根际pH与镉共同胁迫下对超高产杂交稻幼苗光合特性的影响

Effect of Cd^(2+)and Different pH in Rhizosphere on Photosynthetic Characteristics of Super High-yielding Hybrid Rice (Oryza sativa L.) Seedlings

通过测定Cd2+与根际pH双重胁迫下对高产杂交稻两优培九幼苗叶片的有关光合参数,探讨了Cd2+与根际pH值对植物毒害的关系。结果表明,随着pH值的升高,叶片中Cd2+和叶绿素的含量、类囊体膜的室温吸收和发射光谱的峰值均下降,而光合速率、呼吸速率和类囊体膜的光合电子传递活性为先升后降,以pH6.0时最高。类囊体膜的多肽组分分析表明,各pH梯度的类囊体膜蛋白多肽组分降解程度较为一致。Cd2+和pH的双重胁迫并没改变单一pH作用下的变化趋势。因此,在胁迫早期(10d),pH值对杂交稻幼苗光合特性的影响起主导作用。

To elucidate the influence of rhizosphere pH on Cd2+toxicity to rice, the photosynthetic characteristics of Liangyoupeijiu seedlings, a newly developed super high-yielding hybrid rice (Oryza sativa L.) were investigated. The seedlings were grown in culture solutions with Cd2+(10 mg·L-1) and varied pH, from 5.0 to 8.0. The results showed that Cd2+content in leaves decreased with the increasing pH value at rhizosphere and leaves accumulated higher amounts of Cd2+at pH5.0 than at other pH values. At the early stage of stress, the photosynthetic characteristics were complex in character. The chlorophyll contents of leaves decreased under the stress of pH (5.0～8.0) and Cd2+(10 mg·L-1), while, the chlorophyll a/b ratio of leaves firstly increased with pH from5.0 to 6.0, then declined at pH7.0 and significantly increased at pH8.0. At pH 8.0, the leaves accumulated the least Cd2+and the ratio of chlorophyll a/b was the largest. The photosynthetic rate and respiration rate increased at first and then decreased, with a maximum value at pH 6.0. Electron transfer activities of thylakoid membrane and fluorescence emission spectrum of thylakoid membrane at room temperature showed a similar changing pattern with photosynthetic rate and respiration rate. Cd2+had greater effect on PSⅡand all-electronic transfer activity than PSI electron transfer activity. Absorption spectrum of thylakoid membrane at room temperature decreased with increasing of rhizoshpere pH value. Analysis on polypeptide compositions also indicated that thylakoid membrane polypeptide compositions were degraded by Cd2+, but the degradations under thedifferent pH values were almost similar, implying that the Cd2+content in chloroplast might differ from that in leaves and the Cd2+contents at different pH values had no much difference at the early stage of stress. The addition of Cd2+did not alter the photosynthetic changing pattern induced only by rhizosphere pH at early stage. These suggested that rhizosphere pH might play the primary role in the photosynthetic inhibition of rice seedlings at early stage of stress.