Differential Expression of Superoxide Dismutase Genes in Aphid-Stressed Maize (Zea mays L.) Seedlings

The aim of this study was to compare the expression patterns of superoxide dismutase genes (sod2, sod3.4, sod9 and sodB) in seedling leaves of the Zea mays L. Tasty Sweet (susceptible) and Ambrozja (relatively resistant) cultivars infested with one of two hemipteran species, namely monophagous Sitobion avenae F. (grain aphid) or oligophagous Rhopalosiphum padi L. (bird cherry-oat aphid). Secondarily, aphid-elicited alternations in the antioxidative capacity towards DPPH (1,1-diphenyl-2-picrylhydrazyl) radical in insect-stressed plants were evaluated. Comprehensive comparison of expression profiles of the four sod genes showed that both insect species evoked significant upregulation of three genes sod2, sod3.4 and sod9). However, aphid infestation affected non-significant fluctuations in expression of sodB gene in seedlings of both maize genotypes. The highest levels of transcript accumulation occurred at 8 h (sod2 and sod3.4) or 24 h (sod9) post-infestation, and aphid-induced changes in the expression of sod genes were more dramatic in the Ambrozja cultivar than in the Tasty Sweet variety. Furthermore, bird cherry-oat aphid colonization had a more substantial impact on levels of DPPH radical scavenging activity in infested host seedlings than grain aphid colonization. Additionally, Ambrozja plants infested by either hemipteran species showed markedly lower antioxidative capacity compared with attacked Tasty Sweet plants.本研究旨在比较玉蜀黍（Zea mays L.）两个品种——易感品种“美味甜”（Tasty Sweet）与相对抗虫品种“安布罗扎”（Ambrozja）的幼苗叶片中，超氧化物歧化酶基因（superoxide dismutase genes，sod2、sod3.4、sod9与sodB）在被两种半翅目昆虫（专食性麦长管蚜Sitobion avenae F.，即谷物蚜；寡食性禾谷缢管蚜Rhopalosiphum padi L.，即鸟樱桃-燕麦蚜）之一侵染后的表达模式。本研究的次要目标为评估蚜虫侵染后，受虫害胁迫植株针对DPPH（1,1-二苯基-2-三硝基苯肼，1,1-diphenyl-2-picrylhydrazyl）自由基的抗氧化能力所发生的蚜虫诱导变化。对四个sod基因表达谱的全面比较显示，两种蚜虫均显著上调了sod2、sod3.4与sod9的基因表达。然而，蚜虫侵染对两个玉米基因型幼苗的sodB基因表达未造成显著波动。转录本积累的最高水平出现在侵染后8小时（sod2与sod3.4）或24小时（sod9），且安布罗扎品种中sod基因的表达变化幅度较美味甜品种更为显著。此外，鸟樱桃-燕麦蚜定植对受侵染宿主幼苗的DPPH自由基清除活性水平的影响较谷物蚜更为显著。同时，被任意一种半翅目昆虫侵染的安布罗扎植株，其抗氧化能力均显著低于受侵染的美味甜植株。