Department of Biochemistry, University of California, Riverside, CA 92521-0129, USA.
J Exp Bot. 2010 Mar;61(3):857-71. doi: 10.1093/jxb/erp362. Epub 2009 Dec 14.
Ethylene regulates plant growth in response to many adverse environmental conditions, including the induction of aerenchyma, i.e. the formation of air spaces, in flooded roots in an effort to maintain oxygen levels. In this work, quantitative RT-PCR and in situ RNA hybridization were used to determine how the expression of the ethylene biosynthetic machinery in maize roots is spatially and temporally regulated following exposure to 4% oxygen (i.e. hypoxia) for up to 24 h, conditions that induced aerenchyma formation in the fully-expanded region of the root and reduced cytoplasmic density throughout the root. Expression of ACC oxidase, the ethylene forming enzyme, was observed in the root cap, protophloem sieve elements, and companion cells associated with metaphloem sieve elements. Exposure to 4% oxygen induced ACC oxidase expression in these cell types as well as in the root cortex. ACC synthase, which generates the ethylene precursor, was expressed in the root cap and the cortex and its expression was induced in cortical cells following low oxygen treatment. The induction of expression of the ethylene biosynthetic machinery was accompanied by an induction of ethylene evolution and a reduced rate of root growth. These results suggest that maize roots respond to conditions of hypoxia by inducing the spatially restricted expression of the ethylene biosynthetic machinery, resulting in increased ethylene production.
乙烯通过调节植物生长来应对许多不利的环境条件，包括在水淹的根中诱导通气组织（即空气空间的形成），以维持氧水平。在这项工作中，使用定量 RT-PCR 和原位 RNA 杂交来确定玉米根中乙烯生物合成机制在暴露于 4%氧气（即缺氧）长达 24 小时后的时空调节方式，这些条件诱导通气组织在根的完全展开区域形成，并降低整个根的细胞质密度。ACC 氧化酶，即乙烯形成酶，在根冠、原韧皮部筛管分子和与后生韧皮部筛管分子相关的伴胞中表达。暴露于 4%氧气会诱导这些细胞类型以及根皮层中的 ACC 氧化酶表达。生成乙烯前体的 ACC 合酶在根冠和皮层中表达，并且在低氧处理后其在皮层细胞中被诱导表达。乙烯生物合成机制的表达诱导伴随着乙烯释放的诱导和根生长速度的降低。这些结果表明，玉米根通过诱导乙烯生物合成机制的空间限制表达来应对缺氧条件，从而导致乙烯产量增加。
