Larch Cellulose Shows Significantly Depleted Hydrogen Isotope Values With Respect to Evergreen Conifers in Contrast to Oxygen and Carbon Isotopes

The analysis of the stable isotope of the tree-ring cellulose is an important tool for paleo climatic investigations. Long tree-ring chronologies consist predominantly of oaks and conifers in Europe, including larch trees (Larix decidua) and cembran pines (Pinus cembra) that form very long tree ring chronologies in the Alps and grow at the treeline, where tree growth is mainly determined by temperature variations. We analyzed δ13C, δ18O and δ2H isotopes in the cellulose extracted from tree-rings of wood samples collected at high altitude in the Swiss and Tyrol Alps, covering the whole Holocene period. We found that larch cellulose was remarkably more depleted in deuterium than that of cembran pine, with mean δ2H values of −113.4 ± 9.7‰ for larch and of −65.4 ± 11.3‰ for cembran pine. To verify if these depleted values were specific to larch or a property of the deciduous conifers, we extended the analysis to samples from various living conifer species collected at the Bern Botanical Garden. The results showed that not only the larch, but also all the samples of the deciduous larch family had a cellulose composition that was highly depleted in δ2H with regard to the other evergreen conifers including cembran pine, a difference that we attribute to a faster metabolism of the deciduous conifers. The δ18O values were not statistically different among the species, in agreement with the hypothesis that they are primary signals of the source water. While the δ13C values were slightly more depleted for larch than for cembran pine, likely due to metabolic differences of the two species. We conclude that the deciduous larch conifers have specific metabolic hydrogen fractionations and that the larch unique signature of δ2H is useful to recognize it from other conifers in subfossil wood samples collected for paleoclimatic studies. For climate information the absolute δ2H values of larch should be considered carefully and separate from other species

Ground Water Chemistry Changes before Major Earthquakes and Possible Effects on Animals

Prior to major earthquakes many changes in the environment have been documented. Though often subtle and fleeting, these changes are noticeable at the land surface, in water, in the air, and in the ionosphere. Key to understanding these diverse pre-earthquake phenomena has been the discovery that, when tectonic stresses build up in the Earth’s crust, highly mobile electronic charge carriers are activated. These charge carriers are defect electrons on the oxygen anion sublattice of silicate minerals, known as positive holes, chemically equivalent to O− in a matrix of O2−. They are remarkable inasmuch as they can flow out of the stressed rock volume and spread into the surrounding unstressed rocks. Travelling fast and far the positive holes cause a range of follow-on reactions when they arrive at the Earth’s surface, where they cause air ionization, injecting massive amounts of primarily positive air ions into the lower atmosphere. When they arrive at the rock-water interface, they act as •O radicals, oxidizing water to hydrogen peroxide. Other reactions at the rock-water interface include the oxidation or partial oxidation of dissolved organic compounds, leading to changes of their fluorescence spectra. Some compounds thus formed may be irritants or toxins to certain species of animals. Common toads, Bufo bufo, were observed to exhibit a highly unusual behavior prior to a M6.3 earthquake that hit L’Aquila, Italy, on April 06, 2009: a few days before the seismic event the toads suddenly disappeared from their breeding site in a small lake about 75 km from the epicenter and did not return until after the aftershock series. In this paper we discuss potential changes in groundwater chemistry prior to seismic events and their possible effects on animals

Exploration of Nonphotochemical Quenching Mechanisms in A. thaliana via Time Correlated Single Photon Counting Snapshots

As described in chapter 1, during photosynthesis, plants harvest light energy from the sun and, through a series of several steps, convert it to chemical energy to be stored for later use driving cellular processes vital to life. However, under high light conditions, often more light energy is absorbed than can be used for productive photosynthesis. Because excess absorbed energy can cause severe damage to the photosynthetic reaction center proteins, it must be dissipated harmlessly as heat in order to protect the plant. In the first step of photosynthesis, light energy is absorbed by pigment protein complexes designed especially for light harvesting, called light harvesting, or antenna complexes. Because of their location relative to reaction centers, pigment composition, and their density, most absorbed light energy passes through antenna complexes before reaching reaction centers, making them ideal sites for photoprotective quenching, or nonphotochemical quenching. Nonphotochemical quenching, or NPQ, is the reduction in chlorophyll a fluorescence yield caused by the dissipation of excess excitation energy by mechanisms other than photochemistry. Under high light conditions, NPQ switches the function of light harvesting complexes to dissipate the energy they collect as heat in order to protect the reaction centers from damage when their capacity for productive photosynthesis is overwhelmed. The induction of NPQ opens up a new relaxation pathway for electronically excited chlorophyll molecules by altering the distance of the excited chlorophyll from, and/or orientation relative to, a quencher. Neighboring chlorophylls and other xanthophyll pigments have been proposed as potential quenching molecules and as of yet, none have been ruled out and some experimental evidence exists to support each possible quencher. One way to change the distance between, and/or relative orientation of pigments within a pigment protein complex, or PPC, is a conformational change of the PPC. Previous work has demonstrated that the function of some integral biological membrane proteins can be modulated by the lipid composition in the membrane, which in turn modulates the lateral pressure profile, and thereby the protein conformation. Chapter 2 describes fluorescence lifetime measurements taken on LCHII embedded proteoliposomes with different lipid compositions. The results reveal increased quenching in the presence of the nonbilayer forming lipid MGDG, suggesting that the quenching is induced by an increase in lateral pressure in the acyl region of the membrane bilayer. LHCII is likely able to undergo a conformational change modulated by the lipid composition in the thylakoid membrane, which brings relevant pigments closer to one another to allow for the harmless dissipation of excess energy in the form of heat. In chapter 3, two xanthophyll cycles linked to NPQ, the violaxanthin cycle (VAZ cycle) and the lutein epoxide cycle (LxL cycle), are discussed. The cycling of xanthophylls affects the kinetics and extent of the photoprotective response triggered. While the VAZ cycle is ubiquitous among vascular plants and has been studied extensively, the LxL cycle is found in only about 60% of plants studied thus far and does not exist in model plants. Lauriebeth Leonelli, in the Niyogi lab, introduced the LxL cycle into Arabidopsis thaliana and functionally isolated it from the VAZ cycle. We showed an increase in dark-acclimated PSII efficiency associated with Lx accumulation. Time correlated single photon counting (TCSPC) measurements were performed to quantify the dependence of the response of NPQ to changes in light intensity on the presence and accumulation of zeaxanthin and lutein. Changes in the response of NPQ to light acclimation were observed between two successive light acclimation cycles, suggesting that xanthophyll cycles modulate the rapid component of NPQ necessary to prevent photoinhibition. Mathematical models of the response of zeaxanthin- and lutein-dependent reversible NPQ were constructed that describe the modulation. Finally, the wild-type response of NPQ was reconstructed from isolated components with a single common scaling factor, enabling deconvolution of the relative contributions of zeaxanthin- and lutein-dependent NPQ.Chapter 4 describes TCSPC measurements at several excitation and detection wavelengths to determine the location of quenching in a new mutant of Arabidopsis thaliana. In 2013 the Niyogi lab characterized a new mutant, soq1, which displayed a novel form of qI quenching dependent on the protein, SOQ1. Further chemical mutagenesis on the soq1 mutant revealed a second mutant, soq1 otk1, that displayed severe, constitutive quenching. Further characterization and TCSPC snapshot experiments taken at several excitation and detection wavelengths on the soq1 otk1 mutant suggest that the constitutive quenching observed in soq1 otk1 is likely occurring in LHCII trimers. The measured lifetimes are commensurate with lifetimes of aggregated LHCII trimers reported in the literature. Lastly, in chapter 5, the data analysis methods developed to mitigate issues such as very large data sets, low counts, and error analysis are discussed. The MatLab code is provided in an appendix at the end of the chapter

Investigating Masking Effects of Age Trends on the Correlations among Tree Ring Proxies

Age-related trends are present in tree-ring widths (TRW), but their presence in tree rings isotope is debated. It is unclear how cambial age influences the relationships between TRW and isotopes. Tree-ring isotopes of alpine larch and cembran-pine trees showed only trends in the juvenile period (>100 years), which might mask the inter-relations between tree-ring proxies during cambial age. This work tries to unmask the age-trend influences by examining the correlations in TRW—stable isotopes with and without age-trend correction. The non-detrended and linear-detrended values of TRW, of δD and δ18O showed significant correlations for ages up to 100 years, but not afterward. However, the correlation values, after spline or first-difference time-series detrending, were not age-related. Thus, detrending methods affect the correlations in the juvenile phase and may affect climate-related interpretations. The correlations between TRW and δ13C were not age-related, while those among the isotopes were significant throughout the ages. The correlation between δ13C and δD was the exception, as it became significant only after age > 100 years, suggesting a different use of reserves in the juvenile phase. In conclusion, the relationships among the tree-ring parameters are stable in all the different detrend scenarios after the juvenile phase, and they can be used together in multi-proxy paleoclimatic studies. The data of the juvenile phase can be used after spline-detrending or first-difference time-series calculation, depending on the purpose of the analysis to remove age-related trends. The work also provides clues on the possible causes of juvenile age trends

Preliminary evaluation of the potential of tree-ring cellulose content as a novel supplementary proxy in dendroclimatology

Cellulose content (CC (%)) in tree rings is usually utilised as a tool to control the quality of the α-cellulose extraction from tree rings in the preparation of stable-isotope analysis in wooden tissues. Reported amounts of CC (%) are often limited to mean values per tree. For the first time, CC (%) series from two high-Alpine species, Larix decidua Mill. (European Larch, LADE) and Pinus cembra L. (Swiss stone pine, PICE) are investigated in modern wood samples and Holocene wood remains from the Early and mid-Holocene. Modern CC (%) series reveal a species-specific low-frequency trend independent of their sampling site over the past 150 years. Climate–cellulose relationships illustrate the ability of CC (%) to record temperature in both species but for slightly different periods within the growing season. The Holocene CC (%) series illustrate diverging low-frequency trends in both species, independent of sampling site characteristics (latitude, longitude and elevation). Moreover, potential age trends are not apparent in the two coniferous species. The arithmetic mean of CC (%) series in the Early and mid-Holocene indicate low CC (%) succeeding cold events. In conclusion, CC (%) in tree rings show high potential to be established as novel supplementary proxy in dendroclimatology

Characterizing non-photochemical quenching in leaves through fluorescence lifetime snapshots.

We describe a technique to measure the fluorescence decay profiles of intact leaves during adaptation to high light and subsequent relaxation to dark conditions. We show how to ensure that photosystem II reaction centers are closed and compare data for wild type Arabidopsis thaliana with conventional pulse-amplitude modulated (PAM) fluorescence measurements. Unlike PAM measurements, the lifetime measurements are not sensitive to photobleaching or chloroplast shielding, and the form of the fluorescence decay provides additional information to test quantitative models of excitation dynamics in intact leaves

Characterizing non-photochemical quenching in leaves through fluorescence lifetime snapshots.

We describe a technique to measure the fluorescence decay profiles of intact leaves during adaptation to high light and subsequent relaxation to dark conditions. We show how to ensure that photosystem II reaction centers are closed and compare data for wild type Arabidopsis thaliana with conventional pulse-amplitude modulated (PAM) fluorescence measurements. Unlike PAM measurements, the lifetime measurements are not sensitive to photobleaching or chloroplast shielding, and the form of the fluorescence decay provides additional information to test quantitative models of excitation dynamics in intact leaves

A proteoliposome-based system reveals how lipids control photosynthetic light harvesting.

Integral membrane proteins are exposed to a complex and dynamic lipid environment modulated by nonbilayer lipids that can influence protein functions by lipid-protein interactions. The nonbilayer lipid monogalactosyldiacylglycerol (MGDG) is the most abundant lipid in plant photosynthetic thylakoid membranes, but its impact on the functionality of energy-converting membrane protein complexes is unknown. Here, we optimized a detergent-based reconstitution protocol to develop a proteoliposome technique that incorporates the major light-harvesting complex II (LHCII) into compositionally well-defined large unilamellar lipid bilayer vesicles to study the impact of MGDG on light harvesting by LHCII. Using steady-state fluorescence spectroscopy, CD spectroscopy, and time-correlated single-photon counting, we found that both chlorophyll fluorescence quantum yields and fluorescence lifetimes clearly indicate that the presence of MGDG in lipid bilayers switches LHCII from a light-harvesting to a more energy-quenching mode that dissipates harvested light into heat. It is hypothesized that in the in vitro system developed here, MGDG controls light harvesting of LHCII by modulating the hydrostatic lateral membrane pressure profile in the lipid bilayer sensed by LHCII-bound peripheral pigments

A proteoliposome-based system reveals how lipids control photosynthetic light harvesting.

Integral membrane proteins are exposed to a complex and dynamic lipid environment modulated by nonbilayer lipids that can influence protein functions by lipid-protein interactions. The nonbilayer lipid monogalactosyldiacylglycerol (MGDG) is the most abundant lipid in plant photosynthetic thylakoid membranes, but its impact on the functionality of energy-converting membrane protein complexes is unknown. Here, we optimized a detergent-based reconstitution protocol to develop a proteoliposome technique that incorporates the major light-harvesting complex II (LHCII) into compositionally well-defined large unilamellar lipid bilayer vesicles to study the impact of MGDG on light harvesting by LHCII. Using steady-state fluorescence spectroscopy, CD spectroscopy, and time-correlated single-photon counting, we found that both chlorophyll fluorescence quantum yields and fluorescence lifetimes clearly indicate that the presence of MGDG in lipid bilayers switches LHCII from a light-harvesting to a more energy-quenching mode that dissipates harvested light into heat. It is hypothesized that in the in vitro system developed here, MGDG controls light harvesting of LHCII by modulating the hydrostatic lateral membrane pressure profile in the lipid bilayer sensed by LHCII-bound peripheral pigments