Growth, ultrastructural and physiological characteristics of Abelmoschus cytotypes under elevated ozone stress: a study on ploidy-specific responses.

Tropospheric ozone (O3 ) is a significant abiotic stressor whose rising concentration negatively influences plant growth. Studies related to the differential response of Abelmoschus cytotypes to elevated O3 treatment are scarce and need further exploration to recognise the role of polyploidisation in stress tolerance. In this study, we analysed the changes in growth pattern, ultrastructure, physiology and foliar protein profile occurring under O3 stress in Abelmoschus moschatus (monoploid), Abelmoschus esculentus (diploid) and Abelmoschus caillei (triploid). Our findings showed that higher stomatal conductance in A. moschatus triggered higher O3 intake, causing damage to stomatal cells and photosynthetic pigments. Additionally, it caused a reduction in photosynthetic rates, leading to reduced plant growth, total biomass and economic yield. This O3 -induced toxicity was less in diploid and triploid cytotypes of Abelmoschus . Protein profiling by sodium dodecyl sulpate-polyacrylamide gel electrophoresis showed a significant decrease in the commonly found RuBisCO larger and smaller subunits. The decrease was more prominent in monoploid compared to diploid and triploid. This study provides crucial data for research that aim to enhance plant ability to withstand O3 induced oxidative stress. Our findings may help in developing a tolerant variety through plant breeding techniques, which will be economically more advantageous in reaching the objective of sustainable production at the high O3 levels projected under a climate change scenario.

Effect of elevated ozone on the antioxidant response, genomic stability, DNA methylation pattern and yield in three species of Abelmoschus having different ploidy levels.

The majority of polyploids can withstand many stresses better than their monoploid counterparts; however, there is no proven mechanism that can fully explain the level of tolerance at the biochemical and molecular levels. Here, we make an effort to provide an explanation for this intriguing but perplexing issue using the antioxidant responses, genomic stability, DNA methylation pattern and yield in relation to ploidy level under the elevated level of ozone in Abelmoschus cytotypes. The outcome of this study inferred that the elevated ozone causes an increase in reactive oxygen species leading to enhanced lipid peroxidation, DNA damage and DNA de-methylation in all the Abelmoschus cytotypes. The monoploid cytotype of Abelmoschus, that is Abelmoschus moschatus L., experienced the highest oxidative stress under elevated O3, resulting in maximum DNA damage and DNA de-methylation leading to the maximum reduction in yield. While the diploid (Abelmoschus esculentus L.) and triploid (Abelmoschus caillei A. Chev.) cytotypes of Abelmoschus with lower oxidative stress result in lesser DNA damage and DNA de-methylation which ultimately leads to lower yield reduction. The result of this experiment explicitly revealed that polyploidy confers better adaptability in the case of Abelmoschus cytotypes under ozone stress. This study can further be used as a base to understand the mechanism behind the ploidy-induced stress tolerance in other plants mediated by gene dosage effect.

Salinity alleviates the toxicity level of ozone in a halophyte Mesembryanthemum crystallinum L.

Mesembryanthemum crystallinum (Ice plant) is an annual halophytic plant species spread in the coastal areas of the Mediterranean Sea, Egypt. Information about the behaviour of halophytes under the future concentration of ozone (O3) is scanty. Therefore, we have assessed the effects of elevated O3 (ambient + 20 ppb), moderate salinity (200 mM NaCl), and their combined treatment (salinity + elevated O3) on various morphological, growth, physiological, biochemical and anatomical parameters of Egyptian ice plant. Under salinity stress, plant growth, percentage of pigmented leaf and its thickness, ROS levels, antioxidative enzymes, and ROS scavenging activities were increased, while photosynthetic pigments and efficiency were decreased compared to the control. Elevated O3 exposure led to reductions in most of the growth parameters and pigments, while ROS levels, histochemical localization of H2O2 and ·O2-, antioxidative enzymes and non-enzymatic antioxidants (betacyanin, phenolics, thiols and ascorbic acid) showed increases. Surprisingly, salinity alleviated the oxidative stress of elevated O3 due to the rise of SOD activity, antioxidant compounds, and a decrease of ·O2- production rate with concomitant increases of most of the growth parameters. Thick lower collenchyma and enhancement of xylem parenchyma under O3 and combined treatment suggested that anatomical acclimation also operated under O3 stress and salinity played a vital role in the growth of this plant under combined stress. Results showed that salt is essential for the optimum development of this species and its role is extended to alleviate the oxidative damage caused by elevated O3. The results further recommend the use of Egyptian M. crystallinum as a O3 tolerant crop for saline areas along the Mediterranean Sea coast.

The impact of elevated ozone on growth, secondary metabolites, production of reactive oxygen species and antioxidant response in an anti-diabetic plant Costus pictus.

Tropospheric ozone (O3) is a global air pollutant that causes deleterious effect to the plants. The present objective was to investigate the growth response, foliar injury, reactive oxygen species (ROS) accumulation and metabolites production in Costus pictus D. Don (insulin plant) at two developmental stages under ambient O3 (AO) and ambient + 20 ppb O3 (EO) using the open-top chambers (OTCs). A significant reduction in leaf area and total biomass was observed under EO as compared with AO. EO induced ROS (.O2- and H2O2) and lipid peroxidation led to more significant foliar injury and solute leakage. Image obtained from the fluorescence microscope and biochemical estimations reflected high levels of ROS under EO. A differential response in flavonoids and anthocyanin content, ascorbic acid, and antioxidative enzymes such as catalase (CAT), superoxide dismutase (SOD) and peroxidase (POX) has been observed with the growth stages of C. pictus plant. EO exposure negatively affected thiols and protein contents at all the growth stages. Secondary metabolites (tannins, lignin, saponins and alkaloids) were increased in both leaves and rhizomes due to EO, whereas phytosterols were induced only in rhizomes. Apart from other metabolites, the key bioactive compound (corosolic acid) showed its synthesis to be stimulated under EO at later growth stage. The study concludes that O3 is a potent stimulating factor for changing the levels of secondary metabolites and antioxidants in an antidiabetic C. pictus plants as it can alter its medicinal properties.

An assessment of growth, floral morphology, and metabolites of a medicinal plant Sida cordifolia L. under the influence of elevated ozone.

Tropospheric ozone (O3) is a major secondary air pollutant and greenhouse gas, and its impact on growth, yield, and its quality is well established in the case of crop plants. However, the effects of tropospheric O3 have not been comprehensively studied on medicinal plants. Therefore, a field study was planned on a medicinally important Sida cordifolia L. plant (commonly known as country mallow or Bala) to assess the expected changes on the morphology, growth, and leaf injury under elevated O3 (ambient + 20 ppb) by using open-top chambers (OTCs) at 30, 60, and 90 days after treatment (DAT), while leaf and root metabolites were observed at 60 DAT. At all the growth stages, significant leaf damage was recorded as foliar injury symptoms. Most of the growth parameters also showed significant reductions at all the growth stages. Plants under elevated O3 showed a significant negative impact on most of the reproductive parts of the plant. Leaf weight ratio (LWR) showed significant increment at early stages while reduced at 90 DAT; however, root shoot ratio (RSR) showed a significant reduction at 60 DAT. The majority of the steroid metabolites showed an increase in root and leaves under elevated O3, while terpenes showed variable response. Due to O3 stress, most of the major metabolites showed an increase possibly due to their role in defense and other metabolic activities. Based on the outcomes, it is concluded that the future increase in the levels of tropospheric O3 will impact a significant effect on important metabolites of medicinal plants growing in tropical countries like India.

Shallow water channel estimation with energy efficient transmitted signal design.

This paper proposes channel estimation using energy efficient transmission of signal dictionaries for shallow water acoustic communications. Specifically, the multi-columned structure of the channel delay spread is exploited to design partially sampled dictionary in a two-dimensional (2-D) frequency representation of the channel. The key contribution of this work is to achieve considerable energy saving in the transmission of complex exponential signals, designed specifically for real-time shallow water channel estimation at the receiver. This is accomplished by harnessing 2-D frequency localization with compressive transmission and modified-compressive sensing with prior information to exploit the sparse structure of the rapidly fluctuating shallow water acoustic channel in real time. The proposed technique reduces demands on transmitted signal energy by harnessing the reconstruction ability of sparse sensing while retaining key non-sparse channel elements that represent important multipath phenomena. Numerical evidence based on experimental channel estimates demonstrates the efficacy of the proposed work.

Image Reconstruction Using Matched Wavelet Estimated From Data Sensed Compressively Using Partial Canonical Identity Matrix.

This paper proposes a joint framework wherein lifting-based, separable, image-matched wavelets are estimated from compressively sensed images and are used for the reconstruction of the same. Matched wavelet can be easily designed if full image is available. Also compared with the standard wavelets as sparsifying bases, matched wavelet may provide better reconstruction results in compressive sensing (CS) application. Since in CS application, we have compressively sensed images instead of full images, existing methods of designing matched wavelets cannot be used. Thus, we propose a joint framework that estimates matched wavelets from compressively sensed images and also reconstructs full images. This paper has three significant contributions. First, a lifting-based, image-matched separable wavelet is designed from compressively sensed images and is also used to reconstruct the same. Second, a simple sensing matrix is employed to sample data at sub-Nyquist rate such that sensing and reconstruction time is reduced considerably. Third, a new multi-level L-Pyramid wavelet decomposition strategy is provided for separable wavelet implementation on images that leads to improved reconstruction performance. Compared with the CS-based reconstruction using standard wavelets with Gaussian sensing matrix and with existing wavelet decomposition strategy, the proposed methodology provides faster and better image reconstruction in CS application.

Shallow water acoustic channel estimation using two-dimensional frequency characterization.

Shallow water acoustic channel estimation techniques are presented at the intersection of time, frequency, and sparsity. Specifically, a mathematical framework is introduced that translates the problem of channel estimation to non-uniform sparse channel recovery in two-dimensional frequency domain. This representation facilitates disambiguation of slowly varying channel components against high-energy transients, which occupy different frequency ranges and also exhibit significantly different sparsity along their local distribution. This useful feature is exploited to perform non-uniform sampling across different frequency ranges, with compressive sampling across higher Doppler frequencies and close to full-rate sampling at lower Doppler frequencies, to recover both slowly varying and rapidly fluctuating channel components at high precision. Extensive numerical experiments are performed to measure relative performance of the proposed channel estimation technique using non-uniform compressive sampling against traditional compressive sampling techniques as well as sparsity-constrained least squares across a range of observation window lengths, ambient noise levels, and sampling ratios. Numerical experiments are based on channel estimates from the SPACE08 experiment as well as on a recently developed channel simulator tested against several field trials.