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Black-grass (Alopecurus myosuroides) is one of the most problematic agricultural weeds of Western Europe, causing significant yield losses in winter wheat (Triticum aestivum) and other crops through competition for space and resources. Previous studies link black-grass patches to water-retaining soils, yet its specific adaptations to these conditions remain unclear. We designed pot-based waterlogging experiments to compare 13 biotypes of black-grass and six cultivars of wheat. These showed that wheat roots induced aerenchyma when waterlogged whereas aerenchyma-like structures were constitutively present in black-grass. Aerial biomass of waterlogged wheat was smaller, whereas waterlogged black-grass was similar or larger. Variability in waterlogging responses within and between these species was correlated with transcriptomic and metabolomic changes in leaves of control or waterlogged plants. In wheat, transcripts associated with regulation and utilisation of phosphate compounds were upregulated and sugars and amino acids concentrations were increased. Black-grass biotypes showed limited molecular responses to waterlogging. Some black-grass amino acids were decreased and one transcript commonly upregulated was previously identified in screens for genes underpinning metabolism-based resistance to herbicides. Our findings provide insights into the different waterlogging tolerances of these species and may help to explain the previously observed patchiness of this weed's distribution in wheat fields. Black-grass is a problematic weed of winter wheat. To better understand if waterlogging tolerance increases its weediness, we conducted controlled waterlogging studies comparing the physiology and molecular responses of black-grass and wheat. These revealed differences in roots and aerial tissues within and between species. Molecular analyses showed that wheat mounts a significant molecular response, altering gene expression and metabolites with waterlogging, whereas black-grass showed minimal responses to waterlogging despite its apparent tolerance. This article belongs to the Collection Flooding Stress and Hypoxic Responses in Plants. [ABSTRACT FROM AUTHOR]

Climate change poses a significant threat to agricultural sustainability. As the frequency of heavy rainfall has increased globally, waterlogging has become a pressing global issue that has a significant impact on the growth and development of oilseed crops. Due to decreased aerobic respiration in the rhizosphere, various physiological processes, including metabolic reactions, hormone production, and signaling cascades, are adversely impacted by waterlogging. These physiological changes impair reproductive health, resulting in decreased oilseed crop yields. In response to waterlogging, the most common resistance mechanisms developed by crop plants are development of aerenchyma, adventitious roots, and radial oxygen loss barrier. Consequently, the identification and selection of parents with resistance mechanisms, as well as their incorporation into breeding programmes, are essential for sustaining crop production. Thus, a better understanding of the physiological and biochemical mechanisms during waterlogging followed by identification of underlying key regulatory molecules would greatly facilitate the oilseed breeding programs. This review systematically summarizes the response of crop plants to waterlogging through adaptations and the strategies for introduction of waterlogging resistance in oilseed crops. [ABSTRACT FROM AUTHOR]

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Abarrier to radialO2 loss (ROL) in roots is an adaptive trait of waterlogging-tolerant plants. Hordeum marinum Huds. is a waterlogging-tolerant species that, in contrast to its waterlogging-sensitive cultivated relatives, forms a tight barrier toROLin basal root zones. To evaluate the nature of the barrier toROL in roots, we combined measurements ofROL with histochemical and biochemical studies of two contrasting H. marinum accessions. H21 formed greater aerenchyma (up to 38% of cross-sectional area) and a tight barrier toROLwhen grown under deoxygenated stagnant conditions, whereas the barrier was only partially formed in roots of H90 and aerenchyma was up to 26%. A tight barrier to ROL in roots of H21 corresponded with strong suberisation of the exodermis. In agreement with anatomical studies, almost all aliphatic suberin quantities were greater in roots of H21 grown under stagnant conditions compared with roots from aerated controls, and also to those in H90. By contrast to suberin, no differences in root lignification were observed between the two accessions raised in either aerated or stagnant conditions. These findings show that in adventitious roots of H. marinum, suberisation rather than lignification restricts ROL from the basal root zones. [ABSTRACT FROM AUTHOR]

We review waterlogging and submergence tolerances of forage (pasture) legumes. Growth reductions from waterlogging in perennial species ranged from >50% for Medicago sativa and Trifolium pratense to <25% for Lotus corniculatus, L. tenuis, and T. fragiferum. For annual species, waterlogging reduced Medicago truncatula by ~50%, whereas Melilotus siculus and T. michelianum were not reduced. Tolerant species have higher root porosity (gas-filled volume in tissues) owing to aerenchyma formation. Plant dry mass (waterlogged relative to control) had a positive (hyperbolic) relationship to root porosity across eight species. Metabolism in hypoxic roots was influenced by internal aeration. Sugars accumulate in M. sativa due to growth inhibition from limited respiration and low energy in roots of low porosity (i.e. 4.5%). In contrast, L. corniculatus, with higher root porosity (i.e. 17.2%) and O2 supply allowing respiration, maintained growth better and sugars did not accumulate. Tolerant legumes form nodules, and internal O2 diffusion along roots can sustain metabolism, including N2 fixation, in submerged nodules. Shoot physiology depends on species tolerance. In M. sativa, photosynthesis soon declines and in the longer term (>10 d) leaves suffer chlorophyll degradation, damage, and N, P, and K deficiencies. In tolerant L. corniculatus and L. tenuis, photosynthesis is maintained longer, shoot N is less affected, and shoot P can even increase during waterlogging. Species also differ in tolerance of partial and complete shoot submergence. Gaps in knowledge include anoxia tolerance of roots, N2 fixation during field waterlogging, and identification of traits conferring the ability to recover after water subsides. [ABSTRACT FROM AUTHOR]

Hordeum marinum Huds. is a waterlogging-tolerant wild relative of wheat (Triticum aestivum L.). Greater root porosity (gas volume per root volume) and formation of a barrier to reduce root radial O2 loss (ROL) contribute to the waterlogging tolerance of H. marinum and these traits are evident in some H. marinum-wheat amphiploids. We evaluated root porosity, ROL patterns and tolerance to hypoxic stagnant conditions for 10 various H. marinum (two accessions) disomic chromosome addition (DA) lines in wheat (two varieties), produced from two H. marinum-wheat amphiploids and their recurrent wheat parents. None of the DA lines had a barrier to ROL or higher root porosity than the wheat parents. Lack of a root ROL barrier in the six DA lines for H. marinum accessionH21 in Chinese Spring (CS) wheat indicates that the gene(s) for this trait do not reside on one of these six chromosomes; unfortunately, chromosome 3 of H. marinum has not been isolated in CS. Unlike the H21-CS amphiploid, which formed a partial ROL barrier in roots, the H90-Westonia amphiploid and the four derived DA lines available did not. The unaltered root aeration traits in the available DA lines challenge the strategy of using H. marinum as a donor of these traits to wheat. [ABSTRACT FROM AUTHOR]

A radial oxygen loss (ROL) barrier in roots of waterlogging-tolerant plants promotes oxygen movement via aerenchyma to the root tip, and impedes soil phytotoxin entry. The molecular mechanism and genetic regulation of ROL barrier formation are largely unknown. Zea nicaraguensis, a waterlogging-tolerant wild relative of maize ( Zea mays ssp. mays), forms a tight ROL barrier in its roots when waterlogged. We used Z. nicaraguensis chromosome segment introgression lines (ILs) in maize (inbred line Mi29) to elucidate the chromosomal region involved in regulating root ROL barrier formation. A segment of the short-arm of chromosome 3 of Z. nicaraguensis conferred ROL barrier formation in the genetic background of maize. This chromosome segment also decreased apoplastic solute permeability across the hypodermis/exodermis. However, the IL and maize were similar for suberin staining in the hypodermis/exodermis at 40 mm and further behind the root tip. Z. nicaraguensis contained suberin in the hypodermis/exodermis at 20 mm and lignin at the epidermis. The IL with ROL barrier, however, did not contain lignin in the epidermis. Discovery of the Z. nicaraguensis chromosomal region responsible for root ROL barrier formation has improved knowledge of this trait and is an important step towards improvement of waterlogging tolerance in maize. [ABSTRACT FROM AUTHOR]

Cell wall modification (CWM) promotes the formation of aerenchyma in roots under waterlogging conditions as an adaptive mechanism. Lysigenous aerenchyma formation in roots improves oxygen transfer in plants, which highlights the importance of CWM as a focal point in waterlogging stress tolerance. We investigated the structural and functional compositions of CWM genes and their expression patterns under waterlogging conditions in maize. Cell wall modification genes were identified for 3 known waterlogging-responsive cis-acting regulatory elements, namely, GC motif, anaerobic response elements, and G-box, and 2 unnamed elements. Structural motifs mapped in CWM genes were represented in genes regulating waterlogging stress-tolerant pathways, including fermentation, glycolysis, programmed cell death, and reactive oxygen species signaling. The highly aligned regions of characterized and uncharacterized CWM proteins revealed common structural domains amongst them. Membrane spanning regions present in the protein structures revealed transmembrane activity of CWM proteins in the plant cell wall. Cell wall modification proteins had interacted with ethylene-responsive pathway regulating genes (E3 ubiquitin ligases RNG finger and F-box) in a maize protein-protein interaction network. Cell wall modification genes had also coexpressed with energy metabolism, programmed cell death, and reactive oxygen species signaling, regulating genes in a single coexpression cluster. These configurations of CWM genes can be used to modify the protein expression in maize under waterlogging stress condition. Our study established the importance of CWM genes in waterlogging tolerance, and these genes can be used as candidates in introgression breeding and genome editing experiments to impart tolerance in maize hybrids. [ABSTRACT FROM AUTHOR]

Background and aims: Plant adaptation to waterlogged conditions requires a set of morphological and physiological/biochemical changes. The formation of aerenchyma is one of the most crucial adaptive traits for waterlogging tolerance. Enzymatic scavenging may also potentially contribute to waterlogging tolerance by providing detoxification of reactive oxygen species (ROS). Methods: Changes of root porosity (as an indicator of aerenchyma formation) and activities in leaves of four major antioxidant enzymes, γ-amino butyric acid (GABA) and lactic acid contents in roots were evaluated in six barley genotypes contrasting in waterlogging tolerance. Results: Soil waterlogging caused significant increases in adventitious root porosity in all genotypes. Waterlogging-tolerant genotypes showed not only significantly higher adventitious root porosity than sensitive genotypes but also much faster development of aerenchyma. The greatest difference in adventitious root porosity among genotypes was observed after 7 days of waterlogging treatment. At the same time, antioxidant enzyme activities in leaves, GABA and lactic acid contents in roots did not correlate with waterlogging tolerance. Conclusions: A faster formation of aerenchyma in adventitious roots is one of the key factors for waterlogging tolerance in barley. This protocol is recommended to be applied in future studies to identify molecular markers linked to this trait using appropriate mapping populations. [ABSTRACT FROM AUTHOR]

Abstract: Soybean (Glycine max (L.) Merr.) is vulnerable to waterlogging, which threatens soybean productivity in humid regions of Asia. Waterlogging can happen during any growth stage of soybean, but flooding stress before, at or after germination causes severe seed and seedling damage, resulting in substantial reduction of grain yield at maturity. Under waterlogged conditions, seeds imbibe rapidly, destroying seed tissues due to abrupt swelling of the cells. Anatomical observations during water absorption of seeds revealed that the aleurone layer blocks abrupt water penetration into the embryo regardless of genotype. Based on these observations, genetic analyses of waterlogging-tolerant genotypes are currently in progress and attempts to incorporate the genes responsible for such tolerance are being made. Among cultural measures to alleviate waterlogging-induced damage during germination, pre-hydrating seeds prior to sowing proved to be most effective. After emergence, waterlogging impairs root function, primarily due to hypoxia, and thereby the capacity for nutrient uptake and growth. Molecular characterization of enzymes expressed in growing plants subjected to waterlogging treatment has identified several genes involved in anaerobic respiration. In addition, some soybean cultivars were found to form aerenchyma, which transports oxygen from aboveground tissues to the root system, in response to waterlogging. These phenomena should be exploited for breeding waterlogging-tolerant cultivars. Cultural methods including partial tillage and adjustment of the water table also effectively mitigate damage caused by waterlogging. Integration of these approaches should lead to stable soybean production in humid agricultural areas of Asia. [Copyright &y& Elsevier]

Background and Aims: When root-zone O2 deficiency occurs together with salinity, regulation of shoot ion concentrations is compromised even more than under salinity alone. Tolerance was evaluated amongst 34 accessions of Hordeum marinum, a wild species in the Triticeae, to combined salinity and root-zone O2 deficiency. Interest in H. marinum arises from the potential to use it as a donor for abiotic stress tolerance into wheat. [ABSTRACT FROM PUBLISHER]

• The subapical regions of wetland plant roots can develop a barrier to radial O2 loss (ROL), but barrier resistance has rarely been quantified in terms of its O2 diffusivity. • Barrier resistance in adventitious roots of the waterlogging-tolerant Hordeum marinum was assessed from measurements of ROL using cylindrical platinum electrodes while either varying shoot O2 partial pressures or cooling the rooting medium. Anatomical features were examined using fluorescence microscopy. • When grown in stagnant agar nutrient solution, a barrier to ROL was induced over the basal half of 100–120-mm-long roots. Autofluorescence in hypodermal cell walls indicated that putative suberin deposition was coincident with barrier expression. Root cooling revealed a significant respiratory component in barrier resistance. Eliminating the respiration effect by manipulating shoot O2 partial pressures revealed an O2 diffusivity for the barrier of 5.96 × 10−7 cm2 s−1, 96% less than that at the apex, which was ≥ 1.59 × 10−5 cm2 s−1. • It is concluded that the ROL barrier is a manifestation of two components acting synergistically: a physical resistance caused principally by secondary cell-wall deposits in the outer hypodermal layer; and respiratory activity in the hypodermal/epidermal layers; with physical resistance being the dominant component. [ABSTRACT FROM AUTHOR]

Waterlogging is a serious environmental problem that limits agricultural production in low-lying rainfed areas around the world. The major constraint that plants face in a waterlogging situation is the reduced oxygen availability. Accordingly, all previous efforts of plant breeders focused on traits providing adequate supply of oxygen to roots under waterlogging conditions, such as enhanced aerenchyma formation or reduced radial oxygen loss. However, reduced oxygen concentration in waterlogged soils also leads to oxygen deficiency in plant tissues, resulting in an excessive accumulation of reactive oxygen species (ROS) in plants. To the best of our knowledge, this trait has never been targeted in breeding programs and thus represents an untapped resource for improving plant performance in waterlogged soils. To identify the quantitative trait loci (QTL) for ROS tolerance in barley, 187 double haploid (DH) lines from a cross between TX9425 and Naso Nijo were screened for superoxide anion (O2•−) and hydrogen peroxide (H2O2)—two major ROS species accumulated under hypoxia stress. We show that quantifying ROS content after 48 h hypoxia could be a fast and reliable approach for the selection of waterlogging tolerant barley genotypes. The same QTL on chromosome 2H was identified for both O2•− (QSO.TxNn.2H) and H2O2 (QHP.TxNn.2H) contents. This QTL was located at the same position as the QTL for the overall waterlogging and salt tolerance reported in previous studies, explaining 23% and 24% of the phenotypic variation for O2•− and H2O2 contents, respectively. The analysis showed a causal association between ROS production and both waterlogging and salt stress tolerance. Waterlogging and salinity are two major abiotic factors affecting crop production around the globe and frequently occur together. The markers associated with this QTL could potentially be used in future breeding programs to improve waterlogging and salinity tolerance. [ABSTRACT FROM AUTHOR]