问题描述:
英语翻译
Arbuscular mycorrhizal (AM) fungi form a mutualistic
symbiosis with the roots of most land plants.They confer a
nutritional benefit to their hosts by taking up phosphorus (P)
and other macronutrients,trace elements and water from the
soil and transferring them to their host plants.Most attention
has been focused on P acquistion (Smith
et al
.,1994; Harrison& Van Buuren,1995; Smith & Read,1997; Rausch
et al
.,
2001; Ezawa
et al
.,2002)
.
However nitrogen (N) is also an
important element whose uptake from nutrient poor soils
to roots can be improved by AM fungal colonization (Ames
et al
.,1983; Jennings,1995; Johansen
et al
.,1996; Smith &
Read,1997).
The extraradical hyphae of (AM) fungi are able to take up
and assimilate ammonium (NH
4
+
) (Ames
et al
.,1983; George
et al
.,1992; Johansen
et al
.,1992,1993,1996; Frey & Schüpp,
1993),nitrate (NO
3
–
) (Tobar
et al
.,1994; Bago
et al
.,1996;
Johansen
et al
.,1996) and amino acids (AAs; Hawkins
et al.
2000; Hodge
et al
.,2001) from their surroundings andtranslocate N from diverse sources to the plant (Hawkins
et al
.,2000; Azcón
et al
.,2001; Vazquez
et al
.,2001).AM
fungi can apparently also transfer N from one plant to
another (Bethlenfalvay
et al
.,1991; He
et al
.,2003; Cheng &
Baumgartner,2004) and can increase the availability of different
forms of N to plants (Hodge
et al
.,2001).However,
when and where fungal transport of N plays an important
part in plant nutrition remains unclear (Smith & Read,1997;
He
et al
.,2003).
Assimilation of NH
4
+
is a principal means of N absorption
both in ectomycorrhizal (Martin
et al
.,1986; Finlay
et al
.,1989;
Chalot
et al
.,1991; Martin & Botton,1993) and AM fungal
systems (Bago
et al
.,1996; Hawkins
et al
.,2000; Toussaint
et al
.,2004).N uptake and incorporation into AAs via the
glutamine synthetase,glutamate synthase (GS/GOGAT)
cycle has been found in ectomycorrhizal fungi (Martin,1985;
Vèzina
et al
.,1989; Chalot
et al
.,1994).Smith
et al
.(1985)
also described the activity of the GS/GOGAT enzymes in
AM fungi.Also in an AM fungus,Govindarajulu
et al
.(2005)
found support for N assimilation in the extraradical mycelium
(ERM) via the GS/GOGAT pathway by measuring mRNA
levels for key enzymes in the ERM and intraradical mycelium
(IRM) tissues with quantitative real-time polymerase chain
reaction.They also demonstrated the expression of a putative
nicotinamide adenine dinucleotide (NAD)-dependent glutamate
dehydrogenase (GDH ) gene,which is down-regulated
in the ERM tissue supplied with either NO
3
–
or NH
4
+
in the
ERM compartment,consistent with this enzyme having a
catabolic role (Vallorani
et al
.,2002).The report by Breuninger
et al
Arbuscular mycorrhizal (AM) fungi form a mutualistic
symbiosis with the roots of most land plants.They confer a
nutritional benefit to their hosts by taking up phosphorus (P)
and other macronutrients,trace elements and water from the
soil and transferring them to their host plants.Most attention
has been focused on P acquistion (Smith
et al
.,1994; Harrison& Van Buuren,1995; Smith & Read,1997; Rausch
et al
.,
2001; Ezawa
et al
.,2002)
.
However nitrogen (N) is also an
important element whose uptake from nutrient poor soils
to roots can be improved by AM fungal colonization (Ames
et al
.,1983; Jennings,1995; Johansen
et al
.,1996; Smith &
Read,1997).
The extraradical hyphae of (AM) fungi are able to take up
and assimilate ammonium (NH
4
+
) (Ames
et al
.,1983; George
et al
.,1992; Johansen
et al
.,1992,1993,1996; Frey & Schüpp,
1993),nitrate (NO
3
–
) (Tobar
et al
.,1994; Bago
et al
.,1996;
Johansen
et al
.,1996) and amino acids (AAs; Hawkins
et al.
2000; Hodge
et al
.,2001) from their surroundings andtranslocate N from diverse sources to the plant (Hawkins
et al
.,2000; Azcón
et al
.,2001; Vazquez
et al
.,2001).AM
fungi can apparently also transfer N from one plant to
another (Bethlenfalvay
et al
.,1991; He
et al
.,2003; Cheng &
Baumgartner,2004) and can increase the availability of different
forms of N to plants (Hodge
et al
.,2001).However,
when and where fungal transport of N plays an important
part in plant nutrition remains unclear (Smith & Read,1997;
He
et al
.,2003).
Assimilation of NH
4
+
is a principal means of N absorption
both in ectomycorrhizal (Martin
et al
.,1986; Finlay
et al
.,1989;
Chalot
et al
.,1991; Martin & Botton,1993) and AM fungal
systems (Bago
et al
.,1996; Hawkins
et al
.,2000; Toussaint
et al
.,2004).N uptake and incorporation into AAs via the
glutamine synthetase,glutamate synthase (GS/GOGAT)
cycle has been found in ectomycorrhizal fungi (Martin,1985;
Vèzina
et al
.,1989; Chalot
et al
.,1994).Smith
et al
.(1985)
also described the activity of the GS/GOGAT enzymes in
AM fungi.Also in an AM fungus,Govindarajulu
et al
.(2005)
found support for N assimilation in the extraradical mycelium
(ERM) via the GS/GOGAT pathway by measuring mRNA
levels for key enzymes in the ERM and intraradical mycelium
(IRM) tissues with quantitative real-time polymerase chain
reaction.They also demonstrated the expression of a putative
nicotinamide adenine dinucleotide (NAD)-dependent glutamate
dehydrogenase (GDH ) gene,which is down-regulated
in the ERM tissue supplied with either NO
3
–
or NH
4
+
in the
ERM compartment,consistent with this enzyme having a
catabolic role (Vallorani
et al
.,2002).The report by Breuninger
et al
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