Effects of cold‐girdling on flows in the transport phloem in Ricinus communis: is mass flow inhibited?

Abstract

The effects of cold girdling of the transport phloem at the hypocotyl of Ricinus communis on solute and water transport were investigated. Effects on the chemical composition of saps of phloem and xylem as well as of stem tissue were studied by conventional techniques and the water flow in the phloem was investigated by NMR imaging. Cold girdling reduced the concentration of sucrose but not that of inorganic solutes or amino acids in phloem saps. The possibility that cold treatment inhibited the retrieval of sucrose into the phloem, following leaching from the sieve tubes along a chemical gradient is discussed. Leaching of other solutes did not occur, as a result of missing promoting gradients in stem tissue. Following 3 d of cold girdling, sugar concentration increased and starch was synthesized and accumulated in stem tissue above the cold girdling region and along the cold-treated phloem pathway due to leaching of sugars from the phloem. Only in the very first period of cold girdling ( < < < < 15-30 min) was mass flow inhibited, but recovered in the rest of cold treatment period to values similar to the control period before and the recovery period after the cold treatment. It is concluded that cold treatment affected phloem transport through two independent and reversible processes: (1) a permanent leaching of sucrose from the phloem stem without normal retrieval during cold treatment, and (2) a short-term inhibition of mass flow at the beginning of cold treatment, possibly involving P proteins. Possible further mechanisms for reversible inhibition of water flow are discussed.

Seasonal variations of belowground carbon transfer assessed by in situ &lt;sup&gt;13&lt;/sup&gt;CO&lt;sub&gt;2&lt;/sub&gt; pulse labelling of trees

“…The markedly different transfer time of 13 C belowground between the two broadleaved species and the pine highlights differences in the velocity of photosynthate transport via the phloem sap between angiosperm and gymnosperm that were related to differences in phloem anatomy (Dannoura et al, 2011;Wingate et al, 2010). The doubling of time lag and peak time between summer and winter time, as well as the delayed peak time (more than 10 days in the resting season) were consistent with an effect of temperature on phloem loading, especially on retrieval after leaching (Peuke et al, 2006), on the viscosity of phloem sap (Hölttä et al, 2009) or on the carbohydrate sink strength (Wingate et al, 2010) that may affect the velocity of phloem sap (Dannoura et al, 2011).…”

Sieve Tube Geometry in Relation to Phloem Flow

“…Subsequent investigations supported the notion that callose is formed in response to mechanical injury (Esau and Cheadle, 1961;Evert and Derr, 1964;Eschrich, 1975) and that the process can occur within seconds (Currier, 1957;Eschrich, 1965). Reductions of phloem conductivity after heat treatment (McNairn and Currier, 1968;McNairn, 1972) or localized chilling (Giaquinta and Geiger, 1973;Peuke et al, 2006) were also traced back to sieve plate pore constriction by callose formation. Investigations of callose formation by fluorescence intensity measurements suggested that burning leaf tips leads to distant callose formation (Furch et al, 2007).…”

Intact Plant Magnetic Resonance Imaging to Study Dynamics in Long-Distance Sap Flow and Flow-Conducting Surface Area

“…Changing the osmotic pressure in the root medium might induce a response in the rate of refilling, which could indicate the possible role of root pressure. The effect of cold girdling of part of the stem (Peuke et al, 2006) and adding phloem flow results in addition to xylem flow could further indicate the role of starch-to-sugar conversion and transport into embolized conduits, assisted by phloem-driven radial, mass flow (Salleo et al, 2004). Probing radial water motion in refilling vessels with MRI could monitor whether refilling vessels are feeding intact vessels with water.…”