Chunqing Zhang

Seeds with high vigor have strong resistance to various adverse environmental conditions. However, little is known about how seed vigor affects the resistance of seeds to biotic stress. In this study, newly harvested seeds that had high vigor and seeds with low vigor, achieved via an artificially accelerated aging treatment, were used in the germination test after inoculation with Fusariumgraminearum for 24 h. The results showed that high-vigor seed-related germination and seedling growth were not significantly affected by F. graminearum infection, while those related to low-vigor seeds were significantly inhibited. Analysis of transgenic maize seeds expressing the luminescent Ca²⁺ probe encoded by aequorin indicated that the concentration of free Ca²⁺ in the cytoplasm and nucleus of the embryo cells of high-vigor seeds was significantly higher than that of the low-vigor seeds. Through an experiment with Ca²⁺ inhibitor treatment and exogenous Ca²⁺ application, we further confirmed that Ca²⁺ played an important role in seed germination and seedling growth. Interestingly, in the presence of F. graminearum, the Ca²⁺ required for seed germination and seedling growth mainly came from the vacuolar calcium pool, while in the absence of F. graminearum, the required Ca²⁺ mainly came from the apoplastic calcium store. This study helps understand how high-vigor seeds resist disease and provides theoretical support for the wide application of high-vigor seeds in agricultural production.

Low-temperature stress delays seed germination in maize. Different maize inbred lines display various low-temperature resistance, but the dynamic changes in seed germination under low-temperature stress in maize remain unknown, especially at the transcriptome level. In this study, low-temperature-resistant maize (RM) inbred line 04Qun0522-1-1 had a significantly faster germination speed than low-temperature-sensitive maize (SM) line B283-1 under low-temperature stress. Moreover, the total antioxidant capacity, superoxide dismutase, and peroxidase activities were notably higher in the RM line than in the SM line from 3 to 6 d. In contrast, the SM line showed significantly higher malondialdehyde (MDA) content than the RM line at 6 d. Gene ontology (GO) enrichment analysis showed that in 2dvs0d, both SM and RM lines displayed the downregulation of ribosome-related genes. Moreover, photosystem II and heat shock protein binding-related genes were also downregulated in the SM line. In 4dvs2d, the RM line showed a higher degree of upregulation of the ribosome and peroxidase (POD)-related genes than the SM line. In 6dvs4d, POD-related genes were continuously upregulated in both SM and RM lines, but the degree of upregulation of the genes was higher in the SM line than in the RM line. Moreover, vitamin B6-related genes were specifically upregulated in the RM line. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that in 6dvs4d, phenylpropanoid biosynthesis was the most significantly enriched pathway in both SM and RM lines. Moreover, phenylpropanoid biosynthesis was also enriched in the RM line in 4dvs2d. More than half of the differentially expressed genes (DEGs) in phenylpropanoid biosynthesis were peroxidase, and the DEGs were similar to the GO enrichment analysis. The results provide new insights into maize seed germination in response to low-temperature stress.

Water uptake facilitates the initiation of seed germination. It is presumed that aquaporin (AQP)-mediated water inflow contributes to seed germination, but the genetic evidence is still lacking. This study aimed at genome-wide identification of ZmAQPs and further determined the physiological functions. Following a comprehensive search, a total of 41 ZmAQPs were identified according to the latest genome database. Through bioinformatic approaches, the physicochemical characteristics, phylogenetic relationships, and structural features of ZmAQPs were analyzed. The gene expression analysis of 20 high-resolution and multi-tissues samples showed that ZmAQPs had distinct spatiotemporal and tissue-specific expression profiles during seed germination and early seedling development. We then focused on the aquaporin of maize tonoplast intrinsic protein 3 (ZmTIP3), which is specifically expressed in germinating seed. A mutant zmtip3-1 with disruption of the ZmTIP3-1 gene showed shorter shoot and root length, and decreased seedling dry weight compared with the control (W22). The result revealed that ZmTIP3-1 improved the absolute content of seed protein and promoted storage reserves mobilization, suggesting that ZmTIP3 may be a positive regulator of seed vigor. This work provides valuable clues for understanding the function and possible regulatory mechanism of ZmAQPs in seed germination and seedling growth.

On-farm seed priming, which refers to soaking seeds in water, is a pre-sowing seed enhancement technique in agriculture production. This study aimed to investigate the effects of on-farm priming on the germination performance of maize seeds with different vigour levels. Two maize hybrids and four inbred lines were used as experimental materials. Soaking treatment significantly decreased the final germination percentage of low-vigour seeds and had no beneficial effects on high-vigour seeds. With longer soaking times, the reduction in germination increased and there was a positive, negative or neutral effect of water soaking on the germination index. The responses of seeds to on-farm priming varied among the different hybrid / inbred lines used and depending on the length of the treatment. Reducing imbibition damage by PEG soaking had little impact on the poor germination induced by soaking in water. Removal of the seed pericarp alleviated the negative effects of soaking on germination. This study has demonstrated, for the first time, the differential effects of water soaking on maize seeds with different vigour levels. Our results suggested that all influencing factors, such as such as seed initial physiological quality and the technological process, need to be considered to realize the full potential of priming.

Glyphosate (GP)-based herbicides have been widely applied to crops for weed control and pre-harvest desiccation. The objective of this research was to evaluate the effects of pre-harvest GP application on maize or how it physiologically alters this crop. Here, we applied four GP treatment (Control, GP150, GP200, and GP250) on maize lines of Z58 and PH6WC belonging to different maturity groups at grain-filling stages form DAP30 to DAP45. GP application significantly decreased the grain moisture content at harvest by 22–35% for Z58 and by 15–41% for PH6WC. However, the responses of grain weight to glyphosate vary with inbred lines and application time. A high concentration of glyphosate (GP250) reduced the grain weight of Z58 and low concentrations (GP150 and GP200) did not affect, while the grain weight of PH6WC significantly decreased under glyphosate treatment. In summary, our results revealed that timely and appropriate GP application lowers grain moisture content without causing seed yield and quality loss. GP application adversely affected photosynthesis by promoting maturation and leaf senescence. Meanwhile, it also enhanced non-structural carbohydrate (soluble sugars and starch) remobilization from the vegetative organs to the grains. Hence, GP treatment coordinates plant senescence and assimilate remobilization. RNA sequencing revealed that glyphosate regulated the transcript levels of sugar signaling-related genes and induced assimilate repartitioning in grains. This work indicates the practical significance of GP application for maize seed production and harvest, which highlights the contributions of source-sink communication to maize yield in response to external stress or pre-harvest desiccant application.

Seed vigour is an important trait and is often used to evaluate seed quality. A rapid and accurate evaluation of seed vigour is very important for agricultural production. Ca²⁺ is an important secondary messenger in plants, responding to various biotic and abiotic stimuli by Ca²⁺ flux into cytoplasm. To the best of our knowledge, how-ever, no report has been published about seed vigour and Ca²⁺ influx. In this study, we used two hybrid maize (Zea mays L.) lines and their corresponding female parent lines as materials, and performed ageing and ‘ageing + priming’ treatments to obtain seeds with different vigour levels. After seeds were imbibed for 24 h, the intact seeds or embryos were used as materials for determining the Ca²⁺ influx rate using non-invasive micro-test technique (NMT). Results showed that, with the intact embryos as materials, the Ca²⁺ influx rate showed higher stability and higher values. Correlation analysis indicated that there was a significant, positive linear correlation between the shoot dry weight vigour index and Ca²⁺ flux rate into embryo. The results demonstrated that the Ca²⁺ influx rate can be used to evaluate the vigour levels of maize seeds.