叶面喷施S-烯丙基-L-半胱氨酸对水稻砷转运影响机制

Effects of foliar sprayed S-allyl-L-cysteine on arsenic transport in rice plants

膳食稻米是我国人群摄入高致癌风险无机砷(iAs)的主要来源,开发降低稻米砷(As)含量生产措施对保护人体健康具有重要意义。本文以我国南方主栽水稻品种“中早35”为试验材料,采用盆栽试验研究了开花期叶面喷施S-烯丙基-L-半胱氨酸(SAC)对水稻籽粒和营养器官中总As含量的影响并揭示其潜在的分子机制。结果表明:当SAC喷施浓度达到0.2 mmol·L^(-1)时籽粒和根中总As含量分别显著降低42.3%和20.6%,但旗叶中总As含量显著增加了72.4%;荧光染色观察试验表明旗叶中H_(2)O_(2)含量显著降低,同时SOD和CAT酶活性分别显著升高61.8%和105.3%。喷施SAC后水稻顶端第一节中Lsi6转运子编码基因以及Lsi3转运子编码基因分别显著下调59.8%和36.3%,据此推测喷施SAC可能显著降低了水稻从通向旗叶膨大维管束流中卸载As^(Ⅲ)和向连接稻穗弥散维管束装载As^(Ⅲ)的能力,导致籽粒中总As含量显著降低而旗叶中总As含量显著升高。旗叶植物螯合素(PCs)合成酶OsPCS1和负责向细胞液泡中转运As^(Ⅲ)的OsABCC1转运子编码基因分别显著上调57.6%和61.0%,表明喷施SAC增加了旗叶合成PCs并向液泡中区隔As^(Ⅲ)的能力从而降低了叶片的As^(Ⅲ)胁迫。水稻根部Lsi1、Lsi2、Lsi3转运子编码基因分别显著下调了27.2%、23.8%、29.5%,表明水稻根部对As^(Ⅲ)的吸收、转运能力降低,同时可能也预示着As^(Ⅲ)向木质部导管中装载As^(Ⅲ)的能力降低。综上,喷施SAC通过调控As^(Ⅲ)转运子编码基因表达降低了水稻籽粒和根中总As含量,同时缓解了As胁迫。

Dietary rice is the main source of inorganic arsenic(iAs)with a high carcinogenic risk for the population,therefore developing countermeasures to reduce the arsenic(As)content in rice is of great importance.Here,we investigated the effect of foliar spraying of Sallyl-L-cysteine(SAC)on the total As content in rice grains and nutritive organs during flowering and identified the potential molecular mechanism of SAC using the main rice cultivar"ZhongZao 35"in southern China.The experimental results showed that the As content in grains and roots significantly decreased by 42.3%and 20.6%,respectively,when the SAC spraying concentration reached 0.2 mmol·L^(-1),but significantly increased in flag leaves by 72.4%.Fluorescence staining showed that the H_(2)O_(2) content in flag reduced significantly,while the SOD and CAT enzyme activities significantly increased by 61.8%and 105.3%,respectively.The genes encoding Lsi6 and Lsi3 transporters in the first rice node were significantly downregulated by 59.8%and 36.3%,respectively,after SAC spraying;thus,significantly reducing the ability of rice to unload As^(Ⅲ)from the vascular stream leading to the expansion of vascular bundle in the flag leaves and load As^(Ⅲ)into the diffused vascular bundle connected to the rice spike.Moreover,it resulted in a significant decrease in the total As content in the grains and a significant increase in the flag leaves.The genes encoding OsPCS1,a phytochelatins-(PCs)-synthesizing enzyme,and OsABCC1,an As^(Ⅲ)transporter in cell vacuole,were significantly upregulated by 57.6%and 61.0%respectively,indicating that SAC spraying increased the ability of flag leaves to synthesize PCs and compartmentalize As^(Ⅲ)into the vacuole,thereby reducing As^(Ⅲ)stress in the leaves.The genes encoding Lsi1,Lsi2,and Lsi3 transporters in rice roots were significantly downregulated by 27.2%,23.8%,and 29.5%,respectively,indicating that the uptake and transport capacity of As^(Ⅲ)in rice roots was reduced,which further minimized the loading capacity of As^(Ⅲ)into the xylem ducts.In conclusion,spraying SAC reduces As content in grains and roots by regulating the expression of genes encoding As^(Ⅲ)related transporter and alleviates As stress.