Response Mechanisms Of Cyclocarya Paliurus Seedlings For Different Provenances Under Osmotic Stress

Cyclocarya paliurus (Batal.) Iljinskaja is native to China and is the sole species in its genus. The species has become a endanger species because of hard propagation. Howerver, its multiple values make the species have a big potential market. Until now no information has been presented on the salt and drought resistance of the species. Therefore, the paper discussed the mechanism of tested seedlings enduring salt and resisting drought under osmotic stress from cell, tissue and organ levels by the way of hydroponics in phytotron. At the same time, by combining with the measured results of morphological, physiological and growing index, the ability of seedlings enduring salt and resisting drought was comprehensively appraised for tested different provenances. Accordingly, a scientific basis for expanding the planting area of Cyclocaryapaliurus (Batal.) Iljinskaja plantation has been provided reasonably. The main conclusions were drawn as follows:The difference ATPase activity in mesophyll cells and its distributing location in tested provenances seedlings under osmotic stress was more evident. Under normal condition, the ATPase activity was lower and its distributing location difference was not significant among tested provenances, which located on nuclear membrane and karyotin. After osmotic stress, the ATPase activity in tested provenances all increased. However, ATPase distributing location varied from treatments and provenances.Leaf ultrastructure suffered from different degree damages in tested provenances seedlings under osmotic stress. The main performances was that thylakoids swelled, chloroplast disassembled, nuclear membrane disappeared, karyotin concreted and condensed. Moreover, the phenomenon of cytoplasm separating from cell wall was observed.Under osmotic stress, water losing of mesophyll cells resulted in palisade tissues and spongy tissues attenuated, leaf carnification degree reduced and the ability of leaf storing water declined. Furthermore, because of leaf losing water, stoma opening degree became small, especially, the variation was more distinct under PEG stress.Effect of salt stress on ion micro-distribution in root tissues Was significant. Under 0.3 percent and 0.5 percent NaCl stress, the relative concent of Na⁺ and Cl^- increased, while that of K⁺,Ca²⁺ and Mg²⁺ decreased. With the increasing of salinity, generally, the ratio of Na+ to X(K⁺, Ca²⁺, Mg²⁺) in root tissues presented ascending trend, and Na⁺ aggregated to root epidermis and cortex, while the relative content of Cl^- in root stele and cortex was greater.The higher salt concentration was, the greater rhizosphere pH was. Therefore, the potential of root absorbing nutrition from medium decreased. Within the range of salt threshold, the distribution of Na⁺ and Cl^- mainly converged in root stem and petiole, but was fewer in leaf. With the increasing of salt concentration, the ability of seedlings compartmentalizing ions was damaged, thus the content of Na⁺ and Cl^- in leaf quickly increased. During the course of ion-selective transporting, the higher the salinity was, the worse the abilities for selective transporting ion of seedlings aboveground organs were.Under osmotic stress, resulting from leaf water losing in tested seedlings, leaf water potential decreased, cells were dehydrated, cell membrane damaged, the relative penetration of membrane augmented, as well as the integrity of chloroplast structure was destroyed. In addition, because of water waning, stomatal conductance descended, and then the content of chlorophyll decreased, photosynthetic rate and transpiration rate reduced. At same time, leaf water-deficient resulted in seedlings osmotic adjusting function being activated, and the content of proline and soluble sugar in leaf increased.Concerning of organs calorie, energy accumulation increment and energy allocation, generally, leaf was higher, rootstock was normal and petiole was lower under osmotic stress. With the increase of stress intensity, the calorie in seedlings organs, the increment of energy accumulation and the proportion of leaf energy accounting for total energy all decreased, while the proportion of root energy accounting for increased. But proportions stem and petiole accounting for energy varied slightly.The tested seedlings were damaged from osmotic stress, e. g. the developing of rootstock was blocked, and seedlings survival percentage descended. With the increase of stress intensity, the increment of height, caliper, leaf area and biomass of the seedlings all decreased. Concerning of the varying about component and quantity growth, in general, it showed that the height, the number of leaves per individual plant, the number of side-roots and the proportion of leaf biomass decreased compared to CK, while the proportion of root biomass increased.By the method of principal component analysis, properties of seedlings enduring salt and resisting drought in tested different provenances under osmotic stress were evaluated, and the results showed that the level of salt tolerance for tested three provenances seedlings was in the order of Huangshan provenance from Anhui＞Kunming provenance from Yunnan＞Jiujiang provenance from Jiangxi, the level of drought resistance for tested three provenances seedlings was in the order of Kunming provenance from Yunnan＞Huangshan provenance from Anhui＞Jiujiang provenance from Jiangxi. Under iso-osmotic stress and calcium regulation, the variation in enduring salt ability of seedlings among different calcium treatments was slighter. However, the variation in resistingdrought ability of seedlings among different calcium treatments was more remarkable. Under the interaction of high temperature and low salinity stress, the order in seedlings enduring salt and resisting high temperature ability for tested four provenances was Ganzhou provenance＞Huangshan provenance＞Kunming provenance＞Jiujiang Provenance.In conclusion, firstly, for tested seedlings of four provenances, the ability of enduring salt and resisting drought was that Jiujiang provenance from Jiangxi was iow, Kunming provenance from Yunnan was middle, and Ganzhou provenance from Jiangxi and Huangshan provenance from Anhui were relatively better. Secondly, the threshold of tested seedlings enduring salt was about 1.0 gram per liter. Thirdly, under iso-osmotic stress, the effect of calcium regulation was more evident under PEG stress than under salt stress, and using 0.2% Ca(NO₃)₂ regulation was more effective. Fourthly, under the same osmotic stress, the interaction with the high temperature would speed the damage and make the damage more serious.