Evidences of organic acids exudation in aluminium stress responses of two Madeiran wheat (Triticum aestivum L.) landraces

Two wheat (Triticum aestivum L.) Madeiran landraces were subjected to 100 μM and 200 μM of aluminium (Al) in hydroponic culture, assessing the organic acid exudation role in plant’s responses to this metal. Samples of initial landrace populations (F0), F3 and haplodiploid lines (DH) were evaluated using standard tests: eriochrome cyanine R staining, root elongation and callose accumulation in roots. Root exudates were obtained to determine if the accumulation of malic and citric acids in hydroponic medium was a response to Al exposure. Additionally, the presence of ALMT1 gene was determined using five microsatellite markers. Standard tests confirmed that ISOP 76 was Al tolerant and ISOP 239, Al susceptible. ISOP 76, in the presence of 100 μM Al, exuded substantially more malic acid (12.87 to 43.33 mg/L), than ISOP 239 (3.65 to 7.72 mg/L). The levels of both organic acid exudation were substantially lower in ISOP 239 than in the ISOP 76. In the presence of 200 μM Al, ISOP 76 F0 shows a higher root elongation ratio (better tolerates Al), but the DH line was the one that exuded higher content of malic acid. Different gene alleles and promoters were detected in both landraces. Molecular differences could explain the observed dissimilarity in organic acid exudation response to Al stress.