Chin J Plant Ecol ›› 2012, Vol. 36 ›› Issue (9): 973-981.DOI: 10.3724/SP.J.1258.2012.00973

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Arbuscular mycorrhizal fungi improving drought tolerance of maize plants by up-regulation of aquaporin gene expressions in roots and the fungi themselves

LI Tao, CHEN Bao-Dong*()   

  1. State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
  • Received:2011-10-10 Accepted:2012-05-07 Online:2012-10-10 Published:2012-09-06
  • Contact: CHEN Bao-Dong


Aims It has been well demonstrated that arbuscular mycorrhizal (AM) fungi can improve water balance and drought tolerance of host plants under drought stress. However, controversy still exists in mechanisms underlying the mycorrhizal functions. For example, in different experiments AM fungi could up- or down-regulate plant aquaporin gene expression. Furthermore, little information is available on the expression of aquaporin genes in AM fungi under drought stress and its contribution to plant drought tolerance. We investigated the effects of an AM fungus, Glomus intraradices, on expression of a plasma membrane intrinsic protein (PIP) gene family containing 13 PIP genes in maize roots and one aquaporin gene from the AM fungus under simulated drought conditions. Our objectives were to systematically investigate the aquaporin gene expression in the mycorrhizal association in response to drought stress and to help understand the molecular basis for drought tolerance of AM symbiosis.
Methods Maize plants inoculated with/without AM fungus G. intraradices were grown under different water regimes in a controlled-environment climate chamber for 42 days. At harvest, the leaf water potential (Ψ) was determined with an SKPM 1400 pressure chamber, and then shoots and roots were collected and carefully cleaned with tap water. Three grams of mixed roots were used to estimate the percentage root colonization after clearing with 10% KOH and staining with 0.05% (v/v) trypan blue in lactic acid. One gram of mixed roots was used to extract total RNA by using TRIZOL to synthesize cDNA. Real-time PCR analysis was performed to estimate the expression of Zm PIP genes and GintAQP1. Shoots and the rest of roots were dried at 105 °C for 10 min and 80 °C for 48 h to obtain dry weights. About 0.2 g of dried shoots or roots was digested by HNO3 for 12 h. The P concentration was recorded by using microplate reader spectra at the wavelength of 820 nm. Experimental data were subjected to statistical analysis using SPSS 13.0.
Important findings Under drought stress, inoculation with AM fungus significantly enhanced expression of eight PIP genes except for Zm PIP1;3, Zm PIP1;4 Zm PIP1;5 and Zm PIP2;2 (Zm PIP2;7 expression not detected), and drought stress also enhanced expression of GintAQP1 cloned from hyphae of G. intraradices. Enhanced aquaporin gene expression was beneficial to improvement of plant water status and increase of leaf water potential.

Key words: aquaporin, arbuscular mycorrhizal (AM) fungus, drought tolerance, leaf water potential, maize