| Chinese golden elm (Golden Ulmus pumila) is a new color leafed plant variety bredby the Academy of Forestry Sciences of Hebei. For its beautiful golden leaves, Chinesegolden elm can be grown as one of excellent colorful tree species. The ornamental periodfor golden elm in the northern region of China is from July to September in the summer.Chinese golden elm is a natural yellow leaf mutant of ordinary U. pumila, with yellow-leaftrait genetically stable in the next generation. There was a yellow-green traits separationratio1:1for open-pollinated progeny. In recent years, there were many reports about of thecultivation and application of Chinese golden elm, but its photosynthetic characteristicsand leaf coloration mechanism rarely had been reported. In order to explore thephotosynthetic characteristics and leaf coloration mechanism of progeny seedlings ofChina gold elm, several parameters such as growth rate, pigment content, photosyntheticrate, chlorophyll fluorescence and the ultrastructure of chloroplast are measured and theresults showed are as follows：1. Compared with green leaf seedlings, yellow leaf seedlings developed slowly andtheir foliage were thinner and shorter.2. Leaf pigment composition and contents of yellow leaf seedlings and green leafseedlings were analysised and determinated from July to September. The results showedthat the two types of pigment was basically the same. The main pigment were chlorophylla, chlorophyll b, carotenoid and anthocyanin. But the contents of the four for yellowseedlings were all low than green ones．The content of chlorophyll a of yellow leafseedlings was approximately half of the green leaf seedlings, and the content of carotenoidand anthocyanin were less of1/3than green leaf seedlings. The content of carotenoids wasalways less than the chlorophyll in yellow seedlings in3months. The carotenoids contentof green leaf seedlings was higher than chlorophyll in July and September.3. Different with the bimodal curve of green leaf seedlings, the yellow leaf seedlingsdiurnal curve was relatively flat without obvious "lunch break" phenomenon. The stomatalconductance of yellow leaf seedlings was below the green leaf seedlings. Transpiration rate,intercellular CO2concentration and leaf temperature were higher than green leaf seedlings.The yellow leaf seedlings had the higher temperature difference and poor adaptability totemperature. Both seasonal variation of net photosynthetic rate curve showed a single peakand the highest net photosynthetic rate in August. The net photosynthetic rate of yellowleaf seedlings was below the green leaf seedlings. The transpiration rate, intercellular CO2 concentration and leaf temperature of yellow leaf seedlings were higher than the green leafseedlings. The transpiration rate and stomatal conductance of yellow leaf seedlings werebelow the green leaf seedlings in July and September, but was higher in August.4. Seedlings fast chlorophyll fluorescence parameters of yellow and green leafseedlings were measured, and the results showed that the initial fluorescence yield,maximum fluorescence yield and variable fluorescence yield of yellow leaf seedlings wereall less than the green leaf seedlings. Under the direct sunlight, the yellow leaf seedlingsphotosynthetic the institution was under duress, the number of the activied PS II in theyellow leaf seedlings is far below than in green leaf seedlings, the yellow leaf seedlingsphotosynthetic center unit had lower electron transport chain efficiency, resulting inphotosynthetic performance degradation.5. Chloroplasts observed at the subcellular level, the yellow and the green leafseedlings had significant differences on shape, number and arrangement of chloroplast.The chloroplast in yellow leaf seedlings failed in developing endomembrane system. Sothe cytoplasmic concentration is larger and there is material out of the chloroplast. |
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