Physiological characterization of the wild almond Prunus arabica stem photosynthetic capability

Leaves are the major plant tissue for transpiration and carbon fixation in deciduous trees. In harsh habitats, atmospheric CO2 assimilation via stem photosynthesis is common, providing extra carbon gain to cope with the detrimental conditions. We studied two almond species, the commercial Prunus dulcis cultivar “Um-el-Fahem” and the rare wild Prunus arabica. Our study revealed two distinctive strategies for carbon gain in these almond species. While, in P. dulcis, leaves possess the major photosynthetic surface area, in P. arabica, green stems perform this function, in particular during the winter after leaf drop. These two species' anatomical and physiological comparisons show that P. arabica carries unique features that support stem gas exchange and high-gross photosynthetic rates via stem photosynthetic capabilities (SPC). On the other hand, P. dulcis stems contribute low gross photosynthesis levels, as they are designed solely for reassimilation of CO2 from respiration, which is termed stem recycling photosynthesis (SRP). Results show that (a) P. arabica stems are covered with a high density of sunken stomata, in contrast to the stomata on P. dulcis stems, which disappear under a thick peridermal (bark) layer by their second year of development. (b) P. arabica stems contain significantly higher levels of chlorophyll compartmentalized to a mesophyll-like, chloroplast-rich, parenchyma layer, in contrast to rounded-shape cells of P. dulcis's stem parenchyma. (c) Pulse amplitude-modulated (PAM) fluorometry of P. arabica and P. dulcis stems revealed differences in the chlorophyll fluorescence and quenching parameters between the two species. (d) Gas exchange analysis showed that guard cells of P. arabica stems tightly regulate water loss under elevated temperatures while maintaining constant and high assimilation rates throughout the stem. Our data show that P. arabica uses a distinctive strategy for tree carbon gain via stem photosynthetic capability, which is regulated efficiently under harsh environmental conditions, such as elevated temperatures. These findings are highly important and can be used to develop new almond cultivars with agriculturally essential traits

Stability of the In-Plane Room Temperature van der Waals Ferromagnet Chromium Ditelluride and Its Conversion to Chromium-Interleaved CrTe2_2 Compounds

Van der Waals magnetic materials are building blocks for novel kinds of spintronic devices and playgrounds for exploring collective magnetic phenomena down to the two-dimensional limit. Chromium-tellurium compounds are relevant in this perspective. In particular, the 1$T$ phase of CrTe$_2$ has been argued to have a Curie temperature above 300~K, a rare and desirable property in the class of lamellar materials, making it a candidate for practical applications. However, recent literature reveals a strong variability in the reported properties, including magnetic ones. Using electron microscopy, diffraction and spectroscopy techniques, together with local and macroscopic magnetometry approaches, our work sheds new light on the structural, chemical and magnetic properties of bulk 1$T$-CrTe$_2$ exfoliated in the form of flakes having a thickness ranging from few to several tens of nanometers. We unambiguously establish that 1$T$-CrTe$_2$ flakes are ferromagnetic above room temperature, have an in-plane easy axis of magnetization, low coercivity, and we confirm that their Raman spectroscopy signatures are two modes, $E_{2\text{g}}$ (103.5~cm$^{-1}$) and $A_{1\text{g}}$ (136.5~cm$^{-1}$). We also prove that thermal annealing causes a phase transformation to monoclinic Cr$_5$Te$_8$ and, to a lesser extent, to trigonal Cr$_5$Te$_8$. In sharp contrast with 1$T$-CrTe$_2$, none of these compounds have a Curie temperature above room temperature, and they both have perpendicular magnetic anisotropy. Our findings reconcile the apparently conflicting reports in the literature and open opportunities for phase-engineered magnetic properties

Optical control and spin dynamics of an individual Cr in a semiconductor : towards coherent mechanical driving with surface acoustic waves

Grâce à leur long temps de cohérence, les spins individuels localisés dans les semi-conducteurs sont des qubits prometteurs pour la mise en œuvre dans l'état solide de technologies quantiques émergentes, notamment l'informatique quantique et les capteurs quantiques. Cependant, la réalisation d'une interaction à longue portée entre des qubits de spin à l'état solide reste un objectif difficile à atteindre aujourd'hui. Les ondes acoustiques de surface (SAW), des excitations de type phonon liées à la surface d'un solide, sont proposées comme bus quantique efficace permettant le couplage à longue distance d'un large éventail de qubits.Nous avons étudié un nouveau système à spin unique avec une grande interaction intrinsèque entre le spin et la déformation : un atome de Cr individuel dans une boite quantique (BQ) de CdTe. Nous avons d'abord analysé la dynamique de spin d'un ion Cr2+ individuel en utilisant un pompage optique résolu en temps. Nous avons démontré que la relaxation du spin d'un Cr isolé est fortement sensible aux phonons hors équilibre. Nous avons trouvé des conditions d'excitation où l'état de spin préparé optiquement peut être préservé dans l'obscurité sur une échelle de temps µs. Cela ouvre la possibilité de contrôler de manière cohérente le qubit de spin du Cr avec le champ de déformation résonant de SAW. Nous avons conçu et fabriqué des transducteurs SAW dans la gamme GHz sur des structures à base de ZnTe. Malgré le très faible coefficient piézoélectrique du ZnTe, des ondes acoustiques de surface GHz peuvent être lancées sur une surface de ZnTe à l'aide de transducteurs inter-digités réalisés sur une couche de ZnO orientée selon l'axe c déposée sur du ZnTe contenant des BQs CdTe. Nous avons démontré la modulation radiofréquence de l'énergie de BQs CdTe/ZnTe individuelles par SAWs. Une contrainte de l'ordre de 10-4 peut être obtenue sur la couche de BQs. Nous avons observé dans le domaine temporel la propagation d'impulsions mécaniques de l'ordre de 100 ns dans des cavités et démontré la modulation de l'énergie de BQs individuelles par des ondes stationnaires SAW à phase contrôlée.Dans le processus d'optimisation des échantillons de BQs dopées au Cr, nous avons observé que l'état de charge du Cr pouvait fluctuer. Nous avons montré, en particulier, que l'ion Cr+ chargé négativement, un état excité du Cr dans les semi-conducteurs II-VI, peut être stable lorsqu'il est inséré dans une BQ. Le Cr+ attire un trou lourd et forme un complexe stable trou-Cr+. L’étude optique de ce système révèle un couplage ferromagnétique entre les trous lourds et le spin du Cr+. Nous avons étudié la dynamique du nano-aimant formé par l'interaction d'échange trou-Cr+. Les états fondamentaux avec Mz=±4 peuvent être contrôlés par pompage optique résonnant et un temps de relaxation du spin de l'ordre de 20 µs est obtenu à T=4.2 K.Ce travail montre que le Cr2+ est un qubit de spin adressable optiquement potentiellement utilisable dans des systèmes hybrides spin-mécaniques. Son fort couplage spin-contrainte et le développement réussi de dispositifs SAW sur ZnTe permettront un contrôle mécanique cohérent de ce qubit de spin. Ce travail ouvre également la voie à l'étude de nouveaux systèmes de semi-conducteurs magnétiques dilués basés sur le spin de l'accepteur ionisé Cr+.Thanks to their long coherence time, individual localized spins in semiconductors are promising qubits for the implementation in the solid state of emerging quantum technologies including quantum computing and quantum enhanced sensing. However, achieving long-range interaction between remote solid state spin qubits is still a challenging goal today. Surface Acoustic Waves (SAW), phonon-like excitations bound to the surface of a solid, are proposed as efficient quantum bus enabling long-range coupling of a wide range of qubits.We studied a new single spin system with large intrinsic spin to strain interaction: an individual Cr atom in a CdTe quantum dot (QD). We first analyzed the spin dynamics of an individual Cr2+ ion using time resolved optical pumping. We demonstrated that the spin relaxation of an isolated Cr is strongly sensitive to non-equilibrium phonons. We found excitation conditions where the optically prepared spin state can be preserved in the dark on a µs timescale. This opens the possibility to coherently control the Cr spin qubit with the resonant strain field of SAW. We designed and fabricated SAW transducers in the GHz range on ZnTe based structures. Despite the very weak piezoelectric coefficient of ZnTe, SAW in the GHz range can be launched on a ZnTe surface using interdigitated transducers deposited on a c-axis oriented ZnO layer grown on ZnTe containing CdTe QDs. We demonstrated radio-frequency tuning of the energy of individual CdTe/ZnTe QDs by SAWs. Strain in the 10-4 range can be obtained on the QD layer. We observed in the time domain propagation of mechanical pulses in the 100 ns range in cavities and demonstrated modulation of the energy of individual QDs by phase controlled SAW standing waves.In the process of optimizing Cr-doped QDs samples we observed that the charge state of Cr could fluctuate. We showed, in particular, that the negatively charged Cr+ ion, an excited state of the Cr in II-VI semiconductor, can be stable when inserted in a QD. The Cr+ attracts a heavy-hole and forms a stable hole-Cr+ complex. Optical probing of this system reveals a ferromagnetic coupling between heavy-holes and Cr+ spins. We studied the dynamics of the nano-magnet formed by the hole-Cr+ exchange interaction. The ground states with Mz=±4 can be controlled by resonant optical pumping and a spin relaxation time in the 20 µs range is obtained at T=4.2 K.This work shows that Cr2+ is a potential optically addressable spin qubit for hybrid spin-mechanical systems. Its large spin to strain coupling and the successful development of SAW devices on ZnTe will permit mechanical coherent control of this qubit. This work also opens up path towards the study of new diluted magnetic semiconductor systems based on the spin of the ionized acceptor Cr+

Fold-change Response of Photosynthesis to Step Increases of Light Level

Summary: Plants experience light intensity over several orders of magnitude. High light is stressful, and plants have several protective feedback mechanisms against this stress. Here we asked how plants respond to sudden rises at low ambient light, far below stressful levels. For this, we studied the fluorescence of excited chlorophyll a of photosystem II in Arabidopsis thaliana plants in response to step increases in light level at different background illuminations. We found a response at low-medium light with characteristics of a sensory system: fold-change detection (FCD), Weber law, and exact adaptation, in which the response depends only on relative, and not absolute, light changes. We tested various FCD circuits and provide evidence for an incoherent feedforward mechanism upstream of known stress response feedback loops. These findings suggest that plant photosynthesis may have a sensory modality for low light background that responds early to small light increases, to prepare for damaging high light levels. : Biological Sciences; Systems Biology; Plant Biology Subject Areas: Biological Sciences, Systems Biology, Plant Biolog

Physiological analysis of transgenic lines.

<p>Estimation of (a) RWC, (b) lipid peroxidation, (c) electrolyte leakage and (d) proline content from leaves of Wt plants and transgenic lines under control, salinity (250 mM NaCl) and drought stress conditions. Bars represent means ± SD and values with similar letter are non-significant at <i>P</i><0.05.</p

Genetic transformation and tissue culture of putative transgenic lines.

<p>Co-cultivation of deembryonated cotyledon explants (a), transient GUS expression (b), regeneration, selection, elongation, rooting and grafting of putative transgenic shoots (c-j), hardening (k-n), flowering (o-p) and seed harvesting (q).</p

Graphical representation of <i>SbASR-1</i> gene genomic organization.

<p>Total length of the gene is 2549 bp, which comprised of 106 bp 5’-UTR, 414 bp exon I, 1611 bp intron, 195 bp second exon II and 224 bp 3’-UTR. Upstream promoter region of 843 bp contains TATA-box at -32 bp position.</p