Phospholipid Signaling Responses in Salt-Stressed Rice Leaves

Abstract

Salinity is one of the major environmental factors limiting growth and productivity of rice plants. In this study, the effect of salt stress on phospholipid signaling responses in rice leaves was investigated. Leaf cuts were radiolabeled with 32P-orthophosphate and the lipids extracted and analyzed by thin-layer chromatography, autoradiography and phosphoimaging. Phospholipids were identified by co-migration of known standards. Results showed that 32Pi was rapidly incorporated into the minor lipids, phos-phatidylinositol bisphosphate (PIP2) and phosphatidic acid (PA) and, interestingly, also into the structural lipids phosphatidylethanolamine (PE) and phosphatidylglycerol (PG), which normally label relatively slowly, like phosphatidylcholine (PC) and phosphatidylinositol (PI). Only very small amounts of PIP2 were found. However, in response to salt stress (NaCl), PIP2 levels rapidly (<30 min) increased up to 4-fold, in a time- and dose-dependent manner. PA and its phosphorylated product, diacylglyc-erolpyrophosphate (DGPP), also increased upon NaCl stress, while cardiolipin (CL) levels decreased. All other phospholipid levels remained unchanged. PA signaling can be generated via the combined action of phospholipase C (PLC) and diacylglycerol kinase (DGK) or directly via phospholipase D (PLD). The latter can be measured in vivo, using a transphosphatidylation assay. Interestingly, these measurements revealed that salt stress inhibited PLD activity, indicating that the salt stress-induced PA response was not due to PLD activity. Comparison of the 32P-lipid responses in salt-tolerant and salt-sensitive cultivars revealed no significant differences. Together these results show that salt stress rapidly activates several lipid responses in rice leaves but that these responses do not explain the difference in salt tolerance between sensitive and tolerant cultivars.

Nonspecific Phospholipase C NPC4 Promotes Responses to Abscisic Acid and Tolerance to Hyperosmotic Stress inArabidopsis

“…Evidence for this proposition is that both DAG and PA restore the npc4-1 response to ABA to the wild-type response, whereas addition of the DGK inhibitor that blocks the DAG to PA conversion prevents response restoration by DAG. In plants, DAG has been shown to be phosphorylated to PA under hyperosmotic stress conditions (Arisz et al, 2009;Darwish et al, 2009;Munnik and Testerink, 2009). PI-PLC has been thought to be the enzyme activated to produce DAG, but the enzymatic step for DAG production was not genetically established.…”

Characterisation of the wheat phospholipid fraction in the presence of nickel and/or selenium

“…PA constituted around 18 and 3 % of total cell phospholipids in control samples of roots and shoots, respectively. When comparing control samples with those exposed to the (Testerink and Munnik 2005;Darwish et al 2009). In the wheat shoots, significant increases in PA species were accompanied by a lower level of PC.…”

Sodium chloride stress during early growth stages altered physiological and growth characteristics of rice

“…The low and excessive level of salt about threshold level of plants reduced plant growth characteristics, yield, and ultimately plant death (Darwish et al, 2009). In the arid to semi-arid regions of the world, high temperature and water shortage regularly cause salinity problem that bound or hinder staple crop productivity including rice (Nachimuthu et al, 2017).…”

“…It is estimated that 20% of irrigated land is affected by soil salt stress, decreasing crop production (Kader and Lindberg, 2010). After exposure to salt stress, the crop plants are faced with osmotic stress, oxidative stress, ion toxicity, nutritional imbalance, as well as growth stages at which plant subjected to salt stress (Darwish et al, 2009;Habib et al, 2010). The sensitivity of numerous plant species differs at seed germination, early seedling growth, and advance growth stages with respect to salt stress (Mokhtar et al, 2015).…”