| Aluminum toxicity is considered to be one of the main environmental factor which limiting crop growth in acidic red soil. The edible and medicinal value of Trichosanthes kirilowii maxim expand its market demand. So the impact of aluminum toxicity on the growth of T. kirilowii cannot be ignored in promoting the wide cultivation of T. kirilowii in acidic soils. Two varieties of T. kirilowii, which are different in A1resistance, were selected to solve the problem. A culture experiment was conducted to study the effects of different SA concentrations on physiological and growth characteristics, cell wall polysaccharides, photosynthesis, oxidation resistance and root exudates under A1stress. In addition, inter-simple sequence repeat (ISSR) was used to study the genetic diversity of T.kirilowii and its relationship with aluminum resistance. The results were summarized as followings:1. A solution culture experiment was conducted to study the effects of different SA concentration on growth characteristics, photosynthesis, oxidation resistance, UV-B absorbing compounds and MDA content of two Trichosanthes kirilowii cultivars, Anguo(Al-tolerant genotype) and Pujiang(Al-sensitive genotype), under800μmol/L aluminum stress. The results showed that800μmol/L Al3+treated for15days, the relative root length, plant height and fresh shoot weight, chlorophyll content, the maximum energy conversion efficiency(Fv/Fm), maximum fluorescence yield(Fm) and electron transport rate(ETR) were significantly lower of the two T.kirilowii cultivars. SOD, CAT activity changed in the opposite trend, indicating the differences of the two T.kirilowii cultivars in aluminum tolerance, POD activity and UV-B absorbing compounds decreased, MDA content and initial fluorescence(F0) increased. Adding10,30,50μmol/L exogenous SA could reduce MDA content and initial fluorescence(F0), also increase the relative root length, plant height, fresh shoot weight, chlorophyll content, chlorophyll fluorescence of the relevant indicators and antioxidant enzyme activity to a certain extent. By increasing antioxidant enzyme activities and photosynthesis-related indicators, SA enhanced the ability of T.kirilowii to resistance to aluminum toxicity. Comprehensive analyzing evaluation by the method of subjection function, the results showed that the external source of SA can alleviate aluminum toxicity to some extent, but it does not eliminate the inhibition of T.kirilowii growth caused by aluminum.2. A hydroponic experiment was conducted to study the effects of exogenous salicylic acid (SA) on relative aluminum content in the apical cell wall, acid phosphatase (APA) and pectin methyl esterase (PME) activity, root pectin, hemicellulose1(HC1), and hemicellulose2(HC2) contents of Anguo T. kirilowii (Al-tolerant genotype) and Pujiang T. kirilowii (Al-sensitive genotype) under800μmol/L of aluminum stress. The results showed that APA and PME activities were also enhanced for both cultivars. The contents of relative aluminum, pectin, HC1, and HC2, as well as A1accumulation in the root tips were increased under aluminum toxicity. Pujiang T. kirilowii showed higher enzyme activity and cell wall polysaccharide contents than Anguo T. kirilowii. In addition, the root cell wall pectin, HC1, and HC2contents of Pujiang T. kirilowii were increased by a large margin, showing its greater sensitivity to aluminum toxicity. Aluminum toxicity led to the accumulation of pectin and high PME activity, and also increased the number of free carboxyl groups, which have more aluminum binding sites. Different SA concentrations can decrease enzyme activity and cell wall polysaccharide content to some extent. With the addition of different SA concentrations, the root relative aluminum content, cell wall polysaccharide content, APA and PME activities decreased. Aluminum toxicity to both genotypes of T. kirilowii was relieved in different degrees as exogenous SA concentration increased.3. The result of exogenous SA on the root exudates of Trichosanthes kirilowii under aluminum stress show that the citrate synthase (CS) and malate dehydrogenase activities were enhanced in both cultivars. The organic acid content of root exudates was increased, including citrate, oxalic acid, and malate. Citrate content was much higher compared with oxalic acid and malate; However, the total amino acid content was decreased. The SA content of Anguo T. kirilowii was decreased, whereas that of Pujiang T. kirilowii was increased, showing opposite change. This result may be due to the different aluminum resistances between Anguo and Pujiang T. kirilowii. The addition of exogenous SA significantly increased the organic acids of root exudates compared with the To group; Citrate is the main organic acid that alleviates aluminum toxicity. With the increase of SA concentration, the CS activity of Anguo T. kirilowii and the malate dehydrogenase activity of Pujiang T. kirilowii were decreased; however, the CS activity of Pujiang T. kirilowii and the malate dehydrogenase activity of Anguo T. kirilowii were increased. This result indicates that the application of exogenous SA affects organic acid metabolism and increases organic acid efflux, and the A1signal may be mediated by the SA signal transduction pathway. The growth condition of T. kirilowii was recovered with the addition of SA. Therefore, this study proved that SA can alleviate aluminum toxicity to some extent. 4. Inter-simple sequence repeat (ISSR) was used to study polymorphism and cluster on9T. kirilowii materials. The result showing that the genetic differences among T. kirilowii were obvious. The genetic diversity was high in species level, but low in population level. The degree of genetic differentiation within populations was higher, and the genetic variation among populations was greater than that within population. There are gene exchange exist among populations. Cluster analysis showed that Anguo T. kirilowii and Pujiang T. kirilowii belong to different branches, indicating different in aluminum tolerance has a certain correlation with genetic distance, genetic identity, and phylogenetic relationship of T. kirilowii species. |
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