Evaluation of Habitat Preferences of Invasive Macrophyte Egeria densa in Different Channel Slopes Using Hydrogen Peroxide as an Indicator

The distribution of submerged macrophytes in response to intense solar radiation and salinity reveals hydrogen peroxide as an abiotic stress indicator

The feasible condition for submerged macrophyte growth is hard to understand as many environmental factors contribute to establishing macrophyte distribution with different intensities generating excess reactive oxygen species (ROS). Among various kinds of ROS, hydrogen peroxide (H₂O₂) is relatively stable and can be measured accurately. Thus, for the quantification of submerged macrophyte species, H₂O₂ can be used to evaluate their distribution in a lake. Submerged macrophytes, such as Potamogeton anguillanus, were abundant in Lake Shinji. The largest biomass distribution was around 1.35 m deep, under low solar radiation intensity, and nearly no biomass was found less than 0.3 m deep, where solar radiation was high. Tissue H₂O₂ concentrations varied in response to the diurnal photosynthetically active radiation (PAR) intensity, which was followed by antioxidant activities, though slightly delayed. Laboratory experiments were conducted with different PAR intensities or salinity concentrations. A stable level of H₂O₂ was maintained up to about 200 μmol m^-2 s^-1 of PAR for 30 days, followed by a gradual increase as PAR increased. The H₂O₂ concentration increased with higher salinity. A change in Chlorophyll a (Chl-a) concentration is associated with an altering H₂O₂ concentration, following a unique negative relationship with H₂O₂ concentration. If H₂O₂ exceeded 45 μmol/gFW, the homeostasis collapsed, and H₂O₂ and Chl-a significantly declined afterward. The above findings indicate that H₂O₂ has a negative effect on the physiological condition of the plant. The increase in H₂O₂ concentration was prevented by antioxidant activities, which elevated with increasing H₂O₂ concentration.

Developing future heat-resilient vegetable crops

Climate change seriously impacts global agriculture, with rising temperatures directly affecting the yield. Vegetables are an essential part of daily human consumption and thus have importance among all agricultural crops. The human population is increasing daily, so there is a need for alternative ways which can be helpful in maximizing the harvestable yield of vegetables. The increase in temperature directly affects the plants' biochemical and molecular processes; having a significant impact on quality and yield. Breeding for climate-resilient crops with good yields takes a long time and lots of breeding efforts. However, with the advent of new omics technologies, such as genomics, transcriptomics, proteomics, and metabolomics, the efficiency and efficacy of unearthing information on pathways associated with high-temperature stress resilience has improved in many of the vegetable crops. Besides omics, the use of genomics-assisted breeding and new breeding approaches such as gene editing and speed breeding allow creation of modern vegetable cultivars that are more resilient to high temperatures. Collectively, these approaches will shorten the time to create and release novel vegetable varieties to meet growing demands for productivity and quality. This review discusses the effects of heat stress on vegetables and highlights recent research with a focus on how omics and genome editing can produce temperature-resilient vegetables more efficiently and faster.

Measurement of foliar H2O2 concentration can be an indicator of riparian vegetation management

Riparian vegetation is frequently exposed to abiotic stress, which generates reactive oxygen species (ROS) caused by strong differences in a river’s hydrological conditions. Among different ROS, hydrogen peroxide (H₂O₂) is relatively steady and can be measured appropriately. Thus, the quantification of plant H₂O₂ can be used as a stress indicator for riparian vegetation management. The current study examines the spatial distribution of plants by riparian vegetation communities across the elevation gradient of riparian zones through quantification of environmental stress using foliar H₂O₂ concentration. The trees Salix spp., Robinia pseudoacacia, Ailanthus altissima with Juglans mandshurica, and the herbs Phragmites australis, Phragmites japonica, and Miscanthus sacchariflorus were selected for this study. Leaf tissues were collected to analyze H₂O₂ concentration, meanwhile riparian soil was sampled to measure total nitrogen (TN), total phosphorus (TP), and moisture content. The H₂O₂ concentration of tree species increased with higher soil moisture content, which was negatively correlated for Salix and herb spp., in which H₂O₂ concentration always decreased with high soil moisture. In this study, we found a unique significant interaction between soil moisture content and H₂O₂ concentration, both positively or negatively correlated relationships, when compared with other parameters, such as TN or TP concentrations or TN: TP in riparian soil. The species-specific distribution zones can be explained by the H₂O₂ concentration in the plant for gravelly and sandy channels on a theoretical range of soil moisture. Each species’ H₂O₂ concentration was estimated through derived equations and is directly related to an elevation above the channel. The comparison with the observed distribution of plant elevations in the field indicated that all species showed a spatial distribution that acts as species-specific elevations where H₂O₂ concentrations stayed below 40 μmol/gFW. Hence, the present study suggests that foliar H₂O₂ concentration can be a useful benchmark for the distribution potentiality of riparian vegetation.

Hydrogen Peroxide Variation Patterns as Abiotic Stress Responses of Egeria densa

In vegetation management, understanding the condition of submerged plants is usually based on long-term growth monitoring. Reactive oxygen species (ROS) accumulate in organelles under environmental stress and are highly likely to be indicators of a plant's condition. However, this depends on the period of exposure to environmental stress, as environmental conditions are always changing in nature. Hydrogen peroxide (H2O2) is the most common ROS in organelles. The responses of submerged macrophytes, Egeria densa, to high light and iron (Fe) stressors were investigated by both laboratory experiments and natural river observation. Plants were incubated with combinations of 30-200 μmol m-2 s-1 of photosynthetically active radiation (PAR) intensity and 0-10 mg L-1 Fe concentration in the media. We have measured H2O2, photosynthetic pigment concentrations, chlorophyll a (Chl-a), chlorophyll b (Chl-b), carotenoid (CAR), Indole-3-acetic acid (IAA) concentrations of leaf tissues, the antioxidant activity of catalase (CAT), ascorbic peroxidase (APX), peroxidase (POD), the maximal quantum yield of PSII (Fv Fm -1), and the shoot growth rate (SGR). The H2O2 concentration gradually increased with Fe concentration in the media, except at very low concentrations and at an increased PAR intensity. However, with extremely high PAR or Fe concentrations, first the chlorophyll contents and then the H2O2 concentration prominently declined, followed by SGR, the maximal quantum yield of PSII (Fv Fm -1), and antioxidant activities. With an increasing Fe concentration in the substrate, the CAT and APX antioxidant levels decreased, which led to an increase in H2O2 accumulation in the plant tissues. Moreover, increased POD activity was proportionate to H2O2 accumulation, suggesting the low-Fe independent nature of POD. Diurnally, H2O2 concentration varies following the PAR variation. However, the CAT and APX antioxidant activities were delayed, which increased the H2O2 concentration level in the afternoon compared with the level in morning for the same PAR intensities. Similar trends were also obtained for the natural river samples where relatively low light intensity was preferable for growth. Together with our previous findings on macrophyte stress responses, these results indicate that H2O2 concentration is a good indicator of environmental stressors and could be used instead of long-term growth monitoring in macrophyte management.

Hydrogen peroxide can be a plausible biomarker in cyanobacterial bloom treatment

The effect of combined stresses, photoinhibition, and nutrient depletion on the oxidative stress of cyanobacteria was measured in laboratory experiments to develop the biomass prediction model. Phormidium ambiguum was exposed to various photosynthetically active radiation (PAR) intensities and phosphorous (P) concentrations with fixed nitrogen concentrations. The samples were subjected to stress assays by detecting the hydrogen peroxide (H₂O₂) concentration and antioxidant activities of catalase (CAT) and superoxide dismutase (SOD). H₂O₂ concentrations decreased to 30 µmol m^-2 s^-1 of PAR, then increased with higher PAR intensities. Regarding P concentrations, H₂O₂ concentrations (nmol L^-1) generally decreased with increasing P concentrations. SOD and CAT activities were proportionate to the H₂O₂ protein^-1. No H₂O₂ concentrations detected outside cells indicated the biological production of H₂O₂, and the accumulated H₂O₂ concentration inside cells was parameterized with H₂O₂ concentration protein^-1. With over 30 µmol m^-2 s^-1 of PAR, H₂O₂ concentration protein^-1 had a similar increasing trend with PAR intensity, independently of P concentration. Meanwhile, with increasing P concentration, H₂O₂ protein^-1 decreased in a similar pattern regardless of PAR intensity. Protein content decreased with gradually increasing H₂O₂ up to 4 nmol H₂O₂ mg^-1 protein, which provides a threshold to restrict the growth of cyanobacteria. With these results, an empirical formula-protein (mg L^-1) = - 192*Log((H₂O₂/protein)/4.1), where H₂O₂/protein (nmol mg^-1) = - 0.312*PAR²/(50² + PAR²)*((25/PAR)⁴ + 1)*Log(P/133,100), as a function of total phosphorus concentration, P (µg L^-1)-was developed to obtain the cyanobacteria biomass.