The physiological mechanisms of drought-stress response in Quercus acutissima were explored with the aim to develop potentially valuable drought-resistant species that are adapted to arid regions and barren mountains. Potting experiments of Q. acutissima that simulated drought-stress conditions, and morphological, physiological, photosynthetic, and ultrastructural changes were investigated at different stages of drought stress, including after rehydration and recovery. During drought stress and rewatering, the leaves exhibited yellowing and abscission, followed by the sprouting of new leaf buds. The relative water content (RWC) changed under the drought-rewatering treatment, with a decreasing and then increasing trend, while the relative electrical conductivity (REC) had a more gradual increasing and then decreasing trend. The activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), and the proline (Pro) and soluble sugar (SS) contents increased and then decreased. The change in soluble protein (SP) content showed an N-shaped trend of increasing, decreasing, and then increasing again. The malondialdehyde (MDA) content decreased and then slowly increased. From the drought to recovery phase of the experiment, the net photosynthesis (Pn), stomatal conductance (Gs), and transpiration rate (Tr) decreased gradually at first, and then the Pn increased significantly, while the Gs and Tr increased slowly. During this period, the internal CO₂ concentration (Ci) did not decrease significantly until the last stage of the drought treatment, and then it increased slowly thereafter. The open stomata count in the Q. acutissima leaves was reduced significantly as drought stress increased, but after rewatering, the stomata recovered rapidly, with their opening size increasing. The number of leaf epidermal trichomes gradually declined to a low count in response to drought stress, but it rapidly recovered and increased within a short period of time after rehydration. Q. acutissima was found to have a strong drought tolerance and recovery ability after exposure to drought stress, and it may be an effective pioneer species for reforestation in barren lands.

Background/Objectives: Chionanthus retusus Lindl. & Paxton is an ornamental tree species native to North China. Research on the mitochondrial genome can elucidate the evolution and biological characteristics of C. retusus and better protect this important species. Methods and Results: This work aimed to clarify the evolutionary and phylogenetic links by sequencing, assembling, annotating, and analyzing the entire mitochondrial genome of C. retusus. The single-loop structure that made up the mitochondrial genome had a total length of 657,640 bp and a GC content of 44.52%. In total, 37 unique protein-coding genes, 20 tRNA genes, and 3 rRNA genes were identified. Numerous repeat sequences and migrating fragments of chloroplast sequences were found. Using the mitochondrial protein-coding genes to construct evolutionary trees, it was found that the closest relative of C. retusus is C. rupicola (Lingelsh.) Kiew. Conclusions: This research represents the first comprehensive set of data on the mitochondrial genome of an ancient (>500 yr) C. retusus specimen. In addition to elucidating the biological characteristics of C. retusus. The findings contribute to the Oleaceae mitochondrial genome database and offer valuable insights for future studies in molecular breeding, evolutionary biology, and genetic diversity conservation.