Volume changes in red beet vacuoles after hypotonic and hypertonic challenges: experimental and mathematical modelling approaches

MOIRA SUTKA; OSVALDO CHARA; KARINA ALLEVA; MARCELO OZU; RICARDO DORR; GABRIELA AMODEO

Montenvideo, Uruguay

Congreso; 6th Internacional Conference of Biological Physics, ICBP and 5th Southern Cone Biophysics Congress; 2007

ICBP, Sociedad Argentina de Biofísica

The objective of this work was to study the effects of mercury compounds and acidic pHs media on vacuole volume changes following osmotic challenges. Two approaches were developed: experimental and mathematical modelling. In plants, vacuoles represent majority of the volume cell and are responsible of cell volume regulation and pH homeostasis. In the experimental approaches vacuoles were isolated from sugar beet root cells, equilibrated in an isotonic manitol solution and then exposed to hypotonic or hypertonic conditions. The osmotic gradient was imposed using a perfusion system and vacuole volume changes were followed by videomicroscopy. In other experiments vacuoles were pre-incubated in the presence of HgCl2 or at different acidic pHs and then osmotic gradient was applied. In order to deep insight experimental data, three mathematical models were developed. All of them considers that water moves according to an osmotic mechanism. The models explore, essentially, the solute movement by diffusion (D_model), a regulatory volume (RV_model) or a combination of them(D-RV_model). Mathematically, models are characterized by a system of ordinary non linear differential equations subject to a set of initial conditions. Simulations were performed using Euler method with a custom made software developed in Visual Basic code. Simulations were performed fitting to the experimental data and comparing the models and, consequently, the tested hypothesis. In hypotonic conditions simulations done using D_model fitted better than D-RV_model and RV_model. However, D-RV_model showed the best fitting compare to the others in hypertonic conditions. Therefore, presented results indicate that sugar beet vacuoles show a different response after osmotic insult. During hypertonic situations solute movement by diffusion and regulatory volume mechanism follow to water osmotic movement. On the contrary, in hypotonic conditions, only solute diffusion follows to water osmotic fluxes.