PIP AQUAPORINS AND RIPENING IN STRAWBERRY

MERCEDES MARQUEZ; KARINA ALLEVA; GABRIELA AMODEO

Cluj Napoca

Congreso; The First World Congress on Water Channel Proteins; 2011

The GheorgheBenga Foundation

Introduction:In plants, aquaporins known as PIPs are usually expressed at the level of the first membrane barrier: the plasmalemma; however their involvement or association in specific physiological processes is not clear. In previous work, we characterized two strawberry fruit-specific aquaporins,FaPIP1;1 and FaPIP2;1 showing its expression profile associated with ripening (Alleva et al., 2010). Both PIPs have also been studied in terms of their water permeability (Pf). In this work we analyze water-related parameters at the fruit level, PIP1/PIP2 expression profiles at different ripening stages and the pH regulation of both water channels in order to gain insight into role of the water transport components in this framework. Materials and Methods: Water-related parameters at the fruit level such as relative water content and growth rate in a daily pattern measurement, where analyzed for six different ripening stages in greenhouse grown strawberry plants -large green (LG), white (W), 25%, 50%,75%,and 100% red-FaPIP aquaporin water transport activity was studied by means of cRNA injection in an heterologous system. Xenopus oocytes were injected with cRNA of FaPIP1 and/or FaPIP2. Pf was determined by measuring the rate of oocyte swelling induced by a hypo-osmotic shock (Zhang and Verkman, 1991). Oocyte internal (cytosolic) pH was modified pre-incubation for 15 min in different solutions (pH=5.8 - 7.6). Results and Discussion: At the fruit level: To reach 100%R, strawberry ripening process involves a daily course distribution mainly dominated by the LG and W stages, 41% and 22% of the days respectively. Growth rate duplicates from LG to W and later decrease constantly. Also, the larger variation in relative water content is observed from LG to W stage. Interestingly, the aquaporin profile reflects changes inbetween LG to W (both FaPIP increasing) and 100% red (FaPIP1 high, FaPIP2 low). At the molecular level: while there is a relationship between the quantity of FaPIP2 cRNA injected in the oocytes with water permeability, the co-expression of different ratios of FaPIP2/FaPIP1 cRNA do not impact in Pf variations. Regarding pH regulation, EC50 for FaPIP2;1 is 6.0, while FaPIP1;1-FaPIP2;1 is 6.4, showing a different sensing of pH by PIP co-expression. EC50 of the dose-response curves for oocytes co-expressing FaPIP1/FaPIP2 in different ratios is constant, accompanying Pf results. Conclusion: Awareness of transcelular water movements during ripening due to outbreak of aquaporin learning is discussed. Water relations at a fruit level are complex, and aquaporin role in ripening is still unknown, our results contribute to organize some pieces of the process both at whole fruit and at molecular level.