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The Journal of Horticultural Science & Biotechnology
Vol. 81 No: 2
Title:
Cell wall modifications in the pericarp of litchi (Litchi chinensis Sonn.) cultivars that differ in their resistance to cracking
Authors:
XU-MING HUANG, HUI-CONG WANG, XUE-JUAN LU, WEI-QUN YUAN, JIE-MEI LU, JIAN-GUO LI and HUI-BAI HUANG
pp: 231-237
Abstract:
Changes in structural calcium and galacturonan concentrations, the degree of methylesterification of pectins, the activities of pectin methylesterase (PME) and soluble and wall-bound peroxidases (POD), and amino acid compositions of structural proteins in the fruit pericarp (skin) were studied in cracking-resistant 寒uaizhi` and cracking-susceptible 就uomici` litchi. Structural calcium concentrations were higher in 寒uaizhi` than in 就uomici` and decreased from 22 d to 52 d after anthesis (DAA), then increased. Galacturonan concentrations increased over time and were higher in 寒uaizhi`. Methylesterification of pectins increased from 50% at 22 DAA, to 55% at 78 DAA in 寒uaizhi`, but fluctuated around 48% in 就uomici`. PME activity was significantly higher in 就uomici` than in 寒uaizhi` in the later stages of fruit development (⟩ 50 DAA).The activities of soluble (SPOD) and ionically wall-bound POD (IWBPOD) increased with fruit development. Maximum SPOD activity was similar in both cultivars, whereas the peak activity of IWBPOD was higher in 就uomici` than in 寒uaizhi`.Total concentrations of SDS-soluble amino acids were similar in the two cultivars. Total structural proteins (SDS-insoluble amino acids) decreased with fruit development. Among the SDS-insoluble amino acids, hydroxyproline was the only one that increased over time. The results suggest that higher levels of structural calcium and galacturonans may contribute to cracking resistance in 寒uaizhi`, while a higher activity of IWBPOD, which catalyses the formation of phenolic cross-linkages and an irreversible increase in the rigidity of cell walls, may be associated with cracking susceptibility in 就uomici`. Structural proteins may not be involved in resistance to cracking in litchi cultivars.
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