Acclimative changes in root epidermal cell fate in response to Fe and P deficiency: a specific role for auxin?

Abstract

Root hair formation and the development of transfer cells in the rhizodermis was investigated in various existing auxin-related mutants of Arabidopsis thaliana and in the tomato mutant diageotropica. Wild-type Arabidopsis plants showed increased formation of root hairs when the seedlings were cultivated in Fe- or P-free medium. These extranumerary hairs were located in normal positions and in positions normally occupied by nonhair cells, e.g., over periclinal walls of underlying cortical cells. Defects in auxin transport or reduced auxin sensitivity inhibited the formation of root hairs in response to Fe deficiency completely but did only partly affect initiation and elongation of hairs in P-deficient roots. Application of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid or the auxin analog 2,4-dichlorophenoxyacetic acid did not rescue the phenotype of the auxin-resistant axr2 mutant under control and Fe-deficient conditions, indicating that functional AXR2 product is required for translating the Fe deficiency signal into the formation of extra hairs. The development of extra hairs in axr2 roots under P-replete conditions was not affected by auxin antagonists, suggesting that this process is independent of auxin signaling. In roots of tomato, growth under Fe-deficient conditions induced the formation of transfer cells in the root epidermis. Transfer cell frequency was enhanced by application of 2,4-dichlorophenoxyacetic acid but was not inhibited by the auxin transport inhibitor N-1-naphthylphthalamic acid. In the diageotropica mutant, which displays reduced sensitivity to auxin, transfer cells appeared to develop in both Fe-sufficient and Fe-deficient roots. Similar to the wild type, no reduction in transfer cell frequency was observed after application of the above auxin transport inhibitor. These data suggest that auxin has no primary function in inducing transfer cell development; the formation of transfer cells, however, appears to be affected by the hormonal balance of the plants.

Phosphate Transport and Homeostasis in Arabidopsis

“…Although application of IAA increases root hair length and density in plants grown on high Pi, it has little effects on root hairs in plants grown on low Pi (Bates and Lynch, 1996;Ma et al, 2001a). Furthermore, low Pi stimulated root hair elongation in the hairless auxin-resistant mutant axr1 and axr2, as well as in the auxin-insensitive mutant aux1, in a manner similar to wild type (Figure 9) (Ma et al, 2001a;Schikora and Schmidt 2001;Schmidt and Schikora, 2001). Thus, although auxin does affect root hair development, it appears that low Pi can increase root hair length and density in a manner that is at least partially independent of auxin.…”

Phosphate Starvation Root Architecture and Anthocyanin Accumulation Responses Are Modulated by the Gibberellin-DELLA Signaling Pathway in Arabidopsis

“…Growth of Arabidopsis seedlings in Pi-limiting conditions causes an increase in the length and frequency of root hairs, thus enlarging the root surface area and enhancing the ability of the roots to absorb phosphorus (Schikora and Schmidt, 2001;Ma et al, 2003; Fig. 3A).…”

“…Recently, it has been reported that the phytohormones ethylene and auxin are involved in Pi starvationinduced root hair development in Arabidopsis (Schikora and Schmidt, 2001;He et al, 2005). To investigate the possible role of the GA-DELLA system in Pi deficiencyinduced changes in the formation and growth of root hairs, we compared the roots of wild-type, gai-t6 rga-t2 rgl1-1 rgl2-1, ga1-3, and ga1-3 gai-t6 rga-t2 rgl1-1 rgl2-1 seedlings.…”

Interaction between the bHLH Transcription Factor FIT and ETHYLENE INSENSITIVE3/ETHYLENE INSENSITIVE3-LIKE1 Reveals Molecular Linkage between the Regulation of Iron Acquisition and Ethylene Signaling in Arabidopsis

“…A variety of signaling molecules and plant hormones modulate the Fe deficiency response in a positive manner, such as nitric oxide (Graziano et al, 2002;Graziano and Lamattina, 2007;Chen et al, 2010;García et al, 2010) and auxin (Schikora and Schmidt, 2001;Chen et al, 2010), or in a negative manner, like cytokinin (Sé gué la et al, 2008). Experiments with the plant hormone ethylene in different dicot plants indicated a physiological connection between ethylene and iron deficiency signaling.…”