Imaging of Chlorophyll a Fluorescence: A Tool to Study Abiotic Stress in Plants

In normal physiological conditions the fate of absorbed light by photosynthetic pigment is utilized for photosynthetic quantum conversion and only a small portion is de-excited via emission as heat or red and far-red chlorophyll fluorescence. By contrast, under many stress conditions the photosynthetic quantum conversion declines and concomitantly the chlorophyll fluorescence emission increases. For this reason, chlorophyll fluorescence analysis has long been an important tool for the estimation of a range of photosynthetic parameters in leaves. However, it is also known that changes in photosynthetic activity within leaves can be heterogeneous. In fact, the image of chlorophyll fluorescence have been revealed a heterogeneous response to changing light intensity, freezing, fungal or viral infection, ozone, water stress. For this reason, one of the major disadvantages of conventional chlorophyll fluorescence measurements is that it provides information only on a single leaf spot and is not representative of the physiological status of the whole leaf. By contrast, chlorophyll fluorescence imaging can allow detection of the early stages of many different types of stress, in particular when leaf samples are characterised by a large surface heterogeneity of chlorophyll fluorescence emission. Our research group studied from many years on the effect of biotic and abiotic stress on photosynthetic process. in this work we report some results that our research group have obtained. In particular we describe the effect of different abiotic stress on photosynthetic performance of some plant species

Chlorophyll fluorescence imaging for process optimisation in horticulture and fresh food production

Chlorophyll a fluorescence analysis (CFA) has been accepted to study postharvest activity and stability of photosynthesis of vegetables and salad greens, and some fruits. Commercial chlorophyll fluorescence imaging (CFI) systems may provide additional insight into spatial and temporal dynamics of photosynthesis. This yields valuable information on the effects of postharvest handling and processing (sorting, cutting, packaging, etc.) on physiological activity and 'internal quality' of green produce, and its changes. Here, meaning and physiological basics of relevant fluorescence parameters is briefly summarised, while major focus is on recent applications of CFI to evaluate quality and quality maintenance during postharvest handling and minimal processing of fresh fruits and vegetables. CFI is given surprisingly little attention in the monitoring of postharvest quality, although it is suitable for adjusting and/or optimising innovative postharvest techniques. Knowledge of the physiological base and the limit of interpretation is indispensable for meaningful interpretations of results to draw correct consequences

A survey of image-based computational learning techniques for frost detection in plants

Frost damage is one of the major concerns for crop growers as it can impact the growth of the plants and hence, yields. Early detection of frost can help farmers mitigating its impact. In the past, frost detection was a manual or visual process. Image-based techniques are increasingly being used to understand frost development in plants and automatic assessment of damage resulting from frost. This research presents a comprehensive survey of the state-of the-art methods applied to detect and analyse frost stress in plants. We identify three broad computational learning approaches i.e., statistical, traditional machine learning and deep learning, applied to images to detect and analyse frost in plants. We propose a novel taxonomy to classify the existing studies based on several attributes. This taxonomy has been developed to classify the major characteristics of a significant body of published research. In this survey, we profile 80 relevant papers based on the proposed taxonomy. We thoroughly analyse and discuss the techniques used in the various approaches, i.e., data acquisition, data preparation, feature extraction, computational learning, and evaluation. We summarise the current challenges and discuss the opportunities for future research and development in this area including in-field advanced artificial intelligence systems for real-time frost monitoring

Studies of silicon fertilization in citrus to enhance chilling injury resistance

Numerous studies in high-Si accumulators found physiological and biochemical adaptation processes were enhanced by Si application in crops stressed by cold conditions. Meanwhile, there is relatively little information on the impact of Si fertilization on low-Si accumulator crops (dicots) in respect of physiological and biochemical adaptation to stress, including citrus, which is classified as a chilling-sensitive species. The objectives of this study were: 1) To validate the method for Si analysis in citrus plants; 2) To determine factors that influenced Si uptake in citrus and its uptake mechanism; 3) To establish the impact of Si fertilization and cold stress on the photosynthetic efficiency of citrus plants; 4) To determine the impact of Si fertilization and cold stress on fruit quality and yield of citrus plants; 5) To determine the impact of Si fertilization and cold stress on the levels of key sugars, and proline in citrus trees. The method validation showed that the ICP-OES analytic method was fast and sensitive, with a detection limit five times lower than a colorimetric analysis. The uptake study showed that Si uptake in citrus increased significantly (P< 0.05) with the duration of application, leaf age and concentration applied, with 1000 mg L-1 being the optimum concentration tested. Si fertilization onto the roots of citrus trees was shown to be the best method of application compared to foliar application. Dry matter production was significantly increased by Si application. Electron microscopy studies suggested that Si accumulates in the adaxial epidermal cell regions of leaves and constitutes a double Si layer. The levels of Si in citrus leaves increased from young leaves<mature leaves<roots. Winter uptake of Si was close to zero, whereas summer uptake was substantially higher, which suggested that the uptake and transfer of Si into tissues was an active process depending on the prevailing temperature conditions and the physiological activity of the roots. The investigation of the impact of Si fertilization on the physiological adaptations of citrus to cold stress suggested that an improvement in photochemical efficiency occurred in both citrus cultivars (Delta and Nules). Si fertilization of citrus trees made them more cold stress tolerant via physiological factors as well as improvements in the osmotic balance of their sugar (sucrose and fructose) and proline content, resulting in improved membrane rigidity during cold stress. Both factors impacted on water use efficiency via osmoregulation processes. Overall, the current study provided substantial information on the response of citrus to Si fertilization under both normal and lower temperature conditions. The present study also identified crucial parameters in citrus adaptation to cold stress that may be useful in improving the tolerance of citrus crops to abiotic stress and particularly in frost-prone production areas in South Africa, or similar environments.Thesis (PhD (Horticultural Science))--University of Pretoria, 2020.-NRF-THRIP -Citrus Research International (CRI)Plant Production and Soil SciencePhD (Horticultural Science)Unrestricte

Hydrogen Sulfide and Reactive Oxygen Species, Antioxidant Defense, Abiotic Stress Tolerance Mechanisms in Plants

Hydrogen sulfide (H2S), which was previously considered to be toxic, is now regarded as a burgeoning endogenous gaseous transmitter. H2S plays a vital role in the mechanism of response/adaptation to adverse environmental conditions as well as crosstalk with other signaling molecules, including ROS, by affecting the corresponding gene expression and subsequent enzyme activities. Both H2S and ROS are potent signaling molecules that can provoke reversible and irreversible oxidative post-translational modifications on cysteine residues of proteins such as sulfenylation or persulfidation, affecting the redox status and function of the target proteins. The dynamic interplay between persulfidation and sulfenylation occurring on cysteine residues is of great importance in response to environmental changes.The present Special Issue of IJMS has the aim of providing the most current findings on the function of signaling molecules, including H2S and ROS, in higher plants, and it is open to different types of manuscripts, including original research papers, perspectives, or reviews where either ROS, H2S, or related molecules could be involved at the biochemical or physiological levels

Application of modulated chlorophyll fluorescence and modulated chlorophyll fluorescence imaging to study the environmental stress effect

Chlorophyll (Chl) a fluorescence is a widely used tool to monitor the photosynthetic process in plants subjected to environmental stresses. this review reports the theoretical bases of Chl fluorescence, and the significance of the most important Chl fluorescence parameters. it also reports how these parameters can be utilised to estimate changes in photosystem (Ps) ii photochemistry, linear electron flux and dissipation mechanisms. the relation between actual Psii photochemistry and Co2 assimilation is discussed, as is the role of photochemical and non-photochemical quenching in inducing changes in Psii activity. the application of Chl fluorescence imaging to study heterogeneity on leaf lamina is also considered. this review summarises only some of the results obtained by this methodology to study the effects of different environmental stresses, namely water availability, nutrients, pollutants, temperature and salinity

Modern Seed Technology

Satisfying the increasing number of consumer demands for high-quality seeds with enhanced performance is one of the most imperative challenges of modern agriculture. In this view, it is essential to remember that the seed quality of crops does not improve

Seed Priming as a Breeding Tool for Perennial Warm-Season Grasses: Improving Abiotic Stress Tolerance in Pennisetum and Doubling the Chromosomes in Sorghum

Warm-season perennial grasses are leading candidates for lignocellulosic biofuel feedstocks because of their relatively high photosynthetic rates, water use efficiency, and nutrient use efficiency. Interspecific F1 hybrids between pearl millet (Pennisetum glaucum [L.] R. Br.) and napiergrass (Pennisetum purpureum Schumach.) (PMN) are “seeded-yet-sterile” triploids (2n=3x=21) with high biomass yield potential that are well adapted to the southern U.S. Similarly, sterile triploid hybrids can potentially be obtained by crossing annual diploid Sorghum bicolor (L.) Moench with perennial tetraploid S. propinquum (Kunth) Hitchcock to produce novel C4 perennial sorghum biofuel feedstocks. The presowing hydration technique solid matrix priming (SMP) was utilized alone and in combination with the elicitor compounds 5-azacytidine (AZA) and chitosan on three PMN hybrids to improve soil emergence, growth, seedling yield, and chlorophyll fluorescence in ambient, heat, and heat plus drought stress environments. Because S. propinquum is a diploid, tetraploid germplasm is needed to produce triploid hybrids with S. bicolor. SMP and a standard moistening protocol were evaluated as techniques of applying colchicine rates with and without dimethyl sulfoxide (DMSO) to S. propinquum seed to induce chromosome doubling. SMP usually reduced the time to maximum soil emergence in PMN from 4 to 2 d in all three environments. In the heat stress environment, SMP and AZA treatments increased tillering in the elite PMN hybrid 09TX04 relative to the control. The novel chlorophyll fluorescence method developed in this experiment successfully established unstressed, moderate, and severe stress levels. In the heat plus drought stress environment, PMN 09TX04 trended as being less stressed than the other PMN hybrids. Seedling biomass yields for SMP-treated PMN were higher than the control in the ambient (38%) and the heat plus drought (43%) environments. The treatment using SMP for 5 d with 0.1% colchicine plus 2% DMSO was the only one in which S. propinquum chromosome doubling occurred. Seven of 52 surviving plants in this treatment were tetraploids, a 13% success rate, which is a very high frequency of chromosome doubling