弱光胁迫影响夏玉米光合效率的生理机制初探

Physiological mechanism of shading stress on photosynthetic efficiency in summer maize (Zea mays)

大田条件下,以普通夏玉米(Zea mays)‘泰玉2号’为材料,于授粉后1–20天遮光55%(+S),以大田自然光照条件下生长的玉米作为对照(–S),研究了遮光及恢复过程中玉米植株的光合性能、叶绿体荧光参数、叶黄素循环以及光能分配的变化,初步揭示夏玉米开花后弱光条件下光适应的生理机制,为玉米高产稳产提供理论依据。结果表明,遮光后玉米穗位叶叶绿素含量及可溶性蛋白含量均减少,RuBP羧化酶和PEP羧化酶活性显著降低,导致穗位叶净光合速率(Pn)迅速下降,光饱和点也明显降低;恢复初期Pn迅速升高,光合关键酶活性有所增强。遮光后植株的最大光化学效率(Fv/Fm)、实际光化学效率(ФPSII)显著降低,非光化学淬灭(NPQ)则显著升高,而恢复初期植株穗位叶ФPSII有所升高,表明突然暴露在自然光下的光合电子传递速率明显加快,这与其光合速率及光合酶活性的趋势保持一致;遮光处理对穗位叶叶黄素循环库的大小(紫黄质+花药黄质+玉米黄质(V+A+Z))影响不显著,但使叶黄素循环的脱环氧化状态(A+Z)/(V+A+Z)增加;遮光后植株分配于光化学反应的光能明显减少,天线耗散光能比率显著增加,恢复过程中植株主要以过剩非光化学反应的形式耗散过剩的光能。遮光后及恢复初期,玉米植株的PSII原初光化学活性明显下降,限制了光合碳代谢的电子供应从而抑制了光合作用,主要依赖叶黄素循环途径进行能量耗散,而在光照转换后遮光的玉米叶片在适应自然光过程中的光保护机制不断完善,光合能力逐渐得到恢复。

Aims Our objective was to investigate the light-adaptive physiological mechanism of maize on shading stress after anthesis, in order to provide theory behind evidence for high and stable yield in summer maize. Methods In a field experiment, we used common corn （Zea mays） （TY2） to analyze changes of photosynthetic performance, chlorophyll fluorescence parameters, xanthin circle and light partition in maize in the process of shading and recovery stages under （a） shading 55% （＋S） 1–20 d after pollination and （b） natural illumination in field condition （–S）. Important findings The net photosynthetic rate and light saturation point of ear leaves declined rapidly, because the chlorophyll content, soluble protein content and PEPCase and RuBPCase activities in ear leaves markedly decreased after shading. Under shading, the maximal photochemical efficiency （Fv/Fm） and the actual photo-chemical efficiency （ФPSII） significantly declined, but non-photochemistry quenching （NPQ） increased. The ФPSII of ear leaves increased in early recovery, which indicated that the sudden exposure to natural light significantly enhanced the photosynthetic electron transport rate, according with its photosynthetic rate and carbon metabolism activity of maize ear leaves. After shading, the size of xanthin circle sink in ear leaves was not significantly dif-ferent, but the de-epoxidation state of xanthin circle （A ＋ Z）/（V ＋ A ＋ Z） increased after shading. The distribution of light energy in photochemical reaction was lower, but the antenna dissipation rate of light energy increased sig-nificantly. On the other hand, the dissipation of excess light energy in the recovery process mainly depended on non-photochemical reactions. The PSII primary photochemistry activity of maize decreased under after shading and recovery in early stage, which limited electron supply of photosynthetic carbon metabolism and re- strained the photosynthesis. Then the energy dissipation mostly relied on the xanthin circle increased. The light protective mechanism of maize leaves improved in adaptation to the natural light, and photosynthetic capability gradually recovered after illumination switch.