Sugars and auxin have important effects on almost all phases of plant life cycle, which are so fundamental to plants and regulate similar processes. However, little is known about the effect of cross-talk between glucose and indole-3-acetic acid (IAA) on growth and development of apple trees. To examine the potential roles of glucose and IAA in root architecture, root nitrogen (N) metabolism and photosynthetic capacity in ‘Hanfu’ (Malus domestica), a total of five treatments was established: single application of glucose, IAA, and auxin polar transport inhibitor (2, 3, 5-triiodobenzoic acid, TIBA), combined application of glucose with TIBA and that of glucose with IAA. The combined application of glucose with IAA improved root topology system and endogenous IAA content by altering the mRNA levels of several genes involved in root growth, auxin transport and biosynthesis. Moreover, the increased N metabolism enzyme activities and levels of genes expression related to N in roots may suggest higher rates of transformation of nitrate (NO₃^--N) into amino acids application of glucose and IAA. Contrarily, single application of TIBA decreased the expression levels of auxin transport gene, hindered root growth and decreased endogenous IAA content. Glucose combined with TIBA application effectively attenuated TIBA-induced reductions in root topology structure, photosynthesis and N metabolism activity, and mRNA expression levels involved in auxin biosynthesis and transport. Taken together, glucose application probably changes the expression level of auxin synthesis and transport genes, and induce the allocation of endogenous IAA in root, and thus improves root architecture and N metabolism of root in soil with deficit carbon.

Freezing injury in winter is an important abiotic stress that seriously affects plant growth and development. Deciduous fruit trees resist freezing injury by inducing dormancy. However, different cultivars of the same species have different cold resistance strategies. Little is known about the molecular mechanism of apple trees in response to freezing injury during winter dormancy. Therefore, in this study, 1-year-old branches of the cold-resistant cultivar ‘Hanfu’ (HF) and the cold-sensitive cultivar ‘Changfuji No. 2’ (CF) were used to explore their cold resistance through physiological, biochemical, transcriptomics, and metabolomics analyses. Combining physiological and biochemical data, we found that HF had a stronger osmotic regulation ability and antioxidant enzyme activity than CF, as well as stronger cold resistance. The functional enrichment analysis showed that both cultivars were significantly enriched in pathways related to signal transduction, hormone regulation, and sugar metabolism under freezing stress. In addition, the differentially expressed genes (DEGs) encoding galactinol synthase, raffinose synthase, and stachyose synthetase in raffinose family oligosaccharides (RFOs) metabolic pathways were upregulated in HF, and raffinose and stachyose were accumulated, while their contents in CF were lower. HF accumulated 4-aminobutyric acid, spermidine, and ascorbic acid to scavenge reactive oxygen species (ROS). While the contents of oxidized glutathione, vitamin C, glutathione, and spermidine in CF decreased under freezing stress, consequently, the ability to scavenge ROS was low. Furthermore, the transcription factors apetala 2/ethylene responsive factor (AP2/ERF) and WRKY were strongly induced under freezing stress. In summary, the difference in key metabolic components of HF and CF under freezing stress is the major factor affecting their difference in cold resistance. The obtained results deepen our understanding of the cold resistance mechanism in apple trees in response to freezing injury during dormancy.

Most cherry orchards in China have low organic carbon content, though carbon is very important for plant growth. The changes in soil carbon and bacterial diversity were determined after different amounts of ¹²C-glucose were added to the rhizosphere of Cerasus sachalinensis. Soil bacteria diversity was measured using high throughput sequencing, and bacteria containing ¹³C-glucose were identified using DNA-SIP methods. The results demonstrated that soil microbial biomass carbon (MBC) content and the soil respiratory rate were increased at 3 and 7 days after adding glucose. The soil organic carbon (SOC) content was decreased on the 7th day in the treatment where the added glucose-C was equivalent to the MBC content. SOC content was decreased on the 15th day after adding glucose-C equivalent to five times that of the soil MBC. Compared to the controls, the relative abundance of taxa at the phylum level displayed no significant change in the treatments with glucose-C added as 10% and equal amount of soil MBC 3–30 days after treatment. However, the relative abundance of Proteobacteria increased significantly in the treatment with the addition of glucose-C equivalent to five times of soil MBC. The main changes were observed in the bacteria in several genera including A4, Flavisolibacter, Aquicella, and Candidatus Solibacter. DNA-SIP results indicated that the relative abundance of the Proteobacteria and Pseudomonas was the highest; these were the primary bacteria phylum and genus, respectively, from day 3 to day 15. In conclusion, the changing pattern demonstrated that with the addition of more glucose, the range of the bacterial communities changed more. Proteobacteria and Pseudomonas may be the bacteria promoting priming effect.