Chao Wen

Neoagaro-oligosaccharides (NAOS) are degraded seaweed polysaccharides of low molecular weight and high water solubility. Currently, little information is available on the utility of NAOS for seed germination. Here, we investigated seed germination of garden cosmos under NAOS concentrations of 0, 0.01, 0.1, 1, 5, and 10 g/L and monitored the role of 1 g/L NAOS in physiology of germinating seeds and recovery from plant growth inhibitor stress. The results showed that 1 g/L NAOS maximized germination potential of seeds and hypocotyl length, along with increasing α-amylase and β-amylase activities and soluble starch and soluble sugar contents of seedlings. Radicle length and hypocotyl fresh weight showed progressive decrease with the increase in NAOS concentration. The optimal dose of NAOS (1 g/L) decreased abscisic acid level but increased the levels of auxins, gibberellins and strigolactones in germinating seeds. Addition of 1 g/L NAOS to germination medium alleviated the impact of different growth retardants on seed germination and seedling growth, particularly radicle dry weight. This study shows that exogenous NAOS can improve seed germination and alleviate the stress induced by growth retardants on garden cosmos.

Rose is among the most important cut flower crops worldwide. The vase life is an important indicator of cut rose quality. The composition of the vase solution directly affects vase life. Neoagaro-oligosaccharides (NAOS) are degraded seaweed-derived polysaccharides that constitute a group of compounds with small molecular weight and good water solubility. Oligosaccharide treatment can extend the postharvest longevity of certain types of cut flowers; however, little information is available on the utility of NAOS for preservation of cut rose flowers. To explore the effects of NAOS on the longevity and quality of cut flowers of rose ‘Gaoyuanhong’, 100 mg·L ⁻¹ NAOS alone and in combination with 10 g·L ⁻¹ sucrose were incorporated in the vase solution. Distilled water was used as the control. Physiological indicators, comprising maximum flower diameter, fresh weight, water balance, vase life, bacteria number in the vase solution, and hormone contents of the outer petals, were determined in fresh cut flowers and analyzed. Compared with the control, 100 mg·L ⁻¹ NAOS treatment increased the maximum flower diameter (mean 8.21 cm), induced the maximum rates of change in flower diameter and cut flower fresh weight, maintained the best water balance, significantly extended the vase life to 16 days, and reduced the number of bacteria in the vase solution. The abscisic acid content of the outer petals in the control and 100 mg·L ⁻¹ NAOS treatments were significantly lower than that of the other treatments on day 9. The results showed that NAOS is useful to improve the postharvest quality and extend the vase life of cut rose flowers, and might contribute to the development of novel alternative preservatives for the cut rose industry.

Chrysanthemum (Dendranthema grandiflorum cv. Jinba) shoot branching is determined by bud outgrowth during the vegetative growth stage. The degree of axillary bud outgrowth is highly influenced by environmental conditions, such as nutrient availability. Here, we demonstrated that phosphorus (Pi) starvation significantly reduces axillary bud outgrowth in chrysanthemum. A strigolactone (SL) biosynthesis gene, DgCCD7, was isolated and characterized as an ortholog of MAX3/DAD3/RMS5/D17. By using ultra-performance liquid chromatography coupled with mass spectrometry (UPLC-MS), three putative SLs were identified and detected strong induction under Pi starvation conditions. Determinations of the distribution of SLs and negative regulation of DgCCD7/8 time-course in root indicated systemic response of SL. However, temporal expression patterns of biosynthesis and signaling genes in nodes revealed that Pi starvation causes a local response of SL pathway. Application of modified node segments treated with or without auxin and Pi revealed that in the absence of exogenous auxin, Pi delay axillary buds outgrowth and up-regulating local SL pathway genes. These data indicate that an auxin-SL regulatory loop respond to Pi starvation for delaying bud outgrowth locally, root biosynthesized SLs are transported acropetally and function in shoot branching inhibition under Pi starvation. We propose that SLs contribute to chrysanthemum shoot branching control in response to Pi-limiting conditions in a systemic way.