Trans-acting factor designated OSBZ8 interacts with both typical abscisic acid responsive elements as well as abscisic acid responsive element-like sequences in the vegetative tissues of indica rice cultivars

Validation of a high-confidence regulatory network for gene-to-NUE phenotype in field-grown rice

Nitrogen (N) and Water (W) - two resources critical for crop productivity - are becoming increasingly limited in soils globally. To address this issue, we aim to uncover the gene regulatory networks (GRNs) that regulate nitrogen use efficiency (NUE) - as a function of water availability - in Oryza sativa, a staple for 3.5 billion people. In this study, we infer and validate GRNs that correlate with rice NUE phenotypes affected by N-by-W availability in the field. We did this by exploiting RNA-seq and crop phenotype data from 19 rice varieties grown in a 2x2 N-by-W matrix in the field. First, to identify gene-to-NUE field phenotypes, we analyzed these datasets using weighted gene co-expression network analysis (WGCNA). This identified two network modules ("skyblue" & "grey60") highly correlated with NUE grain yield (NUEg). Next, we focused on 90 TFs contained in these two NUEg modules and predicted their genome-wide targets using the N-and/or-W response datasets using a random forest network inference approach (GENIE3). Next, to validate the GENIE3 TF→target gene predictions, we performed Precision/Recall Analysis (AUPR) using nine datasets for three TFs validated in planta. This analysis sets a precision threshold of 0.31, used to "prune" the GENIE3 network for high-confidence TF→target gene edges, comprising 88 TFs and 5,716 N-and/or-W response genes. Next, we ranked these 88 TFs based on their significant influence on NUEg target genes responsive to N and/or W signaling. This resulted in a list of 18 prioritized TFs that regulate 551 NUEg target genes responsive to N and/or W signals. We validated the direct regulated targets of two of these candidate NUEg TFs in a plant cell-based TF assay called TARGET, for which we also had in planta data for comparison. Gene ontology analysis revealed that 6/18 NUEg TFs - OsbZIP23 (LOC_Os02g52780), Oshox22 (LOC_Os04g45810), LOB39 (LOC_Os03g41330), Oshox13 (LOC_Os03g08960), LOC_Os11g38870, and LOC_Os06g14670 - regulate genes annotated for N and/or W signaling. Our results show that OsbZIP23 and Oshox22, known regulators of drought tolerance, also coordinate W-responses with NUEg. This validated network can aid in developing/breeding rice with improved yield on marginal, low N-input, drought-prone soils.

Genomics and transcriptomics to protect rice (Oryza sativa. L.) from abiotic stressors: -pathways to achieving zero hunger

More over half of the world's population depends on rice as a major food crop. Rice (Oryza sativa L.) is vulnerable to abiotic challenges including drought, cold, and salinity since it grown in semi-aquatic, tropical, or subtropical settings. Abiotic stress resistance has bred into rice plants since the earliest rice cultivation techniques. Prior to the discovery of the genome, abiotic stress-related genes were identified using forward genetic methods, and abiotic stress-tolerant lines have developed using traditional breeding methods. Dynamic transcriptome expression represents the degree of gene expression in a specific cell, tissue, or organ of an individual organism at a specific point in its growth and development. Transcriptomics can reveal the expression at the entire genome level during stressful conditions from the entire transcriptional level, which can be helpful in understanding the intricate regulatory network relating to the stress tolerance and adaptability of plants. Rice (Oryza sativa L.) gene families found comparatively using the reference genome sequences of other plant species, allowing for genome-wide identification. Transcriptomics via gene expression profiling which have recently dominated by RNA-seq complements genomic techniques. The identification of numerous important qtl,s genes, promoter elements, transcription factors and miRNAs involved in rice response to abiotic stress was made possible by all of these genomic and transcriptomic techniques. The use of several genomes and transcriptome methodologies to comprehend rice (Oryza sativa, L.) ability to withstand abiotic stress have been discussed in this review.

Gene regulation at transcriptional and post-transcriptional levels to combat salt stress in plants

Soil salinity is a major challenge that will be faced more and more by human population in the near future. Higher salt concentrations in the soil limit the growth and production of crops, which poses serious threats to global food production. Various plant breeding approaches have been followed in the past which are reported to reduce the effect of salt stress by inducing the level of protective metabolites like osmolytes and antioxidants. Conventional breeding approaches are time-consuming and not cost-effective. In recent times, genetic engineering has been largely followed to confer salt tolerance through introgressions of single transgenes or stacking multiple transgenes. However, most of such works are limited only at the laboratory level and field trials are still awaited to prove the long-term efficacy of such transgenics. In this review, we attempt to present a broad overview of the current strategies undertaken to develop halophytic and salt-tolerant crops. The salt-induced damages in the plants are highlighted, followed by representing the novel traits, associated with salt stress, which can be used for engineering salt tolerance in glycophytic crops. Additionally, the role of transcriptional and epigenetic regulation in plants for amelioration of salt-induced damages has been reviewed. The role of post-transcriptional mechanisms such as microRNA regulation, genome editing and alternative splicing, during salt stress, and their implications in the development of salt-tolerant crops are also discussed. Finally, we present a short overview about the role of ion transporters and rhizobacteria in the engineering of salt tolerance in crop species.

PlWRKY13: A Transcription Factor Involved in Abiotic and Biotic Stress Responses in Paeonia lactiflora

Many members of the WRKY family regulate plant growth and development. Recent studies have shown that members of the WRKY family, specifically WRKY13, play various roles in the regulation of plant stress resistance. To study the function of WRKY family members in peony, the PlWRKY13 gene (KY271095) was cloned from peony leaves. Sequence analysis and subcellular localization results revealed that PlWRKY13 has no introns, belongs to the type IIc subgroup of the WRKY family, and functions in the nucleus. The expression pattern of PlWRKY13 was analysed via real-time quantitative RT-PCR (qRT-PCR), which showed that the expression of PlWRKY13 was induced by four types of abiotic stress, low-temperature, high-temperature, waterlogging and salt stress, and was positively upregulated in response to these stresses. In addition, the expression of PlWRKY13 tended to first decrease and then increase after infection with Alternaria tenuissima. Virus-induced gene silencing (VIGS) technology was used to explore the function of PlWRKY13 in the resistance of Paeonia lactiflora to fungal infection further, and the results showed that PlWRKY13-silenced plants displayed increased sensitivity to A. tenuissima. The infection was more severe and the disease index (DI) significantly greater in the PlWRKY13-silenced plants than in the control plants, and the expression of pathogenesis-related (PR) genes was also significantly altered in the PlWRKY13-silenced plants compared with the control plants. The contents of the endogenous hormones jasmonic acid (JA) and salicylic acid (SA) were measured, and the results showed that the JA content increased gradually after infection with A. tenuissima and that JA may play an active role in the resistance of P. lactiflora to pathogen infection, while the SA content decreased after PlWRKY13 silencing. The contents of the two hormones decreased overall, suggesting that they are related to the transcription of PlWRKY13 and that PlWRKY13 may be involved in the disease-resistance pathway mediated by JA and SA. In summary, the results of our study showed that PlWRKY13 expression was induced by stress and had a positive effect on the resistance of P. lactiflora to fungal infection.

Evolutionary relationships and expression analysis of EUL domain proteins in rice (Oryza sativa)

BACKGROUND

Lectins, defined as 'Proteins that can recognize and bind specific carbohydrate structures', are widespread among all kingdoms of life and play an important role in various biological processes in the cell. Most plant lectins are involved in stress signaling and/or defense. The family of Euonymus-related lectins (EULs) represents a group of stress-related lectins composed of one or two EUL domains. The latter protein domain is unique in that it is ubiquitous in land plants, suggesting an important role for these proteins.

RESULTS

Despite the availability of multiple completely sequenced rice genomes, little is known on the occurrence of lectins in rice. We identified 329 putative lectin genes in the genome of Oryza sativa subsp. japonica belonging to nine out of 12 plant lectin families. In this paper, an in-depth molecular characterization of the EUL family of rice was performed. In addition, analyses of the promoter sequences and investigation of the transcript levels for these EUL genes enabled retrieval of important information related to the function and stress responsiveness of these lectins. Finally, a comparative analysis between rice cultivars and several monocot and dicot species revealed a high degree of sequence conservation within the EUL domain as well as in the domain organization of these lectins.

CONCLUSIONS

The presence of EULs throughout the plant kingdom and the high degree of sequence conservation in the EUL domain suggest that these proteins serve an important function in the plant cell. Analysis of the promoter region of the rice EUL genes revealed a diversity of stress responsive elements. Furthermore analysis of the expression profiles of the EUL genes confirmed that they are differentially regulated in response to several types of stress. These data suggest a potential role for the EULs in plant stress signaling and defense.

RNA-seq for comparative transcript profiling of kenaf under salinity stress

Kenaf (Hibiscus cannabinus L.) is an economically important global natural fiber crop. As a consequence of the increased demand for food crops and the reduction of available arable land, kenaf cultivation has increasingly shifted to saline and alkaline land. To investigate the molecular mechanism of salinity tolerance in kenaf, we performed Illumina high-throughput RNA sequencing on shoot tips of kenaf and identified 71,318 unigenes, which were annotated using four different protein databases. In total, 2,384 differentially expressed genes (DEGs) were identified between the salt-stressed and the control plants, 1,702 of these transcripts were up-regulated and 683 transcripts were down-regulated. Thirty-seven transcripts belonging to 15 transcription-factor families that respond to salt stress were identified. Gene ontology function enrichment analysis revealed that the genes encoding antioxidant enzymes were up-regulated. The amino acid metabolism and carbohydrate metabolism pathways were highly enriched among these DEGs under salt stress conditions. In order to confirm the RNA-seq data, we randomly selected 20 unigenes for analysis using a quntitative real-time polymerase chain reaction. Our study not only provided the large-scale assessment of transcriptome resources of kenaf but also guidelines for understanding the mechanism underlying salt stress responses in kenaf.

Abscisic-acid-dependent basic leucine zipper (bZIP) transcription factors in plant abiotic stress

One of the major causes of significant crop loss throughout the world is the myriad of environmental stresses including drought, salinity, cold, heavy metal toxicity, and ultraviolet-B (UV-B) rays. Plants as sessile organisms have evolved various effective mechanism which enable them to withstand this plethora of stresses. Most of such regulatory mechanisms usually follow the abscisic-acid (ABA)-dependent pathway. In this review, we have primarily focussed on the basic leucine zipper (bZIP) transcription factors (TFs) activated by the ABA-mediated signalosome. Upon perception of ABA by specialized receptors, the signal is transduced via various groups of Ser/Thr kinases, which phosphorylate the bZIP TFs. Following such post-translational modification of TFs, they are activated so that they bind to specific cis-acting sequences called abscisic-acid-responsive elements (ABREs) or GC-rich coupling elements (CE), thereby influencing the expression of their target downstream genes. Several in silico techniques have been adopted so far to predict the structural features, recognize the regulatory modification sites, undergo phylogenetic analyses, and facilitate genome-wide survey of TF under multiple stresses. Current investigations on the epigenetic regulation that controls greater accessibility of the inducible regions of DNA of the target gene to the bZIP TFs exclusively under stress situations, along with the evolved stress memory responses via genomic imprinting mechanism, have been highlighted. The potentiality of overexpression of bZIP TFs, either in a homologous or in a heterologous background, in generating transgenic plants tolerant to various abiotic stressors have also been addressed by various groups. The present review will provide a coherent documentation on the functional characterization and regulation of bZIP TFs under multiple environmental stresses, with the major goal of generating multiple-stress-tolerant plant cultivars in near future.

WRKY proteins: signaling and regulation of expression during abiotic stress responses

WRKY proteins are emerging players in plant signaling and have been thoroughly reported to play important roles in plants under biotic stress like pathogen attack. However, recent advances in this field do reveal the enormous significance of these proteins in eliciting responses induced by abiotic stresses. WRKY proteins act as major transcription factors, either as positive or negative regulators. Specific WRKY factors which help in the expression of a cluster of stress-responsive genes are being targeted and genetically modified to induce improved abiotic stress tolerance in plants. The knowledge regarding the signaling cascade leading to the activation of the WRKY proteins, their interaction with other proteins of the signaling pathway, and the downstream genes activated by them are altogether vital for justified targeting of the WRKY genes. WRKY proteins have also been considered to generate tolerance against multiple abiotic stresses with possible roles in mediating a cross talk between abiotic and biotic stress responses. In this review, we have reckoned the diverse signaling pattern and biological functions of WRKY proteins throughout the plant kingdom along with the growing prospects in this field of research.

Characterization of gene expression associated with drought avoidance and tolerance traits in a perennial grass species

To understand molecular mechanisms of perennial grass adaptation to drought stress, genes associated with drought avoidance or tolerance traits were identified and their expression patterns were characterized in C4 hybrid bermudagrass [Cynodon dactylon (L.) Pers.×C. transvaalensis Burtt Davy, cv. Tifway] and common bermudagrass (C. dactylon, cv. C299). Plants of drought-tolerant 'Tifway' and drought-sensitive 'C299' were exposed to drought for 5 d (mild stress) and 10 d (severe stress) by withholding irrigation in a growth chamber. 'Tifway' maintained significantly lower electrolyte leakage and higher relative water content than 'C299' at both 5 and 10 d of drought stress. Four cDNA libraries via suppression subtractive hybridization analysis were constructed and identified 277 drought-responsive genes in the two genotypes at 5 and 10 d of drought stress, which were mainly classified into the functional categories of stress defense, metabolism, osmoregulation, membrane system, signal and regulator, structural protein, protein synthesis and degradation, and energy metabolism. Quantitative-PCR analysis confirmed the expression of 36 drought up-regulated genes that were more highly expressed in drought-tolerant 'Tifway' than drought-sensitive 'C299', including those for drought avoidance traits, such as cuticle wax formation (CER1 and sterol desaturase), for drought tolerance traits, such as dehydration-protective proteins (dehydrins, HVA-22-like protein) and oxidative stress defense (superoxide dismutase, dehydroascorbate reductase, 2-Cys peroxiredoxins), and for stress signaling (EREBP-4 like protein and WRKY transcription factor). The results suggest that the expression of genes for stress signaling, cuticle wax accumulation, antioxidant defense, and dehydration-protective protein accumulation could be critically important for warm-season perennial grass adaptation to long-term drought stress.

Expression profiling of abiotic stress-inducible genes in response to multiple stresses in rice (Oryza sativa L.) varieties with contrasting level of stress tolerance

The present study considered transcriptional profiles and protein expression analyses from shoot and/or root tissues under three abiotic stress conditions, namely, salinity, dehydration, and cold, as well as following exogenous abscisic acid treatment, at different time points of stress exposure in three indica rice varieties, IR-29 (salt sensitive), Pokkali, and Nonabokra (both salt tolerant). The candidate genes chosen for expression studies were HKT-1, SOS-3, NHX-1, SAPK5, SAPK7, NAC-1, Rab16A, OSBZ8, DREBP2, CRT/DREBP, WRKY24, and WRKY71, along with the candidate proteins OSBZ8, SAMDC, and GST. Gene expression profile revealed considerable differences between the salt-sensitive and salt-tolerant rice varieties, as the expression in the latter was higher even at the constitutive level, whereas it was inducible only by corresponding stress signals in IR-29. Whether in roots or shoots, the transcriptional responses to different stressors peaked following 24 h of stress/ABA exposure, and the transcript levels enhanced gradually with the period of exposure. The generality of stress responses at the transcriptional level was therefore time dependent. Heat map data also showed differential transcript abundance in the three varieties, correlating the observation with transcript profiling. In silico analysis of the upstream regions of all the genes represented the existence of conserved sequence motifs in single or multiple copies that are indispensable to abiotic stress response. Overall, the transcriptome and proteome analysis undertaken in the present study indicated that genes/proteins conferring tolerance, belonging to different functional classes, were overrepresented, thus providing novel insight into the functional basis of multiple stress tolerance in indica rice varieties. The present work will pave the way in future to select gene(s) for overexpression, so as to generate broad spectrum resistance to multiple stresses simultaneously.

Differential acetylation of histone H3 at the regulatory region of OsDREB1b promoter facilitates chromatin remodelling and transcription activation during cold stress

The rice ortholog of DREB1, OsDREB1b, is transcriptionally induced by cold stress and over-expression of OsDREB1b results in increase tolerance towards high salt and freezing stress. This spatio-temporal expression of OsDREB1b is preceded by the change in chromatin structure at the promoter and the upstream region for gene activation. The promoter and the upstream region of OsDREB1b genes appear to be arranged into a nucleosome array. Nucleosome mapping of ∼700bp upstream region of OsDREB1b shows two positioned nucleosomes between −610 to −258 and a weakly positioned nucleosome at the core promoter and the TSS. Upon cold stress, there is a significant change in the nucleosome arrangement at the upstream region with increase in DNaseI hypersensitivity or MNase digestion in the vicinity of cis elements and TATA box at the core promoter. ChIP assays shows hyper-acetylation of histone H3K9 throughout the locus whereas region specific increase was observed in H3K14ac and H3K27ac. Moreover, there is an enrichment of RNA PolII occupancy at the promoter region during transcription activation. There is no significant change in the H3 occupancy in OsDREB1b locus negating the possibility of nucleosome loss during cold stress. Interestingly, cold induced enhanced transcript level of OsDREB1b as well as histone H3 acetylation at the upstream region was found to diminish when stressed plants were returned to normal temperature. The result indicates absolute necessity of changes in chromatin conformation for the transcription up-regulation of OsDREB1b gene in response to cold stress. The combined results show the existence of closed chromatin conformation at the upstream and promoter region of OsDREB1b in the transcription “off” state. During cold stress, changes in region specific histone modification marks promote the alteration of chromatin structure to facilitate the binding of transcription machinery for proper gene expression.

Mechanism of salinity tolerance in plants: physiological, biochemical, and molecular characterization

Salinity is a major abiotic stress limiting growth and productivity of plants in many areas of the world due to increasing use of poor quality of water for irrigation and soil salinization. Plant adaptation or tolerance to salinity stress involves complex physiological traits, metabolic pathways, and molecular or gene networks. A comprehensive understanding on how plants respond to salinity stress at different levels and an integrated approach of combining molecular tools with physiological and biochemical techniques are imperative for the development of salt-tolerant varieties of plants in salt-affected areas. Recent research has identified various adaptive responses to salinity stress at molecular, cellular, metabolic, and physiological levels, although mechanisms underlying salinity tolerance are far from being completely understood. This paper provides a comprehensive review of major research advances on biochemical, physiological, and molecular mechanisms regulating plant adaptation and tolerance to salinity stress.

Deciphering the role of various cis-acting regulatory elements in controlling SamDC gene expression in rice

Lately we have published on the characterization of the upstream of SamDC gene from rice and investigated the involvement of various cis-elements present in the promoter region in its transcriptional regulation. Analysis of SamDC expression showed that it was inducible by abiotic stresses like salinity, drought, and cold as well as by light and ABA treatment. Furthermore, DNA protein interaction studies have identified transacting actors responsible for its expression after abiotic stresses or light inducibility. Here we have further discussed on the possible role of these cis-elements in modulating the transcriptional network and comment on their function in relation to polyamine biosynthesis during periods of abiotic stress in rice.

OsRMC, a negative regulator of salt stress response in rice, is regulated by two AP2/ERF transcription factors

High salinity causes remarkable losses in rice productivity worldwide mainly because it inhibits growth and reduces grain yield. To cope with environmental changes, plants evolved several adaptive mechanisms, which involve the regulation of many stress-responsive genes. Among these, we have chosen OsRMC to study its transcriptional regulation in rice seedlings subjected to high salinity. Its transcription was highly induced by salt treatment and showed a stress-dose-dependent pattern. OsRMC encodes a receptor-like kinase described as a negative regulator of salt stress responses in rice. To investigate how OsRMC is regulated in response to high salinity, a salt-induced rice cDNA expression library was constructed and subsequently screened using the yeast one-hybrid system and the OsRMC promoter as bait. Thereby, two transcription factors (TFs), OsEREBP1 and OsEREBP2, belonging to the AP2/ERF family were identified. Both TFs were shown to bind to the same GCC-like DNA motif in OsRMC promoter and to negatively regulate its gene expression. The identified TFs were characterized regarding their gene expression under different abiotic stress conditions. This study revealed that OsEREBP1 transcript level is not significantly affected by salt, ABA or severe cold (5 °C) and is only slightly regulated by drought and moderate cold. On the other hand, the OsEREBP2 transcript level increased after cold, ABA, drought and high salinity treatments, indicating that OsEREBP2 may play a central role mediating the response to different abiotic stresses. Gene expression analysis in rice varieties with contrasting salt tolerance further suggests that OsEREBP2 is involved in salt stress response in rice.

Cross-talk between abscisic acid-dependent and abscisic acid-independent pathways during abiotic stress

Salinity, drought and low temperature are the common forms of abiotic stress encountered by land plants. To cope with these adverse environmental factors, plants execute several physiological and metabolic responses. Both osmotic stress (elicited by water deficit or high salt) and cold stress increase the endogenous level of the phytohormone abscisic acid (ABA). ABA-dependent stomatal closure to reduce water loss is associated with small signaling molecules like nitric oxide, reactive oxygen species and cytosolic free calcium, and mediated by rapidly altering ion fluxes in guard cells. ABA also triggers the expression of osmotic stress-responsive (OR) genes, which usually contain single/multiple copies of cis-acting sequence called abscisic acid-responsive element (ABRE) in their upstream regions, mostly recognized by the basic leucine zipper-transcription factors (TFs), namely, ABA-responsive element-binding protein/ABA-binding factor. Another conserved sequence called the dehydration-responsive element (DRE)/C-repeat, responding to cold or osmotic stress, but not to ABA, occurs in some OR promoters, to which the DRE-binding protein/C-repeat-binding factor binds. In contrast, there are genes or TFs containing both DRE/CRT and ABRE, which can integrate input stimuli from salinity, drought, cold and ABA signaling pathways, thereby enabling cross-tolerance to multiple stresses. A strong candidate that mediates such cross-talk is calcium, which serves as a common second messenger for abiotic stress conditions and ABA. The present review highlights the involvement of both ABA-dependent and ABA-independent signaling components and their interaction or convergence in activating the stress genes. We restrict our discussion to salinity, drought and cold stress.

Inducibility of three salinity/abscisic acid-regulated promoters in transgenic rice with gusA reporter gene

The present study evaluates the pattern of stress inducibility of one natural promoter (from rice Rab16A) and two synthetically designed promoters, viz., 4X ABRE (abscisic acid-responsive element, having four tandem repeats of ABRE) and 2X ABRC (abscisic acid-responsive complex, having two tandem repeats of ABRE and two copies of coupling elements), in response to varying concentrations of NaCl and abscisic acid (ABA). Each promoter, independently linked to gusA (that encodes β glucuronidase, GUS), was introduced into rice (cv. Khitish) through particle bombardment. The T(2) progenies showed integration of gusA in their genome. The accumulation of gusA transcript, driven by each promoter in T(2) transgenics, increased with increasing salt/ABA concentration, with ABA being the better activator of each promoter. Induction in GUS expression, driven by different promoters, was noted on exogenous salt/ABA treatments in a concentration-dependent manner. The maximum induction was observed with 2X ABRC promoter. All the three promoters could drive stress-inducible GUS expression in both vegetative and floral organs. However, prominent GUS expression was noted in the whole seed (both embryo and aleurone layer of endosperm) only by 2X ABRC, whereas it was localized only in the embryo for the other two promoters. Thus, our observation characterizes three efficient salinity/ABA-inducible promoters that have the potentiality in crop biotechnology to drive transgene expression for stress tolerance, whenever abiotic stress is encountered.

Amelioration of salinity stress by exogenously applied spermidine or spermine in three varieties of indica rice differing in their level of salt tolerance

We present here the comparative protective potentiality of exogenously applied polyamines (PAs), namely spermidine (Spd) and spermine (Spm), in mitigating NaCl toxicity and inducing short-term salinity tolerance in three indica rice varieties, namely M-1-48 (salt-sensitive), Nonabokra (salt-tolerant) and Gobindobhog (highly sensitive). The retardation in root length or shoot length and toxic Na(+) accumulation or K(+) loss, the considerable increment in malondialdehyde/H(2)O(2) accumulation or lipoxygenase activity, all of which were particularly noteworthy in M-1-48 and Gobindobhog during salinity stress, was appreciably reduced by co-treatment with Spd or Spm. Both the PAs also inhibited the extent of salt-induced protein carbonylation in all the varieties and enhanced protease activity, especially in Gobindobhog. The prevention of chlorophyll degradation was better with Spd in Nonabokra and Gobindobhog. While the salt-induced increase in anthocyanin or reducing sugar level was further prompted by Spd or Spm in all the varieties, the proline content was elevated by Spd particularly in Gobindobhog. During salinity stress, both the PAs were effective in lowering the putrescine accumulation in M-1-48 and Gobindobhog, and strikingly increasing the Spm level in all the varieties, the highest being in Gobindobhog. In addition, they enhanced the activity of peroxidases and compensated for the decreased catalase activity in all the varieties. Thus the two PAs could recuperate all the three varieties from salt-induced damages to different degrees. The salt injuries, encountered in M-1-48 and Gobindobhog, both of which showed greater susceptibility to salinity stress, were more pronouncedly alleviated and counteracted by the PAs, than the salt-tolerant Nonabokra. The reversal of inhibitory effect of salinity stress was conferred by preventing growth inhibition or various forms of cellular damages, maintaining proper K(+)/Na(+) balance or triggering the level of osmolytes and activity of antioxidant enzymes. Our communication offers a referenced evidence for an understanding of the mechanism by which higher PAs relieve the damages particularly in salt-sensitive rice varieties.