, Volume 239, Issue 3, pp 633–642 | Cite as

Solute accumulation differs in the vacuoles and apoplast of ripening grape berries

Original Article


Phloem unloading is thought to switch from a symplastic route to an apoplastic route at the beginning of ripening in grape berries and some other fleshy fruits. However, it is unclear whether different solutes accumulate in both the mesocarp vacuoles and the apoplast. We modified a method developed for tomato fruit to extract apoplastic sap from grape berries and measured the changes in apoplastic and vacuolar pH, soluble sugars, organic acids, and potassium in ripening berries of Vitis vinifera ‘Merlot’ and V. labruscana ‘Concord’. Solute accumulation varied by genotype, compartment, and chemical species. The apoplast pH was substantially higher than the vacuolar pH, especially in Merlot (approximately two units). However, the vacuole–apoplast proton gradient declined during ripening and in Merlot, but not in Concord, collapsed entirely at maturity. Hexoses accumulated in both the vacuoles and apoplast but at different rates. Organic acids, especially malate, declined much more in the vacuoles than in the apoplast. Potassium accumulated in the vacuoles and apoplast of Merlot. In Concord, by contrast, potassium increased in the vacuoles but decreased in the apoplast. These results suggest that solutes in the fruit apoplast are tightly regulated and under developmental control.


Fruit ripening Grape berry Organic acid Phloem unloading Potassium Sugar Vitis 



Duration of pressurization


Applied gas pressure








Mesocarp solute concentration


Apoplast solute concentration


Vacuole solute concentration


Membrane reflection coefficient


Leaf xylem water potential


Apoplast sap volume



This work was supported by funds from the Chateau Ste. Michelle Distinguished Professorship. We thank Dr. John K. Fellman for critical review of the manuscript.

Supplementary material

425_2013_2004_MOESM1_ESM.tif (60.2 mb)
Fig. S1 Progression of fruit ripening in Merlot and Concord grapes. Total juice solute concentration (a), pH (b), and total organic acids as the sum of all organic acids determined by HPLC (c). Samples were grouped based on visual appearance of the berry skin (1 = green; 2 = blush/pink; 3 = red/purple; 4 = blue) or juice solute concentration (5 = ripe: 20-24 ºBrix; 6 = overripe: > 24 ºBrix). Data are mean ± se where se > symbol size (n = 3-18 samples of 8-12 berries) (TIFF 61691 kb)
425_2013_2004_MOESM2_ESM.tif (18.9 mb)
Fig. S2 Changes in the proton concentration in mesocarp vacuoles and apoplast of ripening Merlot and Concord grape berries. Samples were grouped based on visual appearance of the berry skin (1 = green; 2 = blush/pink; 3 = red/purple; 4 = blue) or juice solute concentration (5 = ripe: 20-24 ºBrix; 6 = overripe: > 24 ºBrix). Data are mean ± se where se > symbol size (n = 3-18 samples of 8-12 berries) (TIFF 19305 kb)
425_2013_2004_MOESM3_ESM.tif (49 mb)
Fig. S3 Relationship between total vacuolar solutes and vacuolar and apoplastic hexoses (a), malate (b), and K+ (c) in ripening Merlot and Concord grape berries. Correlation coefficients are as follows: Concord apoplast, r = 0.97, vacuole, r > 0.99; Merlot apoplast, r = 0.93, vacuole, r > 0.99 (a); Concord apoplast, r = -0.67, vacuole, r = -0.73; Merlot apoplast, r = 0.35, vacuole, r = -0.79 (b); Concord apoplast, r = -0.75, vacuole, r = 0.75; Merlot apoplast, r = 0.74, vacuole, r = 0.87 (c); all P < 0.001, n ≥ 60; curves were fitted using the distance-weighted least squares method (TIFF 50133 kb)
425_2013_2004_MOESM4_ESM.tif (49 mb)
Fig. S4 Changes in the concentrations of oxalate (a), succinate (b), and citrate (c) in mesocarp vacuoles and apoplast of ripening Merlot and Concord grape berries. Samples were grouped based on visual appearance of the berry skin (1 = green; 2 = blush/pink; 3 = red/purple; 4 = blue) or juice solute concentration (5 = ripe: 20-24 ºBrix; 6 = overripe: > 24 ºBrix). Data are mean ± se where se > symbol size (n = 3-18 samples of 8-12 berries) (TIFF 50151 kb)


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Copyright information

© Springer-Verlag Berlin Heidelberg 2013

Authors and Affiliations

  1. 1.Irrigated Agriculture Research and Extension CenterWashington State UniversityProsserUSA
  2. 2.Planta Analytica LLCMeridianUSA

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