Nitric oxide precursors prevent Al-triggered auxin flow inhibition in Triticum aestivum roots

Abstract

Aluminum (Al) is an element widely distributed in soils, even though Al³⁺ is one of the most detrimental cations to plant growth. The effect of nitric oxide (NO) precursors on indole-3-acetic acid (IAA) flow towards roots upon Al treatment is herein reported using two Triticum aestivum (wheat) cultivars with recognized differential Al tolerance. Roots of Al-tolerant seedlings with no treatment (control) accumulated higher amounts of NO than Al-sensitive ones. The treatment with Al further stimulated NO production in root cells while root exposure to NO₃ ^-, L-arginine (Arg) or the NO donor S-nitrosoglutathione (GSNO) decreased both Al and lipid peroxide accumulation in both cultivars. Regardless of the cultivar, NO₃ ^-, Arg or GSNO prevented the blockage of IAA flow towards roots. Overall, the treatment of wheat roots with NO precursors prior to Al treatment effectively guarantees normal IAA flow towards roots, a condition that favors the organ's growth and development.

Keywords: Aluminum; Antioxidant enzymes; Arginine; Auxin; Nitrate; Wheat.

Graphical abstract

Fig. 1

Localization of Al in wheat root apices using morin. Four-day-old seedlings of cultivars Anahuac (Al-sensitive) and BH1146 (Al-tolerant) were hydroponically incubated with 200 µM Ca²⁺ (Ctrl) or 75 µM AlCl₃ in 200 µM Ca²⁺ for 48 h. Alternatively, seedlings were pre-treated with NO₃⁻, L-arginine (Arg) or S-nitrosoglutathione (GSNO) at 300 µM for 24 h followed by exposure to Al for 48 h. Green fluorescence indicates presence of Al. VC, vascular cylinder; Pe, pericycle; C, cortex; E, epidermis. Images are representative of at least two experiments, each done in triplicate. Bar = 100 µm.

Fig. 2

Localization of Al in the stele of wheat root apices using morin. Images correspond to magnifications of those shown in Fig. 1 to better visualize Al in vascular cylinder and neighborhood. VC, vascular cylinder; Pe, pericycle; C, cortex. Images are representative of at least two experiments, each done in triplicate. Bars = 25 µm.

Fig. 3

Localization of NO in wheat root apices using DAF-2DA. Four-day-old seedlings of cultivars Anahuac (Al-sensitive) and BH1146 (Al-tolerant) were hydroponically incubated with 200 µM Ca²⁺ (Ctrl) or 75 µM AlCl₃ in 200 µM Ca²⁺ for 48 h. Alternatively, seedlings were pre-treated with NO₃⁻, L-arginine (Arg) or S-nitrosoglutathione (GSNO) at 300 µM for 24 h followed by exposure to Al for 48 h. Green fluorescence indicates presence of NO. VC, vascular cylinder; Pe, pericycle; C, cortex; E, epidermis. Images are representative of at least two experiments, each done in triplicate. Bar = 100 µm.

Fig. 4

Localization of NO in the stele of wheat root apices using DAF-2DA. Images correspond to magnifications of those shown in Fig. 3 to better visualize NO in vascular cylinder and neighborhood. VC, vascular cylinder; Pe, pericycle; C, cortex. Images are representative of at least two experiments, each done in triplicate. Bars = 25 µm.

Fig. 5

Immunolocalization of auxin in wheat root apices. Four-day-old seedlings of cultivars Anahuac (Al-sensitive) and BH1146 (Al-tolerant) were hydroponically incubated with 200 µM Ca²⁺ (Ctrl) or 75 µM AlCl₃ in 200 µM Ca²⁺ for 48 h. Alternatively, seedlings were pre-treated with NO₃⁻, L-arginine (Arg) or S-nitrosoglutathione (GSNO) at 300 µM for 24 h followed by exposure to Al for 48 h. Blue spots, indicated by the arrow, represent the presence of indole-3-acetic acid (IAA). PM, promeristem; PC, procambium; FM, fundamental meristem; PD, protoderm. Images are representative of experiments done in sextuplicate. Bar = 200 µm.

Fig. 6

Effect of an NO donor on auxin distribution in wheat root apices treated with an inhibitor of auxin transport. Four-day-old seedlings of cultivars Anahuac (Al-sensitive) and BH1146 (Al-tolerant) were hydroponically incubated with 200 µM Ca²⁺ (Ctrl) or 75 µM AlCl₃ in 200 µM Ca²⁺ for 48 h. Alternatively, seedlings were pre-treated with 2,3,5-triiodobenzoic acid (TIBA) at 10 μM or S-nitrosoglutathione (GSNO) at 300 µM or 10 μM TIBA plus 300 µM GSNO for 24 h followed by exposure (or not) to Al for 48 h. Blue spots indicate presence of indole-3-acetic acid (IAA). PM, promeristem; PC, procambium; FM, fundamental meristem; PD, protoderm. Images are representative of experiments done in sextuplicate. Bar = 200 µm.