Implications of tolerance to iron toxicity on root system architecture changes in rice (Oryza sativa L.)

IntroductionToxicity due to excess soil iron (Fe) is a significant concern for rice cultivation in lowland areas with acidic soils. Toxic levels of Fe adversely affect plant growth by disrupting the absorption of essential macronutrients, and by causing cellular damage. To understand the responses to excess Fe, particularly on seedling root system, this study evaluated rice genotypes under varying Fe levels.MethodsSixteen diverse rice genotypes were hydroponically screened under induced Fe levels, ranging from normal to excess. Morphological and root system characteristics were observed. The onset of leaf bronzing was monitored to identify the toxic response to the excess Fe. Additionally, agronomic and root characteristics were measured to classify genotypes into tolerant and sensitive categories by computing a response stability index.ResultsOur results revealed that 460 ppm of Fe in the nutrient solution served as a critical threshold for screening genotypes during the seedling stage. Fe toxicity significantly affected root system traits, emphasizing the consequential impact on aerial biomass and nutrient deprivation. To classify genotypes into tolerant and sensitive categories, leaf bronzing score was used as a major indicator of Fe stress. However, the response stability index provided a robust basis for classification for the growth performance. Apart from the established tolerant varieties, we could identify a previously unrecognized tolerant variety, ILS 12–5 in this study. Some of the popular mega varieties, including BPT 5204 and Pusa 44, were found to be highly sensitive.DiscussionOur findings suggest that root system damage, particularly in root length, surface area, and root volume, is the key factor contributing to the sensitivity responses under Fe toxicity. Tolerant genotypes were found to retain more healthy roots than the sensitive ones. Fe exclusion, by reducing Fe2+ uptake, may be a major mechanism for tolerance among these genotypes. Further field evaluations are necessary to confirm the behavior of identified tolerant and sensitive lines under natural conditions. Insights from the study provide potential scope for enhancement of tolerance through breeding programs as well as throw light on the role root system in conferring tolerance

Influence of inter-layer interactions and external stimuli on MX2_2 (M= Mo/W, X= S/Se) heterobilayers

Understanding the inter-layer interactions in transition metal dichalcogenides (TMDs) based heterostructures plays a vital role owing to the symmetry of the structure, bandgap nature, and excitonic effects. In this present work, we have studied the structural and electronic properties of MX$_2$ (M= Mo/W, X= S/Se) heterobilayers using first-principles calculations based on density functional theory. Unlike the traditional homobilayers of TMDs, these heterobilayers result in broken inversion symmetry and alter their point group from D$_{3d}$ $\rightarrow$ C$_{3v}$. From the calculated Raman spectra of these heterobilayers, we have observed that the shear and layer breathing modes (LBM) at lower frequencies ($<$ 50 cm$^{-1}$), arise due to the interlayer interactions between the different monolayers. We have simulated the electronic properties using the G$_0$W$_0$ method and perceived the nature of the band gap which mainly depends on the chalcogen atoms. Our results clearly indicate that the band gap is of direct nature for hetero bilayers with different chalcogen atoms and indirect nature for the same chalcogen based heterobilayers, with a band gap range between 1.4 to 1.7 eV. The exciton states of these materials are calculated with the Bethe-Salpeter equation (BSE) and found that the binding energies of inter-layer exciton are of the order of $\sim$ 250 meV, which makes them useful for infrared optoelectronic applications. We have also examined the electronic properties under the effect of minimal strain and twist for different chalcogen-based TMDs, and it shows the band gap tunability from direct to indirect due to interlayer interactions.Comment: 11 pages, 6 figure