高温强光胁迫对苹果果皮PPO活性的影响

苹果果实日烧是一种普遍发生的生理病害，最常见的特征之一就是在果实表面出现褐变。通常认为PPO与植物的酶促褐变密切相关。研究了自然和控制条件下，高温强光胁迫对果实PPO活性的影响，以便揭示高温强光胁迫下苹果果实褐变与PPO活性之间的联系。结果表明：高温和强光胁迫与果皮PPO活性变化密切相关。就树冠不同方位而言，西南方位是高温和强光胁迫最严重的区域，其外围裸露果实的PPO活性也最强。在一定范围内，随着处理温度和光照强度的升高，果皮PPO活性也逐渐增强。短时间剧烈升温能够引起PPO活性骤然上升。在同样程度的高温胁迫下，提高环境湿度有利于抑制果皮PPO活性，从而减轻褐变症状的发生。室内外试验一致证实：果实日烧褐变现象与高温强光胁迫下果皮组织PPO活性大幅度提高有直接关系。

Effect of high temperature and excessive light stresses on PPO activity in apple

Apple fruit sunburn is a common disorder and one of the distinguishable symptoms is that browning color appears on the exposed side of a fruit. It has been taken for granted that PPO is absolutely involved in the browning process of plant tissues or organs under stressed conditions. The present experiment was conducted to examine the effect of high temperature and excessive light stresses on PPO activity in fruit peel under both laboratory and field conditions, so that the relationship could be disclosed between the occurrence of fruit browning and PPO activity in peel tissues stressed by high temperature and excessive solar radiation. The results indicated that a close relationship was found between the stressed extent of both high temperature and excessive light, and PPO activity in apple peel. As far as different exposures of a tree canopy were concerned, the highest PPO activity existed in exposed fruits on SW exposure where they were frequently stressed most severely. Within a certain range, PPO activity in fruit peel increased gradually with a rise of temperature and light intensity and an abrupt temperature increasing could result in a dramatic growth in PPO activity. Under the same high-temperature stressed conditions, a higher relative humidity was favorable to inhabiting PPO activity in fruit peel, thus reducing the risk of heat-related damage. The results consistently confirmed that the browning process of sunburn fruit was associated directly with the significant increase in PPO activity in fruit peel.