(1) In dark, the mesocotyl length of 54 maize inbred lines showed a normal distribution with an average length of 3.16 cm, the maximum is 6.52 cm, and the minimum is 0.98 cm. In those, 13% of the inbred lines had long mesocotyl(>5 cm), and 24% had short mesocotyl(<2 cm), the length of other 63% inbred lines varied from 2 to 4 cm. Correlation analysis showed that the mesocotyl length had significant positive correlation with the fresh weight and dry weight of mesocotyl, as well as the total length of the mesocotyl and coleoptile, while the plant height showed remarkable positive correlation with mesocotyl length. Therefore, the long mesocotyl inbred lines used in breeding activities may increase the emergence rate and plant height, but the increase of plant height will cause the decrease of lodging resistance in maize varieties.(2) In dark and light, the mesocotyl length, PAO activity, H2O2 content, POD activity and lignin content of Zheng 58 and PH4 CV were quitely different. In dark, the mesocotyl length, PAO activity, H2O2 content, POD activity and lignin content of Zheng 58 were higher than PH4 CV. Correlation analysis showed significant negative correlation between mesocotyl length and PAO activity, H2O2 content, lignin content(p<0.01), and a remarkable negative correlation between the mesocotyl length and POD activity(p<0.05).(3) 5 mmol/L 2-HEH could promote the growth of maize mesocotyl, but PAO activity significantly decreased, and the expression of PAO encoding gene Zm PAO1 was inhibited. It showed that the change of PAO activity was the main reason responsible for the elongation inhibition of maize mesocotyl. 0.1 mmol/L H2O2 could inhibit the growth of maize mesocotyl, but the PAO activity and expression Zm PAO1 showed no significant difference when compared with control. After 5 mmol/L DMTU treatment, the length of the maize mesocotyl increased significantly, PAO activity was increased, and the expression of Zm PAO1 gene was also promoted in different degree. Cell microstructure and H2O2 histochemical staining assays showed that H2O2 produced by the PAO catalyzed decomposition reaction of PAs may involve in the regulation of the growth of maize mesocotyl. This shows, light can make the increase of PAO activity and accumulation of H2O2 in maize mesocotyl, this will cause synthesis of lignin and inhibition of cell elongation growth by POD pathway. |
