Comparison Of Changes In Root Structure And Photosynthetic Characteristics In Response To Aluminum Toxicity In Two Pigeonpea Cultivars Differing In Al Tolerance

The active form of Al in acidic soil, Al3+, is phytotoxic and can significantly affect plant growth and the formation of crop quality and yield. Pigeon pea (Cajanus cajan (L.) Millsp) is of high productivity and strong resistance to drought, salt and acid soils. In this study, two pigeon pea cultivas, the tolerances of Guimu4(GM4) and Guimu6(GM6) to Al were screened by measuring the root elongation, accumulations of callose and aluminum in root apex under stresses of different Al concentrations (0～200μmol/L) and duration (0～72h). And then, the two cultivars were cultured and stressed in1/5Hoagland containing0～3mmol/L AICl3for14d. The morphological structure of pigeon pea root, photosynthetic gas exchange and chlorophyll a fluorescence characteristics were investigated using Root Analysis Software (WinRhizo), photosynthesis system (LI-6400) and chlorophyll fluorescence analyzer (PAM-2000), respectively. The results show that:(1) GM6is more tolerant to Al than GM4by maintaining root elongation and accumulating less Al and callose in root tips during the whole stress period.(2)Under low concentrations of aluminum(≤l mmol/L), the total root length, root surface area, root volume and root average diameter of GM4increased slightly when is compared with the control, however it is not significant. While the above index of GM6increased more with the average diameter reaching significant level. The root activity of GM4decreased rapidly with the increasing of aluminum concentration, while root activity of GM6rosed slightly in low Al concentrations (≤1mmol/L) stress. The total root length, root surface area, root volume, root average diameter and the root activity of both of the two pigeon pea cultivars is decreased significantly in high level of Al stress. Amplitude of GM6is less than GM4.(3) Under low concentration of aluminum(≤1mmol/L) processing, the net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) of both the two pigeon pea cultivars increased gradually. Guimu6leaf net photosynthetic rate(Pn) and transpiration rate (Tr) increased greater than Guimu4. In high level of Al stress, the net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) of both the two pigeon pea cultivars increased significantly. The decline extent of GM4is greater than GM6.(4) Under low Al concentration (<≤1mmol/L) stress, the initial fluorescence (Fo) of two pigeonpea leaves increased with increasing of aluminum concentration, and GM4increased more significantly than GM6. The maximum fluorescence (Fm) of the two pigeon pea cultivars increased slightly at first time and then decreased rapidly. And GM4had a bigger drop than GM6. With the increasing of aluminum concentration, leaf potential PSII activity (Fv/Fo) of the two pigeon pea cultivars increased notablely and then comes a rapid decline. GM4had a higher potential activity of PSII than GM6. Under Al stress, the actual photochemical efficiency of PS Ⅱ (Yield) of GM4is continued to decline and the extent is notablely when compared with the control. However, GM6displayed a significant increase and then a gradual decline aftewards.In summary, GM6has a stronger resistance to aluminum than GM4. Under Al stress, the structure and activity of root and photosynthetic characteristics of GM6are better than GM4.