丛枝菌根真菌对低温下黄瓜幼苗光合生理和抗氧化酶活性的影响

Effects of AM fungi on leaf photosynthetic physiological parameters and antioxidant enzyme activities under low temperature

塑料连栋大棚栽培条件下,研究接种丛枝菌根真菌(AMF)Glomus m ossea-2对低温下黄瓜(Cucum is sativusL.)幼苗同化产物积累、光合生理和过氧化氢酶(CAT)、过氧化物酶(POD)、超氧化物歧化酶(SOD)、抗坏血酸过氧化物酶(APX)的活性及基因表达的影响。结果表明:低温显著抑制了AMF对黄瓜根系的侵染能力和菌根相对依赖性。接菌后30-45d AMF为快速侵染期。接种AMF植株的鲜重根冠比、总干重、总鲜重均显著大于未接菌处理。低温胁迫下,接种AMF延缓了光合速率、根系活力、羧化效率和叶绿素、可溶性蛋白含量的下降,并且使丙二醛(MDA)的含量保持相对较低的水平,诱导了抗氧化酶基因的表达及活性提高。接种AMF可以使叶片维持较高的抗氧化酶水平和光合能力,增强了对低温胁迫的抗性。

Chilling stress may reduce plant growth by affecting physiological and metabolic processes. It is well known that that a symbiotic association of plant roots with arbuscular mycorrhizal fungi （AMF） improves plant cold tolerance and related studies have received extensive attention during the last decade. Root colonization by AMF might strengthen the ability of cold tolerance in plants through attenuating membrane lipid peroxidation and plasma membrane permeability, and increasing osmolyte accumulation as well. Among a large number of vegetable crops which could be infected by AM fungi, cucumber is relatively easy to establish symbiotic associations with vesicular arbuscular mycorrhizae （VAM）. Previous studies have reported the relief of chilling stress through the use of AMF. However, these were more focused on plant growth and chlorophyll parameters. The biochemical mechanism underlying AMF-mediated low temperature tolerance in vegetable crops warrants further in depth investigation. Uner greenhouse condition, the combined effects of AM fungi and low temperature on cucumber seedlings were investigated with respects to assimilate accumulation, photosynthetic rate, carboxylation efficiency, activities of antioxidant enzymes and＂ related gene expression. AMF inoculums used in this study consisted of spores, soil, hyphae and infected maize root fragment from a stock culture of Glomus mossea-2, which were propagated by AMF inoculums. The experimental design consisted of four treatments crossing two mycorrhizal inoculations levels （ non-AMF and Glomus mossea-2） with two temperature levels （25/15℃ , 15/10℃ ）. The inoculated dosage was 20 g of inoculums per pot containing. Repeat 3 times for each treatment, 10 plants per replicate. The results showed that mycorrhizal colonization abilities and mycorrhizal dependency were significantly inhibited by low temperature. Fungal growth accelerated considerably during the period from 30 d to 45 d after inoculation with AMF. At 45 d after inoculation, mycorrhizal colonization ratio on cucumber roots was 42.68% and 32.15% under room temperature and low temperature, respectively, Mycorrhizal dependency was 21.42% and 5.46% under room temperature and low temperature respectively and this indicated a significant reduction in low temperature （ P 〈 0.05 ）. Regardless of the temperature, the root-shoot ratio, total dry weight and fresh weight of AMF inoculated seedlings were significantly higher than that of the non-AMF control （P〈0.05）. The photosynthesis, root activity, earboxylation efficiency, contents of chlorophyll and soluble proteins increased by 23.67% , 29.13% , 33.10% and 11.78% compared with the control under low temperature. Moreover, Malondialdehyde content stayed at relatively low level in AMF-treated seedlings. On the other hand, the AMF treatment enhanced the activities and transcript levels of antioxidant enzymes. Superoxide dismutase（ SOD ） , peroxidase （ POD ）, catalase （CAT） , ascorbate peroxidase （ APX ） expressions of the AMF-inoculated seedlings were increased by 1.35, 1.44, 1.70, 2.46 folds respectively compared with CK1. Under chilling stress, the expression levels of SOD, G-POD, CAT and APX genes in the AMF-inoculated seedling were increased by 1.68, 1.37, 1.52 and 1.83 folds respectively in control under normal temperature （ CKl ） compared with those under low temperature （CK2 ）. These results indicated that antioxidant enzymes might play a crucial role in AMF-mediated tolerance to chilling stress, thereby maintaining a high photosynthetic capacity in cucumber seedlings.