Mineral Nutrition of Higher Plants, 2nd edition, H. Marschner. Academic Press, London (1995), 889, (ISBN 0-12-473543-6). Price: 29.95 Pound Sterling

Salinity is a major problem affecting crop production all over the world: 20% of cultivated land in the world, and 33% of irrigated land, are salt-affected and degraded. This process can be accentuated by climate change, excessive use of groundwater (mainly if close to the sea), increasing use of low-quality water in irrigation, and massive introduction of irrigation associated with intensive farming. Excessive soil salinity reduces the productivity of many agricultural crops, including most vegetables, which are particularly sensitive throughout the ontogeny of the plant. The salinity threshold (ECt) of the majority of vegetable crops is low (ranging from 1 to 2.5 dS m−1 in saturated soil extracts) and vegetable salt tolerance decreases when saline water is used for irrigation. The objective of this review is to discuss the effects of salinity on vegetable growth and how management practices (irrigation, drainage, and fertilization) can prevent soil and water salinization and mitigate the adverse effects of salinity.

Soil Salinity: Effect on Vegetable Crop Growth. Management Practices to Prevent and Mitigate Soil Salinization

Contents Summary 67 I. Introduction 68 II. Silicon transport in plants: to absorb or not to absorb 69 III. The role of silicon in plants: not just a matter of semantics 71 IV. Silicon and biotic stress: beyond mechanical barriers and defense priming 76 V. Silicon and abiotic stress: a proliferation of proposed mechanisms 78 VI. The apoplastic obstruction hypothesis: a working model 79 VII. Perspectives and conclusions 80 Acknowledgements 81 References 81 SUMMARY: Silicon (Si) is not classified as an essential plant nutrient, and yet numerous reports have shown its beneficial effects in a variety of species and environmental circumstances. This has created much confusion in the scientific community with respect to its biological roles. Here, we link molecular and phenotypic data to better classify Si transport, and critically summarize the current state of understanding of the roles of Si in higher plants. We argue that much of the empirical evidence, in particular that derived from recent functional genomics, is at odds with many of the mechanistic assertions surrounding Si's role. In essence, these data do not support reports that Si affects a wide range of molecular-genetic, biochemical and physiological processes. A major reinterpretation of Si's role is therefore needed, which is critical to guide future studies and inform agricultural practice. We propose a working model, which we term the 'apoplastic obstruction hypothesis', which attempts to unify the various observations on Si's beneficial influences on plant growth and yield. This model argues for a fundamental role of Si as an extracellular prophylactic agent against biotic and abiotic stresses (as opposed to an active cellular agent), with important cascading effects on plant form and function.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/nph.15343

The controversies of silicon's role in plant biology.

Drought and salinity are the main abiotic stresses limiting crop yield and quality worldwide. Improving food production in drought- and salt-prone areas is the key to meet the increasing food demands in near future. It has been widely reported that silicon (Si), a second most abundant element in soil, could reduce drought and salt stress in plants. Here, we reviewed the emerging role of Si in enhancing drought and salt tolerance in plants and highlighted the mechanisms through which Si could alleviate both drought and salt stress in plants. Silicon application increased plant growth, biomass, photosynthetic pigments, straw and grain yield, and quality under either drought or salt stress. Under both salt and drought stress, the key mechanisms evoked are nutrient elements homeostasis, modification of gas exchange attributes, osmotic adjustment, regulating the synthesis of compatible solutes, stimulation of antioxidant enzymes, and gene expression in plants. In addition, Si application decreased Na+ uptake and translocation while increased K+ uptake and translocation under salt stress. However, these mechanisms vary with plant species, genotype, growth conditions, duration of stress imposed, and so on. This review article highlights the potential for improving plant resistance to drought and salt stress by Si application and provides a theoretical basis for application of Si in saline soils and arid and semiarid regions worldwide. This review article also highlights the future research needs about the role of Si under drought stress and in saline soils.

Mechanisms of silicon-mediated alleviation of drought and salt stress in plants: a review.

Silicon (Si) can improve drought tolerance in plants, but the mechanism is still not fully understood. Previous research has been concentrating on Si’s role in leaf water maintenance in Si accumulators, while little information is available on its role in water uptake and in less Si-accumulating plants. Here, we investigated the effects of Si on root water uptake and its role in decreasing oxidative damage in relation to root hydraulic conductance in tomato (Solanum lycopersicum ‘Zhongza No.9’) under water stress. Tomato seedlings were subjected to water stress induced by 10% (w/v) polyethylene glycol-6000 in the absence or presence of 2.5 mM added silicate. The results showed that Si addition ameliorated the inhibition in tomato growth and photosynthesis, and improved water status under water stress. The root hydraulic conductance of tomato plants was decreased under water stress, and it was significantly increased by added Si. There was no significant contribution of osmotic adjustment in Si-enhanced root water uptake under water stress. The transcriptions of plasma membrane aquaporin genes were not obviously changed by Si under water stress. Water stress increased the production of reactive oxygen species and induced oxidative damage, while added Si reversed these. In addition, Si addition increased the activities of superoxide dismutase and catalase and the levels of ascorbic acid and glutathione in the roots under stress. It is concluded that Si enhances the water stress tolerance via enhancing root hydraulic conductance and water uptake in tomato plants. Si-mediated decrease in membrane oxidative damage may have contributed to the enhanced root hydraulic conductance.

/pdf/silicon-enhances-water-stress-tolerance-by-improving-root-55km1t98bv.pdf

Silicon Enhances Water Stress Tolerance by Improving Root Hydraulic Conductance in Solanum lycopersicum L.

The application of grafting in tomato production has substantially improved tomato quality and yields. It has been demonstrated that humidity plays an important role in the graft healing of seedlings. This study focuses on the optimum relative humidity (RH) conditions for scion and rootstock healing of grafted tomato (Solanum lycopersicum L.) seedlings. Two tomato cultivars, ‘Super Sunload’ and ‘Super Dotaerang’, grafted onto ‘B-Blocking’ rootstock were subjected to one of three RH regimens: 70–80, 80–90, or 90–100%. The results showed that the scions of both cultivars showed apparent wilting under the 70–80 and 80–90% RH treatments. On this basis, the 90–100% RH treatment was subdivided into 95–96, 97–98, and 99–100% RH treatments, which were then applied. Among these subdivided RH treatments, the fresh weights of the scions and rootstocks significantly increased in response to the treatments of 97–98 and 99–100% RH, and the graft union connection of both cultivars was also enhanced after two days of healing. Furthermore, lower levels of endogenous H2O2 and less activity of antioxidant enzymes were observed in both cultivars in response to treatment with 95–96 or 97–98% RH, which indicated that less oxidative stress occurred. Overall, it is suggested that 97–98% is the optimal RH level for the graft healing of tomato seedlings.

Slight vapor deficit accelerates graft union healing of tomato plug seedling

Mentha arvensis L. and Mentha × piperita L. are herbal plants belonging to the Lamiaceae family and are widely cultivated for their essential oils and culinary uses. These herbs are commercially valuable mints used in the preparation of herbal formulations, cosmetics, pharmaceuticals, and in food industries. Due to the presence of potential secondary metabolites, mints were employed to treat various disorders since ancient times in traditional medicines. The extracts of M. arvensis and M. × piperita can improve the function of digestive system, central nervous system and respiratory system of the human body. Majority of the health benefits of these herbs are attributed by the essential oil components. In addition, the administration of M. arvensis and M. × piperita under various pathological conditions studied in vitro and in vivo facilitated the recovery of detrimental ailments. Due to the increasing demand for natural product-based medicines, research is focused on the utilization of phytochemicals to treat various ailments. In order to provide a comprehensive overview of health benefits of M. arvensis and M. × piperita, the present endeavor deals with the antioxidant property, anti-inflammatory property, anti-microbial, and anti-cancer activities of both species. However, a deeper knowledge on the specific metabolites of M. arvensis and M. × piperita and their mode of action against different disease targets will accelerate the discovery of novel natural drugs with less side effects and higher efficiency.

/pdf/mentha-arvensis-and-mentha-x-piperita-vital-herbs-with-1kqr8huv.pdf

Mentha arvensis and Mentha × piperita-Vital Herbs with Myriads of Pharmaceutical Benefits

Bioefficacy of Cry55Aa protein was tested against a model nematode, Caenorhabditis elegans and tomato pests viz. Helicoverpa armigera, Spodoptera litura, Tuta absoluta and Meloidogyne incognita. When tested against Caenorhabditis elegans in lawn feeding method, 10.00 percent mortality was observed with severe inhibition of growth on surviving nematodes and live worms looked very sick and did not produce progeny. Bioassay on tomato against H. armigera, S. litura, T. absoluta showed that the Cry55Aa is not effective against these insects. When the protein was tested against root knot nematode, Meloidogyne incognita, a decrease in Gall Index was observed. Besides, significant reduction in number of galls, number of females, number of egg mass and number of eggs per egg mass was also observed.

https://www.entomoljournal.com/archives/2019/vol7issue6/PartB/7-5-284-496.pdf

Toxicity of Bt crystal protein Cry55Aa against pest of tomato and model nematode, Caenorhabditis elegans

Objectives: The condition monitoring was done during the machining of Stainless Steel 316 Grade using a PCB microphone with a view to related the measured Sound Signal with the nozzle wear obtained. Methods/Statistical Analysis: It is done by using a Data Acquisition Device is used to connect the Computer with the microphone to analyze the signal using LAB VIEW Software. Also a Sensor signal conditioner is attached to the microphone to boost the sound signal. The machining is done by changing the abrasive flow rate and pressure parameters and the corresponding sound signal is recorded Findings: Regression analysis was carried out using Minitab 17 software and results showed that abrasive flow rate has more influence on nozzle wear rate. Regression equations were also developed for each nozzle hour based on process parameters. Also it was observed that the nozzle exit diameter increases with increase in nozzle life time. Application/Improvements: The future aspects are to develop a generalized equation for the nozzle wear rate based on the process parameters to develop a closed loop system.

Condition Monitoring of Focusing Nozzle in Abrasive Water Jet Machine using Sound Sensor

Shoot apical meristem (SAM) consists of stem cells that act as a reservoir for the aerial growth. It plays an important role in the differential architectural development in plants. SAM actively performs parallel functions by maintaining the pluripotent of stem cells and continuous organogenesis throughout the plant’s life cycle. Molecular mechanisms regulating the signaling networks of this dual function of the SAM have been progressively understood. In the SAM, the feedback loop of WUSCHEL (WUS)-CLAVATA (CLV) has been found to be the key regulator in stabilizing stem cell proliferation and differentiation. In general, WUS migrates into central zone (CZ) from organizing center (OC) and activates the expression of CLV3 by binding to the promoter elements. CLV3 acts as a ligand to interact with the CLV1, leucine rich repeats (LRR) receptor-like kinase (RLK) and LRR receptor-like protein CLV2, and protein kinase coryne (CRN) (CLV2/CRN) to restrict WUS transcription to the OC. Evolution of CLV3 is one of the main factors contributing to the transformation of two dimensional (2D) to 3D plants. WUS-CLV loop is involved in several pathways and networks that integrate on meristem maintenance and cell identity transition. WUS-CLV maintains stem cells with simultaneous differentiation signals by the spatial-temporal signaling of the phytohormones. WUS-CLV loop has an interaction with reactive oxygen species (ROS), an important signaling molecules regulating cell proliferation and developmental transition. WUS also forms feedback loop with AGAMOUS (AG) for differentiation, proliferation, and termination of floral meristem. These loops might also involve in interaction with vernalization and its regulatory factors that oversees the precise timing of flowering after exposure to cold temperatures. In this review, we highlight the evolutionary and developmental importance of the WUS-CLV feedback loop on SAM maintenance and cell identity transition for inflorescence and floral meristem development.

/pdf/paradigm-and-framework-of-wus-clv-feedback-loop-in-stem-cell-1tzvhgks.pdf

Abinaya Manivannan

Papers

Slight vapor deficit accelerates graft union healing of tomato plug seedling

Mentha arvensis and Mentha × piperita-Vital Herbs with Myriads of Pharmaceutical Benefits

Toxicity of Bt crystal protein Cry55Aa against pest of tomato and model nematode, Caenorhabditis elegans

Condition Monitoring of Focusing Nozzle in Abrasive Water Jet Machine using Sound Sensor

Paradigm and Framework of WUS-CLV Feedback Loop in Stem Cell Niche for SAM Maintenance and Cell Identity Transition