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SUMMARY: Among the three active aldehyde oxidases in Arabidopsis thaliana leaves (AAO1‐3), AAO3, which catalyzes the oxidation of abscisic‐aldehyde to abscisic‐acid, was shown recently to function as a reactive aldehyde detoxifier. Notably, aao2KO mutants exhibited less senescence symptoms and lower aldehyde accumulation, such as acrolein, benzaldehyde, and 4‐hydroxyl‐2‐nonenal (HNE) than in wild‐type leaves exposed to UV‐C or Rose‐Bengal. The effect of AAO2 expression absence on aldehyde detoxification by AAO3 and/or AAO1 was studied by comparing the response of wild‐type plants to the response of single‐functioning aao1 mutant (aao1S), aao2KO mutants, and single‐functioning aao3 mutants (aao3Ss). Notably, aao3Ss exhibited similar aldehyde accumulation and chlorophyll content to aao2KO treated with UV‐C or Rose‐Bengal. In contrast, wild‐type and aao1S exhibited higher aldehyde accumulation that resulted in lower remaining chlorophyll than in aao2KO leaves, indicating that the absence of active AAO2 enhanced AAO3 detoxification activity in aao2KO mutants. In support of this notion, employing abscisic‐aldehyde as a specific substrate marker for AAO3 activity revealed enhanced AAO3 activity in aao2KO and aao3Ss leaves compared to wild‐type treated with UV‐C or Rose‐Bengal. The similar abscisic‐acid level accumulated in leaves of unstressed or stressed genotypes indicates that aldehyde detoxification by AAO3 is the cause for better stress resistance in aao2KO mutants. Employing the sulfuration process (known to activate aldehyde oxidases) in wild‐type, aao2KO, and molybdenum‐cofactor sulfurase (aba3‐1) mutant plants revealed that the active AAO2 in WT employs sulfuration processes essential for AAO3 activity level, resulting in the lower AAO3 activity in WT than AAO3 activity in aao2KO. Significance Statement: The current study demonstrates that impairment of AAO2 causes enhancement of AAO3 activity and carbonyl aldehyde detoxification increase in Arabidopsis. [ABSTRACT FROM AUTHOR]

Glucan phosphorylase is present in plants in two isozymes, namely, a plastidial isoform (PHO1) and a cytosolic isoform (PHO2), and is involved in starch-related carbohydrate metabolism. The aim of this study was to determine whether mutations in the genes encoding glucan phosphorylase caused these plants to have increased resistance to short-term drought. One of the strategies plants use to defend themselves against drought stress is to change their starch content, which may be due to changes in glucan phosphorylase activity. In our greenhouse pot experiment, we used potato leaves from wild-type plants and transgenic mutant lines with reduced expression of genes encoding both PHO isozymes. The plants were exposed to drought or were grown under optimal conditions. A lack of water strongly affected the water saturation deficit (WSD) and leaf protein content. The activity of the plastidial glucan phosphorylase isoform (PHO1) in mutant plants increased under drought stress, in contrast to its activity in wild-type plants. After analyzing several physiological parameters, we found that suppressed expression of the gene encoding one of the subunits of plastidial glucan phosphorylase, PHO1a, resulted in increased tolerance to drought in potatoes. [ABSTRACT FROM AUTHOR]

Abscisic acid (ABA) plays a crucial role in plant defense mechanisms under adverse environmental conditions, but its metabolism and perception in response to heavy metals are largely unknown. In Pisum sativum exposed to CdCl2, an accumulation of free ABA was detected in leaves at different developmental stages (A, youngest, unexpanded; B1, youngest, fully expanded; B2, mature; C, old), with the highest content found in A and B1 leaves. In turn, the content of ABA conjugates, which was highest in B2 and C leaves under control conditions, increased only in A leaves and decreased in leaves of later developmental stages after Cd treatment. Based on the expression of PsNCED2, PsNCED3 (9-cis-epoxycarotenoid dioxygenase), PsAO3 (aldehyde oxidase) and PsABAUGT1 (ABA-UDP-glucosyltransferase), and the activity of PsAOγ, B2 and C leaves were found to be the main sites of Cd-induced de novo synthesis of ABA from carotenoids and ABA conjugation with glucose. In turn, β-glucosidase activity and the expression of genes encoding ABA receptors (PsPYL2, PsPYL4, PsPYL8, PsPYL9) suggest that in A and B1 leaves, Cd-induced release of ABA from inactive ABA-glucosyl esters and enhanced ABA perception comes to the forefront when dealing with Cd toxicity. The distinct role of leaves at different developmental stages in defense against the harmful effects of Cd is discussed. [ABSTRACT FROM AUTHOR]