Effects Of Different Rootstock-scion Combinations On Aluminum-tolerance Of Citrus

Little information is available on the roles of rootstocks and scions in plant Aluminum (Al)-tolerance. Four scion-rootstock combination [i.e., X/X and X/SP,’Xuegan’(Citrus sinensis) grafted on ’Xugan’ and ’Sour pummelo’(Citrus grandis), respectively and SP/X and SP/SP,’Sour pummelo’ grafted on ’Xuegan’ and ’Sour pummelo’, respectively] plants were irrigated for 18 weeks with nutrient solution containing 0 (-Al) and 1.2 mM AlCl3·6H2O (+Al). Thereafter, phosphorus (P) and Al in leaves, stems and roots, organic acids (OAs) in leaves and roots, Al-induced secretion of OA anions (i.e., malate and citrate), leaf gas exchange, chlorophyll (Chi) a fluorescence (OJIP) transients, the contents of organic acid in roots and leaves, organic acid metabolism enzyme activity in roots and leaves and the contens of nonstructurAl carbohydrates in roots and leaves were measured. The purpose was to clarify the different stock-scion combinations on the effects of Al resistance of plants from physiological aspects in this paper. The results of the study were as follows:1. Al inhibited the growth of grafting plants and leaves turned yellow. Al decreased root, shoot and whole plant (root+shoot) DW, and increased the ratio of root DW to shoot DW except that the ratio of SP/SP plants did not significantly change in response to Al. Though ’Xuegan’(Citrus sinensis) of Al resistance is stronger than’Sour pummelo’(Citrus grandis), Al treatment did not cause significant differences in plant growth among four rootstock-scion combinations.2. Al not only inhibited the leaf CO2 assimilation rate, and reduced Chi a+b, Chi a and Chi b concentration, such as the ability of photosynthesis physiological indexes, but also changed in OJIP transients, positive △L-, △K-, △J- and △I-bands and most of the fluorescence parameters [i.e. Fv/Fm, ETo/ABS, REo/ABS, DIo/ABS, ABS/RC, DIoRC and PItot,abs]. Data displayed Al-induced inhibition of photosynthesis and impairment of photosynthetic electron transport chain were less pronounced in X/X and X/SP leaves than in SP/SP and SP/X leaves, which might be associated with higher Al-induced secretion of OA anions and leaf P concentration.3. C. sinensis rootstock alleviated the influences of Al-toxicity on leaf photosynthetic electron transport chain by enhancing Al-induced secretion of root OA anions, hence lessening Al-induced photosynthesis inhibition in SP/X plants, while the reverse was the case for C. grandis rootstock in X/SP plants. However, the contents of organic acid did not significantly correlation between Al-induced secretion of root OA anions. The contents of malate and citrate maybe involved in the biosynthesis and degradation of related enzymes.In conclusion, the tolerance of grafted Citrus plants to Al depends on the scion as well as rootstock genotype, and the scion-rootstock interaction.