Xylem Tissue Research Articles

Combined heat and water stress leads to local xylem failure and tissue damage in pyrethrum flowers.

Flowers are critical for angiosperm reproduction and the production of food, fibre and pharmaceuticals, yet for unknown reasons they appear particularly sensitive to combined heat and drought stress. A possible explanation for this may be the co-occurrence of leaky cuticles in flower petals and a vascular system that has a low capacity to supply water and is prone to failure under water stress. These characteristics may render reproductive structures more susceptible than leaves to run-away cavitation - an uncontrolled feedback cycle between rising water stress and declining water transport efficiency that can rapidly lead to lethal tissue desiccation. We provide modelling and empirical evidence to demonstrate that flower damage in the perennial crop pyrethrum (Tanacetum cinerariifolium), in the form of irreversible desiccation, corresponds with run-away cavitation in the flowering stem after a combination of heat and water stress. We show that tissue damage is linked to greater evaporative demand during high temperatures rather than direct thermal stress. High floral transpiration dramatically reduced the soil water deficit at which run-away cavitation was triggered in pyrethrum flowering stems. Identifying run-away cavitation as a mechanism leading to heat damage and reproductive losses in pyrethrum provides different avenues for process-based modelling to understand the impact of climate change on cultivated and natural plant systems. This framework allows future investigation of the relative susceptibility of diverse plant species to reproductive failure under hot and dry conditions.

Pharmacognostic Study and Hepatoprotective Activity of the Methanolic Extract and Fractions of Leaves of Picralima nitida Apocyanaceae

Picralima nitida the only species in the genus Picralima belongs to the Apocyanaceae family. It is widely known for its medicinal purposes. The aim of the study was to investigate pharmacognostic parameters of the leaf and evaluate the hepatoprotective activity against carbon tetrachloride induced hepatotoxicity using Swiss Albino mice. The physicochemical evaluation indicated 11.75% moisture content, 8.50% total ash, 9.50% acid insoluble ash, 4.00% water soluble ash, 13.75% alcohol extractive value and 11.00% water extractive value. Macroscopic analysis on the fresh leaves revealed an odourless green plant with bitter taste. Microscopic examination indicated the presence of calcium oxalate crystals, starch grains, epidermal cells, xylem, parenchyma cells, paracytic stomata and palisade tissue. Chemomicroscopic evaluation indicated the presence of oxalate crystals, starch grains, lignified tissues, tannins, cellulose, protein and oil. The acute toxicity result revealed that P. nitida had no adverse effect in Swiss Albino mice. The ethyl acetate fraction had hepatoprotective ability on liver enzymes (alanine transaminase, aspartate aminotransferase, alkaline phosphatase) and can produce the same result as ascorbic acid (standard).

Hydrogen isotope fractionation in carbohydrates of leaves and xylem tissues follows distinct phylogenetic patterns: a common garden experiment with 73 tree and shrub species.

Recent methodological advancements in determining the nonexchangeable hydrogen isotopic composition (δ2 Hne ) of plant carbohydrates make it possible to disentangle the drivers of hydrogen isotope (2 H) fractionation processes in plants. Here, we investigated the influence of phylogeny on the δ2 Hne of twig xylem cellulose and xylem water, as well as leaf sugars and leaf water, across 73 Northern Hemisphere tree and shrub species growing in a common garden. 2 H fractionation in plant carbohydrates followed distinct phylogenetic patterns, with phylogeny reflected more in the δ2 Hne of leaf sugars than in that of twig xylem cellulose. Phylogeny had no detectable influence on the δ2 Hne of twig or leaf water, showing that biochemistry, not isotopic differences in plant water, caused the observed phylogenetic pattern in carbohydrates. Angiosperms were more 2 H-enriched than gymnosperms, but substantial δ2 Hne variations also occurred at the order, family, and species levels within both clades. Differences in the strength of the phylogenetic signals in δ2 Hne of leaf sugars and twig xylem cellulose suggest that the original phylogenetic signal of autotrophic processes was altered by subsequent species-specific metabolism. Our results will help improve 2 H fractionation models for plant carbohydrates and have important consequences for dendrochronological and ecophysiological studies.

Valorization of cannabis green waste to cellulose nanomaterials via phosphoric acid hydrolysis

The recent increases in Cannabis sativa (cannabis) production, both in industrial hemp and recreational varieties, has highlighted the need for low-impact and sustainable practices for this expanding industry. Green waste of cannabis, consisting of the vegetative components like plant stalks, offers an unexplored opportunity for valorization through biomass optimization. Like hemp, recreational cannabis varieties contain two high cellulose fiber types: bast fiber (phloem tissue) and hurd fiber (xylem tissue). Using hemp as a model for recreational cultivars, this study demonstrates the ability to isolate cellulose nanomaterials from both bast and hurd fiber through phosphoric acid hydrolysis. Scanning electron microscopy (EM) shows that sodium hydroxide treatment is required for removing all non-cellulose surface components from hurd fiber. Comparison of the two fiber types with transmission EM reveals phosphoric acid-hydrolyzed bast fibers produce cellulose nanocrystals (CNC), while hurd fibers are more prone to producing a mixture of cellulose nanocrystals and nanofibril-like particles (CNF) without chemical pretreatment. Adding hydrogen peroxide to the sodium hydroxide pretreatment decreased the variation in CNC sizes resulting from both bast and hurd. The findings of this study provide several avenues for valorization of green waste, while aiming to minimize the techno-economic impact of pretreatments.

Comparative functional analysis of PdeNAC2 and AtVND6 in the tracheary element formation.

Tracheary elements (i.e. vessel elements and tracheids) are highly specialized, non-living cells present in the water-conducting xylem tissue. In angiosperms, proteins in the VASCULAR-RELATED NAC-DOMAIN (VND) subgroup of the NAC (NAM, ATAF1,2, and CUC2) transcription factor family (e.g. AtVND6) are required for the differentiation of vessel elements through transcriptional regulation of genes responsible for secondary cell wall formation and programmed cell death. Gymnosperms, however, produce only tracheids, the mechanism of which remains elusive. Here, we report functional characteristics of PdeNAC2, a VND homolog in Pinus densiflora, as a key regulator of tracheid formation. Interestingly, our molecular genetic analyses show that PdeNAC2 can induce the formation of vessel element-like cells in angiosperm plants, demonstrated by transgenic overexpression of either native or NAC domain-swapped synthetic genes of PdeNAC2 and AtVND6 in both Arabidopsis and hybrid poplar. Subsequently, genome-wide identification of direct target (DT) genes of PdeNAC2 and AtVND6 revealed 138 and 174 genes as putative DTs, respectively, but only 17 genes were identified as common DTs. Further analyses have found that PdeNAC2 does not control some AtVND6-dependent vessel differentiation genes in angiosperm plants, such as AtVRLK1, LBD15/30 and pit-forming Rho-like GTPases from plant (ROP) signaling genes. Collectively, our results suggest that different target gene repertoires of PdeNAC2 and AtVND6 may contribute to the evolution of tracheary elements.

Vessel diameter polymorphism determines vulnerability-to-embolism curve shape

Summary Sherwin Carlquist proposed several functional interpretations for vessel diameter, including that narrow vessels were hydraulically “safe” while wide diameter vessels were more vulnerable to embolism. He applied these ideas both across species and biomes, and within xylem tissue, where function of growth ring types was inferred from vessel diameter polymorphisms (occurrence of differing vessel diameter classes within a tissue). Following on Carlquist’s ideas, we were interested in evaluating if vessel diameter polymorphism could be linked to vulnerability-to-embolism curve shape. Vulnerability curves were fit with a model that included a continuous shape term (alpha). We predicted that high variation in vessel diameter would result in lower alpha (more r-shaped) curves whereas low variation would produce higher alpha (more s-shaped) curves, with potential for intermediate curve types. Our findings support Carlquist’s functional interpretations of vessel diameter. Vessel diameter polymorphism was strongly correlated to vulnerability curve shape. Homogeneous vessel diameters were associated with more s-shaped curves. As vessel diameter polymorphism increased, alpha declined and curves became more linear. High polymorphism was associated with r-shaped curves. There was no relationship between vessel length and curve shape. Vessel diameter was strongly correlated with a common estimate of embolism resistance (P50), with wider diameter vessels associated with increased vulnerability. Vulnerability curves show enormous variety in shape and scale, and both parameters are likely critical in understanding and predicting plant function. Carlquist’s ecological anatomy data, predictions, and functional inferences will continue to be valuable as we expand our understanding of structure–function links in plant anatomy.

Hydroxyapatite Nanoparticles as Effective Phosphorus Nano-fertilizer on Italian Parsley Plants

Nanomaterials have been developed for various applications due to their unique features, and anew interest is now growing in their use in the agricultural sector as nano-fertilizers. Among the developed nanomaterials, hydroxyapatite nanoparticles (Nano-HAP) possess a relevant potential to be used as a source of nano-phosphorus fertilizer. Here, we evaluated the effect of these nanoparticles on growth traits, herb and essential oil yields, and histological changes of Italian parsley. The following fertilizer treatments were applied: control, NPK normal solution, Nano-HAP (0.25, 0.50, 1.0 g/L). The results showed that the foliar application of Nano-HAP tended to be comparable (and even superior) to that of conventional NPK fertilizer. Italian parsley responded positively to Nano-HAP treatments at 0.5 g/L with higher fresh (~1.5 to 3-fold increase) and dry herb yields and higher essential oil yields (10.64−20.97 L/ha) compared with the control and NPK treatments. Conversely, Nano-HAP at a high concentration of 1.0 g/L adversely influenced the growth and yield characteristics of the Italian parsley. In terms of anatomical traits, the Nano-HAP foliar application showed an improvement in the lamina and petiole measurements. Nano-HAP at 0.5 g/L produced the greatest values for the thickness of lamina, phloem tissue, xylem tissue, main vein of leaf lamina and oil gland diameter, as well as for the thickness of phloem and xylem tissues, and pith diameter of leaf petiole. Overall, our findings indicate that Nano-HAP at 0.5 g/L seems to be the most appropriate treatment for Italian parsley production.

RNA-Sequencing Reveals the Involvement of Sesquiterpene Biosynthesis Genes and Transcription Factors during an Early Response to Mechanical Wounding of Aquilaria sinensis.

Plants respond to wounding by reprogramming the expression of genes involved in secondary metabolism. Aquilaria trees produce many bioactive secondary metabolites in response to wounding, but the regulatory mechanism of agarwood formation in the early response to mechanical wounding has remained unclear. To gain insights into the process of transcriptome changes and to determine the regulatory networks of Aquilaria sinensis to an early response (15 days) to mechanical wounding, we collected A. sinensis samples from the untreated (Asc1) and treated (Asf1) xylem tissues and performed RNA sequencing (RNA-seq). This generated 49,102,523 (Asc1) and 45,180,981 (Asf1) clean reads, which corresponded to 18,927 (Asc1) and 19,258 (Asf1) genes, respectively. A total of 1596 differentially expressed genes (DEGs) were detected in Asf1 vs. Asc1 (|log2 (fold change)| ≥ 1, Padj ≤ 0.05), of which 1088 were up-regulated and 508 genes were down-regulated. GO and KEGG enrichment analysis of DEGs showed that flavonoid biosynthesis, phenylpropanoid biosynthesis, and sesquiterpenoid and triterpenoid biosynthesis pathways might play important roles in wound-induced agarwood formation. Based on the transcription factor (TF)-gene regulatory network analysis, we inferred that the bHLH TF family could regulate all DEGs encoding for farnesyl diphosphate synthase, sesquiterpene synthase, and 1-deoxy-D-xylulose-5-phosphate synthase (DXS), which contribute to the biosynthesis and accumulation of agarwood sesquiterpenes. This study provides insight into the molecular mechanism regulating agarwood formation in A. sinensis, and will be helpful in selecting candidate genes for improving the yield and quality of agarwood.

Investigation of chemical linkages between lignin and carbohydrates in cultured poplar cambium tissues via double isotope labeling

Lignin precursor labeled with 13C (coniferin-13Cα), carbohydrate precursor labeled with D (6,6-D2-glucose) were put into cambium tissue stripped from a growing poplar. The tissue was further cultured in vitro for 18d. Then, the isotopic abundance was determined. The results showed that the labeled precursors could be normally involved in the formation of new xylem. The labeled new xylem tissue was fractionated by ionic liquid DMSO/TBAH system to obtain two components: glucan-lignin complex (GL) and xylan-lignin complex (XL). The X-ray diffraction (XRD) results indicated that the crystalline form of cellulose in the GL component was transformed from type I to type II after the ionic liquid separation. Then the GL and XL were purified and modified by enzymatic and chemical methods, and their structures were elucidated by nuclear magnetic resonance (NMR) spectroscopy. The results showed that lignin subunits in the cultured tissues were mainly connected by β-5 and β-O-4 linkages, of which the β-O-4 substructure unit predominated. Lignin and carbohydrates were mainly connected by acetal bonds, ether bonds, and ester bonds. Combined with the carbohydrate composition and XRD analysis results, the GL components also confirmed the existence of acetal bonds, ester bonds and ether bonds between lignin and cellulose.

Influence of Spraying Nano-Curcumin and Nano-Glycyrrhizic Acid on Resistance Enhancement and Some Growth Parameters of Soybean (Glycine max) in Response to Tetranychus urticae Infestation and Drought Stress.

Modern nanotechnology has been credited as one of the most significant inventions of the 21st century. Many agricultural disciplines have been affected by nanotechnology in agriculture. Pest control based on natural compounds needs to be enhanced, and enhancing plant growth under climate change conditions, with increasing periods of drought in many countries, is a very vital aim. Thus, the effect of curcumin nanoparticles (Cu-NPs) and glycyrrhizic acid nanoparticles (GA-NPs) as a foliar application under water deficit on natural infestation with the two-spotted spider mite Tetranychus urticae, plant growth and yield, anatomical and chemical parameters were investigated during this study. The obtained results revealed that drought stress over the two studied seasons significantly increased the population of T. urticae and decreased all morphological and yield characteristics. The application of three mM GA-NPs reduced the mite population average by 39% while using the same concentration of Cu-NPs caused a 33.9% reduction percentage under drought stress. Using 1 mM GA-NPs gave the highest averages of plant height, number of branches, and leaves/plant fresh and dry weight. Moreover, the number of pods, 100 seed weight and seed yield (kg/ha) increased significantly as a result of spraying with GA-NPs under water deficit. From the results, water deficit decreased the values of the leaf and stem anatomical parameters. Treatment with Cu-NPs or GA-NPs under drought stress increased the thickness of mid-vein, xylem, and phloem tissues. Likewise, such treatment increased stem diameter due mainly to the increase in the thickness of cortex, phloem, and xylem tissues compared with the control. Spraying plants with GA-NPs at 1 mM increased the percentages of nitrogen, phosphor, and potassium in seeds in addition to total chlorophyll. Moreover, glutamate, aspartate, leucine, arginine, Lysine, glycine, tyrosine, tryptophan, and methionine concentrations did not differ significantly (p > 0.05) in response to all the studied levels of Cu-NPs or GA-NPs either under normal irrigation or drought condition. In light of these findings, researchers and producers should apply and test both Cu-NPs and GA-NP as nano-fertilizer natural sources on economically viable crops.

Responses of tomato fruit water balance and xylem hydraulic property of pedicel and calyx to water deficit and salinity stress

Moderate water scarcity and high soil salinization always limit fruit growth but largely promote fruit quality. Water is transported to the fruit via xylem and phloem and lost via transpiration, which is important for fruit growth and quality parameters. So far, few studies have quantified the relationship between fruit water balance and fruit growth and quality under water deficit and salinity stress (especially combined water deficit and salinity stress). In this study, tomato (Solanum lycopersicum) plants were grown under full irrigation (CK), water deficit (WD), salinity stress (SS), and combined water deficit and salinity stress (WS). We measured fruit size and quality parameters, investigated fruit water balance using a subtraction method, evaluated xylem hydraulic resistance of pedicel and calyx applying a hydraulic head, and assessed the xylem functionality by fruit rehydration and dye-tracing experiments. Results showed that WD, SS, and WS decreased plant water status and leaf gas exchange and fruit growth, but increased fruit total soluble solids. These effects were more pronounced in WS than both WD and SS. The inhibition of fruit growth by three treatments was caused by the jointly reduced xylem and phloem flow. Although xylem hydraulic resistance of pedicel and calyx at 35 d after anthesis was not significantly affected under WD and SS, it greatly increased by 112% under WS, which coincided with a significant reduction of daily growth rate and xylem flow computed on a per fruit basis by 83% and 87% under WS. These results also suggested that the xylem tissues were still functional regardless of the applied stress and fruit growth period. Phloem flow computed on a per fruit basis was decreased under all treatments, resulting in a reduction in fruit dry matter quantity, partly due to the decreased photosynthates. Phloem flow and fruit transpiration computed on a per fruit fresh weight basis were not affected due to the synergistic reduction of flow and fruit size by all treatments. This study provides a new understanding on the water relations of plant-fruit system under water deficit and salinity stress.

Genome-wide identification of Fagus sylvatica aquaporins and their comparative spring and summer expression profiles

Key messageA total of 45 aquaporins was identified in Fagus sylvatica, 35 of which were differentially expressed in spring and summer in the leaves, phloem and xylem of 11-year-old trees.European beech (Fagus sylvatica) has been widely studied in terms of its water relations and local adaptation. However, to date, the underlying basis conferring adaptation to differences in water availability are unknown. Therefore, we examined the expression of aquaporins in trees of four different beech provenances representing the southern and northern range margins, as well as core populations, grown in a common garden. We sampled their xylem, phloem and leaf tissue, when leaves had fully expanded, and in late summer. A total of 45 aquaporin isoforms were identified in the beech genome, of which 35 were detected across all sampled tissues. In our phylogenetic analysis, beech aquaporins clustered into the five subfamilies found in other woody species. Members of the plasma membrane intrinsic protein subfamily generally displayed the highest levels of expression, followed by tonoplast intrinsic proteins. Isoforms of the remaining subfamilies, Noduline-26-like intrinsic proteins, small basic intrinsic proteins and uncharacterised intrinsic proteins, were expressed at very low to moderate levels. The expression of most isoforms was stable or declined from spring to summer. Leaves followed a different expression profile from that of vascular tissues, whereas both phloem and xylem were found to express the same FsMIPs. Tissue-specific aquaporin expression was very similar amongst the four beech provenances, indicating that there is no inherent difference in the capability of these provenances to regulate aquaporin activity. The general decrease in FsMIP expression toward the end of the growing period indicates that aquaporins are involved in tree water relations and growth.

Optimisation of sampling and testing for asymptomatic olive trees infected by Xylella fastidiosa in Apulia region, Italy

Early detection of Xylella fastidiosa outbreaks in Apulian olive groves is crucial, especially in buffer zones and pathogen-free areas where olive trees are asymptomatic. Three studies were conducted. Two were on the spatial and temporal progression of X. fastidiosa infections in tree canopies of asymptomatic or mildly symptomatic olive trees of tolerant (‘Leccino’) and susceptible (‘Cellina di Nardò’ and ‘Ogliarola salentina’) cultivars. Despite different trends in pathogen infection rates and concentrations between ‘Leccino’ and susceptible olive cultivars over the study period, results showed that sampling was most effective in the mid-upper part of tree canopies throughout the year, excluding the warmest and coldest periods. Stem xylem tissues were the most appropriate for detecting the pathogen compared to lower parts of mature leaves with petioles, using serological and molecular assays. Based on these results, a third study was conducted to compare molecular and serological tests (qPCR, real-time LAMP, DAS-ELISA, DTBIA) for detection of X. fastidiosa in the mid-upper part of asymptomatic branches of infected ‘Leccino’ trees that were sampled in an appropriate collection time, using stem xylem tissue as the most appropriate matrix for testing. The molecular methods showed the greatest sensitivity, with no undetermined results, while among the serological assays, DTBIA was more sensitive than DAS-ELISA. An improved protocol for monitoring asymptomatic olive trees is recommended.

Oxalate found in wood cell wall during incipient brown rot degradation

Brown rot fungi are a marvel and an enigma of Nature. They are capable of depolymerizing holocellulose within wood cell walls without significantly mineralizing lignin. The exact details behind this feat remain unknown, but a staggered mechanism has been identified: 1) an initial step characterized by oxidative degradation of the wood cell wall biopolymers and hypothesized to involve transport of Fe3+ chelated by oxalate into the cell wall, and 2) a second degradation step dominated by hydrolytic enzymes, primarily endoglucanase activity. We subjected spruce wood (Picea abies) to Rhodonia placenta and isolated xylem tissue in the initial stage of degradation. Confocal Raman microscopy revealed oxalate accumulation in the secondary cell wall of a tracheid having fungal hyphae within the lumen. This observation is the first in situ verification of oxalate accumulation within the cell wall during the first step of brown rot degradation.

Identification of genes involved in oleoresin biosynthesis in Pinus massoniana through the combination of SMRT and Illumina sequencing

Oleoresin, a terpene with important economic and industrial value, is produced via the secondary metabolism of plants in the genus Pinus. Owing to its adaptability and high economic and ecological value, Pinus massoniana (Masson pine) is widely planted in southern China, and this species is also the main species for oleoresin tapping in the world. However, the differences in the expression of genes related to terpene biosynthesis in needles and xylem tissues at the transcriptional level at different time points during oleoresin tapping are still unclear. By combining SMRT and Illumina sequencing, we revealed the key genes involved in terpene biosynthesis in needles and xylem tissues. A total of 32.07 Gb of polymerase reads and 562.60 Gb of Illumina clean reads were obtained in this study. After annotating them in seven databases, we identified 68 genes involved in terpene biosynthesis, and most of them were highly expressed in needles, implying that needles are the biosynthetic sites of oleoresin. Moreover, we found that the TPS genes of gymnosperms more likely to be ‘DDXYD’, compared to the ‘DDXXD’ motif in angiosperms. The genes involved in the MEP pathway are highly expressed in the needles, implying the different efficiency of use of the MEP and MVA pathways in Masson pine. Furthermore, by performing controlled experiments, we found that PmPMK2, PmHDR1, PmTPS09, PmTPS11, PmTPS16, and PmTPS19 genes may play a critical role in oleoresin biosynthesis. This study provide new insights into terpene and oleoresin biosynthesis.

Comparative stem anatomy of three species of Coryphantha (Cactoideae-Cactaceae)

Background: The genus Coryphantha has the second largest number of species of the tribe Cacteae-Cactaceae. Morphologically, it has been reported that the stem presents mainly globose, ovoid and cylindric variations. However, at the anatomical level, descriptions are scarce and focused on particular tissues (epidermis or xylem). The aim of this work is to contribute to the anatomical knowledge of the genus.
 Questions and/or Hypotheses: What are the anatomical characteristics that differentiate one species from another? Does the presence of crystals allow differentiation between species?
 Study species: Coryphantha clavata, Coryphantha cornifera and Coryphantha radians.
 Site and years of study: San Luis Potosí and Querétaro, Mexico; 2017, 2020.
 Methods: Three individuals per species were collected, and conventional histological techniques were applied. Anatomical descriptions were made for different tissues, and structural characteristics were measured for each species.
 Results: The species exhibited the greatest differences in the epidermis and hypodermis, such as the presence of subepidermal stomata (C. radians), three-layered hypodermis (C. clavata), and non-collenchymatous hypodermis (C. cornifera). Crystals were not observed in the epidermises but instead in the hypodermes, which exhibited crystal shapes of druses (C. cornifera and C. radians), prisms and round bodies (C. clavata). In the cortical tissue, C. clavata had abundant mucilage cells. The observed xylem and phloem tissues exhibited characteristics similar to those of other Coryphantha species.
 Conclusions: The anatomical characteristics of the epidermis and hypodermis are considered of high systematic value and could be used to distinguish between species of the genus.

The Interconnected Relationship between Auxin Concentration Gradient Changes in Chinese Fir Radial Stems and Dynamic Cambial Activity

Auxin has been shown to exhibit a striking concentration gradient distribution in radial sections of angiosperm and gymnosperm species, in which peak auxin levels are concentrated in dividing cambial cells, while the absolute auxin concentration sharply declines toward developing secondary phloem and xylem regions. The coincidence of auxin concentration gradient across shoot tissues and xylem cell developmental gradient has prompted that auxin could act as “a plant morphogen” to provide a positional signal for cambial cell development. However, the specific location of vascular cambium and the lack of mutants altering auxin distribution in shoots of woody species made further verification experiments difficult to explore. To address this issue, different concentrations of exogenous IAA were applied to decapitated Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) trunks in this study to induce the change in the auxin concentration gradient in radial stems, and its effects on cambial activities were examined on the physiological, cellular and molecular levels. Our findings manifested that exogenous IAA treatments resulted in vast changes in endogenous hormone concentrations (including IAA, ZR, GA3 and ABA), cambial cell developmental behaviors and transcriptional activities of genes related to polar auxin transport (PAT), auxin signaling, the biosynthesis and signal transduction of other plant hormones and the genetic control of cambial activity. Based on above findings, we postulated a model of auxin concentration gradient involved in the control of cambial activity and secondary growth in tree trunks. In this model, the contrasting expression of AUX1/LAX and PIN family carriers in distinct Chinese fir wood-forming tissues dynamically modulates PAT into the cambial zone adjacent to the secondary phloem side and secondary xylem tissues, resulting in a sharp and wide auxin spatial gradient distribution across shoots in different stages of secondary growth, respectively. This change in auxin concentration gradient distribution in radial sections in turn acts on cambial developmental behaviors by modulating the expression of auxin signaling genes and key transcription factors and the production of other plant hormones in distinct woody tissues. Findings in this study provide important insights for understanding the biological significance of auxin concentration gradient existing in the radial stems of woody species.

Impact of nano-glass (NG) particles on seed germination and it’s accumulation in plant parts of wheat (Triticum aestivum L.)

Micro/nano-contaminants have been the focal pollutants in environmental science, which includes several nanomaterials, nanocomposites, fibers, glass, plastics etc. Micro/nano size pollutants are more harmful than macro pollutants due to their size. Therefore, there is an urgent need for research on the possible fate of glass particles in the environment, especially in plant and soil systems. Here, the synthesized nano-glass (NG) from the waste windshield and analyzed its uptake and effect on the wheat (Triticum aestivum L.) plant system in a hydroponic solution. The findings provided direct evidence that NG reduced the germination % with increasing NG concentrations as 100, 96, 92, and 92% for 10, 20, 30, and 40 mg L−1. The lowest root and shoot height (15.40 and 22.42 cm) was achieved in the 40 mg L−1 NG treatment. Decrement in fresh and dry wt. with a maximum reduction of chlorophyll a, b and total content (6.19, 4.98, and 11.17 mg g−1 fresh wt.) was obtained at 40 mg L−1 at 21 days. Rhodamine B was used for fluorescence imaging in seedlings to detect NG movement, Results showed that NG moves via xylem tissues of root part to other parts of the plant. Based on the currently limited or no data and uncertainty regarding the actual impact of NG on soil and plant systems, suggested considerations to address key knowledge gaps are delineated. Further studies are required as a flora build-up of NG can have both environmental influence and consequences on agronomic sustainability and food safety.

AtABCG14: A Long-Distance Root-to-Shoot Carrier of Cytokinin

Root-synthesized cytokinins regulate the growth, development, and stress responses of aboveground tissues and follow the transport route via xylem tissue. Arabidopsis ATP-binding cassette (ABC) transporter G family member 14 (AtABCG14) is involved in the xylem loading of root-synthesized cytokinins. However, the phloem unloading of root-synthesized cytokinin and shoot distribution have remained elusive. The recent study by Zhao et al., (2021) proved that the AtABCG14 protein mediates the phloem unloading of cytokinins through the apoplastic pathway indicating the AtABCG14 is a master regulator of shoot cytokinin distribution.

Stems matter: Xylem physiological limits are an accessible and critical improvement to models of plant gas exchange in deep time

The evolution of woody stems approximately 400 mya (middle Paleozoic) facilitated the expansion of plants and has likely affected carbon and water budgets across much of the terrestrial surface since that time. Stems are a carbon cost/sink and limit water transport from soil to leaves as it must pass through specialized xylem tissue. While leaf fossils have provided a wealth of quantitative data, including estimates of plant water fluxes utilizing biophysically based models, fossil-informed models integrating stem and leaf physiology are lacking. Integrated stem-leaf physiology may distinguish successors to ecological catastrophes like the end of the Late Paleozoic Ice Age (LPIA). The documented collapse of LPIA tropical forests provides an opportunity to assess the importance of woody stems as a key to understanding differences in survivorship among common plant taxa from the Carboniferous to the Permian. Here, we present an analysis of the limits to leaf water supply and plant function for Paleozoic forest plant types due to (1) cavitation-induced embolism and xylem blockage and (2) insufficient sapwood water transport capacity.—collectively defined here as sapwood dysfunction. We first present a modified ecosystem process model (Paleo-BGC+) that includes sapwood dysfunction. Paleo-BGC + is parameterized using measurements obtainable from fossil xylem and therefore applicable to both modern and ancient ecosystems. We then assess the effect of sapwood dysfunction on ecosystem processes based on previously published fossil leaf measurements and a new fossil xylem dataset for plant types present in the Late Paleozoic. Using daily meteorology from a GCM of the late Carboniferous (GENESIS v3) under a Glacial (low-CO2) and an Inter-glacial (high-CO2) scenario, we found that simulated sapwood dysfunction slowed plant water use and reduced carbon storage. This inhibition occurred particularly in plants with high maximum stomatal conductance and high stem vulnerability to embolism. Coincidentally, plants with these traits were predominantly reduced or missing from the fossil record from the Carboniferous to the Permian. Integrating stem and leaf physiology may improve the fidelity of model representations of soil-to-atmosphere water transport through plants, simulations of long-term climate phenomena like the LPIA, and ecosystem projections under future climate change.