Sugar demand of ripening grape berries leads to recycling of surplus phloem water via the xylem

Abstract

We tested the common assumption that fleshy fruits become dependent on phloem water supply because xylem inflow declines at the onset of ripening. Using two distinct grape genotypes exposed to drought stress, we found that a sink-driven rise in phloem inflow at the beginning of ripening was sufficient to reverse drought-induced berry shrinkage. Rewatering accelerated berry growth and sugar accumulation concurrently with leaf photosynthetic recovery. Interrupting phloem flow through the peduncle prevented the increase in berry growth after rewatering, but interrupting xylem flow did not. Nevertheless, xylem flow in ripening berries, but not berry size, remained responsive to root or shoot pressurization. A mass balance analysis on ripening berries sampled in the field suggested that phloem water inflow may exceed growth and transpiration water demands. Collecting apoplastic sap from ripening berries showed that osmotic pressure increased at distinct rates in berry vacuoles and apoplast. Our results indicate that the decrease in xylem inflow at the onset of ripening may be a consequence of the sink-driven increase in phloem inflow. We propose a conceptual model in which surplus phloem water bypasses the fruit cells and partly evaporates from the berry surface and partly moves apoplastically to the xylem for outflow.

Nutritional Aspects of Grape (<i>Vitis vinifera</i> L.) Clusters Afflicted with SOUR Shrivel Is Related to Functionality of Its Vascular Tissues

“…In order for berries to accumulate mineral nutrients, they need not only intact xylem and phloem tissues within them, but also a viable vascular connection with the parent vine [10] [31] [32]. The healthy clusters met both of these criteria, consequently they accumulated not only high amounts of sugars [1] [4] but also the phloem mobile macronutrients such as P, K, S, and Mg and the xylem mobile Ca (Figure 1, Figure 2).…”

Cycle, physicochemical characterization and climatic adaptation of a white hybrid grape on different rootstocks

“…Grape maturation increases SSC and decreases acidity in berries (Rombaldi et al 2004). Higher SSC is mainly due to the accumulation of sugars, and lower acidity is mainly due to the reduction of the main organic acids involved in fruit maturation (Rizzon et al 2000;Keller et al 2015).…”

Characterization of rhizosphere bacterial community and berry quality of Hutai No.8 (Vitis vinifera L.) with different ages, and their relations

“…Berry diameter was measured using a vernier caliper at equatorial points, marked by Indian ink on each berry, and the results were expressed as the mean ± standard error of individual determinations in millimeters. 25 Grapes were peeled with the help of a sharp knife, and both skin and berry weight were recorded with an analytical balance (AY220, Shimadzu Corporation, Kyoto, Japan) and reported in grams. Berry firmness and separation force were recorded using a hand penetrometer (GY-1, TOP Instrument, Zhejiang, China) supplemented with a plunger 2 mm diameter penetrator or a hook and expressed as newtons.…”