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.

Similarities and Differences in the Acquisition of Fe and P by Dicot Plants

“…In addition to ethylene, other hormones and signaling substances, such as auxin and nitric oxide (NO), have been involved in the up-regulation of Fe and P acquisition genes [3,4,29,68,[75][76][77][78][79][80][81]. In both deficiencies, the activating effect of auxin, ethylene and NO depend on the Fe or P status of the plants [68,69,75,76], which suggests the existence of additional Fe-and P-related signals acting in conjunction with ethylene, auxin and NO [82].…”

Increased Sucrose Accumulation Regulates Iron-Deficiency Responses by Promoting Auxin Signaling in Arabidopsis Plants

“…Since previous studies have shown that auxins play a critical role in the regulation of Fe deficiency responses (Chen et al, 2010b;Jin et al, 2011;Wu et al, 2012b), it is therefore necessary to clarify whether auxins have an association with Suc in the regulation of Fe deficiency responses. As shown in Figure 9, in the presence of the auxin transport inhibitor NPA, the stimulating effect of Suc on root FCR activity and expression of IRT1, FRO2, and FIT in Fedeficient Col-0 plants were completely terminated.…”

“…In addition to the above transcription factors, we and others showed that the chemical molecules, auxins and nitric oxide (NO), both of which accumulate to higher levels in Fe-deficient plants, are also two general regulators controlling the initiation of adaptations to Fe deficiency in Strategy I plants (Graziano and Lamattina, 2007;Jin et al, 2009Jin et al, , 2011Chen et al, 2010b;Bacaicoa et al, 2011;Wu et al, 2012b). The NO acts upstream of FIT to trigger Fe deficiency responses through a mechanism of reducing the proteasomal degradation of FIT (Meiser et al, 2011), while the elevation of auxin levels is required for the regulation of increased synthesis of NO under Fe-deficient conditions (Chen et al, 2010b;Jin et al, 2011).…”

Isolation and functional analysis of MdNAS1, with functions in improved iron stress tolerance and abnormal flower in transgenic tobacco

“…Fe-deficiency induced an obvious increase of IAA level in the branch apex and treatments of IAA to the branch apex induced Fe deficiency responses in M. xiaojinensis (Wu et al 2012). In the present study, the expression levels of MdNAS1 were affected by IAA and ABA treatments in the leaf, and phloem of M. domestica seedlings.…”

“…The expression of MxNAS1 and MxNAS2 in M. xiaojinensis was also affected by IAA and ABA treatments and the expression levels in root and mature leaf of M. xiaojinensis all increased (Han et al 2013. Fe-deficiency also induced a level increase of IAA in the shoot apex of M. xiaojinensis and treatments of IAA to the shoot apex induced Fe deficiency responses (Wu et al 2012).…”