Potassium (K) influences the photosynthesis process in a number of ways; however, the mechanisms underlying the photosynthetic response to differences in K supply are not well understood. Concurrent measurements of gas exchange and chlorophyll fluorescence were made to investigate the effect of K nutrition on photosynthetic efficiency and mesophyll conductance (g_m) in hickory seedlings (Carya cathayensis Sarg.) in a greenhouse. The results show that leaf K concentrations <0.7–0.8% appeared to limit the leaf net CO₂ assimilation rate (A), and that the relative limitation of photosynthesis due to g_m and stomatal conductance (g_s) decreased with increasing supplies of K. However, a sensitivity analysis indicated that A was most sensitive to the maximum carboxylation rate of Rubisco (V_c,max) and the maximum rate of electron transport (J_max). These results indicate that the photosynthetic rate is primarily limited by the biochemical processes of photosynthesis (V_c,max and J_max), rather than by g_m and g_s in K-deficient plants. Additionally, g_m was closely correlated with g_s and the leaf dry mass per unit area (M_A) in hickory seedlings, which indicates that decreased g_m and g_s may be a consequence of leaf anatomical adaptation.

Although brassinosteroids (BRs) play crucial roles in plant development and stress tolerance, the mechanisms by which they have these effects are poorly understood. Here, we investigated the possible mechanism of exogenously applied BRs on reactive oxygen species (ROS), antioxidant defence and methylglyoxal (MG) detoxification systems in Ficus concinna seedlings grown under high-temperature (HT) stress for 48 h. Our results showed that the activities of ascorbate peroxidase (APX), superoxide dismutase (SOD), glutathione S-transferase (GST), glutathione peroxidase (GPX) and glyoxalase II (Gly II) were increased under two levels of HT stress. Compared with control the activities of catalase (CAT) and dehydroascorbate reductase (DHAR) were not changed due to HT stress. The activities of glutathione reductase (GR), monodehydroascorbate reductase (MDHAR) and glyoxalase I (Gly I) were increased only at moderate HT stress. Despite these protective mechanisms, HT stress induced oxidative stress in F. concinna seedlings, as indicated by the increased levels of ROS, malondialdehyde (MDA) and MG, and the reductions in chlorophyll levels and relative water content. The contents of reduced glutathione (GSH) and ascorbate (AsA) were not changed under moderate HT stress. Spraying with 24-epibrassinolide (EBR) alone had little influence on the non-enzymatic antioxidants and the activities of antioxidant enzymes. However, EBR pretreatment under HT stress resulted in an increase in GSH and AsA content, maintenance of high redox state of GSH and AsA, and enhanced ROS and MG detoxification by further elevating the activities of SOD, GST, GPX, APX, MDHAR, GR, DHAR, Gly I and Gly II, as evident by lower level of ROS, MDA and MG. It may be concluded that EBR could alleviate the HT-induced oxidative stress by increasing the enzymatic and non-enzymatic antioxidant defence, and glyoxalase systems in F. concinna seedlings.

Volatile terpenoids (VTs) are key secondary metabolites that play dual roles as endogenous antioxidants and airborne signals in plants under abiotic stress. Their biosynthesis is orchestrated via the mevalonate (MVA) and 2-C-methyl-D-erythritol 4-phosphate (MEP) pathways, with metabolic plasticity regulated by transcription factors, phytohormonal crosstalk, and stress-responsive elements. Recent advances have revealed that VTs such as isoprene, monoterpenes, and sesquiterpenes help mitigate oxidative stress by scavenging reactive oxygen species (ROS) and modulating antioxidant enzyme systems. However, regulatory mechanisms of stress-induced VT emissions remain fragmented and species-dependent. This review synthesizes current knowledge of VT biosynthesis and emission under abiotic stress, highlights their antioxidant functions and regulatory architecture, and underscores their protective roles in redox homeostasis and stress signal transduction. By identifying key metabolic nodes (e.g., TPS, DXS and MYC2) and stress-responsive pathways, we propose potential molecular targets for the development of stress-resilient cultivars. The integration of VT-based traits into breeding strategies and production-oriented metabolic engineering offers promising avenues for improving crop performance, reducing oxidative damage, and supporting sustainable agricultural systems.

Rhododendron × pulchrum, an important horticultural species, is widely distributed in Europe, Asia, and North America. To analyze the phylogenetic and organelle genome information of R. × pulchrum and its related species, the organelle genome of R. × pulchrum was sequenced and assembled. The complete mitochondrial genome showed lineage DNA molecules, which were 816,410 bp long and contained 64 genes, namely 24 transfer RNA (tRNA) genes, 3 ribosomal RNA (rRNA) genes, and 37 protein-coding genes. The chloroplast genome of R. × pulchrum was reassembled and re-annotated; the results were different from those of previous studies. There were 42 and 46 simple sequence repeats (SSR) identified from the mitochondrial and chloroplast genomes of R. × pulchrum, respectively. Five genes (nad1, nad2, nad4, nad7, and rps3) were potentially useful molecular markers. The R. × pulchrum mitochondrial genome collinear alignment among five species of the Ericaceae showed that the mitochondrial genomes of these related species have a high degree of homology with R. × pulchrum in this gene region, and the most conservative genes were trnC-GCA, trnD-GUC, trnM-CAU, trnN-GUU, trnY-GUA, atp4, nad4, nad2, nad5, ccmC, and rrn26. The phylogenetic trees of mitochondrial genome showed that R. simsii was a sister to R. × pulchrum. The results verified that there was gene rearrangement between R. × pulchrum and R. simsii mitochondrial genomes. The codon usage bias of 10 Ericaceae mitochondrial genes and 7 Rhododendron chloroplast genes were influenced by mutation, while other genes codon usages had undergone selection. The study identified 13 homologous fragments containing gene sequences between the chloroplast and mitochondrial genomes of R. × pulchrum. Overall, our results illustrate the organelle genome information could explain the phylogenetics of plants and could be used to develop molecular markers and genetic evolution. Our study will facilitate the study of population genetics and evolution in Rhododendron and other genera in Ericaceae.

Carya cathayensis, an important economic nut tree, is narrowly endemic to eastern China in the wild. The complete cp genome of C. cathayensis was sequenced with NGS using an Illumina HiSeq2500, analyzed, and compared to its closely related species. The cp genome is 160,825 bp in length with an overall GC content of 36.13%, presenting a quadripartite structure comprising a large single copy (LSC; 90,115 bp), a small single copy (SSC; 18,760 bp), and a pair of inverted repeats (IRs; 25,975 bp). The genome contains 129 genes, including 84 protein-coding genes, 37 tRNA genes, and 8 rRNA genes. A total of 252 simple sequence repeats (SSRs) and 55 long repeats were identified. Gene selective pressure analysis showed that seven genes (rps15, rpoA, rpoB, petD, ccsA, atpI, and ycf1-2) were possibly under positive selection compared with the other Juglandaceae species. Phylogenetic relationships of 46 species inferred that Juglandaceae is monophyletic, and that C. cathayensis is sister to Carya kweichowensis and Carya illinoinensis. The genome comparison revealed that there is a wide variability of the junction sites, and there is higher divergence in the noncoding regions than in coding regions. These results suggest a great potential in phylogenetic research. The newly characterized cp genome of C. cathayensis provides valuable information for further studies of this economically important species.