title: Induction of root Fe(lll) reductase activity and proton extrusion by iron deficiency is mediated by auxin-based systemic signalling in Malus xiaojinensis.
abstract: Iron is a critical cofactor for a number of metalloenzymes involved in respiration and photosynthesis, but plants often suffer from iron deficiency due to limited supplies of soluble iron in the soil. Iron deficiency induces a series of adaptive responses in various plant species, but the mechanisms by which they are triggered remain largely unknown. Using pH imaging and hormone localization techniques, it has been demonstrated here that root Fe(III) reductase activity and proton extrusion upon iron deficiency are up-regulated by systemic auxin signalling in a Fe-efficient woody plant, Malus xiaojinensis. Split-root experiments demonstrated that Fe-deprivation in a portion of the root system induced a dramatic increase in Fe(III) reductase activity and proton extrusion in the Fe-supplied portion, suggesting that the iron deficiency responses were mediated by a systemic signalling. Reciprocal grafting experiments of M. xiaojinensis with Malus baccata, a plant with no capability to produce the corresponding responses, indicate that the initiation of the systemic signalling is likely to be determined by roots rather than shoots. Iron deficiency induced a substantial increase in the IAA content in the shoot apex and supplying exogenous IAA analogues (NAA) to the shoot apex could mimic the iron deficiency to trigger the corresponding responses. Conversely, preventing IAA transport from shoot to roots blocked the iron deficiency responses. These results strongly indicate that the iron deficiency-induced physiological responses are mediated by systemic auxin signalling.
authors: Institute for Horticultural Plants, China Agricultural University, Beijing 100193, PR China.
authors: Ting
authors: T
authors: Wu
authors: Heng-Tao
authors: HT
authors: Zhang
authors: Yi
authors: Y
authors: Wang
authors: Wen-Suo
authors: WS
authors: Jia
authors: Xue-Feng
authors: XF
authors: Xu
authors: Xin-Zhong
authors: XZ
authors: Zhang
authors: Zhen Hai
authors: ZH
authors: Han
mesh_terms: D001692:Biological Transport; D038181:FMN Reductase / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000235:genetics*; D006863:Hydrogen-Ion Concentration; D007210:Indoleacetic Acids / Q000032:analysis / Q000378:metabolism*; D007501:Iron / Q000378:metabolism*; D027845:Malus / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics / Q000502:physiology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects / Q000201:enzymology / Q000235:genetics / Q000502:physiology; D018520:Plant Shoots / Q000187:drug effects / Q000201:enzymology / Q000235:genetics / Q000502:physiology; D011522:Protons; D015398:Signal Transduction / Q000502:physiology; D013312:Stress, Physiological / Q000502:physiology; D013997:Time Factors; D015854:Up-Regulation
chemical_list: D007210:Indoleacetic Acids; D010940:Plant Proteins; D011522:Protons; D007501:Iron; D038181:FMN Reductase; C023903:ferric citrate iron reductase