Effects and Mechanisms of Chloride on Canola Seedings' Growth, Nutrient Absorption and Utilization
|School||Nanjing Agricultural College|
|Keywords||canola chloride growth photosynthesis nitrogen proton pump|
Chlorine is one of the essential microelement for plants, and it has many vital physiological functions. The salinization of Agricultural soil is becoming more and more serious, which affect the yield and quality of crops; it becomes an important limiting factor in agricultural production. Widespread concerns and researches were given on the excess of Na+effects on growth, yield and quality of crops in soil and environment, but there was less study about the excessive chlorine excess on crops. In our study, canola(Brassica napus L. cv. Nanyanyou1) was supplied as experimental material and cultivated in pots filled with sand. We mainly investigated the application effects of different chloride concentrations for9and18d on growth, nutrient and ion absorption and distribution of canola seedlings, and their photosynthetic pigments and photosynthetic characteristics. The key enzymes of nitrogen metabolism in different parts of canola leaves and the Hydrolytic activities of plasma membrane H+-ATPase and tonoplast H+-ATPase, H+-PPase under different chloride treatment were also studied. The results showed that:(1) The seedling dry matter accumulation rate (DMAR) exposed to low chloride treatments (25～75mmol·L-1Cl-) was significantly higher than that of control, and the DMAR under50mmol·L-1Cl-treatment achieved peak value. While the DMAR was decreased significantly under200mmol·L-1Cl-treatment, proved that high chloride treatment had an obvious inhibition on canola growth. With the increase of Cl" treatment concentration, NO3-content in canola leaves was gradually decreased, but total N content in leaves has not reduced obviously after18d treatment, indicating that exogenous chloride treatment had no impact on the total N content while reducing NO3-content in canola seeding leaves. K+contents in calona root and petiole were increased under Cl-treatments for9and18d. Ca2+content in root and petiole were significantly descended comparised with control, but the content of Ca2+in leaves were increased first and then decreased followed, indicating that Cl-treatment could inhibit the absorption of Ca2+in root and petiole, but low Cl-treatment had certain promotion on leaf Ca2+distribution. With the increase of concentration of Cl-treatment, Mg2+content was mostly increased first and then decreased in calona roots, petioles and leaves but somewhat higher than that of control. Seen from the Infrared Data:the surface temperature of canola seedling leaves were increased gradually with the increased concentration of Cl-treatment indicated that high Cl" treatment decreased stomatal conductance.(2) Apart from Ci under Cl-treatments for18d, canola leaves were able to maintain high values of Pn, Gs, Ci, and Tr under25～100mmol·L-1Cl-treatments. Pn, Gs, Ci and Tr of canola leaves were significantly decreased under200mmol·L-1Cl-treatment for9and18d. As Cl-concentration was increased, WUE was descended in first and ascended followed. However, Ls was descended in first and ascended followed under Cl-treatment for9d, and increased gradually for18d. Our results implicated that photosynthesis and transpiration of canola seedlings were significantly increased under low Cl" treatment and thus made a contribution to plant growth. However, high Cl-treatment showed an opposite situation, and the photo synthetic limitation was mostly due to stomatal limitation.(3) Apart from glutamate dehydrogenase (GDH), several other key enzymes of nitrogen metabolism:nitrate reductase (NR), glutamine synthetase (GS), glutamate synthase (GOGAT) activity were all first increased, and then decreased. The GS and GOGAT activity reached the maximum under25mmol·L-1Cl-treatment. The activity of GDH were lower than control at different Cl-concentrations, and were reduced to a minimum at50mmol·L-1Cl-treatment.(4) Western blot results showed that the plasma membrane H+-ATPase concentration in root under50mmol·L-1Cl-was significantly higher than the control and25mmol·L-Cl-treatment. Plasma membrane H+-ATPase hydrolysis activity under50mmol·L-1Cl-was significantly higher than that of control while H+-ATPase hydrolysis activity under200mmol·L-1Cl-was significantly lower than control in roots. Plasma membrane H+-ATPase concentration in leaves under50mmol·L-1Cl-was significantly higher than the control and25mmol·L-1Cl-treatment. And the tonoplast H+-ATPase and H+-PPase activities under25and50mmol·L-1Cl-treatments were higher than control,200mmol·L-1Cl-treatment of tonoplast H+-ATPase and H+-PPase hydrolysis activities were significantly lower than control.From the results above we found that, low chloride concentration can actively modulate the proton pump hydrolysis activity of calona seedlings’roots and leaves in cell membrane and vacuole membrane, thereby regulate the transmembrane transport of Cl", N, K and other solutes, which enhance the absorption and utilization of nitrogen, chlorine, and become main dynamic of its growth; NR, GS, GOGAT nitrogen assimilation enzymes could also be activited by low chlorine and at the same time the nitrogen assimilation was accelerated, improving plant nitrogen use efficiency; Low chloride can also adjust the water status of the plant leaves, so as to increase the stomatal conductance and intercellular CO2concentration which lead to the photosynthesis promotion. But the high chloride inhibited the growth of canola seedlings.