‘黄金梨’果顶“硬化症”发生与活性氧代谢的关系

Relationship Between 'Hard End' and Active Oxygen Metabolism in 'Whangkeumbae' Pear Fruit

近年来,‘黄金梨’果实的果顶呈现细胞硬化,俗称‘铁头’‘硬头’‘黄头’‘绿头’,为生理病害。发病果实果肉失去应有的酥脆、多汁的口感。该研究分析了连续多年生长期易发生果顶"硬化症"的树与从未发生果顶"硬化症"的正常树的叶片和果实水势变化的差异,比较了2种类型果实中木质素含量、活性氧清除酶(超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)、抗坏血酸过氧化物酶(APX))活性变化以及H_2O_2、丙二醛(MDA)含量等方面的差异。结果表明:与正常的‘黄金梨’树相比,易发病树的叶、果水势低,果实中的H_2O_2、MDA和木质素含量显著高于不发病树;易发病树的叶片水势与H_2O_2含量呈极显著负相关(r=-0.828 3,P<0.01),H_2O_2含量与MDA含量呈显著正相关(r=0.764 2,P<0.05);SOD活性显著低于不发病树;POD、CAT、APX的活性极显著高于不发病树。因此认为,发生果顶"硬化症"的树体或者结果部位可能由于存在一定程度的水分胁迫,导致了体内的活性氧产生与清除的动态平衡状态的变化,使H_2O_2、MDA过量生成和POD活性增加,从而促进了木质素的合成,这可能是导致近表皮薄壁细胞木质化的原因之一。

‘Whangkeumbae＇pear trees often bear fruits with ‘hard end＇cells in fruit top in recently years,commonly known as the‘iron head＇‘green head＇,which is a kind of physiological disorder.When the disorder happened,the flesh got ‘hard end＇and lost its crisp,juicy taste.Based on many years of investigation,the differences of water potential changes of leaves and fruits,the contents of H_2O_2,MDA,lignin and the activities of scavenger enzymes（SOD,POD,CAT,APX）were analyzed during the fruit development between the normal and abnormal trees.The results showed that comparing with the normal trees,the water potential of leaves and fruits was lower,and the content of H_2O_2,MDA and lignin were higher in disorder happened‘Whangkeumbae＇trees.There was a significant negative correlation（r=-0.828 3,P〈0.01）between water potential and H_2O_2 content,and a significant positive correlation（r=0.764 2,P〈0.05）between H_2O_2 content and MDA content in disorder happened trees.The SOD activity were significant lower,and the POD,CAT,APX activities were markedly higher in disorder happened trees than those in the normal trees.It was believed that there might be some extend of water stress in the disorder happened trees or fruiting positions of the tree,which excited the changes of the dynamic equilibrium of active oxygen production and scavenge status and caused the excessive production of H_2O_2,MDA and increases of POD activity.Thus the lignin synthesis was promoted and the parenchymal cells near epidermal were lignified.