The Functionial Research Of Phosphalipase Dδ In Response To Mechanical Wounding In Arabidopsis Thaliana

Mechanical wounding is a common environmental stress in plant kingdom, usually resulting in the plant injuries via biotic or abiotic factors. These factors include storm, hail, infect or herbivore feeding and so on. Every year mechanical wounding can bring unmeasurable and serious consequences to human society, such as, the loss of crop yield, the reduction of fruit quality and the rottenness of vegetables. The response of plants to wounding, a very complex process, has been extensively concerned for a long time. EspecialIyr, the transduction pathway of wound signaling has always been a research hotspot. Recent studies have shown that phospholipase D (PLD) plays important roles in various stresses. PLD is an emzyme, hydrolyzing phospholipids into phosphatidic acid (PA) and the head group. PLD is composed of a family of heterogeneous enzymes with distinguishable biochemical, regulatory, and structural properties. 12 PLD genes have found in Arabidopsis thaliana, whereas PLDα1 and PLDδare the most abundant. Recent results demonstrate that PLDα1 and PLDδare involved in the response to freezing via different mechanisms, which indicated that both of them could play a different role even if under the same stress. To date, PLDα1 and its lipid product PA are found to be involved in the biosynthesis process of jasmonic acid (JA), a primary component in wound signaling. In addition, recent studies have exhibited PLDδhas played important roles in many stresses, such as drought, low temperature and ozone, but the functional research of PLDδin response to mechanical wounding has not been reported. Therefore, the specific objectives of this study were to:â‘ . profile and compare the wounding-induced changes in lipid molecular species in Arabidopsis wild-type WS and PLDδ-knockout plants.â‘¡. examin the effect of PLDδon wound signal components (jasmonic acid, abscisic acid, hydrogen peroxide) and other pemeters (Fv/Fm and malondialdehyde).â‘¢. compare the effect of PLDδwith PLDα1 on hydrogen peroxide (H₂O₂) generated by wounding. These major results are showed below:1. The hydrolysis product PA levels increased rapidly in wild-type WS and, to a lesser extent, in PLDδ-deficient plants by analysis of the lipid profiling. This result indicates that PLDδmight be involved in the response of plant to wounding. The total levels of lipids decreased greatly and every lipid changed differently. All of them, galactolipids account for 90% of the total reduced lipids. The 34-carbon and 36-carbon lipid species containing polyunsaturated fatty acid have mostly changed in two genetype plants on wounding. In particular, 34:6 MGDG is more prominent in wild-type than that in mutant plants (WS, 33.636 nmol/mg DW; 0.777 nmol/mg DW). MGDG is the major galactolipids of plant chloroplasts and its degradation promoted by PLDδcould affect the function of photosynthesis membrane. Fv/Fm ratio is one of the common parameters used in fluorescence and presents the maximum efficiency of PSII. In my work, Fv/Fm ratio increased after the knockout of PLDδ.2. PLDδhad a little effect on MeJA levels, but the abrogation of PLDδaffected the distribution of MeJA in leaf of plants. That is, the levels of MeJA was higher in wounded leaf than systemic leaf in mutant plants, and the facts observed in wild-type plants were opposite. This result illustrates PLDδcould have an effect on the transport and distribution of MeJA in plants after wounding.3. The depletion of PLDα1 in Arabidopsis decreased H₂O₂ production but the null of PLDδhad little effect on it. These results document PLDα1 and PLDδhave played different roles in response to wounding. H₂O₂ was histochemically detected by DAB-staining method in Arabidopsis leaf where accumulated H₂O₂ generated due to wounding. These results exhibit that H₂O₂ can be accumulated at wounded sites, and thenleaf veins, and the distal systemic leaf in whole plant. In addition, it showed that H₂O₂ could be translocated through vascular cylinder to the systemic leaf.Conclusions: PLDδis involved in plant response to the mechanical wounding and has played an important role. It can hydorlysis the membrance lipids in different degree, and then alter the compositions of biomembrane lipids, their proportion and saturated index. Therefore, it affects the function of biomembrane, especially the chloroplast membrane. In addition, PLDδhas an effect on the transport and distribution of MeJA in plants after wounding and H₂O₂, another wound signaling compound, can be translocated through vascular cylinder to the systemic leaf. Two above facts showed that plants acquire the systemic immunity via the transportion of wound signal compounds in order to improve the ability of plant whole resistance after wounding. What's more, PLDδcould involved in the systemic resistance process of plant in response to mechanical wounding.