López-Millán A F, Morales F, Abadía A, Abadía J
Departamento de Nutrición Vegetal, Estación Experimental de Aula Dei, Consejo Superior de Investigaciones Científicas, Apartado 202, E-50080 Zaragoza, Spain.
Plant Physiol. 2000 Oct;124(2):873-84. doi: 10.1104/pp.124.2.873.
The effects of iron deficiency on the composition of the xylem sap and leaf apoplastic fluid have been characterized in sugar beet (Beta vulgaris Monohil hybrid). pH was estimated from direct measurements in apoplastic fluid and xylem sap obtained by centrifugation and by fluorescence of leaves incubated with 5-carboxyfluorescein and fluorescein isothiocyanate-dextran. Iron deficiency caused a slight decrease in the pH of the leaf apoplast (from 6.3 down to 5.9) and xylem sap (from 6.0 down to 5.7) of sugar beet. Major organic acids found in leaf apoplastic fluid and xylem sap were malate and citrate. Total organic acid concentration in control plants was 4.3 mM in apoplastic fluid and 9.4 mM in xylem sap and increased to 12.2 and 50.4 mM, respectively, in iron-deficient plants. Inorganic cation and anion concentrations also changed with iron deficiency both in apoplastic fluid and xylem sap. Iron decreased with iron deficiency from 5.5 to 2.5 microM in apoplastic fluid and xylem sap. Major predicted iron species in both compartments were FeCitOH in the controls and FeCit(2) in the iron-deficient plants. Data suggest the existence of an influx of organic acids from the roots to the leaves via xylem, probably associated to an anaplerotic carbon dioxide fixation by roots.
缺铁对甜菜（Beta vulgaris Monohil杂交种）木质部汁液和叶片质外体汁液成分的影响已得到表征。通过离心获得的质外体汁液和木质部汁液的直接测量以及用5-羧基荧光素和异硫氰酸荧光素-葡聚糖孵育的叶片荧光来估计pH值。缺铁导致甜菜叶片质外体的pH值略有下降（从6.3降至5.9），木质部汁液的pH值也略有下降（从6.0降至5.7）。在叶片质外体汁液和木质部汁液中发现的主要有机酸是苹果酸和柠檬酸。对照植株质外体汁液中的总有机酸浓度为4.3 mM，木质部汁液中为9.4 mM，而在缺铁植株中分别增加到12.2 mM和50.4 mM。质外体汁液和木质部汁液中的无机阳离子和阴离子浓度也随缺铁而变化。缺铁时，质外体汁液和木质部汁液中的铁从5.5 μM降至2.5 μM。两个区室中主要预测的铁物种在对照中为FeCitOH，在缺铁植株中为FeCit(2)。数据表明存在有机酸通过木质部从根部流入叶片的现象，这可能与根部的回补性二氧化碳固定有关。
