title: The role of shoot-localized processes in the mechanism of Zn efficiency in common bean.
abstract: Zn efficiency (ZE) is the ability of plants to maintain high yield under Zn-deficiency stress in the soil. Two bean ( Phaseolus vulgaris L.) genotypes that differed in ZE, Voyager (Zn-efficient) and Avanti (Zn-inefficient), were used for this investigation. Plants were grown under controlled-environment conditions in chelate-buffered nutrient solution where Zn(2+) activities were controlled at low (0.1 pM) or sufficient (150 pM) levels. To investigate the relative contribution of the root versus the shoot to ZE, observations of Zn-deficiency symptoms in reciprocal grafts of the two genotypes were made. After growth under low-Zn conditions, plants of nongrafted Avanti, self-grafted Avanti and reciprocal grafts that had the Avanti shoot scion exhibited Zn-deficiency symptoms. However nongrafted and self-grafted Voyager, as well as reciprocal grafts with the Voyager shoot scion, were healthy with no visible Zn-deficiency symptoms under the same growth conditions. More detailed investigations into putative shoot-localized ZE mechanisms involved determinations of leaf biomass production and Zn accumulation, measurements of subcellular Zn compartmentation, activities of two Zn-requiring enzymes, carbonic anhydrase and Cu/Zn-dependent superoxide dismutase (Co/ZnSOD), as well as the non-Zn-requiring enzyme nitrate reductase. There were no differences in shoot tissue Zn concentrations between the Zn-inefficient and Zn-efficient genotypes grown under the low-Zn conditions where differences in ZE were exhibited. Shoot Zn compartmentation was investigated using radiotracer ((65)Zn) efflux analysis and suggested that the Zn-efficient genotype maintains higher cytoplasmic Zn concentrations and less Zn in the leaf-cell vacuole, compared to leaves from the Zn-inefficient genotype under Zn deficiency. Analysis of Zn-requiring enzymes in bean leaves revealed that the Zn-efficient genotype maintains significantly higher levels of carbonic anhydrase and Cu/ZnSOD activity under Zn deficiency. While these data are not sufficient to allow us to determine the specific mechanisms underlying ZE, they certainly point to the shoot as a key site where ZE mechanisms are functioning, and could involve processes associated with Zn compartmentation and biochemical Zn utilization.
authors.affiliation: US Plant, Soil and Nutrition Laboratory, USDA-ARS, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Gökhan
authors.initials: G
authors.lastname: Hacisalihoglu
authors.forename: Jonathan J
authors.initials: JJ
authors.lastname: Hart
authors.forename: C Eduardo
authors.initials: CE
authors.lastname: Vallejos
authors.forename: Leon V
authors.initials: LV
authors.lastname: Kochian
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects; D002256:Carbonic Anhydrases / Q000378:metabolism; D002451:Cell Compartmentation; D005838:Genotype; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000378:metabolism; D027805:Phaseolus / Q000235:genetics / Q000502:physiology*; D018515:Plant Leaves / Q000502:physiology; D018520:Plant Shoots / Q000502:physiology*; D013482:Superoxide Dismutase / Q000378:metabolism; D015032:Zinc / Q000172:deficiency / Q000378:metabolism* / Q000494:pharmacology; D015037:Zinc Radioisotopes / Q000378:metabolism
chemical_list: D015037:Zinc Radioisotopes; D013482:Superoxide Dismutase; D009565:Nitrate Reductases; D050901:Nitrate Reductase; D002256:Carbonic Anhydrases; D015032:Zinc