弱光逆境下两种园林植物叶黄素循环及其关键酶的调控机制

Shade tolerance of a given plant is defined as the minimum light under which a plant can survive, which is an important composite traits of a plant. Recent years have seen an increased interest in research on shade tolerance. However, the exact mechanisms of shade tolerance are poorly understood. The value of chl a/b has once been used widely as an indicator for plant shade tolerance, while some investigators suggested that the ratio of lutein to xanthophyll cycle pool was strongly correlated to an index of shade tolerance. In this study, a shade-tolerant landscape plant (Aucuba japonica var. Variegata) and a heliophilous species (Photinia×fraseri) were selected to investigate changes in the composition of pigments in thylakoid membrane, and alteration in the activity of key enzymes involved in xanthophyll cycle in response to low light treatment. And the expression and distribution of these enzymes were examined. Moreover, the mechanisms of the regulation of violaxanthin de-epoxidase were explored. The aim of this study was to disclose the mechanisms of shade tolerance and select more appropriate indicators for shade tolerance. Understanding of the basics of shade tolerance is critical for shade-tolerant landscape plants selection, and it may provide scientific basis for rational allocation of shade-tolerant plants.

植物耐荫性指植物在弱光照条件下的生活能力，它是植物的一种重要的复合性状。近年来有关植物耐荫性的研究受到广泛关注，但其具体机制尚不明确。以往的研究常以叶绿素a/b作为植物耐荫性的指标。但有学者认为黄体素/叶黄素库与植物耐荫性更为相关。本研究选择1种耐荫植物洒金桃叶珊瑚（Aucuba japonica var. Variegata）和1种喜光植物红叶石楠（Photinia×fraseri），研究不同遮光处理对类囊体色素组成、叶黄素循环关键酶活性及酶蛋白表达和分布的影响，以及弱光胁迫下紫黄质脱环氧化酶活性调节机制。通过本项目的研究揭示园林植物的耐荫机理，寻找更为科学的表征植物耐荫性的指示指标，以期为耐荫园林植物的选择和园林植物复层种植耐荫植物的合理配置提供科学依据。

植物耐荫性是植物的一种重要的复合性状，但植物耐荫的具体机制尚不清楚。本研究中，我们选择了耐荫植物洒金桃叶珊瑚（Aucuba japonica var. Variegata）和喜光植物红叶石楠（Photinia×fraseri）作为研究对象探索叶黄素循环与植物耐荫性的关系。通过研究发现，遮荫处理导致紫黄质含量上升，玉米黄质含量下降。同时叶黄素库（V+A+Z）在遮荫处理后均变小，且洒金桃叶珊瑚的叶黄素库小于红叶石楠。遮荫处理后洒金桃叶珊瑚和红叶石楠的VDE活性下降，尤以重度遮荫（20%透光率）降低最为明显。在相同光照条件下，洒金桃叶珊瑚的VDE活性低于红叶石楠。VDE活性变化与抗坏血酸（Vc）含量变化相一致，二者间存在显著正相关。推测抗坏血酸可能是VDE活性的重要调节物质。随着光照强度的增加，洒金桃叶珊瑚和红叶石楠叶片的ΦPSII、Fv / Fm、Fv'/Fm'和qP下降，而NPQ和（1-qP）/ NPQ升高。VDE活性与NPQ及（1-qP）/ NPQ等表征叶黄素循环热耗散能力的指标变化趋势相同。此外，我们对洒金桃叶珊瑚花斑叶片的研究发现，其花斑叶是一种“色素型”花斑叶。这种花斑叶影响洒金桃叶珊瑚的光能利用效率，导致叶片黄色部分具有较高的ΦPSII和较低的NPQ，使得其比叶片绿色部分对光损伤更为敏感。同时，叶片黄色部分的净光合速率和暗呼吸速率更低。本研究结果对揭示园林植物的耐荫机理，合理选择耐荫园林植物具有重要科学意义。