ARS | Publication request: ASSESSING SHOOT-ROOT COMMUNICATION IN THE REGULATION OF IRON HOMEOSTASIS IN THE FEFE MELON MUTANT

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: July 7, 2006
Publication Date: July 7, 2006
Citation: Narayanan, N.N., Grusak, M.A. 2006. Assessing shoot-root communication in the regulation of iron homeostasis in the fefe melon mutant. In: Proceedings of the Thirteenth International Symposium on Iron Nutrition and Interactions in Plants, July 3-7, 2006, Montpellier, France. p. 91.

Technical Abstract: The fefe mutant of musk melon exhibits characteristics of iron deficiency such as interveinal chlorosis of leaves, retarded growth, and finally death unless supplemental Fe is provided. The seedlings have normal green cotyledons but the first true leaves are yellow with green veins. To determine the regulation of iron homeostasis in these plants, parental wild type genotypes (cv. Edisto and Mainstream) and iron deficiency mutant genotype (cv. C940-fe, commonly called "fefe") were grown hydroponically with high (20µM) or low (2µM) supplemental iron. Two-day interval measurements of Fe(III) reductase activity in intact root systems indicated enhanced rates of iron reduction in low-iron-treated wild type plants, relative to high iron growth, but no enhancement in fefe plants. Reductase rates were lower overall in fefe, relative to wild type controls. Iron(III) reductase activity also was visualized by placing the roots in an agarose matrix containing 0.2mM Fe(III)-EDTA and 0.3mM Na2 BPDS. Reduction was found to be widespread over most of the length of the roots in wild type plants under low iron conditions when compared to high iron conditions. By contrast, Fe(III) reductase activity was not visualized in fefe roots in both high and low iron conditions. To determine whether the mutation in fefe was influencing a root or shoot process, reciprocal grafting experiments with wild type Mainstream and mutant fefe plants were conducted. These studies revealed that the leaf chlorosis phenotype is related to the phenotype of the root: plants with Mainstream roots were green, while plants with fefe roots were chlorotic. We also studied root reductase activity in grafted plants and found that fefe shoots could send a putative "iron status" signal to Mainstream roots to enhance reductase activity, while fefe roots could also perceive a low Fe signal from Mainstream shoots to exhibit elevated reductase activity. These studies suggest that the low root reductase phenotype in fefe is not due to a mutation in either roots or shoot. Rather, it appears that the rapid chlorosis witnessed in fefe seedlings prevents adequate photosynthesis required to send a shoot-to-root iron status signal. To test this, foliar iron application to fefe seedling cotyledons was used to green the first leaves and make them photosynthetically competent. This allowed intact fefe plants to demonstrate elevated root reduction, relative to non-treated fefe controls. Why fefe plants are chlorotic is still under investigation, but preliminary results show that fefe roots overaccumulate iron, relative to wild type roots. Experiments are in progress to evaluate the spatial localization of iron in fefe and Mainstream roots. These results will be used to present a model of iron homeostatic dysfunction in the fefe mutant. This work was funded in part by funds from USDA-ARS under Agreement No. 58-6250-6-001 and from the Harvest plus Project under Agreement No. 58-6250-4-F029 to MAG.