© 2005 Heron Publishing—Victoria, Canada
Leaf responses of micropropagated apple plants to water stress: nonstructural carbohydrate composition and regulatory role
of metabolic enzymes
Tian H. Li (1, 2) and Shao H. Li (1, 3)
1. Institute of Botany, The Chinese Academy of Sciences, 100093 Beijing, P.R. China / 2. Department of Fruit Science, College of Agronomy and Biotechnology, China Agricultural University, 100094 Beijing, P.R. China / 3. Corresponding author (shhli@ibcas.ac.cn) / Received June 25, 2004; accepted October 15, 2004; published online February 1, 2005
Summary
We examined changes in nonstructural carbohydrate biosynthesis and activities of related enzymes in leaves of micropropagated
apple plants (Malus domestica Borkh. cv. ‘NaganoFuji’) in response to water stress, with particular emphasis on the enzymes associated with sorbitol, sucrose
and starch metabolism. Water stress resulted in the accumulation of photosynthates in leaves, mainly sorbitol, sucrose, glucose
and fructose, accompanied by a reduction in starch concentration. Correlation and path analysis indicated that water stress
affected the partitioning of newly fixed carbon among terminal products. In response to water stress, ADP-glucose-pyrophosphorylase
(ADPGPPase) activity decreased, becoming a critical and limiting step in shifting partitioning of photosynthetically fixed
carbon. Amylase and ADPGPPase affected sucrose and sorbitol metabolism, mainly by regulating substrate supply; however, competition
for limited substrate had a greater effect on the biosynthesis of sorbitol than of sucrose. Starch metabolism was also strictly
regulated by ADPGPPase and amylase, whereas other related enzymes were downstream of the pathway for synthesis and degradation
of carbohydrates and thus had relatively little effect on starch metabolism. Sorbitol dehydrogenase and sucrose phosphate
synthase were critical regulators of sorbitol and sucrose metabolism, respectively.
Keywords:
carbohydrate metabolism, carbon partitioning, enzyme activity, path analysis.
