| In this research, the test material was thick-skin melon ’Elizabeth’ and thin-skin melon ’Jiuqingmi’. The two melon varieties were treated by two kinds of waterlogging stress, semi-waterlogging and entire-waterlogging. The morphologic changes of the two melon varieties were observed, and simultaneously, the changes of the physiological, biochemical indexes were analyzed. This experiment has attempted to carry out to a preliminary discussion of the changes of physiological and biochemical mechanism of melon seedlings when they suffered from waterlogging stress. Besides, taking’Elizabeth’ as the material, this experiment cut out the adventitious roots which were emerged in the hypocotyls of Elizabeth under semi-waterlogging. By comparing several physiological indexes of it with the melon seedlings remaining adventitious roots, this research has discussed the effect of adventitious roots on melon seedlings under semi-waterlogging. The main results are as follows:1. Waterlogging stress significantly inhibited the growth of the two melon varieties. Under semi-waterlogging, the increase of fresh weight of ’Elizabeth’ and ’Jiuqingmi’ decreased compared to the control. The roots of the two melon varieties became black and rotted gradually. The hypocotyl of some seedlings below the water cracked and created a large number of adventitious roots floating on the water. The fresh weight of ’Elizabeth’ was almost two times of ’Jiuqingmi’. Under entire-waterlogging stress, seedlings died soon. The death rate of ’Elizabeth’ was higher than ’Jiuqingmi’.2. Under Waterlogging stress, the content of photosynthetic pigment and root vigor decreased. Semi-waterlogging had not affected the content of photosynthetic pigment much. Only on the 1st flooding day had photosynthetic pigment fallen. But entire-waterlogging made the content of photosynthetic pigment of the two melon varieties decrease significantly. The content of photosynthetic pigment of ’Elizabeth’ was higher than ’Jiuqingmi’. Both semi-waterlogging and entire-waterlogging made the root vigor of melon seedlings decrease significantly.3. Both the two kinds of waterlogging stress made MDA content of ’Elizabeth’ and ’Jiuqingmi’ increased significantly. Under semi-waterlogging stress, Leaf MDA content of’Elizabeth’ and Jiuqingmi peaked on the 3rd flooding day. But soon afterwards it decreased to control level. Root MDA content of the two melon varieties also peaked on the 3rd flooding day and then changed gently. Under entire-waterlogging stress, Both Leaf and root MDA content of ’Elizabeth’ and ’Jiuqingmi’ were rising along with flooding time. MDA content of ’Elizabeth’ was slightly higher than ’Jiuqingmi’. But the different was not significant.4. Osmotic adjustment substances, proline and soluble protein, of the two melon varieties had changed under waterlogging stress. Semi-waterlogging made leaf Pro content show a rising first and then dropping trend and made root Pro content show an increasingly rising trend. The change of leaf soluble protein of the two melon varieties was small. But root soluble protein content presented a continuous decrease trend. Under entire-waterlogging stress, the leaf and root Pro content of both ’Elizabeth’ and ’Jiuqingmi’ were significantly higher than controls. Leaf and root soluble protein content of the two melon varieties were continuously decreased.5. Waterlogging stress also made antioxidant system of melon seedlings changed. The content of antioxidant non-enzymatic system, AsA and GSH, rose under both semi-waterlogging and entire-waterlogging stress. AsA content of ’Jiuqingmi’ was higher than ’Elizabeth’. Two kinds of waterlogging made GSH content of the two melon varieties rising, but the range was small. As a whole, GSH content of ’Elizabeth’ was higher than ’Jiuqingmi’. The activity of antioxidant enzymatic system, SOD and POD, also rose in different degree under waterlogging condition. Semi-waterlogging made leaf SOD activity of ’Elizabeth’ and ’Jiuqingmi’ continuously increasing. Root SOD activity rose first and then dropped. Under entire-waterlogging, leaf POD activity of’Elizabeth’ and’Jiuqingmi’changed small, only a slight increase while root POD activity rose continuously.6. Under semi-waterlogging, the different of whole plant fresh weight and overground part fresh weight between ’Elizabeth’ seedlings with adventitious roots cut out and seedlings with adventitious roots existed was significant. But primary roots were not affected, as well as root fresh weight and root vigor. Besides, both root vigor and Pro content of adventitious roots reached the control level. |
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