Physio-Biochemical Characteristics Of Dendrobium Nobile Responsed To Grads Drought Stress

Dendrobium nobile is one of adnascent plant in orchid dendrobium. It has large flower with gorgeous color. Combined with flowering in February to April, similar to the Spring Festival time in China, so dendrobium nobile as a new potted flower, has great market potential. In order to adapt to the environment, dendrobium nobile constituted a set of relatively mature in physiology, and structure of drought resistance mechanism. Correspondingly, its vegetative growth is relatively slow, the plant must be2～3years to blossom. Research on the drought resistance mechanism and the growth characteristics,is helpful to provide theoretical basis for dendrobium nobile cultivation, shorten the production cycle. In this experiment, first, making paraffin section to observe dendrobium nobile root、stem and leaf morphological structures, looking for the drought resistance of morphological characteristics. Three kinds of speices under drought stress degrees of7kinds of physiological indexes of dendrobium nobile are measured, including soluble sugar, soluble protein, catalase (CAT), peroxidase (POD), superoxide dismutase (SOD) and malonic ketone (MDA) proline (Pro). When stress started Od14d and28d, take skin to observe stomata of three species of dendrobium nobile under three drought degrees. At the same time, with LI-6400portable photosynthesis system, the physiological characteristics related with light on different dendrobium nobile species were researched. The main results of this study are as follows:The typical characteristics of dendrobium nobile adaptation to environmental stress of drought The stem, leaf, root of dendrobium nobile were studied, we found that root is formed by layers of cells, cells are closely packed and thicken, local suberization; Vascular bundle is hexagonal radiation vascular bundle, primary xylem vessel diameter smaller. The stem and leaf epidermis cells have a thicker layer of cuticle. Stomata only in the leaf lower epidermis. Taken together, the studies of dendrobium nobile morphological and anatomical have shown that it is in line with drought plant characteristics.2. The response of osmotic adjustment under different drought stress degrees in dendrobium nobile. Under different drought stress degrees, the soluble sugar contents increased at first and then decreased later, first peak appeared in the early stress; Soluble protein content increased at first and then decreased later, with bigger change, the peak appeared in the middle and later periods of the stress. In the process of drought stress, praline content is continuously cumulate, but The vary of MDA content was similar to the varies of it. So proline content increased maybe a reflection of its damage, while soluble protein should be the main osmotic regulation substances under drought stress in dendrobium nobile.3. The response of antioxidant enzyme systems under different drought stress degrees in dendrobium noblieUnder moderate stress, the activity of SOD, POD has no difference between CK while CAT activity was slightly higher in3species of dendrobium nobile; Under severe drought stress, the activity of SOD, POD, CAT activity were decreased after rising first. But the peak of SOD appeared in the late stress, SOD, POD early rise rapidly and maintain higher activities, while the CAT was significantly reduced after early rise, explain three enzymes response to drought stress were different, SOD and POD were more likely to be the main antioxidant enzyme in dendrobium nobile.4. The response of photosynthesis and chorophyll flourescence parameters under different drought stress degrees in dendrobium nobileThe photosynthetic physiology and chorophyll flourescence parameters showed that the moderate degree of drought treatment wasn’t significantly in dendrobium. Under severe drought stress, Pn had a significant reduction. The results indicated that, the main reason of the decrease of photosynthetic rate at the initial stage of senescence was due to stomatal limitation but nonstomatal limitation thereafter. The cause of non-stomata factors were probably as follows:(1) MDA content increased rapidly in the end of drought stress, showed that biomembrane and photosynthetic organs may were damaged;(2) LSP decreased significantly and LCP significant rise in the end of drought stress, light adaptation range were smaller, easier to form a light inhibition;(3) Chlorophyll fluorescence parameters showed that Fv/Fm,φ PS Ⅱ, qP and qN values were significantly lower in the end of drought stress. It supposed that the φ PS Ⅱ activity were damaged and the conversion of light energy, electron transfer efficiency, heat dissipation ability both dropped significantly.