Constant-frequency ultrasonic treatment helped to improve seed germination. However, variable-frequency ultrasonic treatment on maize seed germination were rarely reported. In this study, maize seeds were exposed to 20–40 kHz ultrasonic for 40 s. The germination percentage and radicle length of maize seeds increased by 10.4% and 230.5%. Ultrasonic treatment also significantly increased the acid protease, α-amylase, and β-amylase contents by 96.4%, 73.8%, and 49.1%, respectively. Transcriptome analysis showed that 11,475 differentially expressed genes (DEGs) were found in the ultrasonic treatment and control groups, including 5,695 upregulated and 5,780 downregulated. Metabolic pathways and transcription factors (TFs) were significantly enriched among DEGs after ultrasonic treatment. This included metabolism and genetic information processing, that is, ribosome, proteasome, and pyruvate metabolism, sesquiterpenoid, triterpenoid, and phenylpropanoid biosynthesis, and oxidative phosphorylation, as well as transcription factors in the NAC, MYB, bHLH, WRKY, AP2, bZIP, and ARF families. Variable-frequency ultrasonic treatment increased auxin, gibberellin, and salicylic acid by 5.5%, 37.3%, and 28.9%, respectively. Abscisic acid significantly decreased by 33.2%. The related DEGs were upregulated and downregulated to varying degrees. Seed germination under the abiotic stress conditions of salt stress (NaCl solution), drought (PEG solution), and waterlogging (water-saturated sand bed) under ultrasonic treatment were promoted, radicle length was significantly increased by 30.2%, 30.5%, and 27.3%, respectively; and germination percentage by 14.8%, 20.1%, and 21.6%, respectively. These findings provide new insight into the mechanisms through ultrasonic to promote maize seed germination.

Cellobiose is the primary product of cellulose hydrolysis and is expected to be served as pathogen/damage-associated molecular patterns (PAMPs/DAMPs) in evoking plant innate immunity. In the study, cellobiose was demonstrated to be a positive regulator in immune response, but devote to halt autoimmunity when lettuce was exposed to cellobiose higher than 60 mg·L ^–1. When infected by Botrytis cinerea, cellobiose endowed plants with enhanced pre-invasion resistance by activating high levels of β-1,3-glucanase and anti-oxidative enzyme activities at the initial stage of pathogenic infection. Meanwhile, cellobiose-activated core regulatory factors such as EDS1, PTI6, and WRKY70 as well as SA signaling played an indispensable role in modulating plant growth-defense tradeoffs. Transcriptomics data further suggested that the cellobiose-activated plant-pathogen pathways are involved in MAMPs / PAMPs-triggered immune responses (PTI). Genes encoding receptor-like kinases, redox homeostasis, phytohormone signal transduction, transcription factors, and pathogenesis-related proteins were also detected to be up- or down-regulated by cellobiose. Taken together, this study demonstrated that cellobiose serves as an elicitor can directly activate disease resistance-related cellular functions. Besides, multiple genes have been identified as potential modulators of the cellobiose-induced immune response, which could inform efforts to understand underlying molecular events.

Introduction: Salt stress in seed germination and early seedling growth is the greatest cause of crop loss in saline-alkali soils. Microbial seed coating is an effective way to promote plant growth and salt resistance, but these coatings suffer from poor seed adhesion and low survival rates under typical storage conditions.Methods: In this study, the marine bacterium Pontibacter actiniarum DSM 19842 from kelp was isolated and microencapsulated with calcium alginate using the emulsion and internal gelation method.Results: Compared to unencapsulated seeds, the spherical microcapsules demonstrated a bacterial encapsulation rate of 65.4% and survival rate increased by 22.4% at 25°C for 60 days. Under salt stress conditions, the seed germination percentage of microcapsule-embedded bacteria (M-Embed) was 90%, which was significantly increased by 17% compared to the germination percentage (73%) of no coating treatment (CK). Root growth was also significantly increased by coating with M-Embed. Chlorophyll, peroxidase, superoxide dismutase, catalase, proline, hydrogen peroxide and malondialdehyde levels indicated that the M-Embed had the best positive effects under salt stress conditions.Discussion: Therefore, embedding microorganisms in suitable capsule materials provides effective protection for the survival of the microorganism and this seed coating can alleviate salt stress in wheat. This process will benefit the development of sustainable agriculture in coastal regions with saline soils.

Super absorbent polymers (SAPs) have been applied as soil conditioners to reduce soil water loss, but there are few studies about how SAPs affect structures of soil bacterial community, and these associated chemical residues are uncertain. Treatments under different soil moisture conditions by application of sodium polyacrylate in repacked soil columns were used to investigate their effects on the soil bacterial community structures by Illumina MiSeq sequencing. Alpha diversity analysis showed that adding SAPs had an impact on bacterial diversity. On phylum level, adding SAPs significantly reduced the amount of Actinobacteria (1.9–2.4-fold), Bacteroidetes (1.1–2.1-fold) while increased the amount of Firmicutes (1.9–4.6-fold). At genus level, effects of SAPs on the soil bacterial community structures varied with the soil moisture conditions. Under water deficit, SAPs reduced the soil pH, which promoted the proliferation of Lactobacillus (9.9–29.1-fold), and acid production by these bacteria might further promote the reduction of pH, potentially inhibiting growth of Acidobacteria (1.3–1.8-fold) and Chloroflexi (1.6–2.3-fold). The pyrolysis analysis showed that some substances such as methanesulfonyl chloride, long-chain amides and esters, were only derived from water-saturated soil treated with SAPs, which might subsequently have negative impacts on the environment and associated agriculture.