Horst Marschner

The influence of varied Mg supply (10-1000 micromolar) and light intensity (100-580 microeinsteins per square meter per second) on the concentrations of ascorbate (AsA) and nonprotein SH-compounds and the activities of superoxide dismutase (SOD; EC 1.15.11) and the H(2)O(2) scavenging enzymes, AsA peroxidase (EC 1.11.1.7), dehydroascorbate reductase (EC 1.8.5.1), and glutathione reductase (EC 1.6.4.2) were studied in bean (Phaseolus vulgaris L.) leaves over a 13-day period. The concentrations of AsA and SH-compounds and the activities of SOD and H(2)O(2) scavenging enzymes increased with light intensity, in particular in Mg-deficient leaves. Over the 12-day period of growth for a given light intensity, the concentrations of AsA and SH-compounds and the activities of these enzymes remained more or less constant in Mg-sufficient leaves. In contrast, in Mg-deficient leaves, a progressive increase was recorded, particularly in concentrations of AsA and activities of AsA peroxidase and glutathione reductase, whereas the activities of guaiacol peroxidase and catalase were only slightly enhanced. Partial shading of Mg-deficient leaf blades for 4 days prevented chlorosis, and the activities of the O(2) (.-) and H(2)O(2) scavenging enzymes remained at a low level. The results demonstrate the role of both light intensity and Mg nutritional status on the regulation of O(2) (.-) and H(2)O(2) scavenging enzymes in chloroplasts.

Roots of grasses in response to iron deficiency markedly increase the release of chelating substances (;phytosiderophores') which are highly effective in solubilization of sparingly soluble inorganic Fe(III) compounds by formation of Fe(III)phytosiderophores. In barley (Hordeum vulgare L.), the rate of iron uptake from Fe(III)phytosiderophores is 100 to 1000 times faster than the rate from synthetic Fe chelates (e.g. Fe ethylenediaminetetraacetate) or microbial Fe siderophores (e.g. ferrichrome). Reduction of Fe(III) is not involved in the preferential iron uptake from Fe(III)phytosiderophores by barley. This is indicated by experiments with varied pH, addition of bicarbonate or of a strong chelator for Fe(II) (e.g. batho-phenanthrolinedisulfonate). The results indicate the existence of a specific uptake system for Fe(III)phytosiderophores in roots of barley and all other graminaceous species. In contrast to grasses, cucumber plants (Cucumis sativus L.) take up iron from Fe(III)phytosiderophores at rates similar to those from synthetic Fe chelates. Furthermore, under Fe deficiency in cucumber, increased rates of uptake of Fe(III)phytosiderophores are based on the same mechanism as for synthetic Fe chelates, namely enhanced Fe(III) reduction and chelate splitting. Two strategies are evident from the experiments for the acquisition of iron by plants under iron deficiency. Strategy I (in most nongraminaceous species) is characterized by an inducible plasma membrane-bound reductase and enhancement of H(+) release. Strategy II (in grasses) is characterized by enhanced release of phytosiderophores and by a highly specific uptake system for Fe(III)phytosiderophores. Strategy II seems to have several ecological advantages over Strategy I such as solubilization of sparingly soluble inorganic Fe(III) compounds in the rhizosphere, and less inhibition by high pH. The principal differences in the two strategies have to be taken into account in screening methods for resistance to ;lime chlorosis'.

During imbibition and germination of wheat (Triticum aestivum) in the dark over 72 h, activities of the enzymes of the ascorbate (AsA)-dependent H 2 O 2 -scavenging pathway, AsA peroxidase, monodehydroascorbate (MDAsA) reductase, dehydroascorbate (DHAsA) reductase and glutathione (GSSG) reductase as well as superoxide dismutase (SOD), catalase and guaiacol peroxidase were determined both in whole grains and in isolated embryos and endosperm. With the exception of DHAsA reductase, activities of the other enzymes assayed increased in germinating seeds, especially during radicle emergence (between 24-48 h of imbibition)

Journal Article Partitioning of shoot and root dry matter and carbohydrates in bean plants suffering from phosphorus, potassium and magnesium deficiency Get access Ismail Cakmak, Ismail Cakmak 1Department of soil Science and Plant Nutrition, University of CukurovaAdana, Turkey Search for other works by this author on: Oxford Academic PubMed Google Scholar Christine Hengeler, Christine Hengeler 2Institut für Pflanzenernährung, Universität Hohenheim70593 Stuttgart, Germany Search for other works by this author on: Oxford Academic PubMed Google Scholar Horst Marschner Horst Marschner 3 2Institut für Pflanzenernährung, Universität Hohenheim70593 Stuttgart, Germany 3 To whom correspondence should be addressed. Fax: +49 711 459 3295 Search for other works by this author on: Oxford Academic PubMed Google Scholar Journal of Experimental Botany, Volume 45, Issue 9, September 1994, Pages 1245–1250, https://doi.org/10.1093/jxb/45.9.1245 Published: 01 September 1994 Article history Received: 14 February 1994 Accepted: 27 May 1994 Published: 01 September 1994