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Frontiers of Agriculture in China

ISSN 1673-7334

ISSN 1673-744X(Online)

CN 11-5729/S

Front Agric Chin    2010, Vol. 4 Issue (4) : 463-467     DOI: 10.1007/s11703-010-1041-7
RESEARCH ARTICLE |
Effect of high-temperature stress on the activity of key enzymes in the AsA-GSH cycle in ‘Yali’ pears
Yingli LI1, Jianguang ZHANG1,2()
1. College of Horticulture, Agricultural University of Hebei, Baoding 071001, China; 2. Pear Engineering & Technology Research Center of Hebei Province, Baoding 071001, China
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Abstract  

Through treating fruits at higher temperatures, choosing natural fruits on different exposures on a tree canopy and collecting exclusively both sunburn and normal fruits, the metabolic patterns were studied by comparing the activity of key enzymes in the ascorbate-glutathione (AsA-GSH) cycle including ascorbate peroxidase (APX), monodehydroascorbate reductase (MDAR), and glutathione reductase (GR). The results indicated that the activity of three enzymes increased under around less than 35°C acclimating conditions, with no significant changes in membrane electrolyte leakage. The activity of APX, MDAR, and GR rose during the initial stage when fruits were treated at 45°C but decreased significantly as treating time extended. A time response existed in APX, MDAR, and GR to high temperature. For example, APX activity reached the maximum when fruits were treated for 1 h, however, MDAR and GR showed the peak when fruits were treated for 3 h and 5 h, respectively, implying the possible acting sequence relationship of three enzymes in the AsA-GSH cycle. In view of the whole cycle, APX served as the first enzyme directly scavenging active oxygen species, followed by a series of chain reactions to regenerate ascorbic acid (AsA), and GR served as the last post in the cycle. Because various ecological conditions existed in a tree canopy, there was a significant difference in the enzymatic activity among fruits bearing on either exterior or interior canopy. A significantly higher activity of APX and MDAR was found with exterior fruits, compared with interior ones, which may be regarded as a frequent acclimation to high temperature and excessive sunlight.

Keywords ‘Yali’ pear      high-temperature stress      AsA-GSH cycle      antioxidant enzyme      membrane lipid superoxidation     
Corresponding Authors: ZHANG Jianguang,Email:zhjg570315@sina.com   
Issue Date: 05 December 2010
URL:  
http://academic.hep.com.cn/fag/EN/10.1007/s11703-010-1041-7     OR     http://academic.hep.com.cn/fag/EN/Y2010/V4/I4/463
Fig.1  Membrane integrity at different temperatures
Fig.2  APX activity at different temperatures
Fig.3  MDAR activity at different temperatures
Fig.4  GR activity at different temperatures
Fig.5  Comparison of enzymatic activity between exposed and shaded fruits
Fig.6  Comparison of enzymatic activity between normal and browning fruits
Fig.7  Comparison of electrolyte leakage between normal and browning fruits
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