ORCID Profile
0000-0002-9625-6750
Current Organisation
Purdue University
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Plant Physiology | Biological Adaptation | Plant Cell and Molecular Biology | Plant Biology | Ecology | Ecological Physiology
Publisher: Springer Science and Business Media LLC
Date: 16-09-2021
DOI: 10.1038/S42003-021-02576-2
Abstract: C 4 plants frequently experience high light and high temperature conditions in the field, which reduce growth and yield. However, the mechanisms underlying these stress responses in C 4 plants have been under-explored, especially the coordination between mesophyll (M) and bundle sheath (BS) cells. We investigated how the C 4 model plant Setaria viridis responded to a four-hour high light or high temperature treatment at photosynthetic, transcriptomic, and ultrastructural levels. Although we observed a comparable reduction of photosynthetic efficiency in high light or high temperature treated leaves, detailed analysis of multi-level responses revealed important differences in key pathways and M/BS specificity responding to high light and high temperature. We provide a systematic analysis of high light and high temperature responses in S. viridis , reveal different acclimation strategies to these two stresses in C 4 plants, discover unique light/temperature responses in C 4 plants in comparison to C 3 plants, and identify potential targets to improve abiotic stress tolerance in C 4 crops.
Publisher: Oxford University Press (OUP)
Date: 07-10-2016
Abstract: The complex regulatory system controlling stomata involves physical and chemical signals that affect guard cell turgor to bring about changes in stomatal conductance (gs). Abscisic acid (ABA) closes stomata, yet the mechanisms controlling foliar ABA status in tree species remain unclear. The importance of foliage-derived ABA in regulating gas exchange was evaluated under treatments that affected phloem export through girdling and reduced water availability in the tree species, Pinus radiata (D. Don). Branch- and whole-plant girdling increased foliar ABA levels leading to declines in gs, despite no change in plant water status. Changes in gs were largely independent of the more transient increases in foliar non-structural carbohydrates (NSC), suggesting that gradual accumulation of foliar ABA was the primary mechanism for reductions in gs and assimilation. Whole-plant girdling eventually reduced root NSC, hindering root water uptake and decreasing foliar water potential, causing a dramatic increase in ABA level in leaves and concentrations in the xylem sap of shoots (4032 ng ml-1), while root xylem sap concentrations remained low (43 ng ml-1). Contrastingly, the drought treatment caused similar increases in xylem sap ABA in both roots and shoots, suggesting that declines in water potential result in relatively consistent changes in ABA along the hydraulic pathway. ABA levels in plant canopies can be regulated independently of changes in root water status triggered by changes by both phloem export and foliar water status.
Publisher: Oxford University Press (OUP)
Date: 10-01-2017
DOI: 10.1093/AOB/MCW266
Publisher: Wiley
Date: 07-01-2016
DOI: 10.1111/NPH.13846
Abstract: Vascular plant mortality during drought has been strongly linked to a failure of the internal water transport system caused by the rapid invasion of air and subsequent blockage of xylem conduits. Quantification of this critical process is greatly complicated by the existence of high water tension in xylem cells making them prone to embolism during experimental manipulation. Here we describe a simple new optical method that can be used to record spatial and temporal patterns of embolism formation in the veins of water‐stressed leaves for the first time. Applying this technique in four erse angiosperm species we found very strong agreement between the dynamics of embolism formation during desiccation and decline of leaf hydraulic conductance. These data connect the failure of the leaf water transport network under drought stress to embolism formation in the leaf xylem, and suggest embolism occurs after stomatal closure under extreme water stress.
Publisher: Springer Science and Business Media LLC
Date: 09-03-2020
Publisher: Wiley
Date: 23-04-2022
DOI: 10.1111/PCE.14330
Abstract: Leaf water potential (ψ
Publisher: Wiley
Date: 19-01-2022
DOI: 10.1111/PCE.14253
Abstract: Xylem embolism resistance varies across species influencing drought tolerance, yet little is known about the determinants of the embolism resistance of an in idual conduit. Here we conducted an experiment using the optical vulnerability method to test whether in idual conduits have a specific water potential threshold for embolism formation and whether pre‐existing embolism in neighbouring conduits alters this threshold. Observations were made on a erse s le of angiosperm and conifer species through a cycle of dehydration, rehydration and subsequent dehydration to death. Upon rehydration after the formation of embolism, no refilling was observed. When little pre‐existing embolism was present, xylem conduits had a conserved, in idual embolism‐resistance threshold that varied across the population of conduits. The consequence of a variable conduit‐specific embolism threshold is that a small degree of pre‐existing embolism in the xylem results in apparently more resistant xylem in subsequent dehydrations, particularly in angiosperms with vessels. While our results suggest that pit membranes separating xylem conduits are critical for maintaining a conserved in idual conduit threshold for embolism when little pre‐existing embolism is present, as the percentage of embolized conduits increases, gas movement, local pressure differences and connectivity between conduits increasingly contribute to embolism spread.
Publisher: Oxford University Press (OUP)
Date: 07-09-2022
Abstract: The resistance of xylem conduits to embolism is a major factor defining drought tolerance and can set the distributional limits of species across rainfall gradients. Recent work suggests that the proximity of vessels to neighbors increases the vulnerability of a conduit. We therefore investigated whether the relative vessel area of xylem correlates with intra- and inter-generic variation in xylem embolism resistance in species pairs or triplets from the genera Acer, Cinnamomum, Ilex, Quercus and Persea, adapted to environments differing in aridity. We used the optical vulnerability method to assess embolism resistance in stems and conducted anatomical measurements on the xylem in which embolism resistance was quantified. Vessel lumen fraction (VLF) correlated with xylem embolism resistance across and within genera. A low VLF likely increases the resistance to gas movement between conduits, by diffusion or advection, whereas a high VLF enhances gas transport thorough increased conduit-to-conduit connectivity and reduced distances between conduits and therefore the likelihood of embolism propagation. We suggest that the rate of gas movement due to local pressure differences and xylem network connectivity is a central driver of embolism propagation in angiosperm vessels.
Publisher: Wiley
Date: 10-05-2021
DOI: 10.1002/JEMT.23812
Abstract: The genus Disporum Salisb. is widely distributed in East Asia, yet phylogenetically relevant morphological traits useful for differentiating many of the small, perennial, herbaceous species remain poorly described. To address this, leaf, floral, pollen, and orbicule micromorphology of four Korean Disporum species was investigated using light and scanning electron microscopy. All Korean Disporum species examined had hypostomatic leaves, with anomocytic stomatal complexes found only on the abaxial epidermis. Guard cell length varied among species, ranging from 44.30 μm in D. viridescens to 53.49 μm in D. uniflorum . The epidermal cells of the investigated Disporum taxa had sinuate anticlinal cell walls on both adaxial and abaxial surfaces. The surface of the guard and subsidiary cells were either smooth with weak striations or had strongly wrinkled striations. The pollen grains of all Korean Disporum taxa were monads, monosulcate with granular aperture membranes, subprolate to prolate in shape with microreticulate or verrucate exine surfaces. The mean size of pollen grains ranged from 46.38 to 49.92 μm in polar length and from 34.39 to 39.58 μm in equatorial diameter across species. Sexine ornamentation was a taxonomically relevant trait for differentiating Korean Disporum taxa. Additionally, the presence of orbicules as well as the orbicular characters (e.g., size, shape, ornamentation, and association pattern) are described for the first time in species from this genus. The present investigation of leaf and floral micromorphology using light and scanning electron microscopy provides valuable information for the taxonomic differentiation and identification of Disporum species in Korea. A detailed micromorphological description of leaf, floral characters (tepal, stigma, style), pollen and orbicule is provided for Korean Disporum species using scanning electron microscopy (SEM) and light microscopy (LM). The presence of orbicules and their taxonomic implications in Korean Disporum species are described for the first time. Phylogenetically informative pollen and orbicule micromorphological characters are described, improving understanding the systematic relationships of Korean species in the genus Disproum .
Publisher: Frontiers Media SA
Date: 23-06-2020
Publisher: Wiley
Date: 20-05-2021
DOI: 10.1111/PPL.13450
Abstract: Xylem resistance to embolism is a key metric determining plant survival during drought. Yet, we have a limited understanding of the degree of plasticity in vulnerability to embolism. Here, we tested whether light availability influences embolism resistance in leaves and stems. The optical vulnerability method was used to assess stem and leaf resistance to embolism in Phellodendron amurense and Ilex verticillata acclimated to sun and shade microenvironments within the same canopy. In both species, we found considerable segmentation in xylem resistance to embolism between leaves and stems, but only minor acclimation in response to light availability. With the addition of a third species, Betula pubescens , which shows no vulnerability segmentation, we sought to investigate xylem anatomical traits that might correlate with strong vulnerability segmentation. We found a correlation between the area fraction of vessels in the xylem and embolism resistance across species and tissue types. Our results suggest that minimal acclimation of embolism resistance occurs in response to light environment in the same in idual and that the degree of vulnerability segmentation between leaves and stems might be determined by the vessel lumen fraction of the xylem.
Publisher: Oxford University Press (OUP)
Date: 23-10-2015
Abstract: Water deficit associated with drought can severely affect plants and influence ecological interactions involving plant secondary metabolites. We tested the effect of mild water deficit and rewatering on physiological, morphological and chemical traits of juvenile Eucalyptus globulus Labill. and Eucalyptus viminalis Labill. We also tested if responses of juvenile eucalypts to water deficit and rewatering varied within species using provenances across a rainfall gradient. Both species and all provenances were similarly affected by mild water deficit and rewatering, as only foliar abscisic acid levels differed among provenances during water deficit. Across species and provenances, water deficit decreased leaf water potential, above-ground biomass and formylated phloroglucinol compound concentrations, and increased condensed tannin concentrations. Rewatering reduced leaf carbon : nitrogen, and total phenolic and chlorogenic acid concentrations. Water deficit and rewatering had no effect on total oil or in idual terpene concentrations. Levels of trait plasticity due to water deficit and rewatering were less than levels of constitutive trait variation among provenances. The overall uniformity of responses to the treatments regardless of native provenance indicates limited ersification of plastic responses when compared with the larger quantitative variation of constitutive traits within these species. These responses to mild water deficit may differ from responses to more extreme water deficit or to responses of juvenile/mature eucalypts growing at each locality.
Publisher: Oxford University Press (OUP)
Date: 19-06-2020
Abstract: Dynamic variation of the stomatal pore in response to changes in leaf–air vapour pressure difference (VPD) constitutes a critical regulation of daytime gas exchange. The stomatal response to VPD has been associated with both foliage abscisic acid (ABA) and leaf water potential (Ψ l) however, causation remains a matter of debate. Here, we seek to separate hydraulic and hormonal control of stomatal aperture by manipulating the osmotic potential of sunflower leaves. In addition, we test whether stomatal responses to VPD in an ABA-deficient mutant (w-1) of sunflower are similar to the wild type. Stomatal apertures during VPD transitions were closely linked with foliage ABA levels in sunflower plants with contrasting osmotic potentials. In addition, we observed that the inability to synthesize ABA at high VPD in w-1 plants was associated with no dynamic or steady-state stomatal response to VPD. These results for sunflower are consistent with a hormonal, ABA-mediated stomatal responses to VPD rather than a hydraulic-driven stomatal response to VPD.
Publisher: Wiley
Date: 16-06-2017
DOI: 10.1111/NPH.14652
Abstract: Drought can cause major damage to plant communities, but species damage thresholds and postdrought recovery of forest productivity are not yet predictable. We used an El Niño drought event as a natural experiment to test whether postdrought recovery of gas exchange could be predicted by properties of the water transport system, or if metabolism, primarily high abscisic acid concentration, might delay recovery. We monitored detailed physiological responses, including shoot sapflow, leaf gas exchange, leaf water potential and foliar abscisic acid ( ABA ), during drought and through the subsequent rehydration period for a s le of eight canopy and understory species. Severe drought caused major declines in leaf water potential, elevated foliar ABA concentrations and reduced stomatal conductance and assimilation rates in our eight s le species. Leaf water potential surpassed levels associated with incipient loss of leaf hydraulic conductance in four species. Following heavy rainfall gas exchange in all species, except those trees predicted to have suffered hydraulic impairment, recovered to prestressed rates within 1 d. Recovery of plant gas exchange was rapid and could be predicted by the hydraulic safety margin, providing strong support for leaf vulnerability to water deficit as an index of damage under natural drought conditions.
Publisher: Wiley
Date: 17-07-2009
DOI: 10.1111/J.1469-8137.2009.02844.X
Abstract: The stomata of angiosperms respond to changes in ambient atmospheric concentrations of CO(2) (C(a)) in ways that appear to optimize water-use efficiency. It is unknown where in the history of land plants this important stomatal control mechanism evolved. Here, we test the hypothesis that major clades of plants have distinct stomatal sensitivities to C(a) reflecting a relatively recent evolution of water-use optimization in derived angiosperms. Responses of stomatal conductance (g(s)) to step changes between elevated, ambient and low C(a) (600, 380 and 100 micromol mol(-1), respectively) were compared in a phylogenetically and ecologically erse range of higher angiosperms, conifers, ferns and lycopods. All species responded to low C(a) by increasing g(s) but only angiosperm stomata demonstrated a significant closing response when C(a) was elevated to 600 micromol mol(-1). As a result, angiosperms showed significantly greater increases in water-use efficiency under elevated C(a) than the other lineages. The data suggest that the angiosperms have mechanisms for detecting and responding to increases in C(a) that are absent from earlier erging lineages, and these mechanisms impart a greater capacity to optimize water-use efficiency.
Publisher: Cold Spring Harbor Laboratory
Date: 07-2021
DOI: 10.1101/2021.06.30.450579
Abstract: Plant specialized 1,4-naphthoquinones present a remarkable case of convergent evolution. Species across multiple discrete orders of vascular plants produce erse 1,4-naphthoquinones via one of several pathways using different metabolic precursors. Evolution of these pathways was preceded by events of metabolic innovation and many appear to share connections with biosynthesis of photosynthetic or respiratory quinones. Here, we sought to shed light on the metabolic connections linking shikonin biosynthesis with its precursor pathways and on the origins of shiknoin metabolic genes. Downregulation of Lithospermum erythrorhizon geranyl diphosphate synthase (LeGPPS), recently shown to have been recruited from a cytoplasmic farnesyl diphosphate synthase (FPPS), resulted in reduced shikonin production and a decrease in expression of mevalonic acid and phenylpropanoid pathway genes. Next, we used LeGPPS and other known shikonin pathway genes to build a coexpression network model for identifying new gene connections to shikonin metabolism. Integrative in silico analyses of network genes revealed candidates for biochemical steps in the shikonin pathway arising from Boraginales-specific gene family expansion. Multiple genes in the shikonin coexpression network were also discovered to have originated from duplication of ubiquinone pathway genes. Taken together, our study provides evidence for transcriptional crosstalk between shikonin biosynthesis and its precursor pathways, identifies several shikonin pathway gene candidates and their evolutionary histories, and establishes additional evolutionary links between shikonin and ubiquinone metabolism. Moreover, we demonstrate that global coexpression analysis using limited transcriptomic data obtained from targeted experiments is effective for identifying gene connections within a defined metabolic network.
Publisher: Proceedings of the National Academy of Sciences
Date: 22-09-2014
Abstract: A major determinant of plant species distribution on Earth is a specific tolerance to soil drying, yet there are currently no functional or anatomical characteristics that can predict species’ requirement for rainfall. This study examines the systems responsible for controlling water delivery and water loss in the leaves of conifers and finds functional evidence of how conifers have evolved in drying climates over the course of the last 150 million years. Two “strategies” for conserving water during water stress emerged. One group relied on the plant hormone abscisic acid to maintain stomata closed during sustained drought, and another, more derived group allowed leaves to dehydrate and resisted damage by producing a water transport system capable of functioning under the extreme tension that develops in water-stressed plants.
Publisher: Cold Spring Harbor Laboratory
Date: 20-02-2021
DOI: 10.1101/2021.02.20.431694
Abstract: C 4 plants frequently experience damaging high light (HL) and high temperature (HT) conditions in native environments, which reduce growth and yield. However, the mechanisms underlying these stress responses in C 4 plants have been under-explored, especially the coordination between mesophyll (M) and bundle sheath (BS) cells. We investigated how the C 4 model plant Setaria viridis responded to a four-hour HL or HT treatment at the photosynthetic, transcriptomic, and ultrastructural levels. Although we observed a comparable reduction of photosynthetic efficiency in HL- or HT-treated leaves, detailed analysis of multi-level responses revealed important differences in key pathways and M/BS specificity responding to HL and HT. We provide a systematic analysis of HL and HT responses in S. viridis , reveal different acclimation strategies to these two stresses in C 4 plants, discover unique light/temperature responses in C 4 plants in comparison to C 3 plants, and identify potential targets to improve abiotic stress tolerance in C 4 crops.
Publisher: CSIRO Publishing
Date: 20-06-2022
DOI: 10.1071/FP21326
Abstract: Maintaining water transport in the xylem is critical for vascular plants to grow and survive. The drought-induced accumulation of embolism, when gas enters xylem conduits, causes declines in hydraulic conductance (K) and is ultimately lethal. Several methods can be used to estimate the degree of embolism in xylem, from measuring K in tissues to directly visualising embolism in conduits. One method allowing a direct quantification of embolised xylem area is the optical vulnerability (OV) technique. This method has been used across different organs and has a high spatial and temporal resolution. Here, we review studies using the OV technique, discuss the main advantages and disadvantages of this method, and summarise key advances arising from its use. Vulnerability curves generated by the OV method are regularly comparable to other methods, including the centrifuge and X-ray microtomography. A major advantage of the OV technique over other methods is that it can be simultaneously used to determine in situ embolism formation in leaves, stems and roots, in species spanning the phylogeny of land plants. The OV method has been used to experimentally investigate the spreading of embolism through xylem networks, associate embolism with downstream tissue death, and observe embolism formation in the field.
Publisher: Wiley
Date: 08-11-2017
DOI: 10.1111/PCE.13077
Abstract: Species are often classified along a continuum from isohydric to anisohydric, with isohydric species exhibiting tighter regulation of leaf water potential through stomatal closure in response to drought. We investigated plasticity in stomatal regulation in an isohydric (Eucalyptus camaldulensis) and an anisohydric (Acacia aptaneura) angiosperm species subject to repeated drying cycles. We also assessed foliar abscisic acid (ABA) content dynamics, aboveground/belowground biomass allocation and nonstructural carbohydrates. The anisohydric species exhibited large plasticity in the turgor loss point (Ψ
Publisher: Oxford University Press (OUP)
Date: 25-08-2010
DOI: 10.1093/JXB/ERQ260
Publisher: Oxford University Press (OUP)
Date: 07-03-2023
DOI: 10.1093/JXB/ERAD089
Abstract: Senescence vividly marks the onset of the final stages of the life of a leaf, yet the triggers and drivers of this process are still not fully understood. The hormone abscisic acid (ABA) is an important regulator of leaf senescence in model herbs, but the function of this hormone has not been widely tested in deciduous trees. Here we investigate the importance of ABA as a driver of leaf senescence in winter deciduous trees. In four erse species we tracked leaf gas exchange, water potential, chlorophyll content, and leaf ABA levels from the end of summer until leaves were abscised or died. We found that no change in ABA levels occurred at the onset of chlorophyll decline or throughout the duration of leaf senescence. To test whether ABA could enhance leaf senescence, we girdled branches to disrupt ABA export in the phloem. Girdling increased leaf ABA levels in two of the species, and this increase triggered an accelerated rate of chlorophyll decline in these species. We conclude that an increase in ABA level may augment leaf senescence in winter deciduous species but that it is not essential for this annual process.
Publisher: Oxford University Press (OUP)
Date: 21-07-2017
DOI: 10.1104/PP.17.00535
Publisher: Wiley
Date: 13-06-2020
DOI: 10.1111/NPH.16649
Publisher: Wiley
Date: 02-03-2022
DOI: 10.1111/PLB.13404
Abstract: Forest mortality during drought has been attributed to hydraulic failure, which can be challenging to measure. A limited number of alternative proxies for incipient leaf death exist. Here we investigate whether a terminal increase in abscisic acid (ABA) levels in leaves occurs across vascular land plants and is an indicator of imminent leaf death. For different species across vascular plants, we monitored ABA levels during lethal drought as well as leaf embolism resistance, across the canopy as leaves die following senescence, or when leaves are exposed to a heavy, lethal frost late in the growing season. We observed a considerable increase in foliage ABA levels once leaves showed signs of incipient leaf death. This increase in ABA levels upon incipient leaf death, could be induced by embolism during drought, by freezing or as leaves age naturally, and was observed in species spanning the phylogeny of vascular land plants as well as in an ABA biosynthetic mutant plant. A considerable increase in foliage ABA levels may act as an indicator of impending leaf death.
Publisher: Wiley
Date: 26-11-2023
DOI: 10.1002/AJB2.1196
Abstract: The densities of veins and stomata govern leaf water supply and gas exchange. They are coordinated to avoid overproduction of either veins or stomata. In many species, where leaf area is greater at low light, this coordination is primarily achieved through differential cell expansion, resulting in lower stomatal and vein density in larger leaves. This mechanism would, however, create highly inefficient leaves in species in which leaf area is greater at high light. Here we investigate the role of cell expansion and differentiation as regulators of vein and stomatal density in Rheum rhabarbarum, which produces large leaves under high light. Rheum rhabarbarum plants were grown under full sunlight and 7% of full sunlight. Leaf area, stomatal density, and vein density were measured from leaves harvested at different intervals. Leaves of R. rhabarbarum expanded at high light were six times larger than leaves expanded at low light, yet vein and stomatal densities were similar. In high light-expanded leaves, minor veins were continuously initiated as the leaves expanded, while an extended period of stomatal initiation, compared to leaves expanded at low light, occurred early in leaf development. We demonstrate that R. rhabarbarum adjusts the initiation of stomata and minor veins at high light, allowing for the production of larger leaves uncoupled from lower vein and stomatal densities. We also present evidence for an independent control of vein and stomatal initiation, suggesting that this adjustment must involve some unknown developmental mechanism.
Publisher: Wiley
Date: 30-09-2016
DOI: 10.1111/PCE.12817
Abstract: Land plants exhibit a degree of homeostasis in leaf water content to protect against damage to photosynthetic and xylem tissues, and to maintain an efficient allocation of resources. This is achieved by a strong coordination between the systems regulating water delivery (xylem) and water loss (stomata). This review discusses evolution in xylem and stomatal function, specifically focussing on the interactions between them.
Publisher: Wiley
Date: 22-07-2021
DOI: 10.1111/NPH.17577
Abstract: Global warming is expected to dramatically accelerate forest mortality as temperature and drought intensity increase. Predicting the magnitude of this impact urgently requires an understanding of the process connecting atmospheric drying to plant tissue damage. Recent episodes of forest mortality worldwide have been widely attributed to dry conditions causing acute damage to plant vascular systems. Under this scenario vascular embolisms produced by water stress are thought to cause plant death, yet this hypothetical trajectory has never been empirically demonstrated. Here we provide foundational evidence connecting failure in the vascular network of leaves with tissue damage caused during water stress. We observe a catastrophic sequence initiated by water column breakage under tension in leaf veins which severs local leaf tissue water supply, immediately causing acute cellular dehydration and irreversible damage. By highlighting the primacy of vascular network failure in the death of leaves exposed to drought or evaporative stress our results provide a strong mechanistic foundation upon which models of plant damage in response to dehydration can be confidently structured.
Start Date: 04-2014
End Date: 04-2017
Amount: $394,561.00
Funder: Australian Research Council
View Funded ActivityStart Date: 10-2022
End Date: 10-2025
Amount: $347,811.00
Funder: Australian Research Council
View Funded Activity