Sucrose uptake and compartmentation in sugar beet taproot tissue.

Area of Science:

• Plant Physiology
• Biochemistry
• Molecular Biology

Background:

• Sugar beet (Beta vulgaris L.) is a crucial crop for sucrose production.
• Understanding sucrose transport mechanisms is vital for improving crop yield and efficiency.

Purpose of the Study:

• To elucidate the kinetics and mechanisms of active and passive sucrose uptake in sugar beet root tissue.
• To identify the cellular compartments involved in sucrose storage and transport.

Main Methods:

• Analysis of sucrose uptake and efflux kinetics in sugar beet root discs at varying external sucrose concentrations.
• Investigation of the effects of ATPase inhibitors (oligomycin, diethylstilbestrol, N,N-dicyclohexylcarbodiimide, orthovanadate) on active sucrose uptake.
• Compartmental analysis of sucrose distribution within root cells.

Main Results:

• Active sucrose uptake exhibits biphasic kinetics, with a saturable component (K(m) = 3.6 mM) and a linear, non-saturable component at higher concentrations.
• Active transport is dependent on mitochondrial/vacuolar ATPases, not plasmalemma-specific ATPases.
• Sucrose efflux analysis revealed three compartments (cell wall, cytoplasm, vacuole), with vacuolar uptake occurring against a concentration gradient.
• Vacuolar sucrose uptake is primarily active, while cytoplasmic transport appears passive above 20 mM sucrose.

Conclusions:

• Sucrose uptake into sugar beet vacuoles is an active process, potentially rate-limited by passive transport to the uptake site.
• The distinct kinetic properties suggest complex regulation of sucrose transport and storage in sugar beet root cells.