scholarly journals Emergent honeycomb topology of the leaf spongy mesophyll

2019 ◽  
Author(s):  
Aleca M. Borsuk ◽  
Adam B. Roddy ◽  
Guillaume Théroux-Rancourt ◽  
Craig R. Brodersen
Keyword(s):  
Vascular Plants ◽  
Scaling Laws ◽  
Allometric Scaling ◽  
Photosynthetic Performance ◽  
High Cell ◽  
Spongy Mesophyll ◽  
X Ray ◽  
Resource Investment ◽  
Mesophyll Structure ◽  
Microct Imaging

AbstractThe spongy mesophyll layer in leaves is ubiquitous among vascular plants, yet its structure is relatively unknown and typically described as a disordered assemblage of isodiametric cells. We characterized spongy mesophyll structure among diverse taxa using X-ray microCT imaging and found that leaves with small cell sizes, high cell packing densities, and close vein spacing were congruent with the isodiametric paradigm. When these structural traits exceeded well-defined thresholds, the spongy mesophyll domain was instead tessellated with an emergent topological motif of an irregular honeycomb that minimizes cellular investment and obeys Euler’s Law of space filling. Our data suggest spongy mesophyll is governed by allometric scaling laws, with two distinct topologies optimized for either photosynthetic performance or minimal resource investment.One Sentence SummaryConserved topological motifs in the spongy mesophyll are coordinated with leaf photosynthetic performance.

Structural basis for the allosteric regulation of the SbtA bicarbonate transporter by the PII-like protein, SbtB, from Cyanobium sp. PCC7001

2019 ◽  
Author(s):  
Joe A. Kaczmarski ◽  
Nan-Sook Hong ◽  
Bratati Mukherjee ◽  
Laura T. Wey ◽  
Loraine Rourke ◽  
...  
Keyword(s):  
Metal Ion ◽  
Transcriptional Control ◽  
Allosteric Regulation ◽  
Inhibitory Effect ◽  
Photosynthetic Performance ◽  
Regulatory Proteins ◽  
Structural Basis ◽  
Titration Calorimetry ◽  
X Ray ◽  
Bicarbonate Transporter

ABSTRACTCyanobacteria have evolved a suite of enzymes and inorganic carbon (Ci) transporters that improve photosynthetic performance by increasing the localized concentration of CO2 around the primary CO2-fixating enzyme, Rubisco. This CO2-concentrating mechanism (CCM) is highly regulated, responds to illumination/darkness cycles and allows cyanobacteria to thrive under limiting Ci conditions. While the transcriptional control of CCM activity is well understood, less is known about how regulatory proteins might allosterically regulate Ci transporters in response to changing conditions. Cyanobacterial sodium-dependent bicarbonate transporters (SbtAs) are inhibited by PII-like regulatory proteins (SbtBs), with the inhibitory effect being modulated by adenylnucleotides. Here, we used isothermal titration calorimetry to show that SbtB from Cyanobium sp. PCC7001 (SbtB7001) binds AMP, ADP, cAMP and ATP with micromolar-range affinities. X-ray crystal structures of apo- and nucleotide-bound SbtB7001 revealed that while AMP, ADP and cAMP have little effect on the SbtB7001 structure, binding of ATP stabilizes the otherwise flexible T-loop and that the flexible C-terminal C-loop adopts several distinct conformations. We also show that ATP binding affinity is increased ten-fold in the presence of Ca2+ and we present an X-ray crystal structure of Ca2+ATP:SbtB7001 that shows how this metal ion facilitates additional stabilizing interactions with the apex of the T-loop. We propose that the Ca2+ATP-induced conformational change observed in SbtB7001 is important for allosteric regulation of SbtA activity by SbtB and is consistent with changing adenylnucleotide levels in illumination/darkness cycles.GRAPHICAL ABSTRACT

scholarly journals A Study of the Decay Phase of an X-Ray Flare on Algol

1989 ◽  
Vol 104 (2) ◽  
pp. 123-126
Author(s):  
R. Mewe ◽  
G.H.J. van den Oord ◽  
J. Jakimiec
Keyword(s):  
Decay Time ◽  
Scaling Laws ◽  
Decay Phase ◽  
Coronal Loops ◽  
Unique Determination ◽  
X Ray ◽  
Additional Heating ◽  
Loop Volume ◽  
The Common

AbstractWe have re-analyzed the X-ray flare on Algol which was observed with EXOSAT (White et al. (1986)). The common practice of estimating loop volume and length from the decay time of the flare is discussed extensively. We show that during the decay phase of the flare both scaling laws for coronal loops are valid. This implies a unique determination of loop volume and length and allows a check whether additional heating occurs in the decay phase of a flare.

Non-invasive assessment of allometric scaling laws in the human coronary tree

2010 ◽  
Vol 5 (1) ◽  
pp. 15 ◽  
Author(s):  
Damian Craiem ◽  
Mariano E. Casciaro ◽  
Sebastian Graf ◽  
Enrique P. Gurfinkel ◽  
Ricardo L. Armentano
Keyword(s):  
Scaling Laws ◽  
Allometric Scaling ◽  
Non Invasive

scholarly journals Progress in inertial confinement fusion physics at Centre d'Etudes de Limeil-Valenton

1994 ◽  
Vol 12 (3) ◽  
pp. 329-342 ◽  
Author(s):  
M. André ◽  
D. Babonneau ◽  
C. Bayer ◽  
M. Bernard ◽  
J-L. Bocher ◽  
...  
Keyword(s):  
Inertial Confinement Fusion ◽  
Scaling Laws ◽  
Laser Energy ◽  
Hot Spot ◽  
Beam Quality ◽  
Systematic Investigation ◽  
Analytical Models ◽  
Inertial Confinement ◽  
Direct Drive ◽  
X Ray

The laser program developed at the Centre d'Etudes de Limeil-Valenton, Saint-Georges, France (CEL-V) is concentrated on a systematic investigation of indirect drive fusion; by comparison with direct drive, this process is expected to provide the required irradiation uniformity with relaxed constraints on laser beam quality. The main concerns are radiative transfer and preheat, hydrodynamic instabilities, and high-density X-ray driven implosions. Ablative implosion experiments have been conducted with the two beams at the Phebus facility (5 kJ, 1.3 ns, 0.35 μm). Symmetry was proved to be controlled by the casing structure, following scaling laws describing hohlraum physics. A compressed DT density ∼100 ρ0 (ρ0 liquid DT density) has been deduced from activation measurements. Different aspects of the soft X-ray transfer processes, and particularly of the ablation of a low-Z material, which drives the capsule implosion, are dealt with in detailed investigations. Reported here are results on X-ray reemission and penetration in several materials, and on induced hydrodynamics of accelerated foils. The laser energy required to reach fuel ignition conditions has been evaluated from numerical simulations as well as from analytical models, taking into account hohlraum physics, capsule implosion, hot spot formation, and burn propagation. Several crucial parameters have been drawn, the most important being the radiation temperature. A target gain in the order of 10 appears achievable with a 2-MJ laser.

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