Analysis of Xylem Sap from Functional (Nonembolized) and Nonfunctional (Embolized) Vessels of <i>Populus nigra</i>: Chemistry of Refilling

Secchi, Francesca; Zwieniecki, Maciej A.

doi:10.1104/pp.112.200824

Cited by 116 publications

(124 citation statements)

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“…2 and 4, B and C). According to refilling models for angiosperms (Nardini et al, 2011), starch may be degraded to osmotically active sugars, which are released into embolized conduits thereby creating a driving force for water inflow (Bucci et al, 2003;Secchi and Zwieniecki, 2012). Observed starch accumulation in phloem and needle tissues may thus be required to provide sufficient osmotica for local changes in C. Interestingly, we found no significant seasonal changes in Glc or Fru (data not shown).…”

Section: Discussionmentioning

confidence: 43%

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Uptake of Water via Branches Helps Timberline Conifers Refill Embolized Xylem in Late Winter

et al. 2014

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Xylem embolism is a limiting factor for woody species worldwide. Conifers at the alpine timberline are exposed to drought and freeze-thaw stress during winter, which induce potentially lethal embolism. Previous studies indicated that timberline trees survive by xylem refilling. In this study on Picea abies, refilling was monitored during winter and spring seasons and analyzed in the laboratory and in situ experiments, based on hydraulic, anatomical, and histochemical methods. Refilling started in late winter, when the soil was frozen and soil water not available for the trees. Xylem embolism caused up to 86.2% ± 3.1% loss of conductivity and was correlated with the ratio of closed pits. Refilling of xylem as well as recovery in shoot conductance started in February and corresponded with starch accumulation in secondary phloem and in the mesophyll of needles, where we also observed increasing aquaporin densities in the phloem and endodermis. This indicates that active, cellular processes play a role for refilling even under winter conditions. As demonstrated by our experiments, water for refilling was thereby taken up via the branches, likely by foliar water uptake. Our results suggest that refilling is based on water shifts to embolized tracheids via intact xylem, phloem, and parenchyma, whereby aquaporins reduce resistances along the symplastic pathway and aspirated pits facilitate isolation of refilling tracheids. Refilling must be taken into account as a key process in plant hydraulics and in estimating future effects of climate change on forests and alpine tree ecosystems.

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Section: Discussionmentioning

confidence: 43%

“…Because osmotica have to be released only into refilling tracheids, variations in sugar concentrations probably occur on a small spatial scale and thus cannot be detected by analysis of entire tissue samples. In Populus, a special method enabled the analysis of sugar contents in embolized and intact vessels (Secchi and Zwieniecki, 2012).…”

Section: Discussionmentioning

confidence: 99%

Uptake of Water via Branches Helps Timberline Conifers Refill Embolized Xylem in Late Winter

et al. 2014

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“…2). In this scenario, starch degradation appears to play a key role in providing the osmotica (Salleo et al 2004;Secchi and Zwieniecki 2012), while aquaporins are required to reduce hydraulic resistance along the symplastic pathway . Phloem transport has also been demonstrated to be involved in embolism reversal, as different studies showed that phloem girdling inhibits the process (Salleo et al 2004;Nardini et al 2014).…”

Section: Recent Non-destructive Methodsmentioning

confidence: 99%

“…Refilling conduits have more negative osmotic potential than still functioning ones (Secchi and Zwieniecki 2012). In a hypothetical scenario that found partial experimental confirmation, drought-induced rise in abscisic acid (ABA) concentration would lead to upregulation of several genes in vessel-associated parenchyma, including those coding for aquaporins and enzymes related to carbohydrate metabolism and starch degradation (Secchi and Zwieniecki 2010).…”

Section: Processesmentioning

confidence: 99%

Xylem embolism refilling and resilience against drought‐induced mortality in woody plants: processes and trade‐offs

Klein

Zeppel

Anderegg

et al. 2018

Ecological Research

138

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Understanding which species are able to recover from drought, under what conditions, and the mechanistic processes involved, will facilitate predictions of plant mortality in response to global change. In response to drought, some species die because of embolism-induced hydraulic failure, whilst others are able to avoid mortality and recover, following rehydration. Several tree species have evolved strategies to avoid embolism, whereas others tolerate high embolism rates but can recover their hydraulic functioning upon drought relief. Here, we focus on structures and processes that might allow some plants to recover from drought stress via embolism reversal. We provide insights into how embolism repair may have evolved, anatomical and physiological features that facilitate this process, and describe possible trade-offs and related costs. Recent controversies on methods used for estimating embolism formation/repair are also discussed, providing some methodological suggestions. Although controversial, embolism repair processes are apparently based on the activity of phloem and ray/axial parenchyma. The mechanism is energetically demanding, and the costs to plants include metabolism and transport of soluble sugars, water and inorganic ions. We propose that embolism repair should be considered as a possible component of a 'hydraulic efficiency-safety' spectrum. We also advance a framework for vegetation models, describing how vulnerability curves may change in hydrodynamic model formulations for plants that recover from embolism.

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“…The mechanisms involved in refilling without tension are still under debate (see Zwieniecki and Holbrook (2009) and Brodersen and McElrone (2013) for a detailed review). However, there is strong evidence that sugars derived from starch polymerisation in xylem parenchyma generate an osmotic gradient that then drives water inflow from adjacent parenchyma cells into conduits (Salleo et al 2004;Zwieniecki and Holbrook 2009;Nardini et al 2011;Secchi and Zwieniecki 2012). Two important prerequisites therefore are: (I) adequate water supply, with living cells in the xylem and phloem potentially playing a major role (Salleo et al 2004;Brodersen et al 2010;Nardini et al 2011); (II) hydraulic isolation of embolised conduits from water-filled conduits under tension.…”

Section: Introductionmentioning

confidence: 99%

Annual patterns of xylem embolism in high-yield apple cultivars

Beikircher

Mayr

2017

Functional Plant Biol.

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Abstract. Temperate angiosperm species show pronounced annual patterns in xylem embolism. In this study, we investigated whether high-yield cultivars of Malus domestica Borkh. growing under optimised soil water conditions follow similar patterns to wild-type plants, and evaluated crucial factors for the formation of winter embolism and the subsequent restoration of the hydraulic system in spring. In five different cultivars growing at three different sites, various hydraulic and microclimatic parameters were monitored over three successive years. In all cultivars on all sites and in all years, the percentage loss of hydraulic conductivity (PLC) increased in autumn with freeze-thaw events and accumulated over winter. Maximum values were reached in late winter and differed significantly among cultivars. In spring, the hydraulic system was restored and PLC remained negligible during summer. Embolism formation in autumn was significantly correlated with the occurrence of freeze-thaw events, whereas further conductivity losses over winter were related to winter desiccation and influenced by climatic and cultivar-specific parameters. Restoration of the hydraulic system in spring was strongly linked to a decrease in the starch content of wood and buds, and soil temperature. Despite high soil water availability, hydraulic recovery took several weeks and was not completed before bud break. Spring is thus a critical phase for temperate angiosperms, especially for high-yield cultivars with risky hydraulic strategies.

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Analysis of Xylem Sap from Functional (Nonembolized) and Nonfunctional (Embolized) Vessels of Populus nigra: Chemistry of Refilling

Cited by 116 publications

References 50 publications

Uptake of Water via Branches Helps Timberline Conifers Refill Embolized Xylem in Late Winter

Uptake of Water via Branches Helps Timberline Conifers Refill Embolized Xylem in Late Winter

Xylem embolism refilling and resilience against drought‐induced mortality in woody plants: processes and trade‐offs

Annual patterns of xylem embolism in high-yield apple cultivars

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