玉米根系吸水能力细胞水平的杂种优势

Heterosis of Water Uptake Ability by Roots of Maize at Cell Level

在人工气候室水培条件下,以玉米(ZeamaysL.)杂交种F1代户单4号及其母本天四和父本478为材料,用细胞压力探针技术研究了正常供水和PEG-6000模拟–0.2MPa水分胁迫条件下,玉米根皮层细胞水分关系参数的基因型差异。结果表明,根皮层细胞的直径、长度和体积均为F1代>母本>父本;正常供水条件下3个玉米品种的根皮层细胞膨压均在0.6MPa左右且品种间差异不显著,水分胁迫抑制了细胞的延伸生长且F1代和母本的细胞膨压显著高于父本;根皮层细胞壁体积弹性模量均为父本>母本>F1代,水分胁迫条件下的品种间差异显著;与正常供水条件相比,水分胁迫条件下细胞膨压显著降低,而弹性模量则大幅度提高;在两种水分条件下,水分跨细胞膜运转的半时间均为父本>母本>F1代,且半时间在水分胁迫条件下均显著高于正常供水条件下;HgCl2处理引起了半时间的延长,2-巯基乙醇则部分逆转了HgCl2的效应;在两种水分条件下,根皮层细胞水导均为F1代>母本>父本且品种间差异显著,水分胁迫则显著降低了细胞水导。试验证明杂交种F1代的细胞水平根系吸水能力优于亲本,体现了杂种优势。

Cell pressure probe technique has been extensively used to study plant water relations at cell level. Effect of numerous internal or external factors on water uptake by plant root cells has been studied. However, the feasibility of this technique for investigating the difference of water related parameters among varieties of the same plant species has not been reported. In this paper, the cell pressure probe was employed to study cortex cell water related parameters of primary roots among three different maize genotypes （F1 hybrid of HD4, its female parent T4 and male parent 478） under normal and water stress conditions. The water stress was simulated with PEG-6000 with ψs value of –0.2 MPa. As to the size of root cortex cells, the diameter, length and volume of cells represented as F1 〉 female parent 〉 male parent under both conditions, and there was significant differences of volume among the three maize genotypes. Water stress reduced cell diameter and length obviously so as to decreased volume significantly. The root cortex cell turgor of the three maize genotypes was approximately 0.6 MPa and the genotypic difference was not noticeable under normal culture condition. By contrast to normal condition, cell turgor values of the three maize genotypes were decreased by 0.2–0.3 MPa under water stress condition and cell turgor of male parent was significantly lower than that of the other 2 varieties. The volumetric elastic modulus of the cell wall is a property of rigid cell wall which represents the change in turgorof a cell caused by a given change of the relative volume. Value ofelastic modulus represented as male parent 〉 female parent 〉 F1 under the two water levels and enhanced by water stress significantly. Moreover, the differences of elastic modulusamong the three maize genotypes were significant under water stress condition. The half time of water exchange represented as male parent 〉 female parent 〉 F1 under the two water levels, and water stressprolongedhalf time; 50 μmol·L-1 HgCl2 also prolongedhalf time, but 5 mmol L-1 2-mercaptoethanol reversed the effect partly and the final half timewas even larger than the original value. The cell hydraulic conductivity represented as F1 〉 female parent 〉 male parent under the two water levels, and water stress noticeably decreased cell hydraulic conductivity. The results indicated that F1 was better than the parents and showed heterosis in water uptake ability at cell level, and cell pressure probe worked well in the study of genotypic difference of cell water related parameters. The above results also provide scientific references for breeding and selecting new genotypes of maize with improved ability of water uptake by roots and with drought-resistance.