International Journal of Applied Science and Technology Vol. 4 No. 1; January 2014 186 Relationship of Ethylene Production and Aerenchyme Formation on Oxidation Ability and Root Surfaced-Iron (Fe 2+ ) Accumulation under Different Iron Concentrations and Rice Genotypes Siti Maryam Harahap 1),2) , Munif Ghulamahdi 3) , Sandra Arifin Aziz 3) , Atang Sutandi 4) Miftahudin 5) 1) Assesment Institute for Agricultural Technology (AIAT) North Sumatra. Jalan Jend Besar AH.Nasution No. 1B Medan.PO. Box 20143, Indonesia. 2) Agronomy and Horticulture Graduate Program, Graduate School, Bogor Agricultural University, Jalan Meranti, IPB Darmaga Campus, Bogor 16680, Indonesia 3) Department of Agronomy and Horticulture. Faculty of Agriculture, Bogor Agricultural University, Jalan Meranti, IPB Darmaga Campus, Bogor 16680, Indonesia. 4) Department of Soil Science and Land Resources, Faculty of Agriculture, Bogor Agricultural University, Jalan Meranti, IPB Darmaga Campus, Bogor 16680, Indonesia 5) Department of Biology, Faculty Mathematics and Natural Sciences. Bogor Agricultural University, Jalan Meranti, IPB Darmaga Campus , Bogor 16680, Indonesia. Abstract Iron toxicity in rice plant can occur during the vegetative and generative phase. Different rice genotypes show different responses to iron toxicity both morphologically and physiologically. The aim of this study was to evaluate the relationship of root ethylene production and aerenchyme formation on the ability of rice root to oxidize and accumulate iron (Fe 2+ ) on root surface under different iron concentration and rice genotypes. This research was conducted at the greenhouse, Bogor Agricultural University, Indonesia from October to December 2012. experiment that consisted of two factorial was completely randomize designed with three replications. The first factor was four level Fe concentrations, i.e.: 0, 500, 1000, and 1500 ppm and the second factor was IRH108, IR64 and Indragiri rice genotypes. The results showed that there was significant differences on the ethylene production, aerenchyme size, plaque content, and Fe 2+ distribution in root tissue among each genotype. It was concluded that Indragiri was a tolerant genotype to iron toxicity as indicated by the highest ethylene production (116.71 nl.g -1 fresh weight -1 .h -1 ), the highest root Fe 2+ content (21,271 ppm), the largest size of aerenchyme (80,230.11nm), and the highest plaque content (1,864.12). Keywords: Ethylene, Aerenchyme, Rice Genotype, Concentration, Iron Toxicity Introduction Iron (Fe 2+ ) is one of the essential micronutrients, which is required by plants in a small amount ranging from 30- 150 ppm. While critical deficiency of iron content ranging from 50 to150 mg Fe kg -1 dry weight of leaves (Marschner, 1995). If plants absorb excessive iron, the root growth will be retarded and the root become few, short with blunt tip (Yamauchi and Peng,1993). The range of rice tolerance Fe toxicity is quite extensive. The critical limit of Fe content in plant tissue is between 300-500 ppm (Sahrawat, 2000). However, other research reported that the critical limit of Fe content in plant tissue is between 500-2000 ppm (Becker and Asch, 2005; Nozoe et al 2008). Plant could tolerate to 1000-2000 ppm of Fe 2+ in the soil solution (Asch et al. 2005). Koesrini and William (2001) reported that Margasari varietiy that absorbs 400 ppm of Fe 2+ could survive; however, plants will die when absorb about 600 ppm of Fe 2+ .