Radial–axial transport coordination enhances sugar translocation in the phloem vasculature of plants

Abstract

Understanding mass transport of photosynthates in the phloem of plants is necessary for predicting plant carbon allocation, productivity, and responses to water and thermal stress. Several hypotheses about optimization of phloem structure and function and limitations of phloem transport under drought have been proposed and tested with models and anatomical data. However, the true impact of radial water exchange of phloem conduits with their surroundings on mass transport of photosynthates has not been addressed. Here, the physics of the Munch mechanism of sugar transport is re-evaluated to include local variations in viscosity resulting from the radial water exchange in two dimensions (axial and radial) using transient flow simulations. Model results show an increase in radial water exchange due to a decrease in sap viscosity leading to increased sugar front speed and axial mass transport across a wide range of phloem conduit lengths. This increase is around 40% for active loaders (for example, crops) and around 20% for passive loaders (for example, trees). Thus, sugar transport operates more efficiently than predicted by previous models that ignore these two effects. A faster front speed leads to higher phloem resiliency under drought because more sugar can be transported with a smaller pressure gradient.

Pressure and Light Multi-Physics Fields Comodulate the Multi-Length Scales of Chemical Wave Propagation in Diffusion-Fed Gels

“…Figure 5 depicts the effect of different light intensities on the spatio-temporal patterns of chemical wave propagation in the BZ gel system. It can be seen from the figure that the multi-length scales pattern of chemical wave propagation of the system shows period-doubling bifurcation and inverse period-doubling bifurcation, starting from P 4 and developing to P 8 , P 4 , P 2 , and P 1 with increasing light intensity. The complexity of the multi-length scales periodic structure of chemical wave propagation shows a nonlinear variation.…”

“…The chemical pulse waves originate spontaneously at the right open end and propagate toward the left end. The propagation scales exhibit period-doubling bifurcation, 35−37 starting from P 1 (simply periodic) and evolving to P 2 , P 4 , and P 8 (spatial periods 2, 4, and 8, respectively) with time. Then, the chemical pulse wave propagation scales stabilize at P 8 .…”

“…Physical fields are indispensable for the growth of living organisms in nature. For example, photosynthesis of plants requires light, , transport of nutrients requires pressure, , and blood circulation requires a “pressure pump heart”. , The principle of the siphoning effect is the effect of pressure, and the biological clock will be subtly changed by light or temperature. , When the physical field changes, organisms form a variety of complex forms to adapt to the changes in the physical field. For example, the complex outline of leaves, the tree of neural synapses, and pigmentation patterns on sea shells .…”

“…Physical fields are indispensable for the growth of living organisms in nature. For example, photosynthesis of plants requires light, 1,2 transport of nutrients requires pressure, 3,4 and blood circulation requires a "pressure pump heart". 5,6 The principle of the siphoning effect is the effect of pressure, and the biological clock will be subtly changed by light or temperature.…”

Toward a Realistic Representation of Sucrose Transport in the Phloem of Plants

“…Many models for phloem transport have been formulated and discussed (Cabrita et al, 2013;Jensen et al, 2009;Nakad et al, 2021Nakad et al, , 2022bPhillips & Dungan, 1993;Sevanto, 2014;Thompson & Holbrook, 2003). One of the simplifications used in these models is that phloem is presented as a long cylindrical and relatively rigid slender tube with semi-permeable walls that enable water but not sugar to be exchanged between the tube and its surroundings (xylem).…”