Summary• Chilling triggers rapid molecular responses that permit the maintenance of plant cell homeostasis and plant adaptation. Recent data showed that nitric oxide (NO) is involved in plant acclimation and tolerance to cold. The participation of NO in the early transduction of the cold signal in Arabidopsis thaliana was investigated.• The production of NO after a short exposure to cold was assessed using the NOsensitive fluorescent probe 4, 5-diamino fluoresceine diacetate and chemiluminescence. Pharmacological and genetic approaches were used to analyze NO sources and NO-mediated changes in cold-regulated gene expression, phosphatidic acid (PtdOH) synthesis and sphingolipid phosphorylation.• NO production was detected after 1-4 h of chilling. It was impaired in the nia1nia2 nitrate reductase mutant. Moreover, NO accumulation was not observed in H7 plants overexpressing the A. thaliana nonsymbiotic hemoglobin Arabidopsis haemoglobin 1 (AHb1). Cold-regulated gene expression was affected in nia1nia2 and H7 plants. The synthesis of PtdOH upon chilling was not modified by NO depletion. By contrast, the formation of phytosphingosine phosphate and ceramide phosphate, two phosphorylated sphingolipids that are transiently synthesized upon chilling, was negatively regulated by NO.• Taken together, these data suggest a new function for NO as an intermediate in gene regulation and lipid-based signaling during cold transduction.

The signaling events generated by a cold exposure are poorly known in plants. We were interested in checking the possible activation of enzymes of the phosphoinositide signaling pathway in response to a temperature drop. In Arabidopsis suspension cells labeled with 33 PO 4 3Ϫ , a cold treatment induces a rapid increase of phosphatidic acid (PtdOH) content. This production was due to the simultaneous activation of phospholipase C (through diacylglycerol kinase activity) and phospholipase D, as monitored by the production of inositol triphosphate and of transphosphatidylation product, respectively. Moreover, inhibitors of the phosphoinositide pathway and of diacylglycerol kinase reduced PtdOH production. Enzyme activation occurred immediately after cells were transferred to low temperature. The respective contribution of both kind of phospholipases in cold-induced production of PtdOH could be estimated. We created conditions where phospholipids were labeled with 33 PO 4 3Ϫ , but with ATP being nonradioactive. In such conditions, the apparition of radioactive PtdOH reflected PLD activity. Thus, we demonstrated that during a cold stress, phospholipase D activity accounted for 20% of PtdOH production. The analysis of composition in fatty acids of cold-produced PtdOH compared with that of different phospholipids confirmed that cold-induced PtdOH more likely derived mainly from phosphoinositides. The addition of chemical reagents modifying calcium availability inhibited the formation of PtdOH, showing that the cold-induced activation of phospholipase pathways is dependent on a calcium entry.During their development, plants are submitted to various stresses, either abiotic ones like changes in light intensities, in temperature conditions, or in soil water potential, or biotic ones like interactions with microorganisms. Among these stresses, changes in temperature are very important for plants cultivated in temperate climates. They are submitted to temperature variations between day and night, but also over the different seasons. Contrary to mammals, no system to maintain temperature homeostasis exists in plants that are going to adapt to a temperature change by modifying their metabolism. It has been observed for instance that in response to a cold treatment, specific genes are expressed such as those leading to the accumulation of sugar and Pro. Most of these metabolic changes explain why some plants submitted for a while to nonchilling, cold temperatures can resist to subzero temperature thanks to the so called cold-acclimation phenomenon (Thomashow, 1998(Thomashow, , 2001. Although many genes have been shown to be induced by a cold treatment (Seki et al., 2001), the signaling pathway implicated in the perception and in the transduction of cold signal into the cells is poorly known. In Synechocystis sp., Vigh and his collaborators (Vigh et al., 1993) proposed that rigidification of the plasma membrane might be the event that initiates all the downstream signaling cascade. Suzuki and collaborators (Suzuki et al., 20...