Comparative Paraquat Sensitivity of Newly Germinated and Mature Fronds of the Aquatic Macrophyte <i>Spirodela polyrhiza</i>

Here, we compared the intrinsic characteristics of 3-day-(newly germinated;“young”) and 8-week-old (“mature”) fronds of the aquatic plant Spirodela polyrhiza and their sensitivity to paraquat, a toxic herbicide. Endpoints measured were frond area and fresh weight, root length, chlorophyll a and b contents, and chlorophyll a fluorescence. Significant differences were detected in the intrinsic physiological traits between young and mature fronds. Young fronds showed higher root length, chlorophyll contents, maximum quantum yield (Fv/Fm), maximal relative electron transport rate (rETRmax) and saturating photon flux density (PFD), whereas mature fronds exhibited greater frond area and fresh weight. After a 72 h exposure to paraquat, root length and rETRmax were identified as the most sensitive endpoints of paraquat toxicity for both frond types, with EC50 values of 0.66 and 0.76 μg·L-1 for young fronds, respectively, and 5.53 and 2.28 μg·L-1 for mature fronds, respectively. Young fronds of S. polyrhiza showed significantly higher sensitivity to paraquat than mature fronds. A survey of other studies on paraquat toxicity to Lemna species revealed that EC50 values of paraquat-induced inhibition of root regrowth and rETRmax in both stages were the lowest, indicating that these two endpoints were the most sensitive to paraquat. In addition, EC50 values of both endpoints of mature fronds of S. polyrhiza appear to be similar to the current allowable concentrations in drinking water set by the World Health Organization (WHO), indicating that these values may have application for the assessment of toxicity risk of paraquat in aquatic ecosystems.

High-throughput volumetric adaptive optical imaging using compressed time-reversal matrix

Deep-tissue optical imaging suffers from the reduction of resolving power due to tissue-induced optical aberrations and multiple scattering noise.Reflection matrix approaches recording the maps of backscattered waves for all the possible orthogonal input channels have provided formidable solutions for removing severe aberrations and recovering the ideal diffraction-limited spatial resolution without relying on fluorescence labeling and guide stars.However,measuring the full input–output response of the tissue specimen is time-consuming,making the real-time image acquisition difficult.Here,we present the use of a time-reversal matrix,instead of the reflection matrix,for fast high-resolution volumetric imaging of a mouse brain.The time-reversal matrix reduces two-way problem to one-way problem,which effectively relieves the requirement for the coverage of input channels.Using a newly developed aberration correction algorithm designed for the time-reversal matrix,we demonstrated the correction of complex aberrations using as small as 2%of the complete basis while maintaining the image reconstruction fidelity comparable to the fully sampled reflection matrix.Due to nearly 100-fold reduction in the matrix recording time,we could achieve real-time aberration-correction imaging for a field of view of 40×40µm^(2)(176×176 pixels)at a frame rate of 80 Hz.Furthermore,we demonstrated high-throughput volumetric adaptive optical imaging of a mouse brain by recording a volume of 128×128×125µm^(3)(568×568×125 voxels)in 3.58 s,correcting tissue aberrations at each and every 1µm depth section,and visualizing myelinated axons with a lateral resolution of 0.45µm and an axial resolution of 2µm.