Institute of Arctic Biology, University of Alaska, 99775, Fairbanks, AK, USA.
Planta. 1988 Mar;173(3):340-51. doi: 10.1007/BF00401021.
The potential of barley (Hordeum vulgare L.) and tomato (Lycopersicon esculentum Mill.) roots for net NO 3 (-) absorption increased two-to five fold within 2 d of being deprived of NO 3 (-) supply. Nitrogen-starved barley roots continued to maintain a high potential for NO 3 (-) absorption, whereas NO 3 (-) absorption by tomato roots declined below control levels after 10 d of N starvation. When placed in a 0.2 mM NO 3 (-) solution, roots of both species transported more NO 3 (-) and total solutes to the xylem after 2 d of N starvation than did N-sufficient controls. However, replenishment of root NO 3 (-) stores took precedence over NO 3 (-) transport to the xylem. Consequently, as N stress became more severe, transport of NO 3 (-) and total solutes to the xylem declined, relative to controls. Nitrogen stress caused an increase in hydraulic conductance (L p) and exudate volume (J v) in barley but decrased these parameters in tomato. Nitrogen stress had no significant effect upon abscisic acid (ABA) levels in roots of barley or flacca (a low-ABA mutant) tomato, but prevented an agerelated decline in ABA in wild-type tomato roots. Applied ABA had the same effect upon barley and upon the wild type and flacca tomatoes: L p and J v were increased, but NO 3 (-) absorption and NO 3 (-) flux to the xylem were either unaffected or sometimes inhibited. We conclude that ABA is not directly involved in the normal changes in NO 3 (-) absorption and transport that occur with N stress in barley and tomato, because (1) the root ABA level was either unaffected by N stress (barley and flacca tomato) or changed, after the greatest changes in NO 3 (-) absorption and transport and L p had been observed (wild-type tomato); (2) changes in NO 3 (-) absorption/transport characteristics either did not respond to applied ABA, or, if they did, they changed in the direction opposite to that predicted from changes in root ABA with N stress; and (3) the flacca tomato (which produces very little ABA in response to N stress) responded to N stress with very similar changes in NO 3 (-) transport to those observed in the wild type.
大麦（Hordeum vulgare L.）和番茄（Lycopersicon esculentum Mill.）根系吸收硝酸盐（NO3-）的潜力在停止供应硝酸盐（NO3-）后的 2 天内增加了 2 到 5 倍。氮饥饿的大麦根系继续保持高硝酸盐（NO3-）吸收潜力，而番茄根系在氮饥饿 10 天后，硝酸盐（NO3-）吸收能力下降到对照水平以下。当置于 0.2 mM 的硝酸盐（NO3-）溶液中时，与氮充足的对照相比，氮饥饿 2 天后，两种植物的根系向木质部输送更多的硝酸盐（NO3-）和总溶质。然而，根系硝酸盐（NO3-）储存的补充优先于向木质部输送硝酸盐（NO3-）。因此，随着氮胁迫的加剧，硝酸盐（NO3-）和总溶质向木质部的运输相对于对照下降。氮胁迫导致大麦根系水力传导率（Lp）和渗出液体积（Jv）增加，但降低了番茄根系的这些参数。氮胁迫对大麦和 flacca（低 ABA 突变体）番茄根系中的脱落酸（ABA）水平没有显著影响，但防止了野生型番茄根系中 ABA 随年龄的下降。施加的 ABA 对大麦和野生型及 flacca 番茄具有相同的作用：Lp 和 Jv 增加，但硝酸盐（NO3-）吸收和向木质部的硝酸盐（NO3-）通量要么不受影响，要么有时受到抑制。我们得出结论，ABA 不是直接参与氮胁迫下大麦和番茄中硝酸盐（NO3-）吸收和运输的正常变化，因为（1）根 ABA 水平要么不受氮胁迫影响（大麦和 flacca 番茄），要么在观察到硝酸盐（NO3-）吸收和运输以及 Lp 的最大变化之后发生变化（野生型番茄）；（2）硝酸盐（NO3-）吸收/运输特性的变化要么对施加的 ABA 没有反应，要么如果有反应，它们的变化方向与氮胁迫下根 ABA 的变化相反；（3）flacca 番茄（对氮胁迫产生很少的 ABA）对氮胁迫的反应与在野生型中观察到的硝酸盐（NO3-）运输的变化非常相似。
