英语翻译

英语翻译
However,the C atoms of [U-13C]Arg or [U-13C/U-15N]Arg were not incorporated into the free AAs in
mycorrhizal roots even though traces of 15N enrichment
were observed in the AAs,and traces of intact [U-13C]Arg
or [U-13C/U-15N]Arg were found in protein extracted from
the mycorrhizal roots (this work; Govindarajulu et al.,2005).
Subsequently,we confirmed that the intact,labeled Arg
observed in the protein came from contamination with free
Arg in mycorrhizal roots because the protein dialysis process
does not remove it completely.Both [U-13C]Arg and [U-13C/
U-15N]Arg were found intact in extracts of free AAs and
protein AAs when added to uncolonized roots,indicating
that if Arg were transferred by the fungus to the host it would
have been detected (this work; Govindarajulu et al.,2005).
Additionally,when uncolonized roots were labeled with [U-
13C]Arg for 6 wk,low levels of 13C enrichment were observed
in free Gln and Glu.Introduction of [U-13C/U-15N]Arg to
cultured uncolonized roots produced free AAs (especially Glu
and Gln) enriched in 15N and 13C.Thus if roots are exposed
to Arg,it is taken up and utilized.
Arg is the major form in which N is transported from the
ERM to IRM in the mycorrhizal symbiosis,Furthermore,we
determined by 1H NMR that about 50% of the total N found
in mycorrizal roots was delivered from the hyphae under
these experimental conditions.These results indicate that
the amounts of N transported via hyphae can constitute a
large contribution to the N nutrition of the plant,as opposed
to earlier suggestions to the contrary (Hawkins et al.,2000).
Although these data demonstrate the capacity of the fungal
partner to deliver a large proportion of the N taken up by
roots,further study is needed using whole plants to determine
the contribution that the fungus makes to N uptake under
different conditions.
In a model of N uptake,transport and transfer by AM
fungi (Fig.9),we suggest that:(i) AM fungi take up inorganic
N (NH4+,NO3-); (ii) absorbed N is mostly incorporated and
stored in Arg; (iii) AM fungi assimilate the N through GS/
GOGAT,asparagine synthase and the urea cycle; (iv) stored Arg can be co-transported with PolyP intact to the IRM from the ERM of AM fungi,and Arg is also bi-directionally trans-
ported within the ERM; and (v) N released from transported Arg is transferred to the host as NH4+ and can be incorporated into other free AAs in mycorrhizal roots,while C not trans-
ferred to the host is recycled back to the ERM.