Understanding the salinity stress mechanisms is essential for crop improvement and sustainable agriculture. Salinity is prepotent abiotic stress compared with other abiotic stresses that decrease crop growth and development, reducing crop production and creating food security-related threats. Therefore, the input of metal oxide nanoparticles (NPs) such as zinc oxide nanoparticles (ZnO-NPs) can improve salt tolerance in crop plants, especially in the early stage of growth. Therefore, the aim of the current study was to evaluate the impact of ZnO-NPs on inducing salt tolerance in two rice (Oryza sativa L.) genotypes of seedlings. An undocumented rice landrace (Kargi) and salinity tolerance basmati rice (CSR 30) seeds were grown in a hydroponic system for two weeks with and without 50 mg/L concentrations of ZnO-NPs in various doses of NaCl (0, 60, 80, and 100 mM). Both Kargi (15.95–42.49%) and CSR 30 (15.34–33.12%) genotypes showed a reduction in plant height and photosynthetic pigments (chlorophyll a and b, carotenoids, and total chlorophyll), Zn content, and K+ uptake under stress condition, compared with control seedlings. On the other hand, stress upregulated proline, malondialdehyde (MDA), Na+ content, and antioxidant enzyme activities—namely, those of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), and glutathione reductase (GR)—in both O. sativa genotypes over the control. However, ZnO-NP-treated genotypes (Kargi and CSR 30) restored the photosynthetic pigment accumulation and K+ level, reforming the stomata and trichome morphology, and also increased antioxidant enzymes SOD, APX, CAT, and GR activity, which alleviated the oxidative stress, while reducing the level of MDA, proline, and H2O2 under stress condition. The present findings suggest that adding ZnO-NPs could mitigate the salinity stress in O. sativa by upregulating the antioxidative system and enhancing the cultivation of undocumented landrace (Kargi) and basmati (CSR 30) genotypes of O. sativa in salinity-affected areas.

https://www.mdpi.com/2077-0472/12/7/1014/pdf?version=1657713847

Zinc Oxide Nanoparticles Improve Salt Tolerance in Rice Seedlings by Improving Physiological and Biochemical Indices

Canopy temperature depression (CTD), the difference between canopy temperature (CT) and air temperature, is induced by evaporative cooling of the plants when stomata open and transpiration takes place. This review describes that CTD in rice is closely associated with stomatal conductance, and they are both affected by the environmental condition and show similar genotypic variation. It then discusses the importance of lowering CT for high yield under heat stress and different water availability conditions. Canopy temperature declines below air temperature with open stomata, and CTD increases (i.e. larger negative value), linearly with increased vapour pressure deficit of the air, with large CTD of -3 to -5 o C not uncommon under drier conditions. While panicle temperature is often 1-2 o C higher than leaf temperature, there is sufficient cooling effect that reduces panicle temperature well below air temperature to improve spikelet fertility under hot dry conditions. Large genotypic variation in CTD is commonly found in most studies undertaken, and there are cases where larger CTD has contributed to genotypic heat resistance. The capacity of a genotype to lower CT and to maintain higher stomatal conductance is often associated with the genotype producing higher yield under both well-watered flooded and water deficit conditions. There appears to be good prospect for utilising genotypes with the capacity for large CTD under different growing conditions, and this review concludes with suggestions for ways to hasten rice improvement using CTD as a tool for different growing conditions. • Review of published studies on canopy temperature depression in rice • Canopy temperature in rice is reduced greatly in low humidity conditions as in dry season crops • Cooler canopy is maintained with high transpiration, and is advantageous for achieving high spikelet fertility under heat stress conditions particularly at flowering • Genotypes with large canopy temperature depression maintain high stomatal conductance • Cooler canopy genotypes are advantageous for high yield under both well-watered and water deficit conditions 

Role of canopy temperature depression in rice

Rice is a staple food for 350 million people globally. Its yield thus affects global food security. Drought is a serious environmental factor affecting rice growth. Alleviating the inhibition of drought stress is thus an urgent challenge that should be solved to enhance rice growth and yield. This review details the effects of drought on rice morphology, physiology, biochemistry, and the genes associated with drought stress response, their biological functions, and molecular regulatory pathways. The review further highlights the main future research directions to collectively provide theoretical support and reference for improving drought stress adaptation mechanisms and breeding new drought-resistant rice varieties.

Molecular Mechanisms and Regulatory Pathways Underlying Drought Stress Response in Rice

Introduction The anatomy of rice leaves is closely related to photosynthesis and grain yield. Therefore, exploring insight into the quantitative trait loci (QTLs) and alleles related to rice flag leaf anatomical and vein traits is vital for rice improvement. Methods Here, we aimed to explore the genetic architecture of eight flag leaf traits using one single-locus model; mixed-linear model (MLM), and two multi-locus models; fixed and random model circulating probability unification (FarmCPU) and Bayesian information and linkage disequilibrium iteratively nested keyway (BLINK). We performed multi-model GWAS using 329 rice accessions of RDP1 with 700K single-nucleotide polymorphisms (SNPs) markers. Results The phenotypic correlation results indicated that rice flag leaf thickness was strongly correlated with leaf mesophyll cells layer (ML) and thickness of both major and minor veins. All three models were able to identify several significant loci associated with the traits. MLM identified three non-synonymous SNPs near NARROW LEAF 1 (NAL1) in association with ML and the distance between minor veins (IVD) traits. Discussion Several numbers of significant SNPs associated with known gene function in leaf development and yield traits were detected by multi-model GWAS performed in this study. Our findings indicate that flag leaf traits could be improved via molecular breeding and can be one of the targets in high-yield rice development.

/pdf/multi-model-genome-wide-association-studies-of-leaf-1ekkprqb.pdf

Multi-model genome-wide association studies of leaf anatomical traits and vein architecture in rice

Stomata are essential for photosynthesis and abiotic stress tolerance. Here, we used multi-omics approaches to dissect the genetic architecture and adaptive mechanisms that underlie stomatal morphology in a juvenile natural population of Populus tomentosa (303 accessions). We detected 46 candidate genes and 15 epistatic gene-pairs, associated with five stomatal morphologies and 18 leaf development and photosynthesis traits, through genome-wide association studies (GWAS). Expression quantitative trait locus (eQTL) mapping revealed that stomata-associated gene loci were significantly associated with the expression of leaf-related genes; selective sweep analysis uncovered significant differentiation in the allele frequencies of associated genes that underlie stomatal variations. An allelic gene regulatory network operating under drought stress and adequate precipitation conditions, with three key regulators (DUF538, TRA2, and AbFH2) and eight interacting genes, was identified that might regulate leaf physiology via modulation of stomatal shape and density. Validation of candidate gene variations in drought-tolerant and F1 hybrid populations of P. tomentosa showed that the DUF538, TRA2, and AbFH2 loci own functional stabilization of spatiotemporal regulatory, whose favorable alleles can be faithfully transmitted to offspring. This study provides insights concerning leaf physiology and stress tolerance via the regulation of stomatal determination in perennial plants. This article is protected by copyright. All rights reserved.

Leaf physiology variations are modulated by natural variations that underlie stomatal morphology in Populus.

Rice (Oryza sativa) is a water-intensive crop, and like other plants uses stomata to balance CO2 uptake with water-loss. To identify agronomic traits related to rice stomatal complexes, an anatomical screen of 64 Thai and 100 global rice cultivars was undertaken. Epidermal outgrowths called papillae were identified on the stomatal subsidiary cells of all cultivars. These were also detected on eight other species of the Oryza genus but not on the stomata of any other plant species we surveyed. Our rice screen identified two cultivars that had "mega-papillae" that were so large or abundant that their stomatal pores were partially occluded; Kalubala Vee had extra-large papillae, and Dharia had approximately twice the normal number of papillae. These were most accentuated on the flag leaves, but mega-papillae were also detectable on earlier forming leaves. Energy dispersive X-Ray spectrometry revealed that silicon is the major component of stomatal papillae. We studied the potential function(s) of mega-papillae by assessing gas exchange and pathogen infection rates. Under saturating light conditions, mega-papillae bearing cultivars had reduced stomatal conductance and their stomata were slower to close and re-open, but photosynthetic assimilation was not significantly affected. Assessment of an F3 hybrid population treated with Xanthomonas oryzae pv. oryzicola indicated that subsidiary cell mega-papillae may aid in preventing bacterial leaf streak infection. Our results highlight stomatal mega-papillae as a novel rice trait that influences gas exchange, stomatal dynamics, and defense against stomatal pathogens which we propose could benefit the performance of future rice crops.

/pdf/rice-stomatal-mega-papillae-restrict-water-loss-and-pathogen-4cxv53pqls.pdf

Rice Stomatal Mega-Papillae Restrict Water Loss and Pathogen Entry.

Candidate genes affecting stomatal density in rice (Oryza sativa L.) identified by genome-wide association.

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Rice Stomatal Mega-Papillae Restrict Water Loss and Pathogen Entry.

Candidate genes affecting stomatal density in rice (Oryza sativa L.) identified by genome-wide association.