Fischer E S, Lohaus G, Heineke D, Heldt H W
E. S. Fischer (corresponding author, fax 49-30-31471142), Institut für Grundlagen der Pflanzenbauwissenschaften, Pflanzenernährung, Humboldt Univ. zu Berlin, Lentzeallee 55-57, D-14195 Berlin, Germany.
G. Lohaus, D. Heineke and H. W. Heldt, Institut für Biochemie der Pflanze, Univ. Göttingen, Untere Karspüle 2, D-37073 Göttingen, Germany.
Physiol Plant. 1998 Jan;102(1):16-20. doi: 10.1034/j.1399-3054.1998.1020103.x.
Accumulation of assimilates in source leaves of magnesium-deficient plants is a well-known feature. We had wished to determine whether metabolite concentrations in sink leaves and roots are affected by magnesium nutrition. Eight-week-old spinach plants were supplied either with a complete nutrient solution (control plants) or with one lacking Mg (deficient plants) for 12 days. Shoot and root fresh weights and dry weights were lower in deficient than in control plants. Mg concentrations in deficient plants were 11% of controls in source leaves, 12% in sink leaves and 26% in roots, respectively. As compared with controls, increases were found in starch and amino acids in source leaves and in sucrose, hexoses, starch and amino acids in sink leaves, whereas they were only slightly enhanced in roots. In phloem sap of magnesium-deficient and control plants no differences in sucrose and amino acid concentrations were found. To prove that sink leaves were the importing organs they were shaded, which did not alter the response to magnesium deficiency as compared with that without shading. Since in the shaded sink leaves the photosynthetic production of metabolites could be excluded, those carbohydrates and amino acids that accumulated in the sink leaves of the deficient plants must have been imported from the source leaves. It is concluded that in magnesium-deficient spinach plants the growth of sink leaves and roots was not limited by carbohydrate or amino acid supply. It is proposed that the accumulation of assimilates in the source leaves of Mg-deficient plants results from a lack of utilization of assimilates in the sink leaves.
镁缺乏植物源叶中同化物的积累是一个众所周知的特征。我们曾希望确定镁营养是否会影响库叶和根中的代谢物浓度。将八周龄的菠菜植株分别供应完全营养液（对照植株）或缺乏镁的营养液（缺镁植株），持续12天。缺镁植株的地上部和根的鲜重及干重均低于对照植株。缺镁植株源叶中的镁浓度分别为对照植株的11%，库叶中为12%，根中为26%。与对照相比，源叶中的淀粉和氨基酸以及库叶中的蔗糖、己糖、淀粉和氨基酸均有所增加，而根中仅略有增加。在镁缺乏植株和对照植株的韧皮部汁液中，蔗糖和氨基酸浓度没有差异。为了证明库叶是输入器官，对其进行遮光处理，与未遮光相比，这并未改变对镁缺乏的响应。由于在遮光的库叶中可以排除代谢物的光合产生，因此缺镁植株库叶中积累的那些碳水化合物和氨基酸一定是从源叶输入的。得出的结论是，在镁缺乏的菠菜植株中，库叶和根的生长不受碳水化合物或氨基酸供应的限制。有人提出，镁缺乏植株源叶中同化物的积累是由于库叶中同化物利用不足所致。
