In this thesis, 10 species of kiwifruit rootstocks were treated with hydroponics hypoxia to study their root zone hypoxia tolerance. The results were as follows: growth of all kiwifruit seedlings was inhibited. The max length of new root, plant height, plant biomass, root activity, relative growth rate of leaves, and content of chlorophyll in leaves under root zone hypoxia stress obviously declined comparing with control. MDA content, relative conductance in the leaves and roots all increased in 10 kinds of kiwifruit seedlings. The sensitivities of 10 kinds’ kiwifruit seedlings to hypoxia stress were obviously different. With the method of subordinate function and cluster analysis, the adversity resistance coefficient of 10 kinds’ kiwifruit seedlings, were comprehensively evaluated in order to appraise their hypoxia-tolerance abilities. According to the results, “Hayward”, “Qinmei”, “Jinxiang”, “Kuoye”, “Huayou” kiwifruit seedlings held higher tolerance to root zone hypoxia stress, while “Hongyang” kiwifruit seedlings were sensitive to root zone hypoxia stress. The others, including “Xixuan”, “Maohua”, “Jinhua”, “Shanli” kiwifruit seedlings kept moderate resistant intensity to root zone hypoxia stress. The kiwifruit seedlings’ resistance order from strong to weak was: “Hayward” > “Qinmei” > “Jinxiang” > “Kuoye” > “Huayou” > “Xixuan” > “Maohua” > “Jinhua” > “Shanli” > “Hongyang”.
Molecular oxygen is the terminal electron acceptor in the mitochondrial electron transport chain and is also the prerequisite conditions that were required by higher plants during their growth and development. However, anoxia is a common environmental challenge which plants have to face throughout their life. Winter ice encasement, seed imbibitions, floods, soil compaction and excess of rainfall are examples of nature conditions leading to root hypoxia or anoxia. Low oxygen concentration is also a normal natural environmental stress to plants [1,2]. For example, in wetland, the oxygen concentration around the root tissue is nearly zero [3-5]. Plants’ survival, growth, development are drastically effected by root zone hypoxia [6,7]. Climate change models also increased the risks of waterlogging root hypoxia [8,9]. Hypoxia environment can reduce the redox potential of soil, accumulate the reducing materials, damage the plant root plastosome and protein structure, reduce the cell energy charge and make cytoplasmic acidosis, all of which can restrain the plant growth and lead to death. Under waterlogging stress, the treated plants’ height, length and width of leaves, number of green leaves, stem width, root, shoot, and leaf area per plant decreased significantly as well as total dry weight [
Under root zone hypoxia stress, roots and shoots of the plant are inhibited because of the inordinate physiologic processes, such as chlorophyll biosynthesis, reactive oxygen species (ROS) metabolism, and anaerobic metabolism [12-16]. Numerous studies have shown that hypoxia stress triggers can produce ROS and induce oxidative stress in plants [17,18]. At stage of winter rape seedling, waterlogging significantly decreased leaf chlorophyll content and leaf photosynthetic rate, but accumulated leaf malondialdehyde [
Moog and Janiesch [
The kiwifruit (Actinidia deliciosa), native to the Yangtze Valley of China, is a large, woody, deciduous vine. Now it is abroadly planted as a burgeoning commercial planting fruit tree around the world because of the abundant nutrient value. But kiwifruit rootstocks are quite sensitive to waterflooding or excess of rainfall, which can easily produce root zone hypoxia stress and reducing conditions, and these stresses can damage the plants metabolism. So hypoxia stress is incidental to the kiwifruit plants during growing season.
In this thesis, 10 kinds of kiwifruit rootstocks were treated with hydroponics hypoxia to study their root zone hypoxia tolerance. The physiology and biochemical mechanism of hypoxia stress to the rootstocks were discussed, all the above is to provide the theoretic base and technical guideline for the cultivation and soil management.
Experiments were conducted at Forestry College of Henan University of Science and Technology, China. Test for kiwifruit materials, which originated from different climate regions in China, were listed in the table (
The experiments seedlings were subject to hypoxia by flushing nutrient solution with N2 gas for 11 days. The nutrient solution of control plants was continuously
flushed with air with an air pump. Oxygen concentration in the vessels was monitored with an oxygen meter (Dissolved Oxygen FC680, East China University of Science and Technology). Dissolved oxygen concentration was about 8.0 - 8.5 mg∙L−1 (control) at a normal level and about 0.9 - 1.1 mg∙L−1 (hypoxia stress) at a low level. After hypoxia stress treatment, top leaves and roots were randomly sampled so as to analysis each index. Each kind of kiwifruit was treated for 50 seedlings and each index was repeated at least 3 times in order to ensure the accuracy of the experiment.
At the end of treatment, the mortality rate of seedlings was statisticed. After treatment, plant height and max length of new root were measured by a ruler. After water sucked up with absorbent paper, seedlings were put into a drying oven at 105˚C for 15 min fixation, then dried at 75˚C for 72 h to constant weight, used for weighing.
RMP was measured according to the method described by Dionisio-Sese and Tobita [
Data were analyzed with Excel, SPSS V13.0 software.
Selecting several representative growth and physiological indexes, then using subordinate function value method to evaluate the root zone hypoxia resistance of kiwifruit seedlings [
A:; B:;
C:
Calculation of test indexes: positively correlated with anti hypoxia, by A formula above; negative correlation, by B formula above.
Cluster analysis was conducted by method of SPSS software’s euclidean distance. Euclidean’s distance tests were used to determine average linkage clustering. Material resistance grades were determined according to the results of cluster analyses. Resistance classifications were determined according to membership function index of average value.
Under root zone hypoxia stress, most of “Hongyang” and “Shanli” kiwifruit seedlings wilted apparently and death phenomenon happened at the end of treatment. Mortality rate of them could reach 63.33%. However, mortality rate of “Hayward” and “Qinmei” kiwifruit seedlings only reached 13.33%, 20%, respectively (
Under root zone hypoxia stress, length and width growing of each kiwifruit seedlings’ leaf was significantly inhibited (
The whole plant dry weight of kiwifruit seedling was also significantly inhibited by root zone hypoxia stress (
the root zone hypoxia stress to the growth of stronger resistant kiwifruit seedlings was in a small extent. Nevertheless, the inhibition of the weaker was in a much extent. So, resistant abilities to the hypoxia stress existed genotype differences among these 10 kinds of kiwifruit seedlings.
Suffered from root zone hypoxia stress, the kiwi fruit seedlings roots and height growth were inhibited in different degrees (
Root activity was a comprehensive index, which reflected root absorbing capacity. The experimental results showed that kiwifruit seedlings’ root activity was inhibited by root zone hypoxia stress (
Under stress, excessive ROS in plants body could cause the membrane lipid peroxidation, increase the permeability of cell membrane, thereby destroy the cell membrane structure and function, which disturbed the plant membrane system. While MDA was the product of plant cell membrane lipid peroxidation, whose content could reflect the cells extent of injury under stress. Compared with control, leaf membrane permeability and MDA content of kiwifruit seedling increased under root zone hypoxia stress (
Under root zone hypoxia stress, chlorophyll a, chlorophyll b, chlorophyll, chlorophyll a/b and carotenoid content of kiwifruit seedlings were destructed and reduced (
In this study, the resistance capabilities to root zone hypoxia stress were evaluated among the 10 kinds of kiwifruit seedlings. Analysis result showed: the resistance order from strong to weak was: “Hayward” > “Qinmei” > “Jinxiang” > “Kuoye” > “Huayou” > “Xixuan” > “Maohua” > “Jinhua” > “Shanli” > “Hongyang” (
On the basis of index membership function value, 10 kinds of kiwifruit seedlings were evaluated with cluster analysis method (
Data with different letters in the same column indicate a significant difference at p < 0.05 by LSD test.
three levels. Level one was hypoxia tolerance kiwifruit (“Hayward”, “Qinmei”, “Jinxiang”, “Kuoye” and “Huayou” kiwifruit). Level two was the medium of hypoxia tolerance kiwifruit (“Maohua”, “Xixuan”, “Jinhua”, “Shanli” kiwifruit). Level three had no resistance to hypoxia stress (or sensitive) (“Hongyang” kiwifruit).
In view of this, the average subordinate function values of the hypoxia stress-resistant kiwifruit seedling were much larger than 0.6 including “Hayward”, “Qinmei”, “Jinxiang”, “Kuoye” and “Huayou”. The average subordinate function values of medium-resistance were at the range of 0.3 - 0.6, including “Maohua”, “Xixuan”, “Jinhua”, “Shanli”. The average subordinate function value of nonresistance was smaller, which distributed below 0.3 including “Hongyang”. Evaluation and the actual root zone hypoxia stress test results were basically the same (
Oxygen was the final receptor in the process of electron transport and oxidative phosphorylation that conducted on mitochondrial membrane. Oxygen could drive ATP and NAD (P)+ synthesis in order to maintain the necessary for cell growth reduction capacity, which was the core element of plant’s normal life metabolism. Therefore plant’s growth and development would be affected
A: relative growth rate of leaves length; B: relative growth rate of leaves width; C: dry weight; D: max length of new roots; E: height of plant; F: root activity. G: chlorophyll a/b; H: RMP of leaves; I: MDA content of roots; J: MDA content of leaves; K: total photosynthetic pigment content of leaves; L: average of subordinate function values; M: resistance sequencing; N: resistance grade.
by root zone hypoxia. This study showed that, under root zone hypoxia stress, kiwifruit seedling’s growth was inhibited: biosynthesis volume reduced, root activity decreased, absorption function declined, chlorophyll a, chlorophyll b, total chlorophyll and carotenoid content decreased, and the ratio between pigments also changed.
Under hypoxia stress, the whole plant dry weight of the kiwifruit seedling was also inhibited, part of the reason might be that hypoxia stress reduced the leaf pigments content and the photosynthate accumulations were affected. In the present study, dry plant weight reduction varied greatly along with different testing materials. Among them, the inhibition degree of hypoxia stress nonresistance “Hongyang” was bigger, and that of “Hayward”, “Qinmei”, “Jinxiang”, “Kuoye” were lighter. Therefore, under root zone hypoxia stress, 10 kinds of kiwi fruit seedlings’ biomass were closely related to their tolerance-sensitivity. Research results were consistent with that of Malus, chickpea, Brassica napus L. [26-28].
Plant roots were active absorption and synthesis organs, and their growth status and activity level would directly affect nutritional status and yield of plants. The experimental results showed that, under root zone hypoxia stress, the kiwifruit seedling root activity was inhibited, and the reduction degree was obviously different between species. The relative higher activity of “Hayward”, “Qinmei”, “Kuoye” kiwifruit seedlings’ roots will be able to use sufficient nitrate to support photosynthesis and the growth of the aboveground parts. Thereby, low hypoxia-resistant kiwifruit seedling root had easily lost its activity and absorption function under the influence of hypoxia stress. This was because root respiration was inhabited by hypoxia, which caused decrease in the energy supply.
Under root zone hypoxia stress, MDA content in root and leaf increased significantly, which indicated its cell membrane was significantly damaged. Dramatic increasing of MDA content and RMP were caused by the generation of superoxide anion radical and content of hydrogen peroxide [
Chloroplast was an important cell organelle in the photosynthesis and light energy absorbed by chlorophyll can be converted into stable chemical energy and drive ATP formation via ATPase in the chloroplasts [
The hypoxia-resistant kiwifruit seedlings, “Hayward”, “Jinxiang”, “Qinmei”, belonged to Actinidia deliciosa in this experiment. Some varieties, such as “Huayou” that was the natural hybrids of A. delicious × A. chinensis var., lied between the strong and moderate hypoxia-resistant transitional site. While the moderate hypoxia-resistant and nonresistant kiwifruit, such as “Xixuan”, “Hongyang” belonged to A. chinensis var. Under root zone hypoxia stress, these interspecific differences among kiwifruit seedlings might be because of the genetic diversity. Isozyme genetic analysis showed A. deliciosa kiwifruit was a heterologous six ploidy plant, which had 174 chromosomes. While A. chinensis was a homologous tetraploid plant, which had 116 chromosomes [