Espinosa Francisco, Garrido Inmaculada, Ortega Alfonso, Casimiro Ilda, Álvarez-Tinaut Ma Carmen
Departamento de Biología Vegetal, Ecología y Ciencias de la Tierra, Universidad de Extremadura, Avenida Elvas s/n, Badajoz, Spain.
Departamento de Anatomía, Biología Celular y Zoología, Universidad de Extremadura, Avenida Elvas s/n, Badajoz, Spain.
PLoS One. 2014 Jun 26;9(6):e100132. doi: 10.1371/journal.pone.0100132. eCollection 2014.
Roots of intact olive seedlings, axenically cultured, were alternatively placed in contact with Rhizophagus irregularis (mycorrhizal) or Verticillim dahliae (pathogenic) fungi. MeJA treatments were also included. In vivo redox activities in the apoplast of the intact roots (anion superoxide generation, superoxide dismutase and peroxidase activities) were measured. All our results showed that apoplastic redox activities of intact seedling roots in contact with the compatible mycorrhizal fungus were clearly attenuated in comparison with the pathogenic fungus or treated with MeJA, even at the early stages of treatment used. Total phenolics, flavonoids and phenylpropanoid glycosides were also quantified. Roots in contact with the mycorrhizal fungus did not enhance the biosynthesis of phenolic compounds with respect to controls, while those in contact with the pathogenic one significantly enhanced the biosynthesis of all phenolic fractions measured. Reactive oxygen species and nitric oxid accumulation in roots were examined by fluorescence microscopy. All of them presented much higher accumulation in roots in contact with the pathogenic than with the mycorrhizal fungus. Altogether these results indicate that intact olive seedling roots clearly differentiated between mycorrhizal and pathogenic fungi, attenuating defense reactions against the first to facilitate its establishment, while inducing a strong and sustained defense reaction against the second. Both reactive oxygen and nitrogen species seemed to be involved in these responses from the first moments of contact. However, further investigations are required to clarify the proposed crosstalk between them and their respective roles in these responses since fluorescence images of roots revealed that reactive oxygen species were mainly accumulated in the apoplast (congruently with the measured redox activities in this compartment) while nitric oxid was mainly stored in the cytosol.
将无菌培养的完整橄榄幼苗的根交替与不规则球囊霉（菌根真菌）或大丽轮枝菌（致病真菌）接触。实验还设置了茉莉酸甲酯（MeJA）处理。测定了完整根的质外体中的体内氧化还原活性（阴离子超氧产生、超氧化物歧化酶和过氧化物酶活性）。我们所有的结果表明，与致病真菌或用茉莉酸甲酯处理相比，与相容菌根真菌接触的完整幼苗根的质外体氧化还原活性明显减弱，即使在所用处理的早期阶段也是如此。还对总酚类、黄酮类和苯丙素糖苷进行了定量分析。与菌根真菌接触的根相对于对照并没有增强酚类化合物的生物合成，而与致病真菌接触的根显著增强了所有测定酚类组分的生物合成。通过荧光显微镜检查根中活性氧和一氧化氮的积累情况。所有结果表明，与致病真菌接触的根中这些物质的积累比与菌根真菌接触的根中要高得多。总之，这些结果表明，完整的橄榄幼苗根能够清楚地区分菌根真菌和致病真菌，减弱对前者的防御反应以促进其定殖，同时对后者诱导强烈而持续的防御反应。从接触的最初时刻起，活性氧和氮物质似乎都参与了这些反应。然而，由于根的荧光图像显示活性氧主要积累在质外体中（与该区域测定的氧化还原活性一致），而一氧化氮主要储存在细胞质中，因此需要进一步研究来阐明它们之间的相互作用以及它们在这些反应中的各自作用。
