الفهرس 
Response to pretreatment ion concentrationOnly 14 pages are availabe for public view
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Abstract
nitrate utilization by barley plants to be then used in exceeding efficiency of
nitrogen nutrition by plants. The forst experiment series (preliminary expenments) included two
experiments performed to select seedlings having vaned different n rogen concentrations throughout
preted with different nitrogen concentrations of either nitrate or ammonium form of nitrogen and
durations for such pretreatment. The second series (uptake experiments) included two
experiments the first was to evaluate the net flux and kinetic parameters v_
and K., for both ammonium and nitrate uptake by excised barley roots of the previously selected
nitrogen preted seedlings under different conditions of nitrogen nutrition of either nitrate or
..,montum. The second experiment was to complete the picture of fac1Dr1 aflecting twtrogen
(ammonium or nitrate form) uptake by the studied Mleded MeCihng&, res.ponses to internal difterent
nitrogen components In root tinues was 5tatistically evaluated through evaluating the Share of each
parameter In the final output of the indicated uptake of nitrogen.
Data obtained from the first experiment indicated that dry matter content, representing growth, of
the studied· bartey seedlings had no appreciable response to ex1emal nitrogen nutrition.
Status of nitrogen forms In the studied seedlings showed a positive response to nitrogen treatments
(both concentration and time of prefeeding) in both experiments.
Correspondent results obtained from the second experiment indicated that accumulation of either
ammonium or nitrate in the studied roots increaSed with time progress; an opposite trend was
observed for nitrogen uptake starting
from 15 min time interval, values being dependent on the nitrogen form and time interval of
nutrition. Accumulation of nitrate seemed to be generally higher than that of ammonium.
W h regard to mechanics of ion absorption by the concerned excised roots, data generally
showed that two mechanisms were present in the
absorption medium. Both v..... and Km parameters were evaluated as an
expression for kinetics of absorption by roots whose values were gradually increased by
increasing preted concentrations dependent on nitrogen form of nutrition and duration of preted
time interval Value• of Vmax parameter for both ammoniacal and nnrate forms of nitrogen
were generally responded negatively to absorption time Interval, an oppoSite trend being observed
for Km parameter whose values were positively responded.
Regarding the response of nitrogen uptake dynamics to internal nitrogen components of root tissue,
for ammonium-preted plants, both ammonium and nitrate internal contents of the studied roots, were
generally related to both kinetic parameters of nitrogen upgke. Indicated parameters seemed to be
responded positively to ammonium ilut negatively to nnrate content at the 15 min absorption
period, uabso<ptlon time goes on, nitrate
internal content, opposite to ammonium content. started to be stimulative at
least at 1110 minute time Interval. For nltr e-prefed plants, on the other hand, similar to
ammonium-fed plants, Internal Inorganic nitrogen content of the studied roots had a pronounced
effect on both studied parameters of N uptake kinetic•
Finally, regardless of the nitrogen fed form. H could be concluded that equations representing
responses of both Vmax and K m for the uptake of both ammonium and nitrate proved that the internal
inorganic nitrogen content of the studied roots, among all studied internal components. was the
most effective factor.