The Long-Distance Transport of Jasmonates in Salt-Treated Pea Plants and Involvement of Lipid Transfer Proteins in the Process

Abstract

The adaption of plants to stressful environments depends on long-distance responses in plant organs, which themselves are remote from sites of perception of external stimuli. Jasmonic acid (JA) and its derivatives are known to be involved in plants' adaptation to salinity. However, to our knowledge, the transport of JAs from roots to shoots has not been studied in relation to the responses of shoots to root salt treatment. We detected a salt-induced increase in the content of JAs in the roots, xylem sap, and leaves of pea plants related to changes in transpiration. Similarities between the localization of JA and lipid transfer proteins (LTPs) around vascular tissues were detected with immunohistochemistry, while immunoblotting revealed the presence of LTPs in the xylem sap of pea plants and its increase with salinity. Furthermore, we compared the effects of exogenous MeJA and salt treatment on the accumulation of JAs in leaves and their impact on transpiration. Our results indicate that salt-induced changes in JA concentrations in roots and xylem sap are the source of accumulation of these hormones in leaves leading to associated changes in transpiration. Furthermore, they suggest the possible involvement of LTPs in the loading/unloading of JAs into/from the xylem and its xylem transport.

Keywords: Pisum sativum L.; immunoblotting; immunolocalization; jasmonates; lipid transfer proteins; long-distance transport; xylem sap.

Figure 1

Effects of salt treatment on JA localization in the pea root basal part 1.5 (a,c) and 4.5 (b,d) hours after the onset of salt exposure. Root section of control pea plants untreated with NaCl (a,b) and plants treated with NaCl (c,d). The scale bar is 150 µm. end—endodermis; x—xylem; ph—phloem; c—cortex.

Figure 2

Immunoblotting with polyclonal rabbit anti-LTP antibodies of xylem sap of pea plants untreated with NaCl (1) and 1.5 h after the onset of salt exposure (2), total protein 20 μg; M- molecular weight marker (a). Relative staining, arbitrary units, maximal staining taken as 100%, and minimal as 0% (b). The amount of protein in the samples was determined by the Bradford method [30], and equal amounts were loaded for electrophoresis.

Figure 3

Effects of salt treatment on the level and localization of lipid transfer proteins (LTPs) in the central cylinder of the root basal part 1.5 (a,c) and 4.5 (b,d) hours after the onset of salt exposure. Root section of control pea plants untreated with NaCl (a,b) and plants treated with NaCl (c,d). In (a,b), transmission mode images are superimposed on fluorescence images. The scale bar is 50 µm. x—xylem; ph—phloem.

Figure 4

Effects of salt treatment on the level and localization of JAs (a,b,d,e) and LTPs (c,f) in the leaves 4.5 h after the onset of salt exposure. Leaf section of control pea plants untreated with NaCl (a–c) and plants treated with NaCl (d–f). (a,d)—leaf tissues, (b,e)—stomata, and (c,f)—leaf vascular bundles. The scale bar is 10 µm. e—epidermis, m—mesophyll, st—stomata, x—xylem, and ph—phloem. To facilitate discrimination between JAs and LTPs detected by the same label (Alexa 488), we assigned them to different pseudocolors: the cyan pseudocolor is assigned to JAs and the yellow pseudocolor is assigned to LTPs.

Figure 5

Effects of salt treatment on the level and localization of ABA in the stomata of pea plants 1.5 h after the onset of salt exposure. Leaf section of control pea plants untreated with NaCl (a) and plants treated with NaCl (b). The scale bar is 10 µm. e—epidermis, m—mesophyll, and st—stomata.

Figure 6

Effect of exogenous MeJA (10 mM) on the level and localization of JA in the leaves of pea plants 1 h after the onset of shoot treatment. Leaf section of control pea plants untreated with meJA (a) and plants treated with meJA (b). The scale bar is 50 µm. e—epidermis, m—mesophyll, and st—stomata.