GA3 Treatment Delays the Deterioration of 'Shixia' Longan during the On-Tree Preservation and Room-Temperature Storage and Up-Regulates Antioxidants

Gibberellic acids had been proven to improve the fruit quality and storability by delaying deterioration and maintaining the antioxidant system. In this study, the effect of GA₃ spraying at different concentrations (10, 20, and 50 mg L^-1) on the quality of on-tree preserved 'Shixia' longan was examined. Only 50 mg L^-1 GA₃ significantly delayed the decline of soluble solids (22.0% higher than the control) and resulted in higher total phenolics content (TPC), total flavonoid content (TFC), and phenylalanine ammonia-lyase activity in pulp at the later stages. The widely targeted metabolome analysis showed that the treatment reprogrammed secondary metabolites and up-regulated many tannins, phenolic acids, and lignans during the on-tree preservation. More importantly, the preharvest 50 mg L^-1 GA₃ spraying (at 85 and 95 days after flowering) led to significantly delayed pericarp browning and aril breakdown, as well as lower pericarp relative conductivity and mass loss at the later stages of room-temperature storage. The treatment also resulted in higher antioxidants in pulp (vitamin C, phenolics, and reduced glutathione) and pericarp (vitamin C, flavonoids, and phenolics). Therefore, preharvest 50 mg L^-1 GA₃ spraying is an effective method for maintaining the quality and up-regulating antioxidants of longan fruit during both on-tree preservation and room-temperature storage.

Method for fast staining and obtaining high-magnification and high-resolution cell images of Nicotiana benthamiana

As tools of plant molecular biology, fluorescence microscopy and Nicotiana benthamiana have been used frequently to study the structure and function of plant cells. However, it is difficult to obtain ideal micrographs; for example, the images are typically unclear, the inner cell structure cannot be observed under a high-power lens by fluorescence microscopy, etc. Here, we describe a method for observing the cell structure of N. benthamiana. This method significantly improves imaging by fluorescence microscopy and allows clear images to be obtained under a high-power lens. This method is easy to perform with good stability, and the stomatal structure, nucleus, nucleolus, chloroplast and other organelles in N. benthamiana cells as well as protein localizations and the locations of protein-protein interactions have been observed clearly. Furthermore, compared with traditional methods, fluorescent dye more efficiently dyes cells with this method. The applicability of this method was verified by performing confocal scanning laser microscopy (CSLM), and CSLM imaging was greatly improved. Thus, our results provided a method to visualize the subcellular structures of live cells in the leaves of N. benthamiana by greatly improving imaging under a fluorescence microscope and provided new insights and references for the study of cell structures and functions in other plants.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-00931-5.

Genome-wide identification and expression analysis of SWEET gene family in Litchi chinensis reveal the involvement of LcSWEET2a/3b in early seed development

BACKGROUND

SWEETs (Sugar Will Eventually be Exported transporters) function as sugar efflux transporters that perform diverse physiological functions, including phloem loading, nectar secretion, seed filling, and pathogen nutrition. The SWEET gene family has been identified and characterized in a number of plant species, but little is known about in Litchi chinensis, which is an important evergreen fruit crop.

RESULTS

In this study, 16 LcSWEET genes were identified and nominated according to its homologous genes in Arabidopsis and grapevine. Multiple sequence alignment showed that the 7 alpha-helical transmembrane domains (7-TMs) were basically conserved in LcSWEETs. The LcSWEETs were divided into four clades (Clade I to Clade IV) by phylogenetic tree analysis. A total of 8 predicted motifs were detected in the litchi LcSWEET genes. The 16 LcSWEET genes were unevenly distributed in 9 chromosomes and there was one pairs of segmental duplicated events by synteny analysis. The expression patterns of the 16 LcSWEET genes showed higher expression levels in reproductive organs. The temporal and spatial expression patterns of LcSWEET2a and LcSWEET3b indicated they play central roles during early seed development.

CONCLUSIONS

The litchi genome contained 16 SWEET genes, and most of the genes were expressed in different tissues. Gene expression suggested that LcSWEETs played important roles in the growth and development of litchi fruits. Genes that regulate early seed development were preliminarily identified. This work provides a comprehensive understanding of the SWEET gene family in litchi, laying a strong foundation for further functional studies of LcSWEET genes and improvement of litchi fruits.