Growth of Storage Organ and Parenchyma Cells in Red Beet (Beta vulgaris L.): Lower Osmolarity Correlates with Increasing Cell Size, Implying Cell Transport Rather than Diffusion Limitation

The development of greenhouse-grown red beet plants (Beta vulgaris L.) was examined from ages 35 to 98 d after planting. In the storage organ, at the center of the second intervascular ring, large parenchyma cells were observed to have lower osmolarity than smaller cells next to them. We obtained estimates of net flux into the parenchyma storage cells for sucrose as 7.91 x 10⁻¹⁴ mol/cm²/s, and for osmotica as 1.98 x 10⁻¹³ osmol/cm²/s. From these flux estimates, and the width of the intervascular ring, a concentration gradient from the vasculature to the center of the ring was calculated. Our results imply that transport properties of the storage parenchyma cells may limit sugar accumulation to a greater extent than the distance of the cells from the phloem. Modeling of parenchyma cells spherically gave higher estimates of osmolarity than did modeling cells ellipsoidally, but both models gave similar changes in osmolarity with changes in cell size. The growth of red beet storage organs was similar to that previously reported for sugar beets, making it a useful model system.