不同品种西红柿、苋菜盐分胁迫响应机制对吸收土壤Cd的影响

Large areas of saline farmland soil were contaminated with Cd in China. Growing salt tolerant crop cultivars with low Cd accumulation is one of the best choices to reduce its health risk in crops cultivated in middle or slightly Cd polluted saline soils. However, although many studies on the crop salt tolerance and the selecting and breeding pollution-safe cultivars (PSCs) were seperately reported, few studies were carried out on enhancing crop salt tolerance and meanwhile reducing crop Cd accumulation. Our previous research found that many vegetable cultivars with low sodium concentration under saline condition also accumulated lower Cd concentration in crops. Therefore, the objectives of this project are to grow the tomato (Solanum lycopersicum) and edible amaranth (Amaranthus mangostanus), representing fruit vegetable and leaf vegetable respectively, and investigate the differences of salinity stress responces of low/high sodium accumulation cultivars in root exude, rhizosphere microorganism, root cell wall, osmotic regulation and cation transmembrane transport in root, osmotic potential gradient and evapotranspiration. The molecule mechanism of these differences will be revealed.The effects of these factors on the accumulation of Cd in crops also will be surveyed so as to reveal the mechanism of low Cd accumulation in low Na accumulation vegetable cultivars under saline condition. The results will provide useful information and theoretical base for the selecting and breeding of salt tolerant vegetable cultivars with low Cd accumulation, and for the development of techniques enhancing crop salt tolerance and meanwhile reducing crop Cd accumulation.

我国受盐渍化和重金属污染双重影响的农田土壤面积很大，Cd是主要重金属污染物之一。种植既耐盐又Cd低累积品种是实现中轻度Cd污染盐渍土壤安全利用的理想途径。但是，尽管对作物耐盐性及Cd低累积品种已分别开展了大量研究，而针对同时增强作物耐盐性和降低Cd累积方面的研究，却鲜见报道。本项目根据前期研究中发现的许多Na低累积品种也具有Cd低累积特性的现象，选择西红柿和苋菜分别代表果菜和叶菜作为研究对象，针对土壤Cd进入作物体内必须经过的主要环节，研究对比不同Na累积特性品种在根系分泌物、根际微生物、根细胞壁、渗透调节与根细胞膜离子跨膜运输、以及蒸腾等方面产生的盐分胁迫响应差异；探明这些差异的分子机制；弄清这些差异对作物吸收土壤Cd的影响。从理论上揭示Na低累积品种对Cd的低积累机制，为培育既耐盐又低累积Cd的蔬菜品种、研制既增强作物耐盐性同时又降低Cd吸收的调控技术提供理论依据。

我国受盐渍化和重金属Cd污染双重影响的农田土壤面积很大，盐渍土的Cd污染比非盐渍土的Cd污染具有更高的风险。如有可能，种植既耐盐又Cd低累积品种是实现中轻度Cd污染盐渍土壤安全利用的理想途径。本项目根据前期研究中发现的许多Na低累积品种也具有Cd低累积特性的现象，选择西红柿和苋菜作为研究对象，针对土壤Cd进入作物体内必须经过的主要环节：根际土壤镉活化、根细胞壁拦截、根细胞膜镉吸收、从根系转运至茎叶等，研究对比了高/低Na累积品种在盐分胁迫下对上述环节产生的差异响应，分析了这些差异与渗透调节响应机制的关系，并采用代谢组学和基因组学方法弄清了其分子机制。结果表明，盐分促进作物吸收土壤镉的主要原因是根际镉活化大幅增加，根细胞壁拦截、根细胞膜镉吸收、从根系转运至茎叶等环节所起作用不大。盐分对土壤镉活化主要是根际分泌物变化引起的生物活化，约占盐分Cd活化量的50-80%，而非传统认为的氯离子络合与钠离子交换引起的化学活化。代谢组学和基因组学研究显示，根际土壤镉生物活化大幅增加是由于盐分胁迫诱导糖代谢增强，特别是三羧酸循环上调，导致大量的有机酸产生和分泌，二羧酸分泌基因显著上调。特别是高Na累积品种的ALMT基因家族最高上调4.23倍、有5个基因显著上调，使得其根际溶液苹果酸含量增加达29.5倍。细胞壁合成相关基因表达显著下调，细胞壁对Cd的吸附拦截能力下降。低Na累积品种的渗透调节机制中，可溶性蛋白代谢变化较大、糖和有机酸代谢变化较小，根系有机酸分泌基因上调幅度较小，其ALMT基因家族最高只上调2.47倍、只有2个基因显著上调，其根际溶液苹果酸含量只增加15.8倍，细胞壁合成相关基因表达变化不显著，因而对土壤镉的活化较少、细胞壁拦截较多，导致其镉低累积。因此，通过种植低Na累积的耐盐品种来实现Cd污染盐渍土壤的安全利用具有充分的理论基础和科学依据。