Isolation and characterization of lipid in phloem sap of canola

Abstract

Phloem isolated from canola (Brassica napus L.) stems was found to contain phospholipid, diacylglycerol, triacylglycerol, steryl and wax esters, and comparatively high concentrations of unesterified fatty acids. Indeed, the composition of phloem lipid was markedly different from that of microsomal membranes and cytosol isolated from both leaves and stems. Specifically, phloem lipid consisted predominantly of unesterified fatty acids and was enriched in medium-chain fatty acids, in particular, lauric, myristic and pentadecanoic acids. This unique composition also distinguished phloem lipid from that of well-characterized cytosolic lipid particles such as oil bodies found in plant cells. Moreover, levels of medium-chain fatty acids in the phloem increased when canola plants were stressed by exposure to sublethal doses of ultraviolet irradiation. Phloem levels of lauric acid, for example, increased by 11-fold upon treatment with sublethal ultraviolet irradiation. Spherical lipid particles were discernible in isolated phloem sap by electron microscopy, suggesting that the lipid in phloem is in the form of lipid particles. The presence of lipid in phloem may be reflective of long-distance lipid transport in plants, primarily in the form of free fatty acids.

Myzus persicaeSulzer aphid contains oxylipins that originate from phloem sap

“…In the presence of EDTA, callose (1, 3-ß-glucan) formation is blocked at the incision by chelating Ca 2' . It results in enhanced phloem exudation (Madey et al 2002). Oxylipins were extracted and quantified in phloem exudates, revealing only free oxylipins mainly derived from C18:2.…”

“…Phloem sap is responsible for long distance transport of assimilates to non-photosynthesizing organs of the plant (Madey et al 2002). Phloem sap has been considered for a long time as a mere concentrate of carbohydrates.…”

“…Phloem sap has been considered for a long time as a mere concentrate of carbohydrates. It increasingly appears that it has a complex composition containing small molecules (Corbesier et al 2003), peptides and proteins (Giavalisco et al 2006), nucleic acids (Haywood et al 2005) and lipids (Madey et al 2002). Guelette et al (2006) have shown that phloem exudates lipids and total leaf lipids are different.…”

“…Guelette et al (2006) have shown that phloem exudates lipids and total leaf lipids are different. Linolenic acid represents less than three percent of the total fatty acids in phloem but constitutes 20 Á40% of the total fatty acids in leaf microsomes and cytosol (Madey et al 2002). Jasmonates formed through the octadecanoic acid pathway are thought to be transported systematically within wounded plants (Sembdner & Parthier 1993).…”

Categories of Resistance to Greenbug (Homoptera: Aphididae) Biotype I in <B> <I>Aegilops tauschii</I> </B> Germplasm

“…However, the ssi2-determined enhanced antibiosis and resistance to GPA was attenuated in the absence of MPL1 activity in the ssi2 mpl1 double mutant (Louis et al, 2010b). Phloem sap contains lipids (Madey et al, 2002;Nalam et al, 2012), and the salivary glands of phloem-feeding insects contain putative lipases (Shukle et al, 2009), thus suggesting that these insects likely encounter lipids in their diet, one or more of which could be detrimental to GPA.…”