水稻籽粒中镉的来源

Sources of Cadmium Accumulated in Rice Grain

【目的】深入探讨水稻籽粒中镉(Cd)的来源及其与生长环境中Cd供应强度的关系,为稻米Cd污染防控选用恰当的农艺措施和实施时间提供科学依据。【方法】在水稻齐穗期,从Cd污染稻田选取长势一致的水稻植株,分别移入含不同Cd浓度(0、0.2、0.5 mg·L-1)的营养液盆钵中培养,成熟期分别收获各器官测定生物产量和Cd含量;在大田自然条件下生长的水稻分别在齐穗期、灌浆期、腊熟期和成熟期采集长势均匀一致的植株样本测定生物产量和Cd含量。【结果】在营养液中不含Cd(Cd 0处理)的条件下,籽粒中累积的Cd主要来自于根系和茎秆在齐穗前累积的Cd。在齐穗后的生长环境中存在较低有效镉的情况下(即Cd污染稻田自然生长的植株),籽粒中的Cd则同时来自水稻齐穗前各器官累积的Cd和根系从土壤吸收与直接运输的Cd;水稻叶片和谷壳是水稻齐穗后向籽粒净转移Cd的器官,茎秆和根系既是籽粒Cd的源,也是Cd的净累积器官。而在生长介质有效镉含量丰富的情况下(即Cd培养试验处理中的Cd 0.2和Cd 0.5处理),籽粒中的Cd则主要来自生长介质,少部分来自水稻各器官的转移。【结论】籽粒中的Cd来自齐穗前各器官储存Cd的转移和土壤/介质中Cd的吸收和直接运输,土壤/介质中的可利用Cd含量越高,籽粒含Cd量也越高;只有当土壤/介质中不存在可利用Cd时,水稻各器官中储存的Cd才是籽粒中Cd的唯一来源;水稻各器官中,茎秆和根系是体内Cd的主要储存和输出场所。结合水稻生长早期降Cd措施的基础上,在水稻抽穗-成熟期采取恰当的农艺措施降低土壤中Cd的有效性以及根系吸收和向籽粒的直接运输量,就能有效降低稻米中的Cd含量。

【Objective】The objective of this study aimed to understand the sources of cadmium accumulated in the rice grain and to offer scientific support and best timing of agronomic measures to secure safety rice production. 【Method】The study involved a pot hydroponic experiment with three Cd concentrations of 0, 0.2 and 0.5 mg·L^-1 by transplanting uniform rice plants at fully heading stage from a field with Cd contamination. Besides, the rice in the same field were also observed. The rice samples from hydroponic culture were harvested at maturity and those from the field were sampled at full heading stage, milk stage, dough stage and maturity. Dry weight and tissue Cd contents were analyzed for all the samples. 【Result】The results showed that Cd accumulated in the rice grain was mainly transferred from the root and culm where Cd was stored before full heading in the Cd 0 treatment of the hydroponic culture. When available Cd was low in the soil（i.e., the treatment with rice kept growing in the paddy field）, Cd accumulated in the rice grain was from both plant tissues stored Cd before heading and soil Cd uptake by rice after heading. The leaf and chaff appeared as net sources for Cd transferred to the rice grain, while the culm and root behaved as both pools for Cd accumulation and sources to the grain. When the rice grew in relatively high Cd content media（i.e., Cd 0.2 and Cd 0.5 treatments）, Cd accumulated in the rice grain was mainly from direct uptake of Cd by the plant and small portions from different rice organs. 【Conclusion】The Cd accumulated in the grain is transferred from different rice organs before heading stage and from direct uptake from soil/medium; the higher the available Cd in soil/medium, the higher Cd accumulated in the grain; only when there is no available Cd in the soil/medium, the Cd stored in different rice organs becomes the sole source of grain Cd. The culm and root are the two major locations for Cd storage and output in the rice plant. Heading to maturity stages are crucial to control Cd accumulation in rice grain and thus, are key period to secure production of safety rice if proper measures are taken to reduce available Cd in the growth medium as well as its uptake by direct root uptake and transport to the grain.