Wu Yun, Xia Yi-Ping, Zhang Jia-Ping, Du Fang, Zhang Lin, Ma Yi-di, Zhou Hong
Department of Horticulture, College of Agriculture and Biotechnology, Zhejiang University, Hangzhou 310058, China.
College of Horticulture, Shanxi Agricultural University, Taigu 030800, China.
J Zhejiang Univ Sci B. 2016;17(11):892-904. doi: 10.1631/jzus.B1600231.
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 Lilium 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 pyrophosphorylase, 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.
小鳞茎发育是全球百合种球生产中的一个问题，而碳水化合物代谢是一个关键因素。微繁作为一种高效的繁殖替代方法，能够实现更快的繁殖速度，并能提供可控条件来研究种球生长。本研究旨在探讨腐殖酸（HA）对东方百合‘索邦’离体条件下小鳞茎膨大及碳水化合物代谢途径的影响。HA在0.2、2.0和20.0 mg/L时极大地促进了小鳞茎生长，在移栽后45天内，较高HA浓度（≥2.0 mg/L）下小鳞茎蔗糖、总可溶性糖和淀粉含量显著增加。施用HA后，尤其是低浓度HA（LHA），三种主要淀粉合成酶（包括腺苷二磷酸葡萄糖焦磷酸化酶、颗粒结合淀粉合成酶和可溶性淀粉合成酶）的活性显著增强，表明淀粉代谢反应迅速。然而，高剂量HA也导致地上部生物量过度积累并抑制根系生长。因此，通过观察到明显的淀粉降解，较早出现了碳饥饿现象。随着HA剂量增加，小鳞茎相对重量逐渐降低，从而打破了源库平衡。0.2 mg/L的低HA浓度在根系和小鳞茎生长方面表现最佳。根数量和根长度分别在14.5和5.75 cm时达到峰值。新鲜小鳞茎重量和直径分别达到468 mg（是对照处理的2.9倍）和11.68 mm。此外，蔗糖/淀粉利用和转化加快，碳饥饿延迟，小鳞茎平均相对重量为80.09%。据我们所知，这是首次在球根作物离体和体内条件下对HA在淀粉代谢方面的应用及机制研究。
