Boron Alleviates Aluminum Toxicity by Promoting Root Alkalization in Transition Zone via Polar Auxin Transport.

Boron (B) alleviates aluminum (Al) toxicity in higher plants; however, the underlying mechanisms behind this phenomenon remain unknown. Here, we used bromocresol green pH indicator, noninvasive microtest, and microelectrode ion flux estimation techniques to demonstrate that B promotes root surface pH gradients in pea (Pisum sativum) roots, leading to alkalization in the root transition zone and acidification in the elongation zone, while Al inhibits these pH gradients. B significantly decreased Al accumulation in the transition zone (∼1.0-2.5 mm from the apex) of lateral roots, thereby alleviating Al-induced inhibition of root elongation. Net indole acetic acid (IAA) efflux detected by an IAA-sensitive platinum microelectrode showed that polar auxin transport, which peaked in the root transition zone, was inhibited by Al toxicity, while it was partially recovered by B. Electrophysiological experiments using the Arabidopsis (Arabidopsis thaliana) auxin transporter mutants (auxin resistant1-7; pin-formed2 [pin2]) and the specific polar auxin transporter inhibitor1-naphthylphthalamic acid showed that PIN2-based polar auxin transport is involved in root surface alkalization in the transition zone. Our results suggest that B promotes polar auxin transport driven by the auxin efflux transporter PIN2 and leads to the downstream regulation of the plasma membrane-H+-ATPase, resulting in elevated root surface pH, which is essential to decrease Al accumulation in this Al-targeted apical root zone. These findings provide a mechanistic explanation for the role of exogenous B in alleviation of Al accumulation and toxicity in plants.

Cadmium-induced changes in composition and co-metabolism of glycerolipids species in wheat root: Glycerolipidomic and transcriptomic approach.

Lipids are the structural constituents of cell membranes and play crucial roles in plant adaptation to abiotic stresses. The aim of this study was to use glycerolipidomic and transcriptomic to analyze the changes in lipids metabolism induced by cadmium (Cd) exposure in wheat. The results indicated that Cd stress did not decrease the concentrations of monogalactosyldiacyglycerol (MGDG), phosphatidylcholine (PC), lysophosphatidylcholine (LPC) and phosphatidic acid at 6 h, but decreased digalactosyldoacylglycerol (DGDG), MGDG, PC, phosphatidylethanolamine (PE), phosphatidylglycerol (PG), phosphatidylserine (PS) and LPC concentrations in wheat root at 24 h. Although the concentrations of highly abundant glycerolipids PC and PE were decreased, the ratios of PC/PE increased thus contributing to wheat adaptation to Cd stress. Cd did not reduce the extent of total lipid unsaturation due to the unchanged concentrations of high abundance species of C36:4, C34:2, C34:3 and C36:6 at 6 h, indicative of their roles in resisting Cd stress. The correlation analysis revealed the glycerolipids species experiencing co-metabolism under Cd stress, which is driven by the activated expression of genes related to glycerolipid metabolism, desaturation and oxylipin synthesis. This study gives insights into the changes of glycerolipids induced by Cd and the roles in wheat adaptation to Cd stress.

pH-Dependent mitigation of aluminum toxicity in pea (Pisum sativum) roots by boron.

Boron (B) deficiency and aluminum (Al) toxicity are two major constraints on plants grown in acidic soils. B supply mitigates Al toxicity; however, the underlying mechanisms of this process remain elusive. In this work, Pisum sativum plants were used to address this issue. In the absence of pH buffers, B supply had a better mitigation effect on Al-induced root inhibition at pH 4.0 than pH 4.8. However, in MES buffered solution, mitigating effects of B on Al-induced root inhibition were more pronounced at pH 4.8, indicating a strong pH dependency of this process. Quantification of pH-dependent accumulation of Al in various root zones, modification of root pH by an exogenous addition of rapid alkalization factor (RALF), and measuring changes in the rhizosphere pH by fluorescent dyes have revealed operation of two concurrent mechanisms to explain alleviation of the inhibition of root elongation induced by Al toxicity by boron: (1) via enhancing rhizosphere pH under strong acidic stress (pH4.0), and (2) via stabilizing of cell wall by cross-linking with RGII at relatively higher pH (4.8). These findings provide scientific basis and support for the application of B fertilizers in the regions with inherited soil acidity.

Generating Visually Aligned Sound from Videos.

We focus on the task of generating sound from natural videos, and the sound should be both temporally and content-wise aligned with visual signals. This task is extremely challenging because some sounds generated outside a camera can not be inferred from video content. The model may be forced to learn an incorrect mapping between visual content and these irrelevant sounds. To address this challenge, we propose a framework named REGNET. In this framework, we first extract appearance and motion features from video frames to better distinguish the object that emits sound from complex background information. We then introduce an innovative audio forwarding regularizer that directly considers the real sound as input and outputs bottlenecked sound features. Using both visual and bottlenecked sound features for sound prediction during training provides stronger supervision for the sound prediction. The audio forwarding regularizer can control the irrelevant sound component and thus prevent the model from learning an incorrect mapping between video frames and sound emitted by the object that is out of the screen. During testing, the audio forwarding regularizer is removed to ensure that REGNET can produce purely aligned sound only from visual features. Extensive evaluations based on Amazon Mechanical Turk demonstrate that our method significantly improves both temporal and contentwise alignment. Remarkably, our generated sound can fool the human with a 68.12% success rate. Code and pre-trained models are publicly available at https://github.com/PeihaoChen/regnet.

Cell Wall Pectin and its Methyl-esterification in Transition Zone Determine Al Resistance in Cultivars of Pea (Pisum sativum).

The initial response of plants to aluminum (Al) is the inhibition of root elongation, while the transition zone is the most Al sensitive zone in the root apex, which may sense the presence of Al and regulate the responses of root to Al toxicity. In the present study, the effect of Al treatment (30 µM, 24 h) on root growth, Al accumulation, and properties of cell wall of two pea (Pisum sativum L.) cultivars, cv Onward (Al-resistant) and cv Sima (Al-sensitive), were studied to disclose whether the response of root transition zone to Al toxicity determines Al resistance in pea cultivars. The lower relative root elongation (RRE) and higher Al content were founded in cv Sima compared with cv Onward, which were related to Al-induced the increase of pectin in root segments of both cultivars. The increase of pectin is more prominent in Al-sensitive cultivar than in Al-resistant cultivar. Aluminum toxicity also induced the increase of pectin methylesterases (PME), which is 2.2 times in root transition zone in Al-sensitive cv Sima to that of Al resistant cv Onward, thus led to higher demethylesterified pectin content in root transition zone of Al-sensitive cv Sima. The higher demethylesterified pectin content in root transition zone resulted in more Al accumulation in the cell wall and cytosol in Al-sensitive cv Sima. Our results provide evidence that the increase of pectin content and PME activity under Al toxicity cooperates to determine Al sensitivity in root transition zone that confers Al resistance in cultivars of pea (Pisum sativum).