Al exposure increases proline levels by different pathways in an Al-sensitive and an Al-tolerant rye genotype

Abstract

Aluminium (Al) toxicity limits crop productivity, particularly at low soil pH. Proline (Pro) plays a role in protecting plants against various abiotic stresses. Using the relatively Al-tolerant cereal rye (Secale cereale L.), we evaluated Pro metabolism in roots and shoots of two genotypes differing in Al tolerance, var. RioDeva (sensitive) and var. Beira (tolerant). Most enzyme activities and metabolites of Pro biosynthesis were analysed. Al induced increases in Pro levels in each genotype, but the mechanisms were different and were also different between roots and shoots. The Al-tolerant genotype accumulated highest Pro levels and this stronger increase was ascribed to simultaneous activation of the ornithine (Orn)-biosynthetic pathway and decrease in Pro oxidation. The Orn pathway was particularly enhanced in roots. Nitrate reductase (NR) activity, N levels, and N/C ratios demonstrate that N-metabolism is less inhibited in the Al-tolerant line. The correlation between Pro changes and differences in Al-sensitivity between these two genotypes, supports a role for Pro in Al tolerance. Our results suggest that differential responses in Pro biosynthesis may be linked to N-availability. Understanding the role of Pro in differences between genotypes in stress responses, could be valuable in plant selection and breeding for Al resistance.

Arbuscular Mycorrhizae Mitigate Aluminum Toxicity and Regulate Proline Metabolism in Plants Grown in Acidic Soil

“…We found higher N content and NR activity in lotus, especially under stress conditions. NR activity, N levels, and N/C ratios were less reduced in the tolerant rye line, which showed an upregulated Orn pathway [ 71 ]. Overall, Pro content strongly increased in barley and lotus, although through different mechanisms, and possibly is directly linked with the N status in plants.…”

Aluminum-Immobilizing Rhizobacteria Modulate Root Exudation and Nutrient Uptake and Increase Aluminum Tolerance of Pea Mutant E107 (brz)

“…Aluminum affects biosynthesis and disturbs the balance of endogenous amino acids in plants [ 3 , 54 , 55 ]. The roots of wheat seedlings responded to Al toxicity by increased exudation of many proteinogenic amino acids [ 56 ].…”

“…The protective action of amino acids against Al toxicity has been repeatedly reported: arginine is involved in the biosynthesis of putrescine, leading to decreased Al retention in the cell walls of wheat [ 57 ]; cysteine increased the activity of glutathione [ 58 ]; GABA induced the antioxidant system in barley [ 59 ] and Arabidopsis thaliana [ 60 ]; glycine played a stress alleviating role as a component of glycine betaine in rice [ 61 ] and glycine-rich proteins in A. thaliana [ 62 ]; phenylalanine was involved in the biosynthesis of phenylpropanoids and flavonoids with defense functions in alfalfa [ 63 , 64 ]; proline protected root cells as an osmolyte [ 55 , 61 , 65 ]; threonine activated H + -ATPase in soybean [ 66 ]. Four of these amino acids (Arg, Cys, GABA, and Gly) were exuded more by the E107 ( brz ) mutant treated with Al ( Figure 8 a–d).…”

Aluminum in plant: Benefits, toxicity and tolerance mechanisms

“…In buckwheat, proline and total sugar content increased proportionally to Al concentration and was implicated in Al tolerance (Pirzadah et al, 2019). In two rye plants with different Al tolerance, de Sousa et al (2020) demonstrated that proline content increased by threefold and 20% in Al-tolerant and Al-sensitive lines respectively due to the regulation of proline biosynthetic pathways which include enhanced glutamate and ornithine pathways for proline biosynthesis and re-oxidation to 1-pyrroline-5-carboxylate. Moreover, Bera et al (2019) revealed that rice plants accumulated high levels of glycine betaine in response to Al exposure.…”