Carbohydrate metabolism and fruit quality are affected in frost exposed Valencia orange fruit.

FALCONE FERREYRA, M.L.; PEROTTI, V.; FIGUEROA, C.M; GARRÁN, S.; ANDERSON, P.C.; VÁZQUEZ, D.;; IGLESIAS, A.A.;; PODESTÁ, F.E

PHYSIOLOGIA PLANTARUM

Per Gardeström

Año: 2006 vol. 128 p. 224 - 236

0031-9317

Exposure of citrus fruit to frost often results in the development of freeze injury during their maturation in planta. This work was aimed to analyze changes in the biochemistry and enzymology of carbohydrate metabolism in freeze-injured orange fruit (Citrus sinensis var. Valencia late) and the involvement of oxidative stress in frost damage. The activities of pyrophosphate-dependent phosphofructokinase, phosphoenolpyruvate carboxylase and several fermentative enzymes increased in frost-exposed fruit, while NADP-malic enzyme and the mitochondrial isoform of NAD-malate dehydrogenase showed a reduction in their activities. Western blot analysis indicated a correlation between activity levels and proteins content. Respiration rate in whole fruit was reduced by 40%, whereas the flavedo showed a more pronounced decline (53%). Volatile compounds (i.e. ethanol, acetaldehyde) content was significantly higher in frost-exposed fruit than control, as was that of l-malate (3-fold). Additionally, frost-exposed fruit showed a marked decrease in the maturity index (24%) due to a higher titratable acidity (39%). Evidence is presented that oxidative stress is involved in freeze-induced damage of orange fruit, where oxidative damage to lipids, proteins and a greater electrolyte leakage in the flavedo were also observed. The results suggest that freezing temperatures provoke a notable metabolic switch in citrus fruit toward a fermentative stage resulting in low-quality fruits.