Photosynthetically active radiation impacts significantly on root and cell hydraulics in barley (Hordeum vulgare L.)

Root cell wall polysaccharides and endodermal barriers restrict long-distance Cd translocation in the roots of Kentucky bluegrass

Soil Cd pollution is a significant environmental issue faced by contemporary society. Kentucky bluegrass is considered a potential phytoremediation species, as some varieties have excellent cadmium (Cd) tolerance. However, the mechanisms of Cd accumulation and transportation in Kentucky bluegrass are still not fully understood. The Cd-tolerant Kentucky bluegrass cultivar 'Midnight' (M) exhibits lower Cd translocation efficiency and a higher leaf Cd concentration compared to the Cd-sensitive cultivar 'Rugby II' (R). We hypothesized that Cd translocation from roots to shoots in cultivar M is hindered by the endodermal barriers and cell wall polysaccharides; hence, we conducted Cd distribution, cytological observation, cell wall component, and transcriptomic analyses under Cd stress conditions using the M and R cultivars. Cd stress resulted in the thickening of the endodermis and increased synthesis of cell wall polysaccharides in both the M and R cultivars. Endodermis development restricted the radical transport of Cd from the root cortex to the stele, while the accumulation of cell wall polysaccharides promoted the binding of Cd to the cell wall. These changes further inhibited the long-distance translocation of Cd from the roots to the aerial parts. Furthermore, the M cultivar exhibited limited long-distance Cd translocation efficiency compared to the R cultivar, which was attributed to the enhanced development of endodermal barriers and increased Cd binding by cell wall polysaccharides. This study provides valuable insights for screening high Cd transport efficiency in Kentucky bluegrass based on anatomical structure and genetic modification.

Impact of magnetic field on the translocation of iron oxide nanoparticles (Fe3O4) in barley seedlings (Hordeum vulgare L.)

The effect and contribution of an external magnetic field (MF) on the uptake and translocation of nanoparticles (NPs) in plants have been investigated in this study. Barley was treated with iron oxide NPs (Fe3O4, 500 mg/L, 50-100 nm) and grown under various MF strengths (20, 42, 125, and 250 mT). The root-to-shoot translocation of NPs was assessed using a vibrating sample magnetometer (VSM) and inductively coupled plasma optical emission spectrometry (ICP-OES). Additionally, plant phenological parameters, such as germination, protein and chlorophyll content, and photosynthetic and nutritional status, were examined. The results demonstrated that the external MF significantly enhances the uptake of NPs through the roots. The uptake was higher at lower MF strengths (20 and 42 mT) than at higher MF strengths (125 and 250 mT). The root and shoot iron (Fe) contents were approximately 2.5-3-fold higher in the 250 mT application compared to the control. Furthermore, the MF treatments significantly increased micro-elements such as Mn, Zn, Cu, Mo, and B (P < 0.005). This effect could be attributed to the disruption of cell membranes at the root tip cells caused by both the MF and NPs. Moreover, the MF treatments improved germination rates by 28%, total protein content, and photosynthetic parameters. These findings show that magnetic field application helps the effective transport of magnetic NPs, which could be essential for NPs-mediated drug delivery, plant nutrition, and genetic transformation applications.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03727-4.

Magnetic field effects on the magnetic properties, germination, chlorophyll fluorescence, and nutrient content of barley (Hordeum vulgare L.)

The magnetic field (MF) interacts with biological systems and has the potential to increase germination, plant growth and productivity. Although it is known as a low cost and promising approach, the mechanism that increases growth is not fully understood yet. In this study, the effect of different MF strengths (20, 42, 125, and 250 mT) was investigated on barley (Hordeum vulgare L.). In addition to phenological parameters, possible cell damage, electron transport rate, chlorophyll fluorescence, magnetic character and elemental status of tissues were determined. Results showed that lower strengths (≤125 mT) of MF treatment improve germination. Confocal microscopy analyzes revealed MF-induced cell membrane damage in roots that could alter the elemental content of tissues. Elemental analyzes found that the content of macroelements (Ca, Mg, P, and K) are gradually reduced with increasing MF forces; in opposite the microelement contents (Fe, B, Cu, Mn, Zn, and Mo) are increased in roots. Diamagnetism is the dominant magnetic character in all root and leaf samples. However, the roots became surprisingly superparamagnetic in 250 mT application. It seems that MF treatment at higher strength (250 mT in this study) could influence the orientation of magnetic moments. These findings suggest that MF application: i) can alter the magnetic character of plants, ii) enhances the germination, photosynthetic machinery, and growth, and iii) affects the nutrient uptake and abundance in tissues, depending on the MF strength. This comprehensive study can help in understanding the interaction of magnetic field with plants.

Drought-Induced Root Pressure in Sorghum bicolor

Root pressure, also manifested as profusive sap flowing from cut stems, is a phenomenon in some species that has perplexed biologists for much of the last century. It is associated with increased crop production under drought, but its function and regulation remain largely unknown. In this study, we investigated the initiation, mechanisms, and possible adaptive function of root pressure in six genotypes of Sorghum bicolor during a drought experiment in the greenhouse. We observed that root pressure was induced in plants exposed to drought followed by re-watering but possibly inhibited by 100% re-watering in some genotypes. We found that root pressure in drought stressed and re-watered plants was associated with greater ratio of fine: coarse root length and shoot biomass production, indicating a possible role of root allocation in creating root pressure and adaptive benefit of root pressure for shoot biomass production. Using RNA-Seq, we identified gene transcripts that were up- and down-regulated in plants with root pressure expression, focusing on genes for aquaporins, membrane transporters, and ATPases that could regulate inter- and intra-cellular transport of water and ions to generate positive xylem pressure in root tissue.

Salt stress reduces root water uptake in barley (Hordeum vulgare L.) through modification of the transcellular transport path

The aim of the study was to understand the hydraulic response to salt stress of the root system of the comparatively salt-tolerant crop barley (Hordeum vulgare L.). We focused on the transcellular path of water movement across the root cylinder that involves the crossing of membranes. This path allows for selective water uptake, while excluding salt ions. Hydroponically grown plants were exposed to 100 mM NaCl for 5-7 days and analysed when 15-17 days old. A range of complementary and novel approaches was used to determine hydraulic conductivity (Lp). This included analyses at cell, root and plant level and modelling of water flow. Apoplastic barrier formation and gene expression level of aquaporins (AQPs) was analysed. Salt stress reduced the Lp of root system through reducing water flow along the transcellular path. This involved changes in the activity and gene expression level of AQPs. Modelling of root-Lp showed that the reduction in root-Lp did not require added hydraulic resistances through apoplastic barriers at the endodermis. The bulk of data points to a near-perfect semi-permeability of roots of control plants (solute reflection coefficient σ ~1.0). Roots of salt-stressed plants are almost as semi-permeable (σ > 0.8).