花粉直感效应促进山核桃果实增大的光合作用机理

Hickory (Carya cathayensis) seeds, has a high nutritional value, however, the market demand for its low yield has not been satisfied. It has been found that hickory has larger-size fruits/seeds with greener pericarp after pollinated with pollen from pecan (C. illionensis) than control (trees pollinated with hickory pollen). Previous studies have revealed that this phenomenon is not caused by genetic changes in terms of molecular markers and embryology, indicating this is the effect of metaxenia. We have found in the previous study that there is no change in the photosynthetic rate of hickory leaves, but a higher photosynthetic rate in the pericarp of hickory fruits after pollinated with pollen from pecan, which preliminarily indicates that pollen has some effects on an important photosynthetic source (the photosynthesis of pericarp) directly associated with fruit development. In order to elucidate the effect of metaxenia on the photosynthesis of pericarp and to explore the effect of photosynthesis of pericarp on fruit development, we intend to study in terms of molecular biology and physiology the dynamic changes in photosynthetic property of pericarp and clarify differences in the photosynthetic responses to photosynthetic regulators of pericarp during the fruit development of hickory when pollinated with pollen from both hickory itself and pecan. The results will be of important practical value for achieving a high yield with the use of metaxenia and improving economic benefits.

山核桃（Carya cathayensis）种仁营养价值高，但产量低，难以满足市场需求。授美国山核桃（C. illionensis）花粉的山核桃果实明显增大，前人已从分子标记和胚胎学层面证实授粉子代增大不是由于遗传物质的变化引起的，果实变异为花粉直感效应。申请者前期研究发现授美国山核桃花粉的山核桃叶片光合速率未发生变化，但其外果皮的光合能力明显提高，初步证明果实增大可能是由于父本花粉影响了与果实发育直接相关的另一个重要光合源，即外果皮的光合作用引起的。本项目拟从生理和分子生物学层面，研究授不同花粉（山核桃和美国山核桃花粉）的山核桃果实发育期内外果皮光合性能的变化，揭示花粉直感对山核桃外果皮光合特性的影响作用，明晰授不同花粉的外果皮对光合调节剂的光合响应差异，探讨花粉直感下山核桃外果皮光合作用对其果实发育的影响。研究成果对利用花粉直感效应实现山核桃增产、提高经济效益具有重要的实践价值。

基于授美国山核桃花粉（pp）的山核桃子代其遗传物质与母本之间无明显差异、且果实增大及外果皮光合作用显著增强的前期基础，本项目从生理和分子层面揭示不同花粉授粉对山核桃外果皮光合特性差异的影响机制，分析授不同花粉的山核桃外果皮对光合调节剂的光合响应差异，探讨花粉直感下山核桃外果皮光合作用对其果实发育的影响。结果表明：1)果实发育前期（授粉后50-73天）和后期（授粉后103-120天），pp授粉的山核桃果实表面积和干质量的日增量均显著高于山核桃花粉（hp）授粉的，且果实的干质量日均增量与其单果的光合速率日均增量之间呈显著相关；授粉后103-120天，hp授粉果实外果皮的Y(NO)显著增加，pp授粉果实外果皮的Y(NO)无明显变化，且pp授粉果实外果皮具有较高的Y（II）和较低的Y（NO）。2)在授粉后81天，无论强光(HL)处理与否，pp授粉的山核桃外果皮中的RuBPC酶活均显著高于hp授粉的；与hp授粉的山核桃相比，HL处理前后pp授粉的山核桃外果皮中的MDA、O2·-和H2O2含量较低，且具有较强的抗氧化酶（POD、SOD、CAT）、ASA-GSH系统及GR和DHAR活性。3)授粉后65天，在2种花粉授粉的山核桃外果皮中的1894个差异基因中筛选出66个与山核桃果皮光合相关的基因，主要富集在叶绿素合成通路及光合固碳途径中。4)山核桃CcHEMA1基因的相对表达量与外果皮叶绿素含量明显相关；蛋白进化树显示山核桃CcHEMA1与同为胡桃科的核桃CcHEMA1同源性最高，且亚细胞定位表明CcHEMA1定位于叶绿体中。5)整个果实发育时期内，pp授粉的山核桃外果皮中的Rubisco活性、叶绿素含量和氮含量均明显高于hp授粉的，且与其果皮的真实光合速率呈显著正相关；叶绿体超微结构显示，pp授粉的山核桃外果皮细胞(1-6层)的叶绿体数量明显多于hp授粉的；DCMU处理后不同授粉的山核桃整个果实、种仁干质量及其含油率明显减少，且pp授粉的山核桃果实的降低幅度明显大于hp授粉的。6)授粉后75天时，DCMU处理薄壳山核桃后，其果实大小、果仁干质量/鲜质量及含油率均明显降低。结果可望充分挖掘山核桃外果皮的光合增产潜力和优势，为探寻提高山核桃果实产量的可能技术措施提供了理论基础和技术指导，保障山核桃产业的可持续发展。