Plant stem cells under low oxygen: metabolic rewiring by phytoglobin underlies stem cell functionality.

Root growth in maize (Zea mays L.) is regulated by the activity of the quiescent center (QC) stem cells located within the root apical meristem. Here, we show that despite being highly hypoxic under normal oxygen tension, QC stem cells are vulnerable to hypoxic stress, which causes their degradation with subsequent inhibition of root growth. Under low oxygen, QC stem cells became depleted of starch and soluble sugars and exhibited reliance on glycolytic fermentation with the impairment of the TCA cycle through the depressed activity of several enzymes, including pyruvate dehydrogenase (PDH). This finding suggests that carbohydrate delivery from the shoot might be insufficient to meet the metabolic demand of QC stem cells during stress. Some metabolic changes characteristic of the hypoxic response in mature root cells were not observed in the QC. Hypoxia-responsive genes, such as PYRUVATE DECARBOXYLASE (PDC) and ALCOHOL DEHYDROGENASE (ADH), were not activated in response to hypoxia, despite an increase in ADH activity. Increases in phosphoenolpyruvate (PEP) with little change in steady-state levels of succinate were also atypical responses to low-oxygen tensions. Overexpression of PHYTOGLOBIN 1 (ZmPgb1.1) preserved the functionality of the QC stem cells during stress. The QC stem cell preservation was underpinned by extensive metabolic rewiring centered around activation of the TCA cycle and retention of carbohydrate storage products, denoting a more efficient energy production and diminished demand for carbohydrates under conditions where nutrient transport may be limiting. Overall, this study provides an overview of metabolic responses occurring in plant stem cells during oxygen deficiency.

Causes and consequences of endogenous hypoxia on growth and metabolism of developing maize kernels.

Maize (Zea mays) kernels are the largest cereal grains, and their endosperm is severely oxygen deficient during grain fill. The causes, dynamics, and mechanisms of acclimation to hypoxia are minimally understood. Here, we demonstrate that hypoxia develops in the small, growing endosperm, but not the nucellus, and becomes the standard state, regardless of diverse structural and genetic perturbations in modern maize (B73, popcorn, sweet corn), mutants (sweet4c, glossy6, waxy), and non-domesticated wild relatives (teosintes and Tripsacum species). We also uncovered an interconnected void space at the chalazal pericarp, providing superior oxygen supply to the placental tissues and basal endosperm transfer layer. Modeling indicated a very high diffusion resistance inside the endosperm, which, together with internal oxygen consumption, could generate steep oxygen gradients at the endosperm surface. Manipulation of oxygen supply induced reciprocal shifts in gene expression implicated in controlling mitochondrial functions (23.6 kDa Heat-Shock Protein, Voltage-Dependent Anion Channel 2) and multiple signaling pathways (core hypoxia genes, cyclic nucleotide metabolism, ethylene synthesis). Metabolite profiling revealed oxygen-dependent shifts in mitochondrial pathways, ascorbate metabolism, starch synthesis, and auxin degradation. Long-term elevated oxygen supply enhanced the rate of kernel development. Altogether, evidence here supports a mechanistic framework for the establishment of and acclimation to hypoxia in the maize endosperm.

Mechanosensitive ion channels investigated simultaneously by scanning probe microscopy and patch clamp.

Mechanosensitive ion channels play an important role for the perception of mechanical signals such as touch, balance, or sound. Here, a new experimental strategy is presented providing well-defined access to single mechanosensitive ion channels in living cells. As a representative example, the investigation of mechanosensitive transduction channels in cochlear hair cells is discussed in detail including all essential technical aspects. Three different techniques were combined: atomic force microscopy (AFM) as a device for local mechanical stimulation, patch clamp for recording the current response of mechanosensitive ion channels, and differential interference contrast (DIC) microscopy equipped with an upright water-immersion objective lens. A major challenge was to adapt the mechanical design of the AFM setup to the small working distance of the light microscope and the electrical design of the AFM electronics. Various protocols for the preparation and investigation of the organ of Corti with AFM are presented.

A fractional Fourier transform analysis of the scattering of ultrasonic waves.

Many safety critical structures, such as those found in nuclear plants, oil pipelines and in the aerospace industry, rely on key components that are constructed from heterogeneous materials. Ultrasonic non-destructive testing (NDT) uses high-frequency mechanical waves to inspect these parts, ensuring they operate reliably without compromising their integrity. It is possible to employ mathematical models to develop a deeper understanding of the acquired ultrasonic data and enhance defect imaging algorithms. In this paper, a model for the scattering of ultrasonic waves by a crack is derived in the time-frequency domain. The fractional Fourier transform (FrFT) is applied to an inhomogeneous wave equation where the forcing function is prescribed as a linear chirp, modulated by a Gaussian envelope. The homogeneous solution is found via the Born approximation which encapsulates information regarding the flaw geometry. The inhomogeneous solution is obtained via the inverse Fourier transform of a Gaussian-windowed linear chirp excitation. It is observed that, although the scattering profile of the flaw does not change, it is amplified. Thus, the theory demonstrates the enhanced signal-to-noise ratio permitted by the use of coded excitation, as well as establishing a time-frequency domain framework to assist in flaw identification and classification.

Can homogeneous preparation encoding (HoPE) help reduce scan time in abdominal MRI? A clinical evaluation.

PURPOSE: To evaluate time efficiency, image quality, and diagnostic value of a clinical routine homogeneous preparation encoding (HoPE) imaging protocol in different malign and inflammatory abdominal conditions. MATERIALS AND METHODS: A total of 14 healthy volunteers and 40 patients were examined after written informed consent and approval of the local ethics committee. A standard abdominal T1-weighted (T1W) fat-saturated gradient-echo protocol was compared to the HoPE sequence protocol ensuring for comparable imaging parameters. Examinations were performed on a 1.5-T Siemens Avanto equipped with a multichannel body-array coil. Image analysis was performed with respect to contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR), level of fat suppression (FS), generation of artifacts, and overall image quality by two blinded radiologists. RESULTS: In addition to comparable results in overall image quality and FS level, the HoPE sequence protocol provided a reduction in acquisition time of up to 40%. In addition, artifact generation was same or even reduced with respect to pulsation. Quantitative SNR analysis showed strong correlation between HoPE and the conventional method. CONCLUSION: The HoPE technique is a feasible and time-saving alternative for clinical abdominal MRI. Future studies will have to be conducted on larger patient collectives to strengthen the impact of this promising technique for FS imaging and to prove its accuracy.

Metal ion recognition via 'selective detuning'. The interaction of selected transition and post-transition metal ions with a mono-N-benzylated O2N3-donor macrocycle and its xylyl-bridged ring analogue.

The interaction of cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), silver(I) and lead(II) with symmetrical mono-N-benzylated and xylyl-linked macrocyclic ligands derived from the O2N3-macrocycle, 1,12,15-triaza-3,4:9,10-dibenzo-5,8-dioxacycloheptadecane, has been investigated. The log K values for the respective 1 : 1 complexes in 95% methanol (I= 0.1; Et4NClO4, 25 degrees C) of the mono-benzylated derivative have been determined potentiometrically and the results compared with the values obtained previously for the parent (non-benzylated) ring system as well as for related di- and tri-benzylated macrocyclic species. Mono-benzylation results in slightly enhanced stability for the 1 : 1 silver(I) complex while the values for the corresponding complexes of the other six ions are in each case decreased even though the highest stability is still maintained for the 1 : 1 copper(II) complex. The log K results are in accord with a previous proposal that N-benzylation of amine-containing macrocyclic rings of the present type will normally have only a minor (positive or negative) influence on the affinity towards silver(I) while the corresponding binding strengths towards the remaining six metal ions are significantly reduced-behaviour we term 'selective detuning'. Competitive seven-metal transport experiments across a bulk chloroform membrane have been performed using both ligand systems as ionophores. In parallel to the log K results, transport selectivity for copper(II) was exhibited by both systems, with similar transport efficiencies being evident when compared on a 'per macrocyclic cavity' basis.