GLUTAMINE-SYNTHETASE ACTIVITY, AMMONIUM ACCUMULATION AND GROWTH OF CALLUS-CULTURES OF ASPARAGUS-OFFICINALIS L EXPOSED TO HIGH AMMONIUM OR PHOSPHINOTHRICIN
Jf. Seelye et al., GLUTAMINE-SYNTHETASE ACTIVITY, AMMONIUM ACCUMULATION AND GROWTH OF CALLUS-CULTURES OF ASPARAGUS-OFFICINALIS L EXPOSED TO HIGH AMMONIUM OR PHOSPHINOTHRICIN, Journal of plant physiology, 146(5-6), 1995, pp. 686-692
Glutamine synthetase (GS) activity, ammonium accumulation and growth r
esponses of callus cultures of Asparagus officinalis L, were investiga
ted following 4 weeks exposure to media with added ammonium, and again
after a further 4 weeks on a modified basal medium (MBM) containing n
o added ammonium. Calli grown on MBM supplemented with 40 or 160 mM am
monium for 4 weeks had reduced GS activity, greatly enhanced ammonium
content and reduced growth compared with calli exposed to 10 mM added
ammonium. When calli were transferred back to MBM, GS activity increas
ed, ammonium content decreased, and growth was enhanced. Phosphinothri
cin (PPT) was used to endogenously alter the ammonium content of callu
s tissue. Exposing calli to 10 or 100 mu M PPT for 4 weeks reduced GS
activity, enhanced ammonium accumulation and reduced growth compared w
ith calli not exposed to PPT, and markedly enhanced callus glutamine c
ontent. Calli exposed to 100 mu M PPT did not regrow when transferred
back to basal media (BM) without added PPT for an additional 4 weeks.
We also separated the effect of PPT-induced ammonium accumulation from
alterations in tissue amino acid concentrations by adding up to 25 mM
glutamine in addition to PPT during the initial 4-week treatment peri
od. Glutamine supplementation overcame the PPT-induced reduction in gr
owth even though GS activity was severely reduced and ammonium accumul
ated to high concentrations in calli exposed to 100 mu M PPT. All call
i continued to grow vigorously when transferred back to BM for an addi
tional 4 weeks. The results demonstrate that ammonium accumulation per
se was not lethal to asparagus callus tissue, and suggest other effec
ts of using PPT as a selective inhibitor of GS.