Abstract: The shading experiment was conducted in the field in 2004–2005, using the maize cultivar ND108, to study the effects of shading at different stages on key enzymes involved in starch synthesis of maize, and provide theoretical evidence to improve yield and quality of summer maize. The field was shaded by shading nets which prevented 50% sunlight. The heights of the nets were raised with the growth of maize plant, and the distance between the nets and the top of maize plant remained about 2.5 m. Only the illumination condition was changed after shading, while the aeration condition and relative humidity were not changed. Other environmental factor changes were due to the change of illumination intensity. The treatments were designed at seedling to jointing, jointing to flowering, and flowering to maturity stages, with 24, 28, and 48 days shading respectively. The activities of SPS (sucrose-phosphate synthase), SS (sucrose synthase), SSS (soluble starch synthase), GBSS (granule-bound-starch synthase), ADPGPPase (adenosine diphosphorate glucose pyrphorylase), and UDPGPPase (uridine diphosphorate glucose pyrophorylase) were determined every 10 days after shading, and kernel yield was measured after maturity stage. The results showed that the biomass and kernel yield of ND108 decreased significantly after shading. Compared with the control (nature sunlight without shading), the biomass of ND108 decreased by 23.9%, 31.4%, and 38.9% from seedling to jointing, jointing to flowering, and flowering to maturity stages, respectively, while the kernel yield decreased by 24.6%, 35.6%, and 68.2%, respectively. Leaf SPS activity and kernel SS, GBSS, SSS, ADPGPPase, and UDPGPPase activities of maize decreased significantly after shading, and different shading phases had different effects with the sequence of flowering to maturity > joining to flowering > seedling to join-ing. The results suggested that the main causes of grain yield and starch content decreasing after shaded were the decreasing of both photosynthesis and starch synthesis key enzyme activities which caused the decreasing of the transportation and distribution of photosynthate from leaf to grain.

Key words: Summer maize(Zey mays L.), Shading, Starch, Starch synthesis enzymes