外源油菜素内酯对镉胁迫下菊芋幼苗光合作用及镉富集的调控效应

Regulation of exogenous brassinosteroid on growth and photosynthesis of Helianthus tuberosus seedlings and cadmium biological enrichment under cadmium stress

以两种菊芋(Helianthus tuberosus L.)品系南芋2号(NY2)和南芋5号(NY5)为材料,研究了外源24-表油菜素内酯(24-EBL)对镉胁迫下菊芋幼苗干重、根冠比(R/S)、光合色素含量、叶片气体交换参数和水分利用效率(WUE)的调节效应,还测定了其不同器官的镉(Cd)含量。结果表明:在镉胁迫下,2种菊芋幼苗的干重、R/S、光合色素含量、净光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)、WUE均呈下降趋势,而胞间二氧化碳浓度(Ci)升高。(2)与镉胁迫相比,胁迫下外源喷施10-10、10-9、10-8、10-7mol/L 24-EBL作用下,两品系植株干重和R/S值均不同程度的上升,NY2、NY5的植株干重分别在10-9mol/L 24-EBL(EBL2)和10-8mol/L 24-EBL(EBL3)处理下达到最大值,分别增加50%和64%。镉胁迫下,外源24-EBL处理均提高菊芋的叶绿素(Chl)和类胡萝卜素(Car)含量,Pn、Gs、Tr也由此得到不同程度的上升,而Ci均下降,NY5的Ci下降更显著。镉胁迫下,外源EBL2和EBL3作用下均不同程度地提高其WUE,NY5的WUE增幅远大于NY2。镉胁迫下NY5的新完全展开叶Cd含量的积累明显高于NY2;而EBL2处理下可降低NY2的新完全展开叶Cd含量,但EBL3却显著增加NY5的叶片Cd含量。镉胁迫下,喷施EBL2的NY2的不同器官、NY5根的Cd含量均显著下降,而NY5其他器官的Cd含量变化不显著。NY5不同器官的Cd含量均明显高于NY2。上述表明,24-EBL可明显提高菊芋的耐镉水平,主要是因为外源喷施24-EBL能显著促进其光合和提高水分利用效率,从而改善Cd胁迫下菊芋幼苗的生长;而24-EBL对菊芋NY5非气孔限制的更显著改善是其促进其光合、水分利用的重要原因,也是其对NY5的生长调控效果优于NY2的重要原因之一。结果还显示,菊芋NY5植株生物量大,从环境中提取Cd的能力较好,因此可作为重金属污染土壤的植物修复的材料来利用。

Helianthus tuberosus is well-known Asteraceae plant for its high environmental adaptation ability. It is easy to cultivate, which tempts gardeners to simply leave them completely alone to grow. However, growth and development of this plant is also sensitive to cadmium. In order to evaluate the regulation effects of brassinosteroid on plant cadmium resistance of H. tuberosus, this experiment studied the regulation effect of exogenous foliar spraying 24-brassinosteroid （24-EBL） on seedling dry weight, root shoot ratio （R/S）, photosynthetic pigment content, leaf gas exchange parameters, water use efficiency （WUE）, cadmium （Cd） content of two H. tuberosus varieties （NY2 and NY5） under 100 μmol/L cadmium （Cd） stress. The results showed that： （1） Compared with control, the plant dry weight, R/S ratio, photosynthetic pigment content, net photosynthetic rate （Pn）, stomatal conductance （Gs）, transpiration rate （Tr） and WUE were decreased, while the values of intercellular CO2 concentration （Ci） were increased in NY2 and NY5 seedlings under Cd stress. （2） Compared to only Cd treatment, the plant dry weight and R/S ratio were increased to varying degrees with exogenous spraying different 24-EBL concentrations （10-10, 10-9, 10-8, 10-7 mol/L） under Cd stress. 10-9 mol/L 24-EBL （EBL2） and 10-8 mol/L 24-EBL （EBL3） treatments made the dry weight of NY2 and NY5 peaked, and 50% and 64% higher than the values of only Cd stress treatment, respectively. （3） Compared to only Cd treatment, 24-EBL application increased the contents of both chlorophyll （Chl） and carotenoid （Car） in two H. tuberosus seedlings under Cd stress, and also increased their Pn, Gs, Tr in NY2. However, 24-EBL decreased the values of Ci in both H. tuberosus seedlings, and Ci decrease of NY5 showed more significantly than that of NY2. （4） Under Cd stress, 24-EBL increased the WUE values of NY2 and NY5 in varing degrees, respectively, and WUE increase of NY5 showed greater than that of NY2. （5） Under Cd stress, Cd accumulation in new expanded leaves of NY5 was much higher than that of NY2, and EBL2 reduced its Cd content of NY2, but EBL3 enhanced its Cd content of NY5. （6） Under Cd stress, foliar spraying 24-EBL significantly decreased Cd content in all of organs of NY2 and in root of NY5, but did not markedly affect Cd content in the other organs of NY5. Generally, the suitable concentration of 24-EBL could significantly improve cadmium resistance of H. tuberosus, and it was mainly due to improvement of photosynthesis and water use caused by 24-EBL. Furthermore, compared with NY2, the better amelioration of non-stomatal restrictions on the NY5 plant applied with 24-EBL leads to its better improvement of photosynthesis and WUE, and its higher growth stimulation under cadmium stress. The results that NY5 plants has much larger biomass, more Cd accumulation and better biomass increase applied with 24-EBL under cadmium stress than NY2 also implied that NY5 can be considered as an excellent candidate for phytoremediation of metal-contaminated soils.