毛白杨幼苗叶片生长及其光合参数和硼转运蛋白基因对高硼胁迫的响应

该研究采用毛白杨(Populus tomentosa)为试验材料,分析了温室条件下沙培幼苗对短期高硼胁迫(1、5、10 mmol/L硼酸)下的叶片生长、光合参数和硼转运蛋白的响应特征。结果显示:(1)与对照(0.05 mmol/L硼酸)相比,1 mmol/L硼酸处理导致毛白杨幼苗叶片叶绿素荧光参数上调,活性氧含量上升,树苗基部叶片出现少量黑色坏死斑;5 mmol/L硼酸胁迫下,叶片净光合速率、气孔导度和蒸腾速率下调,胞间二氧化碳浓度上升,叶绿素荧光参数和过氧化氢含量进一步上调,超氧阴离子含量较1 mmol/L硼酸胁迫时下调但仍然高于对照,除顶部叶片之外的其他叶片上出现大量坏死斑;10 mmol/L硼酸胁迫下,气体交换参数、叶绿素荧光参数和活性氧含量与5 mmol/L硼酸胁迫时相似,所有叶片均在平行于次级叶脉的方向出现呈带状分布的坏死斑。(2)毛白杨幼苗根和茎硼含量在硼胁迫条件下与对照相比变化幅度较小,而叶片硼含量在5 mmol/L和10 mmol/L硼酸胁迫下比对照显著上升,此时硼转移系数和生物富集系数均维持较高的水平。(3)硼转运蛋白(BOR)基因家族成员中PtoBOR4和PtoBOR8在根中的表达水平随着外界硼浓度的增加呈先上升后下降的趋势;在茎中,PtoBOR3基因下调表达,PtoBOR5上调表达;在叶片中,PtoBOR4表达先上升后下降,而PtoBOR7和PtoBOR8上调表达。研究表明,毛白杨幼苗叶片叶绿素荧光参数、活性氧、气体交换参数及硼转运蛋白基因家族表达对高硼胁迫较为敏感,硼胁迫症状在较短的时间内在叶片上以坏死斑的形式出现,可能与其较强的控制根系硼浓度的能力和向地上部分迅速运输硼的能力有关。

Responses of Leaf Growth, Photosynthesis and Boron Transporter Genes of Populus tomentosa Saplings to Excessive Boron

In this study, we used Populus tomentosa saplings as experimental material to analyze the leaf growth, photosynthesis and boron transporter (BOR) genes in response to short term excessive boron stress (1, 5, 10 mmol/L boric acid). The results showed that: (1) compared with the control (0.05 mmol/L boric acid, CK), 1 mmol/L boric acid treatment (BS₁) could lead to up regulation of chlorophyll fluorescence parameters and increase of reactive oxygen species in leaves, and a small amount of black necrotic spots appeared in the leaves at the base of the saplings. Under 5 mmol/L boric acid stress, the net photosynthetic rate, stomatal conductance and transpiration rate decreased, while intercellular CO₂ concentration increased. Chlorophyll fluorescence parameters and hydrogen peroxide content increased further, while ultra oxygen anion content was lower than BS₁, but still higher than CK. Necrotic spots showed up on most of the leaves. Under 10 mmol/L boric acid stress, gas exchange parameters, chlorophyll fluorescence parameters and reactive oxygen species content were similar to that of BS₅. All leaves showed necrotic spots with banded distribution that parallel to secondary veins. (2) The boron content in roots and stems changed slightly compared with CK, while in leaves it increased significantly under 5 mmol/L and 10 mmol/L boric acid stress. Boron translocation factor and bio concentration factor maintained at a high level. (3) Several members of BOR gene family showed responses. In roots, following the increase of boron treatment concentration, the expression level of PtoBOR4 and PtoBOR8 increased firstly and then decreased. In stems, PtoBOR3 was down regulated while PtoBOR5 was up regulated. In leaves, PtoBOR7 and PtoBOR8 was up regulated. The present study showed that P. tomentosa leaves are sensitive to high boron stress in terms of chlorophyll fluorescence parameters, gas exchange parameters, reactive oxygen species, and the expression patterns of BOR genes, probably due to the strong ability to control the boron concentration in roots and the ability to transport boron rapidly from roots to aerial parts.