JrSUT1, a putative xylem sucrose transporter, could mediate sucrose influx into xylem parenchyma cells and be up‐regulated by freeze–thaw cycles over the autumn–winter period in walnut tree (Juglans regia L.)

Abstract

JrSUT1 , a putative xylem sucrose transporter, could mediate sucrose influx into xylem parenchyma cells and be upregulated by freeze-thaw cycles over the autumn-winter period in walnut tree ( Juglans regia L.) MÉLANIE ABSTRACTSucrose has been reported to play multiple roles in the winter biology of temperate woody species. However, no report on the molecular basis of sucrose transport in xylem tissue has yet been made. In the walnut tree, it is demonstrated that during the autumn-winter period, active absorption of sucrose from xylem vessels to parenchyma cells (sucrose influx) is much higher when samplings were taken shortly after a period of freezing temperatures. Here, the question of whether this increased sucrose influx mirrors a regulation of sucrose transporters in xylem tissue was tested. A putative sucrose transporter cDNA ( JrSUT1: Juglans regia sucrose transporter 1) was isolated. Over the autumn-winter period, JrSUT1 transcripts and respective proteins were present in xylem parenchyma cells and highly detected when samplings were performed shortly after a freeze-thaw cycle. This up-regulation of JrSUT1 level was confirmed in controlled conditions and was not obtained in bark. Immunolocalization studies showed that JrSUT1 and plasma membrane H + + + + -ATPase (JrAHA) were colocalized to vessel-associated cells (VACs), which control solute exchanges between parenchyma cells and xylem vessels. We propose that JrSUT1 could be involved in the retrieval of sucrose from xylem vessel. All these data are discussed with respect to the winter biology of the walnut tree.

In Vivo Quantification of Cell Coupling in Plants with Different Phloem-Loading Strategies

“…Suc transporters in the vacuolar membrane have been identified in poplar (Populus spp.) and other trees, which belong to the passive symplasmic loaders (according to Davidson et al [2011]), and their significance for carbon export was demonstrated (Decourteix et al, 2006;Payyavula et al, 2011). In gymnosperms, Suc transporters have so far not been identified, but they are likely to be present (Shaukat et al, 1975;Canny, 1993).…”

Involvement of CBF Transcription Factors in Winter Hardiness in Birch

“…It is possible that freeze-induced genes such as dehydrins encode proteins that have similar protective functions in low and freezing temperatures, or that they are needed specifically in freeze-thaw conditions. For example, Decourteix et al (2006) showed that the transcript level of the xylem Suc transporter gene JrSUT1, which shows annual variation in walnut (Juglans regia) tree, did not increase in response to freezing but rather to freeze-thaw treatment. The authors suggest that JrSUT1 participates in the repair of freeze-induced xylem vessel embolism by increasing Suc concentrations in xylem sap, which results in active refilling of embolized vessels through the creation of winter stem pressure.…”

Aspen SUCROSE TRANSPORTER3 Allocates Carbon into Wood Fibers

“…Suc is the main transported form of carbon in several trees, and SUTs responsible for the proton gradient-driven transport of Suc have been identified from several tree species, including Betula pendula (Wright et al, 2000), Juglans regia (Decourteix et al, 2006), and Populus spp. (Payyavula et al, 2011).…”

“…Although SUT3RNAi was expected to be primarily active in secondary cell wall-forming cells, a direct effect on young leaves and shoot tip cannot be excluded. A general sink role for the J. regia group II SUT (JrSUT1) was postulated based on high JrSUT1 transcript levels in diverse sink tissues such as roots, female flowers, and stem, while the transcripts were barely detected in source leaves (Decourteix et al, 2006). However, qPCR analysis detected no PtaSUT1 transcripts in shoot tip and developing leaves and only very low levels of PtaSUT3, arguing against a function of Populus spp.…”