Xylem Transport Research Articles

Cadmium uptake and transport in vegetables near a zinc–lead mine: Novel insights from Cd isotope fractionation

In this study, Cd isotope analysis was conducted on drought-tolerant (cowpea and sesame) and less drought-tolerant vegetables (water spinach, green pepper, and mung bean) to elucidate the mechanisms underlying Cd uptake and transport. Cd isotopes in plants were identical to or lighter than those in the available pool and exhibited negative fractionation from roots to straws (Δ114/110Cd = −0.22 ‰ to −0.17 ‰) in drought-tolerant vegetables, whereas contrasting results were obtained for less drought-tolerant vegetables (Δ114/110Cd = −0.050 ‰ to 0.39 ‰). Positive Cd isotope fractionation from straws to fruits in drought-tolerant vegetables (Δ114/110Cd = 0.33 ‰ ± 0.03 ‰ and 0.10 ‰ ± 0.03 ‰, respectively) was observed, whereas negligible or negative fractionation was found in less drought-tolerant vegetables (Δ114/110Cd = 0.01 ‰ ± 0.04 ‰ and −0.34 ‰ ± 0.02 ‰, respectively). The vast secretion of organic acids might have led to positive available pool-to-roots and negative roots-to-straws isotope fractionation in drought-tolerant vegetables. In contrast, preferential xylem transport resulted in negative straws-to-fruits isotope fractionation in less drought-tolerant vegetables. This study demonstrated that Cd isotope fractionation in the soil-plant system is associated with plant drought tolerance, and drought-tolerant and less-tolerant plants developed a distinct Cd detoxification mechanism, corresponding to a reversed fractionation of Cd isotopes.

Phosphate Turnover in Various Parts of Nodulated Soybean (Glycine max (L.) Merr.) Plants and the Relation to the Xylem Transport

Phosphorus is a major essential element in plants, and the absorption and transport of P are related to crop growth and productivity. Phosphate (Pi) is absorbed in the roots and transported to the shoot. Plants store surplus Pi in the vacuoles. The characteristics of Pi storage and turnover in various parts of the nodulated soybeans might be related to plant growth and P-use efficiency. This research focused on the changes in the Pi concentrations and Pi contents in each part of young soybean plants grown in Pi-sufficient (50 μM Pi) or Pi-deficient (0 μM Pi) conditions. Also, the Pi flux rate in xylem sap from roots to shoot was determined. The growth of the plants was the same after 7 days of Pi-sufficient and Pi-deficient treatments. During the Pi-deficient period, the Pi concentrations in the roots, leaves, and stems decreased significantly but did not deplete. The decrease in Pi concentration in nodules was much slower than the other parts. After the re-supply of 50 μM Pi in the solution, the Pi concentration increased only a little in each part of the Pi-deficient plants. The Pi concentration and Pi flux in the xylem sap quickly responded to the changes in the Pi concentration in the culture solution.

Active protein ubiquitination regulates xylem vessel functionality.

Xylem vessels function in the long-distance conduction of water in land plants. The NAC transcription factor VASCULAR-RELATED NAC-DOMAIN7 (VND7) is a master regulator of xylem vessel cell differentiation in Arabidopsis (Arabidopsis thaliana). We previously isolated suppressor of ectopic xylem vessel cell differentiation induced by VND7 (seiv) mutants. Here, we report that the responsible genes for seiv3, seiv4, seiv6, and seiv9 are protein ubiquitination-related genes encoding PLANT U-BOX46 (PUB46), an uncharacterized F-BOX protein (FBX), PUB36, and UBIQUITIN-SPECIFIC PROTEASE1 (UBP1), respectively. We also found decreased expression of genes downstream of VND7 and abnormal xylem transport activity in the seiv mutants. Upon VND7 induction, ubiquitination levels from 492 and 180 protein groups were upregulated and downregulated, respectively. VND7 induction resulted in the ubiquitination of proteins for cell wall biosynthesis and protein transport, whereas such active protein ubiquitination did not occur in the seiv mutants. We detected the ubiquitination of three lysine residues in VND7: K94, K105, and K260. Substituting K94 with arginine significantly decreased the transactivation activity of VND7, suggesting that the ubiquitination of K94 is crucial for regulating VND7 activity. Our findings highlight the crucial roles of target protein ubiquitination in regulating xylem vessel activity.

Absorption and Xylem Transport of 33P-Labeled Phosphorus in Nodulated Soybean Plants

Phosphorus (P) is an essential macro-element for plants, and understanding the characteristics of the absorption and transport of P in crops is essential. The low availability of P restricts the growth, nitrogen fixation, and yield of soybean plants. In this research, the radioisotope 33P was supplied to the culture solution to trace the absorption and transport of P in nodulated soybean plants monitored using an imaging plate. The absorption rate of 33P was almost the same under the light and dark conditions. The absorption rate of 33P in the decapitated roots was near to that of the intact plants under light. These results indicate that the P absorption is not affected by evapotranspiration over a short time period. Conversely, the 33P transport from the roots to the shoot was significantly lower under dark conditions than it was under light conditions, although some 33P reached the top of the shoots under both the light and dark conditions. The transport of P to the shoots depends on the transpiration supplemented by the root pressure. The multiplication value of the 33P concentration in the xylem sap and transpiration rate was almost equivalent to the transport rate of 33P in the intact shoots. This value may be adaptable and used to estimate the transport rate of P for the diagnosis.

The Long-Distance Transport of Jasmonates in Salt-Treated Pea Plants and Involvement of Lipid Transfer Proteins in the Process.

The adaption of plants to stressful environments depends on long-distance responses in plant organs, which themselves are remote from sites of perception of external stimuli. Jasmonic acid (JA) and its derivatives are known to be involved in plants' adaptation to salinity. However, to our knowledge, the transport of JAs from roots to shoots has not been studied in relation to the responses of shoots to root salt treatment. We detected a salt-induced increase in the content of JAs in the roots, xylem sap, and leaves of pea plants related to changes in transpiration. Similarities between the localization of JA and lipid transfer proteins (LTPs) around vascular tissues were detected with immunohistochemistry, while immunoblotting revealed the presence of LTPs in the xylem sap of pea plants and its increase with salinity. Furthermore, we compared the effects of exogenous MeJA and salt treatment on the accumulation of JAs in leaves and their impact on transpiration. Our results indicate that salt-induced changes in JA concentrations in roots and xylem sap are the source of accumulation of these hormones in leaves leading to associated changes in transpiration. Furthermore, they suggest the possible involvement of LTPs in the loading/unloading of JAs into/from the xylem and its xylem transport.

Metabolite responses of cucumber on copper toxicity in presence of fullerene C60 derivatives

Copper (Cu) toxicity in crops is a result of excessive release of Cu into environment. Little is known about mitigation of Cu toxicity through the application of carbon-based nanomaterials including water-soluble fullerene C60 derivatives. Two derivatives of fullerene were examined: polyhydroxylated C60 (fullerenol) and arginine C60 derivative. In order to study the response of Cu-stressed plants (Cucumis sativus L.) to these nanomaterials, metabolomics analysis by gas chromatography-mass spectrometry (GC-MS) was performed. Excess Cu (15 μM) caused substantial increase in xylem sap Cu, retarded dry biomass and leaf chlorosis of hydroponically grown cucumber. In Cu-stressed leaves, metabolomes was disturbed towards suppression metabolism of nitrogen (N) compounds and activation metabolism of hexoses. Also, upregulation of some metabolites involving in antioxidant defense system, such as ascorbic acid, tocopherol and ferulic acid, was occurred in Cu-stressed leaves. Hydroponically added fullerene adducts decreased the xylem sap Cu and alleviated Cu toxicity with effectiveness has been most pronounced for arginine C60 derivative. Metabolic responses of plants subjected to high Cu with fullerene derivatives were opposite to that observed under Cu alone. Fatty acids up-regulation (linolenic acid) and antioxidant molecules (tocopherol) down-regulation might indicate that arginine C60 adduct can alleviate Cu induced oxidative stress. Although fullerenol slightly improved cucumber growth, its effect on metabolic state of Cu-stressed plants was not statistically significant. We suggest that tested fullerene C60 adducts have a potential to prevent Cu toxicity in plants through a mechanism associated with their capability to restrict xylem transport of Cu from roots to shoot, and to maintain antioxidative properties of plants.

Linkages among stem xylem transport, biomechanics, and storage in lianas and trees across three contrasting environments.

Stem xylem transports water and nutrients, mechanically supports aboveground tissues, and stores water and nonstructural carbohydrates. These three functions are associated with three types of cells-vessel, fiber, and parenchyma, respectively. We measured stem theoretical hydraulic conductivity (Kt), modulus of elasticity (MOE), tissue water content, starch, soluble sugars, cellulose, and xylem anatomical traits in 15 liana and 16 tree species across three contrasting sites in Southwest China. Lianas had higher hydraulic efficiency and tissue water content, but lower MOE and cellulose than trees. Storage traits (starch and soluble sugars) did not significantly differ between lianas and trees, and trait variation was explained mainly by site, highlighting how environment shapes plant storage strategies. Kt was significantly positively correlated with vessel diameter and vessel area fraction in lianas and all species combined. The MOE was significantly positively correlated with fiber area fraction, wood density, and cellulose in lianas and across all species. The tissue water content was significantly associated with parenchyma area fraction in lianas. Support function was strongly linked with transport and storage functions in lianas. In trees, transport and support functions were not correlated, while storage function was tightly linked with transport and support functions. These findings enhance our understanding of the relationship between stem xylem structure and function in lianas and trees, providing valuable insights into how plants adapt to environmental changes and the distinct ecological strategies employed by lianas and by trees to balance the demands of hydraulic transport, mechanical support, and storage.

Bark structure is coordinated with xylem hydraulic properties in branches of five Cupressaceae species.

The properties of bark and xylem contribute to tree growth and survival under drought and other types of stress conditions. However, little is known about the functional coordination of the xylem and bark despite the influence of selection on both structures in response to drought. To this end, we examined relationships between proportions of bark components (i.e. thicknesses of tissues outside the vascular cambium) and xylem transport properties in juvenile branches of five Cupressaceae species, focusing on transport efficiency and safety from hydraulic failure via drought-induced embolism. Both xylem efficiency and safety were correlated with multiple bark traits, suggesting that xylem transport and bark properties are coordinated. Specifically, xylem transport efficiency was greater in species with thicker secondary phloem, greater phloem-to-xylem thickness ratio and phloem-to-xylem cell number ratio. In contrast, species with thicker bark, living cortex and dead bark tissues were more resistant to embolism. Thicker phellem layers were associated with lower embolism resistance. Results of this study point to an important connection between xylem transport efficiency and phloem characteristics, which are shaped by the activity of vascular cambium. The link between bark and embolism resistance affirms the importance of both tissues to drought tolerance.

Experimental and computational comparison of freeze-thaw-induced pressure generation in red and sugar maple.

Sap exudation is the process whereby trees such as sugar (Acer saccharum Marsh.) and red maple (Acer rubrum L.) generate unusually high positive stem pressure in response to repeated cycles of freeze and thaw. This elevated xylem pressure permits the sap to be harvested over a period of several weeks and hence is a major factor in the viability of the maple syrup industry. The extensive literature on sap exudation documents competing hypotheses regarding the physical and biological mechanisms that drive positive pressure generation in maple, but to date, relatively little effort has been expended on devising mathematical models for the exudation process. In this paper, we utilize an existing model of Graf etal. (J Roy Soc Interface 12:20150665, 2015) that describes heat and mass transport within the multiphase gas-liquid-ice mixture in the porous xylem tissue. The model captures the inherent multiscale nature of xylem transport by including phase change and osmotic transport in wood cells on the microscale, which is coupled to heat transport through the tree stem on the macroscale. A parametric study based on simulations with synthetic temperature data identifies the model parameters that have greatest impact on stem pressure build-up. Measured daily temperature fluctuations are then used as model inputs and the resulting simulated pressures are compared directly with experimental measurements taken from mature red and sugar maple stems during the sap harvest season. The results demonstrate that our multiscale freeze-thaw model reproduces realistic exudation behavior, thereby providing novel insights into the specific physical mechanisms that dominate positive pressure generation in maple trees.

Mutation of OsNRAMP5 reduces cadmium xylem and phloem transport in rice plants and its physiological mechanism

Natural resistance associated macrophage protein 5 (NRAMP5) is a key transporter for cadmium (Cd) uptake by rice roots; however, the effect of OsNRAMP5 on Cd translocation and redistribution in rice plants remains unknown. In this study, an extremely low Cd-accumulation mutant (lcd1) and wild type (WT) plants were utilized to investigate the effect of OsNRAMP5 mutation on Cd translocation and redistribution via the xylem and phloem and its possible physiological mechanism using field, hydroponic and isotope-labelling experiments. The results showed that OsNRAMP5 mutation reduced xylem and phloem transport of Cd, due to remarkably lower Cd translocation from roots to shoots and from the leaves Ⅰ–Ⅲ to their corresponding nodes, as well as lower Cd concentrations in xylem and phloem sap of lcd1 compared to WT plants. Mutation of OsNRAMP5 reduced Cd translocation from roots to shoots in lcd1 plants by increasing Cd deposition in cellulose of root cell walls and reducing OsHMA2-and OsCCX2-mediated xylem loading of Cd, and the citric acid- and tartaric acid-mediated long-distance xylem transport of Cd. Moreover, OsNRAMP5 mutation inhibited Cd redistribution from flag leaves to nodes and panicles in lcd1 plants by increasing Cd sequestration in cellulose and vacuoles, and decreasing OsLCT1-mediated Cd phloem transport in flag leaves.

Bark wounding triggers gradual embolism spreading in two diffuse-porous tree species.

Xylem transport is essential for the growth, development and survival of vascular plants. Bark wounding may increase the risk of xylem transport failure by tension-driven embolism. However, the consequences of bark wounding for xylem transport are poorly understood. Here, we examined the impacts of the bark wounding on embolism formation, leaf water potential and gas exchange in the terminal branches of two diffuse-porous tree species (Acer platanoides L. and Prunus avium L.). The effects of bark removal were examined on field-grown mature trees exposed to increased evaporative demands on a short-term and longer-term basis (6h vs 6 days after bark wounding). Bark removal of 30% of branch circumference had a limited effect on the xylem hydraulic conductivity when embolized vessels were typically restricted to the last annual ring near the bark wound. Over the 6-day exposure, the non-conductive xylem area had significantly increased in the xylem tissue underneath the bark wound (from 22-29% to 51-52% of the last annual ring area in the bark wound zone), pointing to gradual yet relatively limited embolism spreading to deeper xylem layers over time. In both species, the bark removal tended to result in a small but non-significant increase in the percent loss of hydraulic conductivity compared with control intact branches 6 days after bark wounding (from 6 to 8-10% in both species). The bark wounding had no significant effects on midday leaf water potential, CO2 assimilation rates, stomatal conductance and water-use efficiency of the leaves of the current-year shoot, possibly due to limited impacts on xylem transport. The results of this study demonstrate that bark wounding induces limited but gradual embolism spreading. However, the impacts of bark wounding may not significantly limit water delivery to distal organs and leaf gas exchange at the scale of several days.

Monitoring Xylem Transport in Arabidopsis thaliana Seedlings Using Fluorescent Dyes.

Fluorescent dyes are often used to observe transport mechanisms in plant vascular tissues. However, it has been technically challenging to apply fluorescent dyes on roots to monitor xylem transport in vivo. Here, we present a fast, noninvasive, and high-throughput protocol to monitor xylem transport in seedlings. Using the fluorescent dyes 5(6)-carboxyfluorescein diacetate (CFDA) and Rhodamine WT, we were able to observe xylem transport on a cellular level in Arabidopsis thaliana roots. We describe how to apply these dyes on primary roots of young seedlings, how to monitor root-to-shoot xylem transport, and how to measure xylem transport velocity in roots. Moreover, we show that our protocol can also be applied to lateral roots and grafted seedlings to assess xylem (re)connection. Altogether, these techniques are useful for investigating xylem functionality in diverse experimental setups.

Stomatal closure prevents xylem transport of green leaf volatiles and impairs their systemic function in plants.

Plants perceive environmental stresses as whole organisms via distant signals conveying danger messages through their vasculature. In parallel to vascular transport, airborne plant volatile compounds, including green leaf volatiles (GLVs), can bypass the lack of vascular connection. However, some small volatile compounds move through the vasculature; such vascular transport is little known about GLVs. Here we illustrate GLV alcohols as solutes move within xylem vessels in Zea mays. We describe GLV alcohols, including Z-3-hexen-ol and its isomer E-3-hexen-ol, which is not synthesized in maize, moving through the transpiration stream via xylem vessels. Since transpiration is mediated by the stomatal aperture, closing stomata by two independent methods diminishes the transport of GLV alcohol and its isomer. In addition, the lower transport of GLV alcohols impairs their function in inducing terpenoid biosynthesis, suggesting that xylem transport of GLV alcohols plays a significant role in their systemic function. Our study suggests that GLV alcohols, in addition to airborne signals, are transported through xylem vessels. Our findings can be critical in future studies about the perception and function of these compounds in plants.

Angiosperms follow a convex trade-off to optimize hydraulic safety and efficiency.

Intervessel pits are considered to function as valves that avoid embolism spreading and optimize efficient transport of xylem sap across neighbouring vessels. Hydraulic transport between vessels would therefore follow a safety-efficiency trade-off, which is directly related to the total intervessel pit area (Ap ), inversely related to the pit membrane thickness (TPM ) and driven by a pressure difference. To test this hypothesis, we modelled the relative transport rate of gas (ka ) and water (Q) at the intervessel pit level for 23 angiosperm species and correlated these parameters with the water potential at which 50% of embolism occurs (Ψ50 ). We also measured ka for 10 species using pneumatic measurements. The pressure difference across adjacent vessels and estimated values of ka and Q were related to Ψ50 , following a convex safety-efficiency trade-off based on modelled and experimental data. Minor changes in TPM and Ap exponentially affected the pressure difference and flow, respectively. Our results provide clear evidence that a xylem safety-efficiency trade-off is not linear, but convex due to flow across intervessel pit membranes, which represent mesoporous media within microporous conduits. Moreover, the convex nature of long-distance xylem transport may contribute to an adjustable fluid balance of plants, depending on environmental conditions.

Occurrence of Microplastics in Most Consumed Fruits and Vegetables from Turkey and Public Risk Assessment for Consumers.

Microplastics are transferred to humans through the food chain by consuming food contaminated with microplastics. However, the knowledge about the risks of dietary exposure for humans to these particles is very limited. Moreover, only a few studies on microplastic pollution in fruit and vegetables have been carried on. Thus, this study aims to investigate the presence of microplastics in some of the most consumed fruits and vegetables (pear (Pyrus communis), apple (Malus domestica), tomato (Solanum lycopersicum), onion (Allium cepa), potatoes (Solanum tuberosum), and cucumber (Cucumis sativus)) from Turkey and to evaluate the potential risk for consumers. Fruits and vegetable samples were purchased from different markets and fruiterer (two of each) in Muğla province, Southwest of Turkey. Microplastic extraction processes were carried out on the edible parts of the samples. According to the results obtained, a total of 210 particles (2.9 ± 1.6 particle g-1) were detected in all samples. Any significant difference occurred among the different markets. The maximum average amount of microplastic was determined in tomato samples (3.63 ± 1.39 particle g-1). The highest microplastic intake was with tomato (398,520 particles individual-1 year-1 for Estimated Annual Intake (EAI) and Estimated Daily Intake (EDI) for children 68.24 particles kg-1 day-1). The occurrence of microplastics of big size, that are not allowed to pass by plant xylem transport, suggests that fresh vegetables and fruits can be contaminated with plastic, especially during the production phase, during agricultural activities and during the marketing process (transport to the market and purchasing process).

Genetic regulation of nitrogen use efficiency in Gossypium spp.

Cotton (Gossypium spp.) is the most important fibre crop, with desirable characteristics preferred for textile production. Cotton fibre output relies heavily on nitrate as the most important source of inorganic nitrogen (N). However, nitrogen dynamics in extreme environments limit plant growth and lead to yield loss and pollution. Therefore, nitrogen use efficiency (NUE), which involves the utilisation of the 'right rate', 'right source', 'right time', and 'right place' (4Rs), is key for efficient N management. Recent omics techniques have genetically improved NUE in crops. We herein highlight the mechanisms of N uptake and assimilation in the vegetative and reproductive branches of the cotton plant while considering the known and unknown regulatory factors. The phylogenetic relationships among N transporters in four Gossypium spp. have been reviewed. Further, the N regulatory genes that participate in xylem transport and phloem loading are also discussed. In addition, the functions of microRNAs and transcription factors in modulating the expression of target N regulatory genes are highlighted. Overall, this review provides a detailed perspective on the complex N regulatory mechanism in cotton, which would accelerate the research toward improving NUE in crops.

Consistent responses to moisture stress despite diverse growth forms within mountain fynbos communities

Understanding climate change impacts on the Cape Floristic Region requires improved knowledge of plant physiological responses to the environment. Studies examining physiological responses of mountain fynbos have consisted of campaign-based measurements, capturing snapshots of plant water relations and photosynthesis. We examine conclusions drawn from prior studies by tracking in situ physiological responses of three species, representing dominant growth forms (proteoid, ericoid, restioid), over 2 years using miniature continuous sap flow technology, long-term observations of leaf/culm water potential and gas exchange, and xylem vulnerability to embolism. We observed considerable inter-specific variation in the timing and extent of seasonal declines in productivity. Shallow-rooted Erica monsoniana exhibited steep within-season declines in sap flow and water potentials, and pronounced inter-annual variability in total daily sap flux (Js). Protea repens showed steady reductions in Js across both years, despite deeper roots and less negative water potentials. Cannomois congesta—a shallow-rooted restioid—was least negatively impacted. Following rehydrating rain at the end of summer, gas exchange recovery was lower in the drier year compared with the normal year, but did not differ between species. Loss of function in the drier year was partially accounted for by loss of xylem transport capacity in Erica and Cannomois, but not Protea. Hitherto unseen water use patterns, including inter-annual variability of gas exchange associated with contrasting water uptake properties, reveal that species use different mechanisms to cope with summer dry periods. Revealing physiological responses of key growth forms enhances predictions of plant function within mountain fynbos under future conditions.

Relationships between Xylem Transport, Anatomical, and Mechanical Traits at Organ Level of Two Cupressaceae Species

Compared to arid regions, forests in humid regions can be more vulnerable to drought as they are not used to, and thus not adapted to, water stress. Therefore, it is vital to understand the drought responses of woodland species in humid areas. Xylem structures and functions of species growing in the humid regions are the key to their drought responses. Two Cupressaceae species (including three taxa: Sequoia sempervirens, Taxodium distichum and its variety Taxodium distichum var. imbricatum) grown in a mesic common garden were targeted, and their xylem hydraulic function (hydraulic conductivity, Ks; cavitation resistance, P50), anatomical structure (tracheid and pit structure), and mechanical support (wood density, WD; tracheid thickness-to-span ratio, Ttob) were measured. Likewise, we analyzed the differences in hydraulic function and anatomical structure of xylem in branches and roots, and the quantitative relationship between xylem water transport, anatomical structure, and mechanical support. Our results showed that roots had a higher hydraulic conductivity and a weaker cavitation resistance than branches. There was no safety–efficiency trade-off in the branches and roots within species. Tracheid mechanical support had a trade-off relationship with Ks or P50 (negative correlation appeared in branch Ks ~ WD and root Ks ~ Ttob of S. sempervirens, root P50 ~ Ttob of T. distichum var. imbricatum, and branch P50 ~ WD). There was no trade-off in anatomical structure, which led to no safety–efficiency trade-off in xylem function. Our results suggest that the two species exhibit both low efficiency and low safety in xylem, and that there is no safety–efficiency trade-off in branches and roots. The reason behind this is that the structural demand for high safety and high efficiency differs (i.e., the root Ks of S. sempervirens was strongly controlled by Dh; in contrast, the root P50 of S. sempervirens was strongly determined by tracheid density, N). Namely, the structural basis for a safety–efficiency trade-off does not exist and therefore trade-offs cannot be achieved.

Preliminary Studies on the In Vitro Interactions Between the Secondary Metabolites Produced by Esca-Associated Fungi and Enological Saccharomyces cerevisiae Strains.

Esca-affected vines alter the carbohydrate metabolism, xylem transport of water and photosynthesis and show regular grapes (but berries do not reach maturity), and phenolic compounds are reduced in concentration, oxidate and polymerizate. Pullulan and a mixture of scytalone and isosclerone (9:1; w/w), secondary metabolites produced in vitro and in planta by Phaeoacremonium minimum (syn. P. aleophilum) and Phaeomoniella chlamydospora, were assayed against the strains Byosal HS1 and IOC 18-2007 in microvinifications with synthetic grape must. The presence of pullulan and pentaketides mix affects the growth and metabolism of the tested Saccharomyces cerevisiae strains. Assays at 100 and 1000 µg mL−1 inhibited the growth of both strains, while no effects were recorded when evaluated at 1 and 5 µg mL−1. In comparison with the controls, pullulan and the scytalone/isosclerone mixture at 10 µg mL−1 had a growth reduction, a lower alcohol yield, reduced the concentration of tartaric acid and malic acid; and slowed down the production of lactic acid, acetic acid and total polyphenol content of the tested S. cerevisiae strains. These metabolites could be applied as an alternative to the sulfite addition in the early stages of vinification to support the action of selected Saccharomyces. Appealing is the subtractive action of pullulan against tartaric acid. Further data are needed to confirm and validate the enological performance in freshly pressed grape juice.

Effects of Cd uptake, translocation and redistribution in different hybrid rice varieties on grain Cd concentration

In order to identify the key transport process that determines the Cd concentration in brown rice, this study used 21 hybrid rice varieties as experimental materials and conducted field experiments in Qiyang (cadmium-contaminated site) and Yongding (low-cadmium site). Cd concentrations in 8 organs were measured, and bioconcentration factors and transfer factor were further calculated. The results showed that the Cd concentrations of the organs related to the xylem transport were as follows: root > node > stem > leaf sheath > leaf. In the phloem, the Cd concentrations were as follows: rachis > brown rice > rice husk. And the results of the correlation analysis found that Cd concentration between brown rice and root showed a significant positive correlation in Cd-contaminated site, but no significant correlation in low-cadmium site. Meanwhile, at both experimental sites, the Cd concentration of brown rice showed the most significant correlation with the phloem transfer factor from leaf and leaf sheath to brown rice. Principal Component Analysis (PCA) and stepwise regression analysis likewise found that Cd concentration in leaf and leaf sheath and their phloem transport of Cd to brown rice were significantly and positively correlated with Cd concentration in brown rice. The above results showed that the transport of leaf and leaf sheath to brown rice was a key process, and played a more important role in the accumulation of cadmium in brown rice than in root.