• Phospholipase D (PLD) hydrolyzes phospholipids to produce phosphatidic acid (PA) and a head group, and is involved in the response to various environmental stresses, including salinity. Here, we determined the roles of PLDα and PA in the mediation of salt (NaCl)-stress signaling through the regulation of mitogen-activated protein kinase (MAPK or MPK) in Arabidopsis thaliana. • NaCl-induced changes in the content and composition of PA were quantitatively profiled by electrospray ionization-tandem mass spectrometry (ESI-MS/MS). A specific PA species (a MAPK 16:0-18:2 PA), which was increased in abundance by exposure to NaCl, bound to a MPK6, according to filter binding and ELISA. The effect of PA on MPK6 activity was tested using in-gel analysis. • 16:0-18:2 PA stimulated the activity of MPK6 immunoprecipitated from Arabidopsis leaf extracts. Treatment with NaCl induced a transient activation of MPK6 in wild-type plant, but the activation was abolished in the pldα1 plant mutant. A plasma membrane Na(+)/H(+) antiporter (SOS1) was identified as a downstream target of MPK6. MPK6 phosphorylated the C-terminal fragment of SOS1. The MPK6 phosphorylation of SOS1 was stimulated by treatment with NaCl, as well as directly by PA. • These results suggest that PA plays a critical role in coupling MAPK cascades in response to salt stress.

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A salt-sensitive mutant designated rice salt sensitive 2 (rss2) was isolated from the M2 generation of the rice cultivar Nipponbare mutagenized with ethyl methanesulfonate (EMS). This mutant exhibited a greater decrease in salt tolerance with a significant increase in Na(+) content in its shoots. Genetic analysis indicated that the increase in Na(+) in rss2 was controlled by a single recessive gene. Further genome-wide analysis of the linkage map constructed from the F2 population of rss2/Zhaiyeqing 8 (ZYQ8) showed that two quantitative trait loci (QTLs) on chromosomes 1 and 6 were responsible for the Na(+) concentration in shoots, which explained 14.5% and 53.3%, respectively, of the phenotypic variance. The locus on chromosome 1, but not that on chromosome 6, was also detected in the F2 population of Nipponbare/ZYQ8, suggesting that the QTL on chromosome 6 was responsible for the salt sensitivity in rss2. By analyzing the recombination events in 220 mutant individuals of an enlarged mapping population of rss2/ZYQ8, the rss2 locus was precisely mapped to an interval of 605.3 kb between insertion/deletion (InDel) markers IM21962 and IM22567. This finding will facilitate the cloning of the rss2 locus and provide insight into the physiological mechanisms of salt sensitivity in rice.

Single‐gene mutants tolerant or sensitive to salt stress are ideal materials for identifying and cloning genes related to salt tolerance in rice (Oryza sativa L.). In the present study, a salt‐sensitive mutant was obtained from the ethyl methanesulfonate (EMS)‐induced Nipponbare bank. The mutant, designated rice salt sensitive 4 (rss4), showed a significant increase in salt sensitivity at the seedling stage and accumulated high levels of Na+ in shoots, particularly in the blades of old leaves, under conditions of NaCl stress. Genetic analysis indicated that the mutation was controlled by a single recessive gene. Quantitative trait locus (QTL) analysis for shoot Na+ content was performed using an F2 population derived from a cross between the rss4 mutant and the indica cultivar Zhaiyeqing 8 (ZYQ8). Three QTLs were identified and one located on the long arm of chromosome 6 was determined to be the candidate locus of the rss4 gene based on comparison and analysis, which explained 40.5% of the phenotypic variance in the shoot Na+ content of the F2 population. Further analysis of recombination events in 165 mutant individuals of an enlarged mapping population of rss4/ZYQ8 defined the rss4 locus to an interval of 230.5 kb bracketed by markers RM20566 and IM28706 on chromosome 6.

Background: Image processing techniques have been widely used in the analysis of leaf characteristics. Earlier techniques for processing digital RGB color images of plant leaves had several drawbacks, such as inadequate de-noising, and adopting normal-probability statistical estimation models which have few parameters and limited applicability. Results: We confirmed the skewness distribution characteristics of the red, green, blue and grayscale channels of the images of tobacco leaves. Twenty skewed-distribution parameters were computed including the mean, median, mode, skewness, and kurtosis. We used the mean parameter to establish a stepwise regression model that is similar to earlier models. Other models based on the median and the skewness parameters led to accurate RGB-based description and prediction, as well as better fitting of the SPAD value. More parameters improved the accuracy of RGB model description and prediction, and extended its application range. Indeed, the skewed-distribution parameters can describe changes of the leaf color depth and homogeneity. Conclusions: The color histogram of the blade images follows a skewed distribution, whose parameters greatly enrich the RGB model and can describe changes in leaf color depth and homogeneity.