Journal of Integrative Plant Biology 2008, 50 (12): 1557–1562 Iron Deficiency-induced Increase of Root Branching Contributes to the Enhanced Root Ferric Chelate Reductase Activity Chong-Wei Jin 1,2 , Wei-Wei Chen 2 , Zhi-Bin Meng 2 and Shao-Jian Zheng 2 * ( 1 Ministry of Education Key Laboratory of Environment Remediation and Ecosystem Health, College of Environmental and Resource Science, Zhejiang University, Hangzhou 310029, China; 2 State Key Laboratory of Plant Biochemistry and Physiology, College of Life Sciences, Zhejiang University, Hangzhou 310058, China) Abstract In various plant species, Fe deficiency increases lateral root branching. However, whether this morphological alteration contributes to the Fe deficiency-induced physiological responses still remains to be demonstrated. In the present research, we demonstrated that the lateral root development of red clover (Trifolium pretense L.) was significantly enhanced by Fe deficient treatment, and the total lateral root number correlated well with the Fe deficiency-induced ferric chelate reductase (FCR) activity. By analyzing the results from Dasgan et al. (2002), we also found that although the two tomato genotypes line227/1 (P1) and Roza (P2) and their reciprocal F1 hybrid lines (“P1 × P2” and “P2 × P1”) were cultured under two different lower Fe conditions (10 -6 and 10 -7 M FeEDDHA), their FCR activities are significantly correlated with the lateral root number. More interestingly, the -Fe chlorosis tolerant ability of these four tomato lines displays similar trends with the lateral root density. Taking these results together, it was proposed that the Fe deficiency-induced increases of the lateral root should play an important role in resistance to Fe deficiency, which may act as harnesses of a useful trait for the selection and breeding of more Fe-efficient crops among the genotypes that have evolved a Fe deficiency-induced Fe uptake system. Key words: Fe deficiency; ferric chelate reductase; lateral root; red clover; tomato. Jin CW, Chen WW, Meng ZB, Zheng SJ (2008). Iron deficiency-induced increase of root branching contributes to the enhanced root ferric chelate reductase activity. J. Integr. Plant Biol. 50(12), 1557–1562. Available online at www.jipb.net In most soils, although the total Fe content is much higher than plants require, low Fe bioavailability is a primary constraint to plant growth in terrestrial ecosystems, particularly in calcareous soils (Imsande 1998). Generally, plants undergo both morpho- logical and physiological changes when grown under Fe-limited conditions (Marschner et al. 1986); such as increasing later root development in Arabidopsis and tomatoes (Moog et al. 1995; Dasgan et al. 2002). Generally, the increases of root branching Received 29 Nov. 2007 Accepted 20 Dec. 2007 Supported by the National Natural Science Foundation of China (30625026) and the Program for New Century Excellent Talents in University (NCET-04- 0554). ∗ Author for correspondence. Tel(Fax): +86 (0)571 8820 6438; E-mail: <sjzheng@zju.edu.cn>. C  2008 Institute of Botany, the Chinese Academy of Sciences doi: 10.1111/j.1744-7909.2008.00654.x is proposed to facilitate the uptake of nutrients (Drew 1975; Hell and Hillebrand 2001). However, in comparison with other Fe deficiency-induced responses (e.g. ferric reductase, proton secretion), relatively little evidence has been related to the role of lateral roots in plant Fe nutrition thus far. Therefore, whether the increases of root branching are also important for plants tolerating Fe deficiency still remains unknown. It has been demonstrated that the nongraminaceous mono- cots and dicots (Strategy I plants) must enzymatically reduce Fe(III) to Fe(II) before the root cells can take it up (Chaney et al. 1972). The Arabidopsis frd1 (defective in FRO2) mutant exhibited reduced Fe uptake and growth when Fe in the growth medium was limited (Yi and Guerinot 1996; Robinson et al. 1999). In most cases, the Fe deficiency-induced ferric chelate reductase (FCR) was confined to the young lateral root apex (R¨ omheld and Marshner 1981; Zheng et al. 2003), subapical root regions or young lateral roots (Marschner et al. 1986). Therefore, the increases of lateral root density are expected to provide more sites for FCR inducing in a Fe-deficient plant, and hence increase the total FCR activity.