采后果实敏化反应的细胞机制及其对果实蔗糖代谢和苯丙烷类代谢调控作用的研究

Recently, induced resistance by biological, physical or chemical elicitors has become one of the most effective strategies to inhibit postharvest disease in harvested fruits. Nevertheless, the disease resistance can urge the normal metabolism of material and energy turning to stress response, resulting in the quality decline in harvested fruits. The Priming action induced by various elicitors can cause plants into defense preparation state, and the Priming-induced plants exhibit the activated disease resistance only when the plants are infected by pathogens, which therefore consumes less material and energy in plants. However, the specific cellular mechanism and regulation mechanism of metabolism of sucrose and phenylpropnaoid involved in Priming action in harvested fruit are largely unknown. With the typical climacteric fruit peaches and apples and non-climacteric fruit grapes and strawberries as test material, the effects of Priming action in harvested fruit induced by Priming-elicitors such as MeJA, riboflavin and BABA on metabolism of fruit sucrose and phenylpropnaoid are treated as core contents in the present study. Starting with the analysis of cellular mechanism of Priming action in harvested fruit, the present study is to interpret the relation between Priming action and metabolism of fruit sucrose and phenylpropnaoid and to determine the effect of induced disease resistance on fruit quality and antioxidant activity, which lay the foundation for improving fresh-keeping technique in postharvest storage and distribution.

现阶段采用生物、物理或化学等激发子来诱导果实抗病性正成为抑制采后果实病害发生的有效策略。但抗病反应可使果实物质和能量代谢转向于逆境响应，易导致果实品质下降。激发子诱导的敏化反应（Priming）可使植物进入防御准备状态，仅在植物受到病原菌侵染时才表现出己被激活的抗性，因此物质与能量消耗较少。但目前采后果实Priming反应确切的细胞机制及其对果实物质代谢的调控作用仍不清楚。本项目拟以采后跃变型果实水蜜桃和苹果以及非跃变型果实葡萄和草莓果实为试材，以Priming激发子（MeJA、核黄素和BABA）诱导的采后果实Priming反应对果实蔗糖代谢和苯丙烷类代谢的影响为核心研究内容，从解析采后果实Priming 反应细胞机制入手，进而从分子水平阐明采后果实Priming反应与蔗糖代谢和苯丙烷类代谢之间的关联机制并明确诱导抗病对采后果实品质和抗氧化活性的影响，为完善果实贮运保鲜技术提供理论支撑。

激发子诱导的采后果实抗病性可分为直接诱导和Priming方式，但目前采后果实 Priming反应确切的细胞机制及其对果实物质代谢的调控作用仍不清楚。本项目从解析采后果实Priming 反应细胞机制入手，进而从分子水平阐明采后果实 Priming反应与蔗糖代谢和苯丙烷类代谢之间的关联机制并明确诱导抗病对采后果实品质和抗氧化活性的影响，为完善果实贮运保鲜技术提供理论支撑。首先，我们明确了低浓度的激发子处理（如0.1 mmol/L BTH、10 μmol/L MeJA和10 mmol/L BABA、1 mmol/L 核黄素）处理可显著诱导采后果实水蜜桃、杨梅、葡萄和苹果的Priming反应，而高浓度的激发子处理（如1-10 mmol/L BTH、100-500 μmol/L MeJA）则诱导果实直接抗病反应。在此基础上，我们培养了葡萄悬浮细胞来特征性研究相关抗性机理。结果显示，低浓度的激发子（BTH和MeJA）处理并不直接激活葡萄细胞防卫反应；但细胞受到病原模拟激发子（隐地蛋白）刺激后，细胞中PR基因表达、抗病相关酶活性和植保素合成量明显提高，从而赋予细胞强烈的抗病性。同时，高浓度激发子处理也可直接诱导葡萄细胞中VvNPR1和PRs基因（包括PR1）的表达，暗示细胞直接诱导抗性是一种典型的SAR反应模式。此外，我们同样发现，高浓度BTH诱导的桃果实直接诱导作用（SAR抗性）虽提高了果实抗病性，但同时也降低了桃果实乙烯合成相关酶（ACS和ACO）的活性从而抑制乙烯合成并减慢果实后熟进程；高浓度BTH或MeJA处理也可降低葡萄细胞中苯丙烷类代谢相关酶（PAL、C4H、4-CL和CHS）和蔗糖合成相关酶活性（SS-合成方向、SPS和SPP）活性，抑制培养期间葡萄细胞中花色苷和可溶性糖的积累以及重量的增加；高浓度BTH和硼处理则降低了葡萄和杨梅中蔗糖合成相关酶活性，却提高了SS-分解方向活性，使苯丙烷类代谢途径中的中间体——UDPG大量积累，从而为植保素的合成提供底物。相反，低浓度BABA、MeJA、BTH和核黄素诱导的水蜜桃、杨梅、葡萄和苹果果实Priming反应不仅增强了果实抗病性，同时也促进了葡萄和杨梅果实中可溶性糖和花色苷的积累，维持了水蜜桃和苹果果实的后熟效应。因此，上述研究结果明确了Priming 反应是一种可有效平衡果实防卫反应和物质消耗的诱导抗性机制。