Salt stress is a severe type of environmental stress. It adversely affects agricultural production worldwide. The overproduction of reactive oxygen species (ROS) is the most frequent phenomenon during salt stress. ROS are extremely reactive and, in high amounts, noxious, leading to destructive processes and causing cellular damage. However, at lower concentrations, ROS function as secondary messengers, playing a critical role as signaling molecules, ensuring regulation of growth and adjustment to multifactorial stresses. Plants contain several enzymatic and non-enzymatic antioxidants that can detoxify ROS. The production of ROS and their scavenging are important aspects of the plant’s normal response to adverse conditions. Recently, this field has attracted immense attention from plant scientists; however, ROS-induced signaling pathways during salt stress remain largely unknown. In this review, we will discuss the critical role of different antioxidants in salt stress tolerance. We also summarize the recent advances on the detrimental effects of ROS, on the antioxidant machinery scavenging ROS under salt stress, and on the crosstalk between ROS and other various signaling molecules, including nitric oxide, hydrogen sulfide, calcium, and phytohormones. Moreover, the utilization of “-omic” approaches to improve the ROS-regulating antioxidant system during the adaptation process to salt stress is also described.

Lysophosphatidyl acyltransferase (LPAT) is a pivotal enzyme controlling the metabolic flow of lysophosphatidic acid into different phosphatidic acids in diverse tissues. We examined putative LPAT genes in Arabidopsis thaliana and characterized two related genes that encode the cytoplasmic LPAT. LPAT2 is the lone gene that encodes the ubiquitous and endoplasmic reticulum (ER)–located LPAT. It could functionally complement a bacterial mutant with defective LPAT. LPAT2 and 3 synthesized in recombinant bacteria and yeast possessed in vitro enzyme activity higher on 18:1-CoA than on 16:0-CoA. LPAT2 was expressed ubiquitously in diverse tissues as revealed by RT-PCR, profiling with massively parallel signature sequencing, and promoter-driven β-glucuronidase gene expression. LPAT2 was colocalized with calreticulin in the ER by immunofluorescence microscopy and subcellular fractionation. LPAT3 was expressed predominately but more actively than LPAT2 in pollen. A null allele (lpat2) having a T-DNA inserted into LPAT2 was identified. The heterozygous mutant (LPAT2/lpat2) had minimal altered vegetative phenotype but produced shorter siliques that contained normal seeds and remnants of aborted ovules in a 1:1 ratio. Results from selfing and crossing it with the wild type revealed that lpat2 caused lethality in the female gametophyte but not the male gametophyte, which had the redundant LPAT3. LPAT2-cDNA driven by an LPAT2 promoter functionally complemented lpat2 in transformed heterozygous mutants to produce the lpat2/lpat2 genotype. LPAT3-cDNA driven by the LPAT2 promoter could rescue the lpat2 female gametophytes to allow fertilization to occur but not to full embryo maturation. Two other related genes, putative LPAT4 and 5, were expressed ubiquitously albeit at low levels in diverse organs. When they were expressed in bacteria or yeast, the microbial extract did not contain LPAT activity higher than the endogenous LPAT activity. Whether LPAT4 and 5 encode LPATs remains to be elucidated.

In plants, subcellular triacylglycerol granules in seeds (oil bodies) and floral tapetum (tapetosomes) are stabilized by amphipathic structural protein called oleosin. We hereby report a novel group of oleosins that is present inside the pollen ofArabidopsis thaliana. We have used the conserved sequence of oleosins to locate, via the DNA database, all 16 oleosin genes in the Arabidopsis genome. The oleosin genes can be divided into three groups according to their sequences and tissue-specific expressions, as probed by RNA blot hybridization and reverse transcriptase-PCR. The first group includes eight genes specifically expressed in the floret tapetum. The second group includes five genes specifically expressed in maturing seeds. The third, novel group includes three genes expressed in both maturing seeds and floral microspores, which will become pollen. Transgenic study using the promoter of one of these genes attached to a reporter gene has provided corroborative evidence for the specific expression of the gene in the microspores in the florets. One of the pollen oleosins can be identified by microsequencing and specific immunoblotting. Pollen oleosins synthesized by recombinant bacteria can collaborate with phospholipids in stabilizing reconstituted oil bodies. Thus, pollen has oleosins to stabilize the abundant subcellular oil bodies. Seed oil bodies and floret tapetosomes have been isolated from the miniatureArabidopsis plants, and the success indicates that the organelles can be subjected to future biochemical and genetic studies.

Lysophosphatidyl acyltransferase (LPAAT) is a pivotal enzyme controlling the metabolic flow of lysophosphatidic acid into different phosphatidic acids in diverse tissues. A search of the Arabidopsis genome database revealed five genes that could encode LPAAT-like proteins. We identified one of them, LPAAT1, to be the lone gene that encodes the plastid LPAAT. LPAAT1 could functionally complement a bacterial mutant that has defective LPAAT. Bacteria transformed with LPAAT1 produced LPAAT that had in vitro enzyme activity much higher on 16:0-coenzyme A than on 18:1-coenzyme A in the presence of 18:1-lysophosphatidic acid. LPAAT1 transcript was present in diverse organs, with the highest level in green leaves. A mutant having a T-DNA inserted into LPAAT1 was identified. The heterozygous mutant has no overt phenotype, and its leaf acyl composition is similar to that of the wild type. Selfing of a heterozygous mutant produced normal-sized and shrunken seeds in the Mendelian ratio of 3:1, and the shrunken seeds could not germinate. The shrunken seeds apparently were homozygous of the T-DNA-inserted LPAAT1, and development of the embryo within them was arrested at the heart-torpedo stage. This embryo lethality could be rescued by transformation of the heterozygous mutant with a 35S:LPAAT1 construct. The current findings of embryo death in the homozygous knockout mutant of the plastid LPAAT contrasts with earlier findings of a normal phenotype in the homozygous mutant deficient of the plastid glycerol-3-phosphate acyltransferase; both mutations block the synthesis of plastid phosphatidic acid. Reasons for the discrepancy between the contrasting phenotypes of the two mutants are discussed.

Plants are immobile and, to overcome harsh environmental conditions such as drought, salt, and cold, they have evolved complex signaling pathways. Abscisic acid (ABA), an isoprenoid phytohormone, is a critical signaling mediator that regulates diverse biological processes in various organisms. Significant progress has been made in the determination and characterization of key ABA-mediated molecular factors involved in different stress responses, including stomatal closure and developmental processes, such as seed germination and bud dormancy. Since ABA signaling is a complex signaling network that integrates with other signaling pathways, the dissection of its intricate regulatory network is necessary to understand the function of essential regulatory genes involved in ABA signaling. In the present review, we focus on two aspects of ABA signaling. First, we examine the perception of the stress signal (abiotic and biotic) and the response network of ABA signaling components that transduce the signal to the downstream pathway to respond to stress tolerance, regulation of stomata, and ABA signaling component ubiquitination. Second, ABA signaling in plant development processes, such as lateral root growth regulation, seed germination, and flowering time regulation is investigated. Examining such diverse signal integration dynamics could enhance our understanding of the underlying genetic, biochemical, and molecular mechanisms of ABA signaling networks in plants.