| Rare earth elements had significant effect to improve the efficiency of photosynthesis of plants. In this paper, the experimental material were winter wheat (Shannong129) and spinach, by the effect of rare earth elements (lanthanum and praseodymium) on chlorophyll fluorescence characteristics, chlorophyll protein content,protection enzymes (POD and SOD) activity, isozyme spectrum and the content of photosynthetic phosphorylation coupling factor, the study explored rare earth elements to improve the physiological mechanisms of plant photosynthesis, and researched the execute solution by improving plant photosynthetic electron transport and photosynthetic phosphorylation in a safe and efficient; has great significance for the application and promotion of rare earth in agriculture, and improving crop yield and quality.The main results of this study were as follows:(1)The LaCl3could improve photosynthetic efficiency of photosystem Ⅱ (PS Ⅱ). The LaCl3solution of different concentrations had effect on chlorophyll fluorescence parameters of the wheat by foliar spray treatment in different periods, and the most obvious result was40μmol·L-1.First, the light maximum fluorescence of the wheat by LaCl3solution processing during the chilling stress was higher than that of control groups, showed the resistance to chilling injury of wheat at seedling stage was better than that of the control groups, LaCl3enhanced the resistance to cold of wheat.Second, comparing with the control group, the relative electron transfer rate of wheat light system by LaCl3treating in the reviving could improve, light damage can be reduced under low light PS Ⅱ,LaCl3foliar spray could protect PSII. In the case of disruption of body-side electron transfer, the reaction center complexes are exposed to light damage whether the presence of either aerobic or anaerobic. Except Chla, β-Car also was obviously destroyed. In the case of disruption of the receptor side of the electron transfer, the degree of optical damage of reaction center complexes depended on the presence of oxygen. The ion pairs of original charge separation formation occurred charge recombination because of electron transfer receptor side blocked, and produced part of the3P680, and these3P680could react with dissolved oxygen generating singlet oxygen (1O2). Highly reactive1O2damaged primary electron donor P680, Pheo and His residue, resulting in degradation of the D1protein, decreasing of photosynthetic rate.Wheat heading stage is the maximum period of the year. At11:00to15:00, the excess photon was especially obvious for wheat light damage. The study showed that the LaCl3foliar spray could improve the wheat leaves photosynthetic efficiency, and the PS II quantum yield (Y (II)) increased. PS Ⅱ reaction center deal with excess light energy through zeaxanthin cycle consuming excess excited electrons, for the protection of PS II reaction center from light damage. In this case, the necessary consumption of excited-state electron reduced Chla fluorescence quantum yield. After the LaCl3foliar spraying, the non-photochemical quenching (NPQ) of wheat functional leaves increased,and showed LaCl3could protect PS II from light damage, increasing the photosynthetic efficiency of PS Ⅱ. The increase of regulatory energy dissipation (Y (NPQ)) and the reduce of non-regulatory energy dissipation (Y (NO)) showed the wheat by LaCl3foliar spray protected PS II through more heat dissipation, and improved the efficiency of photosynthesis of wheat.(2)LaCl3has protective effect on PS II in yellowing of adversityFirst, LaCl3could enhance POD, SOD enzyme of wheat leaves in yellowing of adversity. This study showed that, the electrons of the H2O photolysis producing by Mn oxidation passed from P680to Pheo, then passed to the two quinone molecules QA and QB. P680+was deoxidized by D1protein tyrosine residues Z (Z163). In photoinhibition conditions, the accumulation of acceptor side QA would make P680form3P680,the latter could form1O2with O2, singlet oxygen and the oxidation state of P680+could destroy the chlorophyll, carotene and D1protein, named PS II destruction. The rate of PS II from the donor side accepting Electronic in bright light was much lower than that of offering the electron to the acceptor side, and extended the time of P680*,which was easy to form P680*, thereby forming1O2with the O2. Through the determination of POD and SOD activity as well as the PAGE analysis results of POD and SOD enzymes showed, the LaCl3solution treatment improved the POD and SOD activity of wheat functional leaves, which effectively reduce the damage of optical system through active oxygen in wheat functional leaves.Second, LaCl3had the inhibitory effect on chlorophyll degradation during yellowing of adversity. The test results showed that the two methods (soaking and spraying) did not have significant difference, and the two methods have little effect on the results. The experimental design were, LaCl3concentration of10mol·L-1,20mol·L-1,40mol·L-1and80mol·L-1, the degree of reduction of the chlorophyll content with the increase of the number of etiolation days was lower than the control groups, that showed10-40mol·L-1LaCl3facilitated the synthesis of chlorophyll and the effect was obvious with the concentration increased significantly, while the80mol·L-1LaCl3inhibited the synthesis of chlorophyll on the first day, after that promoted the synthesis of chlorophyll under the yellowing. The test results showed that the appropriate concentration of LaCl3had a certain extent inhibition effect on the reduction of the chlorophyll content under yellowing duress. Chlorophyll was the pigment capturing light energy and transforming light energy, and had a close relationship with the size of the leaf photosynthetic performance, the appropriate concentration of LaCl3could promote the improvement of photosynthetic capacity in the yellowing process. Microscopy studies showed that rare earth could increase the number of chloroplasts in the mesophyll tissue, improve the density of the arrangement of the vascular bundles, and improve the efficiency of photosynthesis.(3)LaCl3inhibited the degradation of the reaction center D1protein of PSII in yellowing of adversity The leaves by appropriate concentration of LaCl3treatment made the PQ restore, QB binding sites could not be combined with reduced PQ, and the degradation of D1protein was inhibited. The facilitation of LaCl3and PrCl3on the photosynthetic phosphorylation and the rate of electron transfer had little relationship, and the affected area may be in the process of phosphorylation. Determination the effect of LaCl3and PrCl3on the chloroplasts Mg2+-ATPase and coupling factor Ca2+-ATPase activity by chloroplast eluting, LaCl3and PrCl3had activation effect on these two reactions. LaCl3and PrCl3could directly affect the phosphorylation reaction by coupling factor catalyzing. After LaCl3and PrCl3spraying crops blade, it could improve the photosynthesis, and that may be the main reason for the increase of yield.(4)La3+concentration was in the range of0-20mol/L, regardless of the CFl-ATPase activated by heat-DTT, or ATP vitality hydrolyzed CFl-ATPase activated by heat-DTT on thylakoid membrane heat-DTT, its kinetics of curve were "S". Because of the Hill coefficient closing to1.5, it indicated that La3+had activation effect on CF1-ATPase. In addition, the kinetic curves of CF1-ATPase activity for La3+concentrations in the range of0-20mol/L were similar with these of the chloroplasts Hill reaction activity for La3+concentration in the range of0-20mol/L which our previous studies reported. Therefore, the key parts of chloroplasts Hill reaction activity affected by La3+were likely to the CF1site of CF1-CF0 complex on the membrane. There remained to be further in-depth study, which was what kind of CF1subunit and the exact location of La3+function, and causing allosteric activation effect.Rare Earth had a significant impact on plant photosynthesis, the test results showed that a certain concentration of rare earth promoted the activity of plant PSII protein complex and accelerated the rate of photosynthetic electron transport, thereby contributing to the entire solar energy conversion and photochemical reactions. Low concentrations of rare earth could increase the fluorescence emission of light system I and the development of chloroplast plasma membrane. Meanwhile, rare earth could increase the number of chloroplasts in the mesophyll tissue and improve the density of the arrangement of the vascular bundles, thus improving the efficiency of photosynthesis. Therefore, the rare earth participated in or influenced the metabolism of photosynthetic pigment, electron transport, photosynthetic phosphorylation, and maintenance of the structure and function of photosynthetic system, thereby affecting plant photosynthesis and photosynthetic performance. From determination the effect of LaCl3and PrCl3on the chloroplasts Mg2+-ATPase and coupling factor Ca2+-ATPase activity by chloroplast eluting, LaCl3and PrCl3had activation effect on these two reactions. This indicated that LaCl3and PrCl3had directly effect on the coupling factor catalyzing phosphorylation reaction. The ATP hydrolysis activity changes by LaCl3treating the hot-DTT activation CF1-ATPase and the heat-DTT activation CF1-ATPase on thylakoid membrane, demonstrated the influence of La3+. |
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