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Discharge of surplus phloem water may be required for normal grape ripening.

ABSTRACT: At the onset of ripening, some fleshy fruits shift the dominant water import pathway from the xylem to the phloem, but the cause for the decline in xylem inflow remains obscure. This study found that xylem-mobile dye movement into grape berries decreased despite transient increases in berry growth and transpiration during early ripening, whereas outward dye movement continued unless the roots were pressurized. Modeling berry vascular flows using measurements of pedicel phloem sap sugar concentration, berry growth, solute accumulation, and transpiration showed that a fraction of phloem-derived water was used for berry growth and transpiration; the surplus was recirculated via the xylem. Changing phloem sap sugar concentration to a much higher published value led to model simulations predicting xylem inflow or backflow depending on the developmental stage and genotype. Mathematically preventing net xylem flow resulted in large variations in phloem sap sugar concentration in pedicels serving neighboring berries on the same fruit cluster. Moreover, restricting water discharge via the xylem and/or across the skin impaired berry solute accumulation and color change. Collectively, these results indicate that discharge of surplus phloem water via berry transpiration and/or xylem backflow may be necessary to facilitate normal grape ripening.

SUBMITTER: Zhang Y

PROVIDER: S-EPMC5444433 | biostudies-literature | 2017 Jan

REPOSITORIES: biostudies-literature

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Discharge of surplus phloem water may be required for normal grape ripening.

Zhang Yun Y Keller Markus M

Journal of experimental botany 20170101 3

At the onset of ripening, some fleshy fruits shift the dominant water import pathway from the xylem to the phloem, but the cause for the decline in xylem inflow remains obscure. This study found that xylem-mobile dye movement into grape berries decreased despite transient increases in berry growth and transpiration during early ripening, whereas outward dye movement continued unless the roots were pressurized. Modeling berry vascular flows using measurements of pedicel phloem sap sugar concentra ...[more]

PMID: 28082510

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Project description:Grapes (Vitis vinifera L.) are economically the most important fruit crop worldwide. However, the complexity of molecular and biochemical events that lead to ripening of nonclimacteric fruits is not fully understood. In particular the role of polyaminesM-BM-4 catabolism has been little explored. Ripening of Trincadeira grapes submitted to mock and guazatine treatments, a potent inhibitor of polyamine oxidase activity, was studied taking into account the transcriptional and metabolic profilings complemented with biochemical data. The mRNA expression profiles of one time point (EL 38) corresponding to harvest stage was compared between mock and guazatine treatments using the Affymetrix GrapeGenM-BM-. genome array containing 23096 probesets corresponding to 18711 unique sequences. A total of 2113 probesets (1877 unigenes) were significantly differentially expressed (1.5 fold) between these samples. These unigenes were assigned to the functional categories of M-bM-^@M-^\metabolismM-bM-^@M-^], M-bM-^@M-^\regulation overviewM-bM-^@M-^], M-bM-^@M-^\signalingM-bM-^@M-^], M-bM-^@M-^\cellular processM-bM-^@M-^], M-bM-^@M-^\transport overviewM-bM-^@M-^], M-bM-^@M-^\response to stimulus, stressM-bM-^@M-^], M-bM-^@M-^\diverse/miscellaneous functionsM-bM-^@M-^], M-bM-^@M-^\xenoprotein, transposable elementM-bM-^@M-^], M-bM-^@M-^\developmentM-bM-^@M-^] and M-bM-^@M-^\unknownM-bM-^@M-^]. Quantitative RT-PCR validated microarrays results being carried out for seven selected genes and three developmental stages (EL 35, EL 36 and EL 38). Functional enrichment analysis revealed that genes involved in amino acid, carbohydrate and water transport were more up-regulated in mock treated samples which may suggest that the strong dehydrated phenotype obtained in guazatine treated samples may be due to impaired transport mechanisms. In addition, genes involved in terpenesM-BM-4 metabolism were differentially expressed between guazatine and mock treated samples. Altogether, the results support an important role of polyamine catabolism in normal grape ripening namely in aroma development and cell expansion. 1 time point in 2010 season at EL 38. 3 biological replicates. 2 treatments

Project description:IntroductionClimate change is impacting the wine industry by accelerating ripening processes due to warming temperatures, especially in areas of significant grape production like California. Increasing temperatures accelerate the rate of sugar accumulation (measured in ⁰Brix) in grapes, however this presents a problem to wine makers as flavor profiles may need more time to develop properly. To alleviate the mismatch between sugar accumulation and flavor compounds, growers may sync vine cultivars with climates that are most amenable to their distinct growing conditions. However, the traits which control such cultivar specific climate adaptation, especially for ⁰Brix accumulation rate, are poorly understood. Recent studies have shown that higher rates of fruit development and sugar accumulation are predicted by larger phloem areas in different organs of the plant.MethodsHere we test this phloem area hypothesis using a common garden experiment in the Central Valley of Northern California using 18 cultivars of the common grapevine (Vitis vinifera) and assess the grape berry sugar accumulation rates as a function of phloem area in leaf and grape organs.ResultsWe find that phloem area in the leaf petiole organ as well as the berry pedicel is a significant predictor of ⁰Brix accumulation rate across 13 cultivars and that grapes from warm climates overall have larger phloem areas than those from hot climates. In contrast, other physiological traits such as photosynthetic assimilation and leaf water potential did not predict berry accumulation rates.DiscussionAs hot climate cultivars have lower phloem areas which would slow down brix accumulation, growers may have inadvertently been selecting this trait to align flavor development with sugar accumulation across the common cultivars tested. This work highlights a new trait that can be easily phenotyped (i.e., petiole phloem area) and be used for growers to match cultivar more accurately with the temperature specific climate conditions of a growing region to obtain satisfactory sugar accumulation and flavor profiles.

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Discharge of surplus phloem water may be required for normal grape ripening.

Publications

Discharge of surplus phloem water may be required for normal grape ripening.

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