Enhancement in photosynthesis characteristics and phytohormones of flowering Chinese cabbage (Brassica campestris L. var. utilis Tsen et Lee) by exogenous alginate oligosaccharides

Alginate oligosaccharides (AOS), a kind of marine oligosaccharides, involve in regulating in seed germination, seedling growth and response to stress. However, the growth promotion mechanism of AOS on plant remains unclear. Water cultivation experiments were conducted to study the effects of AOS on photosynthesis characteristics and phytohormones accumulation of flowering Chinese cabbage (Brassica campestris L. var. utilis Tsen et Lee). The results showed that the net photosynthetic rate (Pn), water use efficiency (WUE), CO2 carboxylation efficiency (CE) and light saturation point (LSP) of functional leaves were raised by AOS, whereas light compensation point (LCP) was reduced. AOS increased the accumulation of sucrose and starch by inducing the activity of sucrose synthase (SS) and sucrose phosphate synthase (SPS), resulting in an increase in the yield. AOS enhanced the biosynthesis and transport of gibberellic acid (GA(3)), and the transport of indolacetic-3-acid (IAA) to the root and trans-zeatin riboside (ZR) to the shoot, whereas did not affect abscisic acid (ABA), leading to the increase in concentration ratio of ZR/ABA, ZR/GA(3), ZR/IAA and GA(3)/IAA in leaves. These results identified that improvement in the yield and quality of Chinese cabbage of application AOS was through modification of phytohormonal metabolism and photosynthetic physiology of plant.