Cucumber cultivation suffers from severe yield and quality decline due to cold damage. Cucurbita ficifolia is used as a rootstock for grafting cucumber to improve resistance due to its excellent resistance. This study used Yunnan C. ficifolia as the rootstock and Jingyan Xiamei 2 cucumber as the scion, simulating common low-temperature stress of 15 °C, 10 °C, and 5 °C in an artificial climate chamber, to study the mechanism of cucumber-grafted seedlings responding to low temperatures in terms of growth and development, photosynthesis, osmotic regulation substances, antioxidant system, and gene expression. The results showed that the growth and development of grafted seedlings of C. ficifolia was less inhibited, the chlorophyll content was less reduced, and the content of osmoregulatory substances was significantly increased under low-temperature stress. The activity of antioxidant enzymes in grafted seedlings of C. ficifolia was significantly upregulated at low temperatures, and the expression of antioxidant enzyme genes was consistently higher in grafted seedlings of C. ficifolia. These results confirmed that C. ficifolia as a rootstock could improve the cold resistance of cucumber. Collectively, this study provides the basis for revealing the physiological and molecular mechanism of grafting seedlings to improve cucumber’s low temperature tolerance.

Chloroplast development and the chloroplast-to-chromoplast transition affect fruit development and quality. To further understand the effect of fruit coloration on fruit quality, tomato fruits with differentially colored shoulders were investigated at the microstructural, pigment, transcriptomic, and metabolic levels. Compared with fruits with a uniformly colored shoulder (US), chloroplast degradation was incomplete in green variegated shoulder I (VSI) fruits, and the number of plastoglobuli increased significantly in both VSI and yellow variegated shoulder II (VSII) fruits. Metabolite analysis showed that the contents of soluble solids, total organic acids, and vitamin C were significantly elevated in VSI fruits. In particular, sucrose accumulation in both VSI and VSII fruits increased to more than five times that of US fruits. Measurements of pigment contents in the fruit shoulder showed that both VSI and VSII fruits had significantly lower lycopene content than US fruits, whereas VSI fruits had higher chlorophyll content. Transcriptome analysis revealed that differentially expressed genes (DEGs) were significantly enriched in pathways related to sugar metabolism, carotenoid biosynthesis, lipid metabolism, and abiotic stress responses. In summary, the formation of variegated shoulders in tomato fruits was associated with defective chloroplast-to-chromoplast transition and altered pigment and metabolite accumulation.