蓖麻叶片光合和光谱特征对镉毒害的响应

Responses of Photosynthetic and Spectral Properties to Cadmium Toxicity in Leaves of Castor Bean

以蓖麻为研究对象,通过营养液培养试验,探讨蓖麻生长和光合特性对不同浓度镉胁迫的响应.研究结果表明,10～50μmol.L-1Cd对蓖麻幼苗生长、光合作用、光合色素含量、叶绿素荧光参数以及反射光谱特征均具有明显抑制作用.根系生物量随着镉浓度的增加而逐渐降低,但地上部分生物量却不表现出浓度效应,从而导致植株的根冠比显著增大.随着镉浓度的升高,光合速率、气孔导度和蒸腾速率显著降低,而胞间CO2浓度和叶绿素a/b比值(Chla/b)则在10μmol.L-1Cd处理下升高,随后下降至对照水平.光合色素含量(叶绿素a、叶绿素b、叶绿素a+b、类胡萝卜素)、叶绿素荧光参数(Fv/Fm、Fv/F0及ΦPS Ⅱ)以及Red/Green和SIPI在不同浓度Cd处理之间均无显著差异.镉胁迫导致光合速率降低的原因与Cd浓度密切相关.在低浓度下,光合速率的降低主要是由于光合色素含量下降、PS Ⅱ活性中心受到抑制等非气孔因素所致;而在高浓度镉胁迫下,光合速率的降低受气孔限制因素和非气孔限制因素的双重影响.

To study the growth and photosynthetic response of castor bean to cadmium （Cd） stress, the pigment, chlorophyll fluorescence, gas exchange, and spectral properties of castor bean seedlings treated with different Cdconcentrations （10, 25 and 50 μmol · L^-1 CdCh） were investigated by hydroponics culture experiment. The results showed that 10-50 μmol· L^-1Cd had a significant inhibitory effect on growth, photosynthesis, pigmentcontents and spectral reflectance in castor bean seedling. The root biomass reduced with the increasing of Cd concentration. However, the shoot biomass showed a concentration independent manner, as a result, leading to an increase in the root/shoot ratio, especially at low Cd levels. With the Cd concentration increased, thephotosynthetic rate （Pn）, stomatal conductance and transpiration rate were significantly reduced, while the intercellular CO2 concentration and chlorophyll a/b ratio firstly increased at 10 μmol· L^-1 Cd treatment and thendeclined to the control levels. No significant difference in pigment contents （hlorophyll a, chlorophyll b, chlorophyll a＋b, carotenoids）, chlorophyll fluorescence parameters （Fv/Fm, Fv/F0 and ФPS Ⅱ）, as well as Red/Green and SIPI was observed between 10 μmol · L^-1, 25 μmol · L^-1 and 50 μmol · L^-1 Cd treatments. It isconcluded that the mechanism of Cd - induced decline in Pn in castor bean may be concentration dependent. At low Cd levels, the decrease in Pn mainly resulted from the nonestomatal factors such as the reduction of pigment contents, and destruction of the reactive center in photosystem Ⅱ, whereas, at high Cd levels, both the stomatal and nonestomatal limitation is involved.