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Lee, Bok-Rye,Muneer, Sowbiya,Avice, Jean-Christophe,Jung, Woo-Jin,Kim, Tae-Hwan Springer-Verlag 2012 Mycorrhiza Vol.22 No.7
<P>To compare the effect of arbuscular mycorrhiza (AM) and P-supplement on N uptake and N assimilation under well-watered or drought-stressed conditions, Glomus intraradices-colonised, P-supplemented non-mycorrhizal (P) and non-mycorrhizal (control) plants of Lolium perenne were exposed to 12 days of water treatment. Leaf water potential (ψ (w)), photosynthetic ability, and N and P nutritional status were measured at the beginning (day 0) and end (day 12) of water treatment. N absorption, amino acid and protein synthesis were quantified using the isotopic tracer (15)N at day 12. Under well-watered conditions, growth response and physiological parameters were similar in AM and P plants, as compared to controls. Drought (10% water) significantly decreased these parameters in all three treatments. As compared to control plants, the negative impact of water deficit on the ψ (w), photosynthesis, biomass, and N and P content was highly alleviated in AM plants, while only slightly improved or remained the same level in P plants. The effect of AM symbiosis on N absorption and N assimilation was greater than that of the P supplement under well-watered and drought-stressed conditions, and this effect was highly enhanced under drought-stressed conditions. At terminal drought stress on day 12, the effect of AM colonisation on de novo synthesis of amino acids and proteins was 4.4- and 4.8-fold higher than that of the P supplement. These results indicate that the AM symbiosis plays an integrative role in N nutrition by alleviating the negative impacts of drought on N or P uptake and N assimilation, whereas the efficiency of a direct P supplement is very limited under drought-stressed conditions.</P>
Lee, Bok‐,Rye,Jin, Yu Lan,Avice, Jean‐,Christophe,Cliquet, Jean‐,Bernard,Ourry, Alain,Kim, Tae‐,Hwan Blackwell Publishing Ltd 2009 The New phytologist Vol.182 No.3
<P><B>Summary</B></P><P><P>The aim of this study was to investigate the physiological significance of increased proline loading to phloem caused by water‐deficit stress in relation to nitrogen (N) uptake and assimilation.</P><P>N uptake and N assimilation were quantified by <SUP>15</SUP>N tracing in well‐watered (control) and water deficit‐stressed white clover (<I>Trifolium repens</I>). <I>De novo</I> proline synthesis and proline loading to the phloem were also compared between treatments. The relationships among proline concentrations in phloem exudates, N uptake, and assimilation of newly absorbed N were assessed.</P><P>The newly synthesized proline in the phloem exudates increased rapidly after 3 d of water deficit. The water‐deficit treatment significantly reduced the maximum nitrate reductase activity (NRA), and also attenuated <I>de novo</I> synthesis of amino acids and proteins in the roots. The increase in proline concentrations in phloem exudates was closely related to reductions in NRA in the roots, N uptake, and the assimilation of newly absorbed N. The accumulation of proline induced in roots by exogenous proline and NH<SUB>4</SUB>Cl treatments was closely associated with the decrease in NRA.</P><P>These results indicate that increased proline transport to roots via phloem caused by water deficit has a significant influence on the down‐regulation of N uptake and the assimilation of newly absorbed N.</P></P><!--<abstractinfo format='display'> <P> <I>New Phytologist</I> (2009) <B>182</B>: 654–663</P><P></br><B>doi</B>: 10.1111/j.1469-8137.2009.02795.x</P> </abstractinfo>-->
Lee, Bok‐,Rye,Muneer, Sowbiya,Jung, Woo‐,Jin,Avice, Jean‐,Christophe,Ourry, Alain,Kim, Tae‐,Hwan Blackwell Publishing Ltd 2012 Physiologia plantarum Vol.145 No.3
<P>To investigate the effects of arbuscular mycorrhizal (AM) fungus <I>Glomus intraradices</I> on antioxidative activity and lignification under drought‐stressed (DS) conditions, the enzyme activities, growth, lignin contents and some stress symptomatic parameters as affected by drought treatment were compared in AM colonized or non‐colonized (non‐AM) perennial ryegrass plants for 28 days. Drought significantly decreased leaf water potential (Ψ<SUB>w</SUB>), photosynthesis rate and biomass. The negative impact of drought on these parameters was much highly relived in AM plants compared to non‐AM ones. Drought increased H<SUB>2</SUB>O<SUB>2</SUB>, lipid peroxidation, phenol and lignin levels, with significantly higher in non‐AM relative to AM plants at day 28 after drought treatment. The enhanced activation of guaiacol peroxidase (GPOX), coniferyl alcohol peroxidase (CPOX), syringaldazine peroxidase (SPOX) and polyphenol oxidase (PPO) was closely related with the decrease in Ψ<SUB>w</SUB> in both AM and non‐AM plants. GPOX, CPOX, SPOX and PPO highly activated with a concomitant increase in lipid peroxidation and lignin as the Ψ<SUB>w</SUB> decreased below −2.11 MPa in non‐AM plants, while much less activated by maintaining Ψ<SUB>w</SUB>≥−1.15 MPa in AM ones. These results indicate that AM symbiosis plays an integrative role in drought stress tolerance by alleviating oxidative damage and lignification, which in turn mitigate the reduction of forage growth and digestibility under DS conditions.</P>