Papaya fruit softening, endoxylanase gene expression, protein and activity

Abstract

Papaya (Carica papaya L.) cell wall matrix polysaccharides are modified as the fruit starts to soften during ripening and an endoxylanase is expressed that may play a role in the softening process. Endoxylanase gene expression, protein amount and activity were determined in papaya cultivars that differ in softening pattern and in one cultivar where softening was modified by the ethylene receptor inhibitor 1-methylcyclopropene (1-MCP). Antibodies to the endoxylanase catalytic domain were used to determine protein accumulation. The three papaya varieties used in the study, 'Line 8', 'Sunset', and 'Line 4-16', differed in softening pattern, respiration rate, ethylene production and showed similar parallel relationships during ripening and softening in endoxylanase expression, protein level and activity. When fruit of the three papaya varieties showed the respiratory climacteric and started to soften, the level of endoxylanase gene expression increased and this increase was related to the amount of endoxylanase protein at 32 kDa and its activity. Fruit when treated at less than 10% skin yellow stage with 1-MCP showed a significant delay in the respiratory climacteric and softening, and reduced ethylene production, and when ripe was firmer and had a 'rubbery' texture. The 1-MCP-treated fruit that had the 'rubbery' texture showed suppressed endoxylanase gene expression, protein and enzymatic activity. Little or no delay occurred between endoxylanase gene expression and the appearance of activity during posttranslational processing from 65 to 32 kDa. The close relationship between endoxylanase gene expression, protein accumulation and activity in different varieties and the failure of the 1-MCP-treated fruit to fully soften, supported de novo synthesis of endoxylanase, rapid posttranslation processing and a role in papaya fruit softening.

The role of hydrolases in the loss of firmness and of the changes in sugar content during the post-harvest maturation of Carica papaya L. var solo 8

“…2). These results are supported by several studies (Brummell et al 2004;Manenoi and Paull 2007;SanudoBarajas et al 2009), which indicated that the softening of Carica papaya L. resulted from the modification of cell wall polysaccharides by enzymes such as polygalacturonase, β- (n03) galactosidase (β-gal), and pectin methylesterase. Other authors (Paull and Chen 1983;Lazan et al 1995) suggested that enzymes found in papayas during maturation included exo-and endo-polygalacturonase, pectin methylesterase, β-1-4-glucanase, galactosidase, and xylanase.…”

Papaya Nutritional Analysis

“…Gene transcripts for softening-related enzymes have been identifi ed, but are ethylene dependent. Genetic techniques that inhibit ethylene or disrupt polygalacturonase and endoxylanase will delay softening, but the fruit will have an undesirable, rubbery texture (Manenoi and Paull 2007 ;Fabi et al 2009 ). Other untested possibilities include increasing vitamin C levels through over expression of a gene encoding for d -galacturonic acid reductase, as has been proposed for strawberries (Agius et al 2003 ), or increasing sugar content by controlling gene expression for sucrose synthase and acid invertase with fruit-specifi c promoters (Zhou and Paull 2001 ).…”

Xylanase activity and T2 (MRI) relationship during lulo la selva P32 ripening process

“…The low activity seen at the end of storage will then correspond to the stage of fruit aging. Therefore, the xylanase activity in the lulillo could generate the breaking of hemicellulose, and thus actively participate in softening, such as it happens during fruit ripening of papaya fruits (Carica papaya) (Manenoi & Paull 2007) and possibly yellow pitahaya (pitajaya amarilla) (Dueñas et al 2008). Changes associated with the ripening in the lulillo not only correspond to the xylanase activity, but also to the possible activity of other enzymes endogenous to the post-harvest storage conditions (where, for example, variations in temperature during a single day interfere in the acceleration of this type of hydrolytic activity), to cases where the fruits differ markedly in their botanical origin; to the composition of polysaccharides and proteins; to the structure of the cell membrane; to the enzymatic metabolism; to the patterns of growth and ripening; as well as to the behavior during softening; whose answers are turned into changes in flesh firmness, in the rate of softening and in texture in general.…”

“…The activity of the xylanaseas and β-xylosidasas have been reported in ripe fruits such as avocado (Persea americana M) (Ronen et al 1991), papaya (Carica papaya) (Manenoi & Paull 2007). In strawberries (Fragaria chiloensis and Fragaria x ananassa), although the amount of xylans has not been determined directly on the cell wall, it has been noted a high connection of xylose: glucose in the hemi-cellulosic fraction (Huber 1984, Koh & Melton 2002, suggesting the presence of polymers containing Xylose.…”