Abstract: The present experiment was conducted to reveal the effect of microenvironments and exogenous substance application on 5'-nucleotidase activities in apple peel tissue. By means of enclosing apple fruits
in bags, treating with exogenous active oxygen species and regulative agents or placing them under controlled conditions at different fruit temperatures or relative humidity, the 5'-nucleotidase activitieswere compared with
the corresponding controls. The results indicated that, a considerable effect of microenvironments was found on 5'-nucleotidase activities in fruit peel tissue. The highest enzymatic activity appeared in fruits on southwest canopy, regardless of bagged or non-bagged fruits, significantly higher than those from any other exposures.Fruitswith bags had a significantly higher 5'-nucleotidase activity than the exposed ones. A variation of enzymatic activities was observed in fruits enclosed with different types of bags, which were supposed to alter the
microenvironments around them. Within a certain range, gradual or fluctuant rise of fruit temperatures could favor the increase of 5'-nucleotidase activities as a result of heat adaptation, whereas the activitywould be inhabited if the temperature-rising period was too short or temperature differentialwas too huge. No matter what temperatures fruits were subjected to, high relative humidity was favorable to stimulating the 5'-nucleotidase activities, which might partly explain why fruit sunburn wouldnpt happen in humid climates. Treatments with four kinds of exogenous active oxygen species could reduce the 5'-nucleotidase activities significantly but spraying with CaCl₂ was able to enhance 5'-nucleotidase activities by 55.39% , reaching a significant level.

Key words: Apple, Microenvironment, Exogenous substance, Fruit, 5'-nucleotidase, Enzymatic activity