Low humic acids promote in vitro lily bulblet enlargement by enhancing roots growth and carbohydrate metabolism

低浓度腐殖酸处理通过促进根系发育及碳水化合物代谢促进百合离体小鳞茎膨大（英文）

Bulblet development is a problem in global lily bulb production and carbohydrate metabolism is a crucial factor. Micropropagation acts as an efficient substitute for faster propagation and can provide a controllable condition to explore bulb growth. The present study was conducted to investigate the effects of humic acid （HA） on bulblet swelling and the carbohydrate metabolic pathway in Li/ium Oriental Hybrids ＇Sorbonne＇ under in vitro conditions. HA greatly promoted bulblet growth at 0.2, 2.0, and 20.0 mg/L, and pronounced increases in bulblet sucrose, total soluble sugar, and starch content were observed for higher HA concentrations （_〉2.0 mg/L） within 45 d after transplanting （DAT）. The activities of three major starch synthetic enzymes （including adenosine 5＇-diphosphate glucose pyro- phosphorylase, granule-bound starch synthase, and soluble starch synthase） were enhanced dramatically after HA application especially low concentration HA （LHA）, indicating a quick response of starch metabolism. However, higher doses of HA also caused excessive aboveground biomass accumulation and inhibited root growth. Accordingly, an earlier carbon starvation emerged by observing evident starch degradation. Relative bulblet weight gradually decreased with increased HA doses and thereby broke the balance between the source and sink. A low HA concentration at 0.2 mg/L performed best in both root and bulblet growth. The number of roots and root length peaked at 14.5 and 5.75 cm respectively. The fresh bulblet weight and diameter reached 468 mg （2.9 times that under the control treatment） and 11.68 mm, respectively. Further, sucrose/starch utilization and conversion were accelerated and carbon famine was delayed as a result with an average relative bulblet weight of 80.09%. To our knowledge, this is the first HA application and mechanism research into starch metabolism in both in vitro and in vivo condition in bulbous crops.

目的:小鳞茎发育问题研究是缩短百合育种周期、加快百合种球产业化生产的关键,而碳水化合物代谢则是影响小鳞茎发育的重要因子。离体快繁技术因更高效的繁殖速率及易控的环境条件,是鳞茎发育问题研究的替代途径,但目前有关离体条件下鳞茎发育机制研究鲜有报道。本文采用腐殖酸处理东方百合‘索邦’,研究其对于鳞茎膨大的影响及碳水化合物代谢调控路径。创新点:本研究首次采用安全无残留型植物生长调节物质腐殖酸处理,并探讨了其对百合离体鳞茎发育的有效影响及内在的碳水化合物代谢生理生化机制。方法:以构建的离体模式体系下形成的百合单芽,接种至含不同浓度腐殖酸(0、0.2、2.0和20.0 mg/L)的培养基上,每隔15天取样一次,测定株高等7个形态指标;同时,取鳞茎测定主要非结构性碳水化合物(蔗糖、可溶性糖、淀粉)含量及关键淀粉合成酶(AGPase、SSS和GBSS)活性。结论:随腐殖酸处理浓度升高,相对鳞茎重量下降,从而打破库–源平衡,低浓度腐殖酸(0.2 mg/L)处理效果最佳,鳞茎重量为468 mg(为对照的2.9倍),鳞茎直径达11.68 mm。具体来说,低浓度腐殖酸处理可促进根系发育,并在发育早期大幅促进淀粉合成相关酶活性,并通过加速蔗糖/淀粉利用及转换延缓了碳饥饿出现时间。