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Cassava (Manihot esculenta) is one of the most important staple food crops worldwide. Its starchy tuberous roots supply over 800 million people with carbohydrates. Yet, surprisingly little is known about the processes involved in filling of those vital storage organs. A better understanding of cassava carbohydrate allocation and starch storage is key to improving storage root yield. Here, we studied cassava morphology and phloem sap flow from source to sink using transgenic pAtSUC2::GFP plants, the phloem tracers esculin and 5(6)-carboxyfluorescein diacetate, as well as several staining techniques. We show that cassava performs apoplasmic phloem loading in source leaves and symplasmic unloading into phloem parenchyma cells of tuberous roots. We demonstrate that vascular rays play an important role in radial transport from the phloem to xylem parenchyma cells in tuberous roots. Furthermore, enzymatic and proteomic measurements of storage root tissues confirmed high abundance and activity of enzymes involved in the sucrose synthase-mediated pathway and indicated that starch is stored most efficiently in the outer xylem layers of tuberous roots. Our findings form the basis for biotechnological approaches aimed at improved phloem loading and enhanced carbohydrate allocation and storage in order to increase tuberous root yield of cassava.

Contents Summary  799 I.  Introduction  800 II.   The origins of Cu homeostasis  800 III.  Copper homeostasis in unicellular photosynthetic model organisms  801 IV.  Functions of Cu in plants  802 V.  Typical levels of Cu in plants, deficiency and toxicity  802 VI.  Copper abundance in soils and appropriate Cu concentrations in media  804 VII.  Uptake in the root and distribution to aerial tissues  804 VIII.  Uptake in the shoot symplast, redistribution of Cu during flowering, seed set and senescence  806 IX.  Cu delivery inside the cell  806 X.  Regulation of Cu homeostasis  809 XI.  Conclusions and outlook  811 Acknowledgements  811 References  811 Summary Copper (Cu) is a cofactor in proteins that are involved in electron transfer reactions and is an essential micronutrient for plants. Copper delivery is accomplished by the concerted action of a set of evolutionarily conserved transporters and metallochaperones. As a result of regulation of transporters in the root and the rarity of natural soils with high Cu levels, very few plants in nature will experience Cu in toxic excess in their tissues. However, low Cu bioavailability can limit plant productivity and plants have an interesting response to impending Cu deficiency, which is regulated by an evolutionarily conserved master switch. When Cu supply is insufficient, systems to increase uptake are activated and the available Cu is utilized with economy. A number of Cu‐regulated small RNA molecules, the Cu‐microRNAs, are used to downregulate Cu proteins that are seemingly not essential. On low Cu, the Cu‐microRNAs are upregulated by the master Cu‐responsive transcription factor SPL7, which also activates expression of genes involved in Cu assimilation. This regulation allows the most important proteins, which are required for photo‐autotrophic growth, to remain active over a wide range of Cu concentrations and this should broaden the range where plants can thrive.

Anatomical, physiological, and molecular analysis revealed that yield losses in nitrogen-deficient maize were more closely associated with limited capacity of sugar utilization in developing ears than sucrose export from leaves. Abstract Maize (Zea mays) plants exhibit altered carbon partitioning under nitrogen (N) deficiency, but the mechanisms by which N availability affects sugar export out of leaves and transport into developing ears remain unclear. Maize was grown under field conditions with different N supply. Plant growth, sugar movement, and starch turnover in source or sink tissues were investigated at silking and 20 or 21 days after silking. Nitrogen deficiency stunted plant growth and grain yield compared with N-sufficient plants, and resulted in greater starch concentrations in leaves due to more as well as larger starch granules in bundle sheath cells. Transmission electron microscopy revealed an open symplastic pathway for sucrose movement in N-deficient leaves, while the expression levels of transporters responsible for sucrose efflux and phloem loading were lower than in N-sufficient leaves. Nonetheless, greater starch concentrations in the apical cob portion of N-deficient plants implied sufficient carbon supply relative to the diminished sink strength (decreased kernel number and weight). Together with the high sugar concentrations in the developing kernels, the results indicated that reduced sink capacity and sugar utilization during grain filling may limit the yield in N-deficient plants, which in turn imposes a feedback inhibition on sugar export from leaves.

Calcium (Ca) is a unique macronutrient with diverse but fundamental physiological roles in plant structure and signalling. In the majority of crops the largest proportion of long-distance calcium ion (Ca 2+ ) transport through plant tissues has been demonstrated to follow apoplastic pathways, although this paradigm is being increasingly challenged. Similarly, under certain conditions, apoplastic pathways can dominate the proportion of water flow through plants. Therefore, tissue Ca supply is often found to be tightly linked to transpiration. Once Ca is deposited in vacuoles it is rarely redistributed, which results in highly transpiring organs amassing large concentrations of Ca ([Ca]). Meanwhile, the nutritional flow of Ca 2+ must be regulated so it does not interfere with signalling events. However, water flow through plants is itself regulated by Ca 2+ , both in the apoplast via effects on cell wall structure and stomatal aperture, and within the symplast via Ca 2+ -mediated gating of aquaporins which regulates flow across membranes. In this review, an integrated model of water and Ca 2+ movement through plants is developed and how this affects [Ca] distribution and water flow within tissues is discussed, with particular emphasis on the role of aquaporins.

Background The heavy metal cadmium (Cd) accumulates in the environment due to anthropogenic influences. It is unessential and harmful to all life forms. The plant cell wall forms a physical barrier against environmental stress and changes in the cell wall structure have been observed upon Cd exposure. In the current study, changes in the cell wall composition and structure of Medicago sativa stems were investigated after long-term exposure to Cd. Liquid chromatography coupled to mass spectrometry (LC-MS) for quantitative protein analysis was complemented with targeted gene expression analysis and combined with analyses of the cell wall composition. Results Several proteins determining for the cell wall structure changed in abundance. Structural changes mainly appeared in the composition of pectic polysaccharides and data indicate an increased presence of xylogalacturonan in response to Cd. Although a higher abundance and enzymatic activity of pectin methylesterase was detected, the total pectin methylation was not affected. Conclusions An increased abundance of xylogalacturonan might hinder Cd binding in the cell wall due to the methylation of its galacturonic acid backbone. Probably, the exclusion of Cd from the cell wall and apoplast limits the entry of the heavy metal into the symplast and is an important factor during tolerance acquisition.

Industrialization and inevitable mining have resulted in the release of some metals in environment, which have different uses on the one hand and also showed environmental toxicity. Lithium (Li) is one of them; however, its excess use in different fields or inappropriate disposal methods resulted in high Li accumulation in soil and groundwater. This subsequently is affecting our environment and more potentially our arable crop production system. In humans, Li has been extensively studied and causes numerous detrimental effects at different organ levels. Moreover, increases in Li in groundwater and food items, cases for mental disorders have been reported in different regions of the world. In plants, only a few studies have been reported about toxic effects of lithium in plants. Moreover, plant products (fruits, grains or other plant parts) could be a major source of Li toxicity in our food chain. Therefore, it is more imperative to understand how plants can be developed more tolerant to Li toxicity. In this short mini-review article, we primarily highlighted and speculated Li uptake, translocation and Li storage mechanism in plants. This article provides considerable information for breeders or environmentalist in identifying and developing Li hyperaccumulators plants and environment management.

The article describes the current knowledge about the impact of nanoparticles on plant development with a particular emphasis on crop plants. Nanotechnology is an intensively developing field of science. This is due to the enormous hopes that have been placed on the achievements of nanotechnology in various areas of life. Increasingly, it has been noted that apart from the future benefits of nanotechnology in our everyday life, nanoparticles (NPs) may also have adverse effects that have not been sufficiently explored and understood. Most analyses to date have been focused on the influence of nanomaterials on the physiological processes primarily in animals, humans and bacteria. Although our knowledge about the influence of NPs on the development of plants is considerably smaller, the current views are presented below. Such knowledge is extremely important since NPs can enter the food chain, which may have an influence on human health.

Main conclusionSulfated phenolic acids are widely occurring metabolites in plants, including fruits, vegetables and crops.The untargeted UHPLC-QTOF-MS metabolomics of more than 50 samples from plant, fungi and algae lead to the discovery of a small group of sulfated metabolites derived from phenolic acids. These compounds were detected in land plants for the first time. In this study, zosteric acid, 4-(sulfooxy)benzoic acid, 4-(sulfoooxy)phenylacetic acid, ferulic acid 4-sulfate and/or vanillic acid 4-sulfate were detected in a number of edible species/products, including oat (Avena sativa L.), wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), tomato (Solanum lycopersicum L.), carrot (Daucus carota subsp. Sativus Hoffm.), broccoli (Brassica oleracea var. Italica Plenck), celery (Apium graveolens L.), cabbage (Brassica oleracea convar. sabauda L.), banana tree (Musa tropicana L.), pineapple fruit (Ananas comosus L.), radish bulb (Raphanus sativus L.) and olive oil (Olea europaea L.). The structural identification of sulfated compounds was performed by comparing retention times and mass spectral data to those of synthesized standards. In addition to above-mentioned compounds, isoferulic acid 3-sulfate and caffeic acid 4-sulfate were putatively identified in celery bulb (Apium graveolens L.) and broccoli floret (Brassica oleracea var. Italica Plenck), respectively. While sulfated phenolic acids were quantified in concentrations ranging from 0.34 to 22.18 µg·g−1 DW, the corresponding non-sulfated acids were mostly undetected or present at lower concentrations. The subsequent analysis of oat symplast and apoplast showed that they are predominantly accumulated in the symplast (> 70%) where they are supposed to be biosynthesized by sulfotransferases.

In recent years; the interaction of nanoparticles (NPs) with plants has been intensively studied. Therefore, more and more aspects related to both the positive and negative impact of NP on plants are well described. This article focuses on two aspects of NP interaction with plants. The first is a summary of the current knowledge on NP migration through the roots into the plant body, in particular, the role of the cell wall. The second aspect summarizes the current knowledge of the participation of the symplast, including the plasmodesmata (PD), in the movement of NP within the plant body. We highlight the gaps in our knowledge of the plant–NP interactions; paying attention to the need for future studies to explain the mechanisms that regulate the composition of the cell wall and the functioning of the PD under the influence of NP.

The membrane transporters of plants are important for the transport and distribution of heavy metals, which is the basis for accumulation of heavy metals in hyperaccumulators. Pot and hydroponic experiments were conducted in order to understand effects of Cd dose (0, 10, 20 mg·kg −1 ) on the transport pathway of Cd in hyperaccumulator Arabis alpina, the concentrations of transporter CAX (cation/H + reverse transporter) and HMA (heavy metal ATPase), and the response of Cd distribution to the inhibitors DNP (2,4-dinitrophenol), which is oxidative phosphorylation uncoupling agent and reduce HMA activity. The results showed that the concentrations of transporter CAX and HMA in roots under 20 mg∙kg −1 Cd treatment decreased by 31% and 561% compared with under 10 mg∙kg −1 Cd treatment, respectively. The Cd contents of the roots and leaves under 20 mg∙kg −1 Cd treatment were significantly increased by 1.95 and 1.84 times compared with 10 Cd mg∙kg −1 Cd treatment ( P  < 0.05), the similar increase trend for subcellular components. Cd contents in saps of apoplast, symplasm, phloem, and xylem under 20 mg∙kg −1 Cd treatment significantly increased by 78%, 287%, 238%, and 191% compared with 0 mg∙kg −1 Cd treatment, respectively. The internal flow rates of Cd 2+ showed in sequence: endodermis > leaf vein > epidermis (root xylem). Cd with DNP treatment was mainly distributed in the cell wall, which accounted for 92%. The Cd contents of A. alpina leaves decreased by 17% and 33% with 10 mg·L −1 Cd + 25 or 50 µmol·L −1 DNP treatments, respectively. The results suggested that the symplast should be the main pathway of Cd transport in A. alpina root related to transporter CAX. Cd loading from endodermis to xylem based on HMA and Cd transport in phloem should be the key for Cd distribution of A. alpina . Graphical Abstract