Functional Diversity in Blueberries and Their Responses to Extreme Drought

Climate change is expected to lead to novel climate conditions with an increase in frequency and severity of drought across many places around the globe including the north-eastern (NE) United States. Therefore, experimental studies that test the impacts of changing environmental conditions over long time scales or experimental studies that mimic these conditions are crucial to understand the potential impact on crops in this region. Wild lowbush blueberries and highbush blueberries are two important crops in NE USA. In this study, the leaf functional, structural, nutrient traits across genotypes of wild blueberries (Vaccinium angustifolium and V. myrtilloides) at Blueberry Hill Farm, Jonesboro, Maine were monitored across two crop growth cycles for four years and were related to changing environmental conditions. Additionally, I investigated how four blueberry population- varieties (two V. angustifolium populations and two V. corymbosum varieties) respond to extreme experimental drought conditions to reveal the physiological mechanisms regulating their drought responses. The results showed that wild blueberries showed strong variation both within and across genotypes in leaf structure, physiology, and nutrient status. The variation could be explained more by intra-genotype variance than by inter-genotype variance. Comparing their leaf economic spectrum (LES) traits to the Glopnet (a global dataset of plant leaf traits), the blueberries fell within the domain of Glopnet species, but global LES relationships were not always found. Also, I found that these two species showed similar or higher values across most traits compared to Vaccinium species in the Glopnet. Further, a principal component analysis (PCA) with all leaf functional, nutrient, structural traits, soil properties, rainfall and temperature showed overlaps in the soil nutrient requirements but clear separation in leaf nutrient, structural traits, physiological traits, and rainfall. Therefore, there was a clear differentiation in water and nutrient use between these two species and temporal variation in environmental conditions also shifted the traits. These findings can help us to predict how these species will respond to future climate change, and how changes in environmental conditions will shape the trait development and coordination, as well as the community composition. In the drought experiment, the two lowbush populations (Ang 1 and Ang 2) and two highbush varieties (Bluecrop and Patriot) showed a coordinated response of all the physiological processes including stomatal conductance, photosynthesis rate, transpiration rate, photochemistry, and plant hydraulic systems under declining stem water potential (Ψstem; a measure of water tension within the plant) and soil moisture conditions. Notably, there were quick declines in stomatal conductance, photosynthesis, and water loss before the turgor loss point (TLP) and the progressive decline of photochemistry, leaf browning, and leaf dropping after the TLP as Ψstem and soil moisture declined across all population- varieties of blueberries and reached -4.0MPa to -4.5MPa Ψstem and less than 5% soil moisture at the end of the drought treatment. Importantly, physiological processes, for example, Fv/Fm in Ang 2 and Patriot declined more quickly compared to Ang 1 and Bluecrop during the drought treatment. Ang 1 and Patriot showed 100% loss of hydraulic conductivity (PLC), while the Ang 2 and Bluecrop reached 87% and 83% PLC at the end of the 4-week-long drought. Ang 1 and Ang 2 populations had high regrowth of new stems from underground rhizomes in the following season, indicating the resilience of wild lowbush blueberries. All groups showed high stem mortality when water potentials were as low as -4.0MPa to -4.5 MPa, indicating that these population- varieties are vulnerable to extreme drought. The results of this study not only allowed us to understand the drought responses of these population- varieties but also allowed us to understand the turgor loss point as a threshold beyond which damages in photochemistry, leaf shedding, hydraulic failure, and plant mortality occur. In the blueberry fields, blueberry population- varieties may respond to drought in different ways especially for Angustifolium populations. The wild blueberry populations in the field conditions might show higher resistance compared to potted plants because of their large rhizome systems in the field. Therefore, the findings from this study could be further tested at larger scales in the field

Catalytic Intermolecular Hydroamination of Vinyl Ethers

This manuscript details the development of a palladium-catalyzed hydroamination of vinyl ethers. It is proposed that palladium catalyzes the hydroamination via Brønsted base catalysis, where palladium is protonated by the relatively acidic sulfonamide to generate a palladium hydride as well as the active anionic sulfonamide nucleophile. Thus, this process is distinct from known palladium-catalyzed hydroaminations of styrene derivatives that utilize less acidic amines

Decarboxylative Cyclizations and Cycloadditions of Palladium-polarized Aza-ortho-Xylylenes

Previously we have shown that palladium catalysts effect the decarboxylation of vinyl oxazinones to form zwitterionic π-allyl palladium intermediates (A, Scheme 1).1 Thus, vinyl oxazinones can be equated with zwitterionic synthons (B). In the absence of other electrophiles, the zwitterionic intermediate cyclizes to form vinyl azetidines with high diastereoselectivity. Moreover, in the presence of suitably electrophilic Michael acceptors,2 the intermediates undergo diastereoselective cycloadditions to generate highly substituted piperidine derivatives.3 The related vinyl benzoxazinones (3) undergo similar palladium-induced decarboxylation (Scheme 2).4 However, these substrates give rise to aza-ortho-xylylene synthons (C).5 The decarboxylation of vinyl benzoxazinones under conditions of palladium catalysis occurs at 25 °C and is thus significantly milder than thermal decarboxylation of benzoxazinones which typically requires temperatures near 200 °C.6 In addition, the aza-ortho-xylylene equivalents generated in the presence of palladium are more polarized than standard aza-ortho-xylylenes. Thus, while standard aza-ortho-xylylenes preferentially react with electron rich olefins, palladium-polarized aza-ortho-xylylenes (D) prefer to react with electron deficient olefins. Herein, we further describe the cyclization and cycloaddition chemistry of these unique intermediates

Contrasting water use, stomatal regulation, embolism resistance, and drought responses of two co-occurring mangroves

The physiological mechanisms underlying drought responses are poorly documented in mangroves, which experience nearly constant exposure to saline water. We measured gas exchange, foliar abscisic acid (ABA) concentration, and vulnerability to embolism in a soil water-withholding experiment of two co-occurring mangroves, Avicennia marina (Forsskål) Vierhapper (Verbenaceae) and Bruguiera gymnorrhiza (L.) Savigny (Rhizophoraceae). A. marina showed higher photosynthesis and transpiration than B. gymnorrhiza under well-watered conditions. Cavitation resistance differed significantly between species, with 50% cavitation occurring at a water potential (P50) of −8.30 MPa for A. marina and −2.83 MPa for B. gymnorrhiza. This large difference in cavitation resistance was associated with differences in stomatal closure and leaf wilting. The rapid stomatal closure of B. gymnorrhiza was correlated with ABA accumulation as water potential declined. Meanwhile, stomatal closure and declining water potentials in A. marina were not associated with ABA accumulation. The safety margins, calculated as the difference between stomatal closure and embolism spread, differed between these two species (1.59 MPa for A. marina vs. 0.52 MPa for B. gymnorrhiza). Therefore, A. marina adopts a drought tolerance strategy with high cavitation resistance, while B. gymnorrhiza uses a drought avoidance-like strategy with ABA-related sensitive stomatal control to protect its vulnerable xylem

Formation of N-Alkylpyrroles via Intermolecular Redox Amination

This document is the Accepted Manuscript version of a Published Work that appeared in final form in the Journal of the American Chemical Society, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://doi.org/10.1021/ja907357g.Redox isomerization reactions are of particular interest because they exhibit perfect atom economy, and they often utilize the inherent reducing power of hydrogen that is embedded in molecules to effect reduction of other functional groups.1–3 In doing so, redox isomerizations are able to circumvent the requirement for exogenous reducing agents, which tend to be high energy reagents. The power of redox isomerizations is arguably increased when it is used in conjunction with C–X bond-forming reactions. The Tishchenko reaction is a classic example of such a coupling reaction that has been proposed to proceed via an intermediate redox isomerization. 2 More recently, Seidel has demonstrated several intriguing reactions where an intramolecular redox reaction is used to effect a reductive amination in concert with a second C–N bond forming reaction (eq 1).3 Herein, we report a related, acid-catalyzed intermolecular redox amination that takes advantage of the inherent reducing power of 3-pyrroline (eq 2). Ultimately, redox isomerization can be used to form N-alkyl pyrroles via reductive amination, a reaction that cannot typically occur since pyrrole is a weak N-nucleophile. Moreover, the mild conditions, atom-economy, and operational simplicity of the redox amination reported herein make redox amination a viable alternative to more standard syntheses of N-alkyl pyyroles.