Low Night Temperature Affects the Phloem Ultrastructure of Lateral Branches and Raffinose Family Oligosaccharide (RFO) Accumulation in RFO-Transporting Plant Melon (Cucumismelo L.) during Fruit Expansion

Abstract

Due to the importance and complexity of photo assimilate transport in raffinose family oligosaccharide (RFO)-transporting plants such as melon, it is important to study the features of the transport structure (phloem) particularly of the lateral branches connecting the source leaves and the sink fruits, and its responses to environmental challenges. Currently, it is unclear to what extents the cold environmental temperature stress would alter the phloem ultrastructure and RFO accumulation in RFO-transporting plants. In this study, we firstly utilized electron microscopy to investigate the changes in the phloem ultrastructure of lateral branches and RFO accumulation in melons after being subjected to low night temperatures (12°C and 9°C). The results demonstrated that exposure to 9°C and 12°C altered the ultrastructure of the phloem, with the effect of 9°C being more obvious. The most obvious change was the appearance of plasma membrane invaginations in 99% companion cells and intermediary cells. In addition, phloem parenchyma cells contained chloroplasts with increased amounts of starch grains, sparse cytoplasm and reduced numbers of mitochondria. In the intermediary cells, the volume of cytoplasm was reduced by 50%, and the central vacuole was present. Moreover, the treatment at 9°C during the night led to RFO accumulation in the vascular bundles of the lateral branches and fruit carpopodiums. These ultrastructural changes of the transport structure (phloem) following the treatment at 9°C represented adaptive responses of melons to low temperature stresses. Future studies are required to examine whether these responses may affect phloem transport.

Combined analysis of mRNA and miRNA identifies dehydration and salinity responsive key molecular players in citrus roots

“…As expected, one TPS gene, here, was up-regulated by both dehydration and salt. Raffinose family oligosaccharides (RFO) including raffinose, stachyose, and verbascose significantly accumulate in leaves of plants experiencing environmental stress such as cold, drought or high salinity 53 54 55 56 . GolS (galactinol synthase) and StS (Stachyose synthase) are two important enzymes in RFO pathway.…”

“…In this study, two GolS members and two StS members were positively responded to dehydration or/and salt. In Arabidopsis, over-expressing GolS lead to accumulating high levels of galactinol and raffinose and more tolerant to drought and salinity stress 54 56 . However, upon StS gene, no data, to date, is available, which remains to be elucidated.…”

Phosphoproteomic analysis of lettuce (Lactuca sativa L.) reveals starch and sucrose metabolism functions during bolting induced by high temperature

“…The contents of sugar components and starch in lettuce were measured with proper modification [14,15].…”

Exogenous Calcium Alleviates Nocturnal Chilling-Induced Feedback Inhibition of Photosynthesis by Improving Sink Demand in Peanut (Arachis hypogaea)

“…Specifically, chilling stress reduces leaf expansion rates and leaf area in sorghum (Sorghum bicolor), maize, and sunflower (Helianthus annuus; Tardieu et al, 1999). LNT stress can also reduce leaf growth, the concentration of photosynthetic pigments and shoot and root dry matter accumulation in tomato (Latef and He, 2011), melon (Hao et al, 2016), and peanut (Song et al, 2020). We demonstrated that even a short-term (11 HoL) overnight chilling stress significantly increased soluble sugar, starch, and total nonstructural carbohydrate concentrations in leaves (Figures 2A-C).…”