Articles
PECTIN AND CALCIUM DISTRIBUTION IN CELL WALL FRACTIONS OF PHYSIOLOGICAL DISORDER-AFFECTED MANGOSTEEN FRUITS
Article number
984_44
Pages
365 – 370
Language
English
Abstract
The two most important physiological disorders of mangosteen fruit are trans-lucent flesh (TFD) and gamboges (GD). Both are very detrimental to the quality of the fruits, particularly when combined.
Previous studies on mangosteen showed that: 1) either foliar sprays or soil applications of calcium (Ca) significantly reduced the occurrence of these disorders, and 2) the concentration of Ca in the flesh of affected fruits was actually higher than that found in normal fruits.
Although these two results appeared contradictory, similar observations have been reported in studies with other fruits such as mango and apple.
The reason for this apparent discrepancy remains unclear and has not been thoroughly investigated.
In this study, it was hypothesized that the reduction in the number of affected fruits after the applications of Ca could be directly correlated not to the total amount of Ca in the flesh, but rather to a specific fraction of Ca located in the cell wall.
Therefore, the objective was to compare not only the total amount of Ca in the flesh but also the Ca concentrations in various cell wall fractions in healthy and disorder-affected mangosteen fruits.
This was done by a 6-step extraction process using: 1) water (dissolving free pectin); 2) 0.05 M CDTA (which frees ionically-bound pectin); 3) 0.05 M Na2CO3 (which cleaves ester linkages) at 4°C; 4) 0.05 M Na2CO3 at 20°C; 5) 1 M KOH, and 6) 4 M KOH (solubilizing hemicellulose). The Ca in the CDTA-extracted fraction represented the amount of Ca bound inside the cell wall, which was previously speculated to be low in disorder-affected fruits.
However, it was found that the total concentrations of pectin and Ca extracted by CDTA were higher in the TFD and GD fruits than in normal ones.
While this result might be unexpected, it was also in line with results of other studies.
We hypothesize that a larger proportion of Ca bound to the cell wall may cause a reduction in apoplastic Ca, in turn affecting plasma membrane structure and function and eventually leading to the development of TFD.
Previous studies on mangosteen showed that: 1) either foliar sprays or soil applications of calcium (Ca) significantly reduced the occurrence of these disorders, and 2) the concentration of Ca in the flesh of affected fruits was actually higher than that found in normal fruits.
Although these two results appeared contradictory, similar observations have been reported in studies with other fruits such as mango and apple.
The reason for this apparent discrepancy remains unclear and has not been thoroughly investigated.
In this study, it was hypothesized that the reduction in the number of affected fruits after the applications of Ca could be directly correlated not to the total amount of Ca in the flesh, but rather to a specific fraction of Ca located in the cell wall.
Therefore, the objective was to compare not only the total amount of Ca in the flesh but also the Ca concentrations in various cell wall fractions in healthy and disorder-affected mangosteen fruits.
This was done by a 6-step extraction process using: 1) water (dissolving free pectin); 2) 0.05 M CDTA (which frees ionically-bound pectin); 3) 0.05 M Na2CO3 (which cleaves ester linkages) at 4°C; 4) 0.05 M Na2CO3 at 20°C; 5) 1 M KOH, and 6) 4 M KOH (solubilizing hemicellulose). The Ca in the CDTA-extracted fraction represented the amount of Ca bound inside the cell wall, which was previously speculated to be low in disorder-affected fruits.
However, it was found that the total concentrations of pectin and Ca extracted by CDTA were higher in the TFD and GD fruits than in normal ones.
While this result might be unexpected, it was also in line with results of other studies.
We hypothesize that a larger proportion of Ca bound to the cell wall may cause a reduction in apoplastic Ca, in turn affecting plasma membrane structure and function and eventually leading to the development of TFD.
Authors
S. Poovarodom, N. Phanchindawan
Keywords
Garcinia mangostana L., translucent flesh disorder, gamboges
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