Study On Low Temperature Resistance Of Euonymus Radicans 'Emorald & Gold'

Euonymus radicans 'Emorald & Gold' is one of the about ten of evergreen and color-leaved plant species introduced from England in the spring of 2000 by our research group. Not only popular in greening the city due to its good ornamental value, it is also valuable to be introduced and acclimated for its strong endurance to low temperature stress. Due to the long and severe winter in Beijing, low temperature became the chief restriction factor for introducing and acclimating plants. Euonymus radicans has the strongest enduring ability to low temperature compared with other evergreen and color-leaved plants introduced at the same time, and it could live through the severe winter with a little mulch covered.As the partial staggered achivement of National "948" Research Project, this dissertation aims to study the cold-resistance mechanism of evergreen and color-leaved plants with good enduring ability to low temperature, and to provide more experimental data and reference informations for enriching the cold-resistance theory and introducing and acclimating plants. The cold-resistance characteristics of Euonymus radicans was first systematically investigated from the different levels of morphology, phsiology, biochemistry and molecular biology. And its cold-resistance mechanism was further disscussed depend on the aspect of the cold-resistance decided by the stability of cell membrane. The major experimental contents and conclusions were summarized as follows:1. A comparative observation was carried out on the changes of anatomical structure and starch content in the leaves of Euonymus radicans during overwintering and cold acclimation. The results indicated that there were a series of adaptive changes of tissue structure and starch content in the leaves of Euonymus radicans. The cold-resistance of plants was positively correlated to the ratio(CTR) of the thickness of palissade tissues tothe whole thickness of leaves. Conversely, the cold-resistance was negatively correlated to the ratio(SR) of the thickness of spongy tissues to the whole thickness of leaves.The changes of chloroplasts arrangements, the disintegration and reparation of spongy cells, and the vacuole division and plasmolization were highly correlated to the cold-resistance of plants. So were the starch accumulation before the acclimation, the starch degradation after the acclimation and starch accumulation again after de-acclimation. After being cold-acclimated , the control seedlings with only a few starch grains in the parenchyma cells of leaves showed much stronger enduring ability to low temperature than unacclimated seedlings, indicating that the protein might play a more important role than starch in the course of enhancing the cold-resistance of plants.2. The photosynthesis-light response curves with the leaves of seedlings in Eitonymus radicans between acclimated and unacclimated as well as the leaf photosynthetic rate of acclimated and unacclimated seedlings under the low temperature stress were studied comparatively. The results showed that the leaf photosynthetic rate and photosynthetic light compensation point of acclimated seedlings decreased, but photosynthetic light saturation point increased slightly compared with unacclimated seedlings. And the leaf photosynthetic rate of acclimated seedlings were always higher than those of unacclimated seedlings during the different duration of low temperature stress. Furthermore, the leaf photosynthetic rate of unacclimated seedlings became negentropy at the third day under the low temperature stress, but the leaf photosynthetic rate of acclimated seedlings still maintained at a higher level. Therefore, the capacity of utilizing low light intensity of seedlings could be enhanced by cold acclimation, and the increase of photosynthetic light saturation point and the decrease of photosynthetic rate of seedlings in Euonymus radicans might be the adaptive adjustment to the cold acclimation so as to raise the stability of photosynthesis of seedlings under low temperature stress and then enhance the c...