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Seed priming is a widely used technique in crops to obtain uniform germination and high-quality seedlings. In this study, we found a long-term effect of seed priming with gibberellic acid-3 (GA3) on plant growth and production in Leymus chinensis. Seeds were germinated on agar plates containing 0–200 μM GA3, and the germinated seedlings were transplanted to clay planting pots and grown for about one year. The clonal tillers grown from the mother plants were transplanted to field conditions in the second year. Results showed that GA3 treatment significantly increased seed germination rate by 14–27%. GA3 treatment also promoted subsequent plant growth and biomass production, as shown by a significant increase in plant height, tiller number, and fresh and dry weight in both pot (2016) and field (2017) conditions. It is particularly noteworthy that the growth-promoting effect of a single seed treatment with GA3 lasted for at least two years. In particular, GA3 treatment at 50 μM increased aboveground fresh and dry weight by 168.2% and 108.9% in pot-grown conditions, and 64.5% and 126.2% in field-grown conditions, respectively. These results imply a transgenerational transmission mechanism for the GA-priming effect on clonal offspring growth and biomass production in L. chinensis.

SUMMARYSaline-sodic soils are widely distributed in the western Songnen Plain of Northeast China and planting rice has been found to be an effective and feasible approach for improving saline-sodic soil and increasing food production. Assessment of the effectiveness and sustainability of this method requires monitoring of the changes in soil salinity and nutrient content. The objective of the current study was to investigate the changes of soil salinity and nitrogen (N) contents over 1, 3, 6 and 9 years of cultivation, four application rates of N (N0: no N, N1: 100 kg N/ha, N2: 200 kg N/ha and N3: 300 kg N/ha) and two irrigation water types: ground water irrigation (GWI) and river water irrigation (RWI). Salinity and N contents of soil and water samples were analysed before planting and after harvest throughout the experiments. Soil pH and electrical conductivity (EC), especially in the surface layer of 0–40 cm depth, decreased with years of cultivation with both GWI and RWI, while soil inorganic N and total N contents increased. Moreover, with increasing N application rates, soil inorganic N and total N contents increased significantly in the 0–20 cm soil layer. Increasing N application had little effect on soil pH and EC. Reclaiming and planting rice promoted desalination of the surface and formation of a fertile tillage layer in saline-sodic paddy fields. In terms of irrigation and drainage in saline-sodic paddy fields, both soil salinity and N contents increased. Soil total salinity increased annually by 34 and 12·8 kg/ha, and inorganic N contents increased annually by 9 and 13·5 kg/ha with GWI and RWI, respectively. Therefore, comprehensive agricultural practices should be adopted for improving and cropping rice in saline-sodic paddy fields.

Background and aims Alkaline soils, characterized by high pH, are representative of degraded regions throughout the world. Studying germination in relation to alkalinity can contribute to understanding how species cope with such conditions. Although the effects of pH have been widely studied, it is unknown whether germination response to pH gradients created with buffer solutions is representative of the conditions experienced inalkalinesoils.Our aimswereto(1) determineif high pH gives an accurate assessment of the effects of alkaline soils on germination, and (2) identify the inhibitory factors for germination in alkaline soils. Methods Using Leymus chinensis seeds, germination was tested over a gradient of pH solutions prepared using Tris (50 mM and 100 mM) and H2O buffers and eight germination media prepared from non-alkaline and alkaline soils with different pH and electrical conductivities (EC). Additionally, solutions of 10–100 mM NaCl, Na2SO4 ,N a2CO3 and NaHCO3 were used to determine the main ions inhibiting seed germination. Results H2O-buffered pH had no effect on seed germination, and seed germination was much lower at all pH levels in 50 mM Tris–HCl solutions (pH 7.0–10.35) than in the H2O control (pH 7.05). No seeds germinated in 100 mM Tris–HCl buffers irrespective of the pH. In alkalinegermination media (pH 10.04–10.61), highgermination was obtained only at low EC. The rank order of the inhibitory effect of salts was Na2CO3>NaHCO3> NaCl>Na2SO4. Conclusions Buffer solutions used to simulate alkaline environments did not provide a reliable indicator of the effects of alkalinesoils onseedgermination.High pH of alkaline soil had no negative effects, and results suggest that salt composition and concentration, especially CO3 2� and HCO3 � , are key inhibitors.

Saline-alkaline stress is characterized by high salinity and high alkalinity (high pH); alkaline stress has been shown to be the primary factor inhibiting rice seedling growth. In this study, we investigated the potential priming effect of abscisic acid (ABA) on tolerance of rice seedlings to alkaline stress simulated by Na2CO3. Seedlings were pretreated with ABA at concentrations of 0 (control), 10, and 50 μM by root-drench for 24 h and then transferred to a Na2CO3 solution that did not contain ABA. Compared to control treatment, pretreatment with ABA substantially improved the survival rate of rice seedlings and increased biomass accumulation after 7 days under the alkaline condition. ABA application at 10 μM also alleviated the inhibitory effects of alkaline stress on the total root length and root surface area. Physiologically, ABA increased relative water content (RWC) and decreased cell membrane injury degree (MI) and Na(+)/K(+) ratios. In contrast, fluridone (an ABA biosynthesis inhibitor) decreased the RWC and increased MI in shoots under the alkaline conditions. These data suggest that ABA has a potent priming effect on the adaptive response to alkaline stress in rice and may be useful for improving rice growth in saline-alkaline paddy fields.

In response to pathogen attack, plants prioritize defense reactions generally at the expense of plant growth. In this work, we report that changes in phytohormone signaling pathways are associated with the stunted plant growth caused by blast disease in rice seedlings. Infection of rice seedlings with blast fungus Magnaporthe oryzae (race 007.0) at the four-leaf stage (three true leaves) resulted in considerable inhibition of the growth of the upper uninfected distal leaves; the length of leaf blade and leaf sheath of the sixth and seventh leaf was reduced by 27 and 82%, and 88 and 72%, respectively, compared to that in the uninoculated plant control. Interestingly, cutting off the blast-infected fourth leaf blade within 2 days post inoculation (dpi) significantly rescued the inhibition of leaf growth, implying that an inhibitory substance(s) and/or signal was generated in the blast-infected leaves (fourth leaf) and transmitted to the upper distal leaves (sixth and seventh) during the 2-dpi period that induced growth inhibition. Expression analysis of marker genes for phytohormone pathways revealed acute activation of the jasmonate (JA) and abscisic acid (ABA) signaling pathways, and repression of auxin, gibberellic acid (GA) and salicylic acid (SA) signaling pathways, in the sixth leaf. The genes related to cell wall expansion were also significantly downregulated. In the blast-infected fourth leaf, JA pathway was activated within 2 dpi, followed by activation of ABA pathway 3 dpi. Further, leaf inhibition caused by blast infection was partially rescued in the rice mutant line coleoptile photomorphogenesis 2 (cpm2), which is defective in the gene encoding allene oxide cyclase (OsAOC). These results indicate that the JA signaling pathway is at least partly involved in the growth inhibition processes. Collectively, our data suggest that, upon pathogen attack, rice seedlings prioritize defense reactions against the infecting pathogen by temporarily ceasing plant growth through the systemic control of phytohormone pathways.

Saline–alkaline (SA) stress is a complex effect of three main factors: ion toxicity from high salinity, alkalinity, and high osmotic pressure. In this study, we dissected response of rice (Oryza sativa L.) to above-mentioned SA stress factors simulated by using NaCl, Na₂CO₃, and PEG6000, respectively. Seed germination was most strongly affected by osmotic stress, followed by alkaline and salt stresses. Meanwhile, the seedling growth was most reduced under alkaline stress. The alkaline treatment significantly reduced total biomass, total root length (TRL), root surface area (RSA), root numbers (RN), and root volume (RV), while it increased root diameter (RD) and Na⁺/K⁺ ratio. Further, it caused severe damages to the root system as shown by a remarkable increase in degree of cell injury and expression of the cell death-related gene OsNAC4. On the other hand, salt stress reduced the total biomass, RSA and RV, and increased the Na⁺/K⁺ ratio, while to less extent than those under alkaline stress. These results suggest that the deleterious effect of alkaline stress on rice seedlings is due mainly to high alkalinity that induces cell injury in the root system. In contrast, the response to osmotic stress exhibited the typical adaptive responses to dehydration: reduced relative water content (RWC), RD, RV, and shoot biomass; whereas increased TRL, RSA, RN, and root biomass. In addition, we show that proline was accumulated most abundantly in response to alkaline treatment, and which was corroborated by the transcriptional induction of OsP5CS1 and OsP5CS2, the genes encoding proline carboxylate synthase.

The objectives of this study were to evaluate the effects of different fertilizer types and application rates on ammonia volatilization loss and to explore nitrogen distribution and nitrogen use efficiency using the 15N isotope tracing technique in different alkaline salt-affected conditions in the Songnen Plain, Northeast China. The results showed a decreasing trend in ammonia volatilization loss from ammonium nitrate and ammonium sulfate, but not that from urea, as the electrical conductivity gradient increased, whereas the reverse trend was found as the pH gradient increased. Ammonia volatilization loss increased in moderately salt-affected soil compared with that in slightly salt-affected soil, particularly during the tillering stage, regardless of the N fertilizer rate. The percentage of N absorbed by rice plants increased from urea but decreased from the soil as the amount of nitrogen was increased. Interestingly, the N retention rate in soil decreased and rice grain yield and nitrogen agronomic efficiency increased as the amount of nitrogen increased in both salt-affected soil conditions. The nitrogen application amount of highest N physiological efficiency was 225 kg·N/ha. Considering high rice production and a minimal environmental threat, we should fully consider controlling ammonia volatilization losses by adjusting the fertilizer type and the crop stage when the fertilizer is applied.

Field experiments were conducted to investigate the effects of drip irrigation on seed germination and Puccinellia tenuiflora growth in saline-sodic soils in the Songnen Plain, northeast China. The experiment included five treatments in which the soil matric potential (SMP) at 0.2 m depth was controlled at -5, -10, -15, -20 and -25 kPa after the P. tenuiflora germinated. Consequently, the total water applied increased with increased matric potential. The results showed that drip irrigation influenced the water content, electrical conductivity of saturated-soil extract (ECe) and pH distributions, and inhibited the buildup of salts in the root zone, which enabled seeds to germinate and emerge. The ECe and pH in the whole soil profiles decreased as the SMP increased. After two years of the experiment, the tiller numbers, height, spike number and length, aboveground biomass and coverage of P. tenuiflora all increased greatly; and the growth of -15 and -20 kPa treatments were better than other treatments. Taken together, these results indicate that drip irrigation can be used to provide suitable conditions for the germination of P. tenuiflora seeds in the Songnen Plain and induce good growth, and the SMP of -15 and -20 kPa at a depth of 0.2 m immediately under a drip emitter can be used as an indicator for saline-sodic P. tenuiflora grassland restoration in Songnen Plain. The results provide theoretical and technological guidance for reclamation and use of salt-affected soil, as well as for easy and quick restoration and reconstruction of saline-sodic grasslands. (C) 2012 Elsevier B.V. All rights reserved.

The effect of nitrogen (N) application on seed yields and yield components in Leymus chinensis (Trin.) Tzvel., a perennial rhizomatous grass, was measured in a field experiment with two saline-sodic soils at Da’an Sodic Land Experiment Station during 2010–11. Two grassland field sites were classified as moderately saline–sodic (MSSL) and severely saline–sodic (SSSL). Application rates of N at each site were 0, 30, 60, 90, 120, 150, 180 and 210 kg ha–1. Application of N significantly improved seed yield mainly through increased spike number (R2 = 0.96, P ≤ 0.001). Compared with nil N, seed yield increased 7.4–10.9 times with N application of 150 kg ha–1 at MSSL, and 5.3–7.5 times with N application of 120 kg ha–1 at SSSL. However, absolute increases at SSSL were relatively small. Some significant differences (P ≤ 0.01) in seed yield occurred between 2010 and 2011 with different N application rates in the same soil, and between MSSL and SSSL in the same year. Increasing N application rate significantly decreased N physiological efficiency (NPE) but increased N apparent-recovery fraction (NRF) and N partial-factor productivity (NPP) at both sites. Seed yield and NPP indicated that the optimal N application rates to increase yield were 150 kg ha–1 at MSSL and 120 kg ha–1 at SSSL. High soil pH was the major factor adversely impacting seed yield, and pH and soil salinity were major factors negative affecting NPE, NRF and NPP as well as decreasing the positive effect of N application. Nitrogen application is a practical and effective method to increase seed yield of L. chinensis in saline-sodic grasslands of Northeast China, particularly when soil pH and salinity are not limiting.

Aims Leymus chinensis is an original dominant plant in the Songnen grass- land, and it has great value for restoration of severely degraded land. However, seeds are dormant, and low germination percentage is a problem for restoringL.chinensis grassland. The mechanism of seed dormancy is not been well understood. The primary aims of the pres- ent study were to investigate the dormancy mechanism ofL.chinensis seeds (caryopses) with reference to the role of embryo-covering layers, endogenous hormones and temperature. Methods Changes in concentration of the endogenous hormones GA3, indole- acetic acid (IAA), zeatin riboside (ZR) and abscisic acid (ABA) inL.chi- nensis seeds from anthesis to maturity were measured by the enzyme- linked immunosorbent assay method. Germination at different stages of maturity were tested at 16/28C, 5/28C and 5/35C for intact seeds with glumes (control), intact seeds with glumes removed (naked- whole seeds) and intact seeds with glumes and one-half of the endo- sperm removed (naked-half seeds). Important Findings Of the four endogenous hormones monitored, only the concentra- tion of ZR differed significantly between the beginning and the end of seed development (increased); the GA3/ABA ratio also did not differ. Rank of germination percentage of control at the three tem- perature regimens was 5/28C > 16/28C > 5/35C. Germination per- centage of the naked-half seeds reached 100% under the three temperature regimens. We concluded that dormancy of L.chinensis seeds is not mainly controlled by endogenous hormones. Germina- tion temperature, mechanical resistance of glumes and inhibition of endosperm are the main factors controlling dormancy and germina- tion of L.chinensis seeds.

The net photosynthetic rate of flag leaves and influencing factors under saline sodic soil conditions were investigated at the full heading stage of rice. The net photosynthetic rate of rice leaves showed a double-peak curve in a day in both non-saline sodic and saline sodic soil treatments. The first peak of the net photosynthetic rate appeared at 9:00–10:00 and 9:00 in the saline sodic and non-saline sodic soil treatments, respectively, whereas the second peak both at 14:00. The midday depression of the net photosynthetic rate always appeared regardless of non-saline sodic or saline sodic soil conditions. In addition, the net photosynthetic rate significantly decreased in all day under saline sodic conditions compared with that under non-saline sodic conditions. Some differences were observed in correlation characters between the net photosynthetic rate and all influencing factors during 9:00–13:00. Under non-saline sodic conditions, the diurnal changes of the net photosynthetic rate in a day were mainly caused by stomatal conductance, and the limitation value and the stomatal factors served as determinants; whereas under saline sodic stress, the diurnal changes of the net photosynthetic rate in a day were mainly caused by non stomatal factors including light intensity and air temperature.

Many rice cultivars that originated from lower-latitude regions exhibit a strong photoperiod sensitivity (PS) and show extremely late heading under long-day conditions. Under natural day-length conditions during the cropping season in Japan, the indica rice cultivar 'Nona Bokra' from India showed extremely late heading (202 days to heading) compared to the japonica cultivar 'Koshihikari' (105 days), from Japan. To elucidate the genetic factors associated with such extremely late heading, we performed quantitative trait locus (QTL) analyses of heading date using an F(2) population and seven advanced backcross progeny (one BC(1)F(2) and six BC(2)F(2)) derived from a cross between 'Nona Bokra' and 'Koshihikari'. The analyses revealed 12 QTLs on seven chromosomes. The 'Nona Bokra' alleles of all QTLs contributed to an increase in heading date. Digenic interactions were rarely observed between QTLs. Based on the genetic parameters of the QTLs, such as additive effects and percentage of phenotypic variance explained, these 12 QTLs are likely generate a large proportion of the phenotypic variation observed in the heading dates between 'Nona Bokra' and 'Koshihikari'. Comparison of chromosomal locations between heading date QTLs detected in this study and QTLs previously identified in 'Nipponbare' x 'Kasalath' populations revealed that eight of the heading date QTLs were recognized nearby the Hd1, Hd2, Hd3a, Hd4, Hd5, Hd6, Hd9, and Hd13. These results suggest that the strong PS in 'Nona Bokra' was generated mainly by the accumulation of additive effects of particular alleles at previously identified QTLs.

An F2 and an equivalent F3 population derived from a cross between a high salt-tolerance indica variety, Nona Bokra, and a susceptible elite japonica variety, Koshihikari, were produced. We performed QTL mapping for physiological traits related to rice salt-tolerance. Three QTLs for survival days of seedlings (SDSs) under salt stress were detected on chromosomes 1, 6 and 7, respectively, and explained 13.9% to 18.0% of the total phenotypic variance. Based on the correlations between SDSs and other physiological traits, it was considered that damage of leaves was attributed to accumulation of Na+ in the shoot by transport of Na+ from the root to the shoot in external high concentration. We found eight QTLs including three for three traits of the shoots, and five for four traits of the roots at five chromosomal regions, controlled complex physiological traits related to rice salt-tolerance under salt stress. Of these QTLs, the two major QTLs with the very large effect, qSNC-7 for shoot Na+ concentration and qSKC-1 for shoot K+ concentration, explained 48.5% and 40.1% of the total phenotypic variance, respectively. The QTLs detected between the shoots and the roots almost did not share the same map locations, suggesting that the genes controlling the transport of Na+ and K+ between the shoots and the roots may be different.

Fine mapping of Hd4 and Hd5, quantitative trait loci (QTLs) for heading date in rice, was performed by using advanced backcross progeny derived from a cross between a japonica rice variety, Nipponbare, and an indica variety, Kasalath. Hd4 was mapped between restriction fragment length polymorphism (RFLP) markers R46 and C39 in the proximal region of chromosome 7, and Hd5 was mapped between C166 and R902 on the short arm of chromosome 8; both QTLs mapped as single Mendelian factors. We used marker-assisted selection to develop two nearly isogenic lines (NIL), designated NIL(Hd4) and NIL(Hd5), in which small chromosomal segments of Kasalath including Hd4 and Hd5, respectively, each were substituted into the genetic background of Nipponbare. Compared with that of Nipponbare, days-to-heading of NIL(Hd4) and NIL(Hd5) increased under long-day and natural-field conditions, but no differences were observed between those of the two NILs and Nipponbare under short-day conditions. Epistatic interaction was detected between Hd5 and Hd1, a key photoperiod sensitivity QTL, on the basis of an analysis of the F2 population derived from a cross between the NIL(Hd5) and NIL(Hd1). This result suggests that Hd5 is involved in photoperiod sensitivity and may act downstream or upstream of Hd1 in the same photoperiodic pathway. In comparison, the genetic effect of Hd5 was additive to that of Hd2, another key photoperiod-sensitivity QTL, indicating that Hd2 acts in a different photoperiodic pathway other than that of Hd1 and Hd5. The genetic effect of Hd4 was additive to those of Hd1 and Hd2; thus, epistatic interaction between these loci was not detected.

We report the characterization of seedlings of LM10 which is one of the four short-root mutants derived from an M2 population of rice (Oryza sativa L., cv. IR8) seeds treated with NaN3. The morphological characteristics in the M3 generation of LM10 was the same as their M2 and there was no segregation in M3. The lengths of the seminal root, the crown root and the lateral root of LM10 seedlings were significantly shorter than those of IR8, but the number of crown roots and the density of lateral roots were higher in LM10. There was no difference in plant length between the two. The embryo and the radicle length of the mature embryo were shorter in LM10, but no difference was observed in the plumule. The cortex cell length of the maturation zone was remarkably shorter in LM10 than in IR8, though cell division of the meristem zone was normal in the two. Although it is well known that the shoot and root growth of the wild-type are inhibited by light exposure compared to dark, root growth of IM10 was accelerated by light exposure, but shoot growth was inhibited. These results indicated that LM10 is different from mutants reported previously in rice and represents a new mutant concerning root growth of rice.

We analyzed the inheritance of a mutation that causes short roots. The mutant, called LM 10, was derived from an M2 population of rice (Oryza sativa L., cv. IR8) seeds treated with NaN3. In reciprocal crosses between the mutant and wildtype, all F1 progeny had the same root length as the wildtype, however, F2 progeny segregated wildtype and short root lengths in a 13:1 ratio. Segregation analysis for short-root was also carried out in reciprocal backcrosses, with short root heterozygotes (i. e., LM 10/IR 8) backcrossed onto the short root parent. When the short root parent was female, segregation was 1:1 as expected, but when the short root parent was male, the wildtype to mutant segregation ratio was 6:1. From this result, we infer that the distorted segregation (13:1) in the F2 could be caused by a difference in fertilization ratio between wild type and short-root type pollen (about 6:1 in the F1 population). Altoget:her, these results indicate that the short-root phenotype in LM 10 is controlled by a single recessive gene (srt-2). Additionally, allelism was checked between srt-2 and two other mutations known to cause short ro, ots (srt-1 and rt) by pairwise crosses between the three lines. All such crosses produced only wildtype progeny, indicating that the genes of srt-1, srt-2 and rt are locat, ed at different loci.

In order to ascertain the optimal harvest time of Puccinellia tenuiflora in practical production scientifically, PPC (Projection Pursuit Classification) model based on RAGA (Real coding based Accelerating Genetic Algorithm) was applied. Projection direction was optimized and high-dimension data were converted into low-dimension space with PPC, value of projection indexes could be obtained. Based on these projection function values, the sequence of samples from the big to the small was gained, at the same time, subjective impact on weight matrix farthest could be avoided with PPC model. The results showed that the initial biloom stage have the biggest value of projection indexes, which was 2.2572, and its comprehensive evaluation was the best based on the data from 2007 to 2008. Puccinellia tenuiflora harvested in the initial bloom stage had higher nutritive value, higher output and lower coarse fibre content. This model offered a new method to solve the evaluating problem of the optimal harvest time of Puccinellia tenuiflora.

It is well-known that nitric oxide ( NO) is an important component in nitrogen biogeochemical cycling produced through biological process of nitrification and denitrification in soils, but the production and the consumption processes of NO in sodic saline soil are less understood. Through a series of laboratory experiments focusing on NO biogenic emissions from four kinds of saline sodic soils of different land use in western Songnen Plain northestern China, we found that the optimum soil moisture for the maximum NO production and emission were 14.0%, 9.0%, 9.5%, and 18% water-filled pore space (WFPS) for soil samples from natural pasture, man-made pasture, paddy field of saline sodic soil mixed sandy soil, and paddy field of pure saline sodic soil, respectively. For a given moisture, NO fluxes increased exponentially with soil temperature at any given soil moisture. The optimum soil moisture for the maximum NO emission for a certain soil type, however, was constant and independent of soil temperature. The NO consumption processes for different land uses were similar in all studied saline sodic soils since the difference of NO consumption rate constant in these soils was small ( ranged from 1.07 x 10(-6) to 7.45 x 10(-6) m 3 kg(-1) s(-1)). The NO emission potential for paddy field soils was about 1.2-2-fold higher than pasture soils. On the basis of laboratory results and field monitoring data of soil water content and soil temperature, the average NO fluxes from these saline sodic soils in the region were estimated to be 1.3-4.9 ng m(-2) s(-1) for an entire plant growth period. NO fluxes for pastures mainly occurred in the dry season and were about threefold higher than that for paddy fields, which was strongly influenced by field management.

Salinization and alkalization are worldwide problems of soil. To compare the effects of saline-alkaline stress on seedling growth between rice mutant and its wild type, we selected NaCl, Na2CO3 and NaHCO3 to simulate saline-alkaline stress, respectively, and selected two rice materials, ML04 is rice mutant and G19 is its wild type. Under salinealkaline stress, the rice biomass sharply decreased, and the shoot fresh weight of ML04 was higher than that of G19. The saline-alkaline stress promoted the rice taking up Na+ but inhibited absorbing K+ in shoots. The Na+ and K+ contents under the alkaline stress were much more than those of under saline stress, and the Na+ content of ML04 was higher than that of G19 under alkaline stress treatments. The saline-alkaline stress reduced the root numbers (RN), total root length (TRL), root surface area (RSA), root volume (RV) and shoot length, but increased the Na+/K+ ratio and the root diameter (RD). And all these root indices of ML04 were higher than G19 under alkaline stress treatments. The high pH of alkaline salt stress might be an important reason for the severe damage to rice root system, which further limited the rice aboveground parts growth. In conclusion, the salinealkaline stress inhibited the rice seedling growth, and most of the indices showed that the rice mutant (ML04) was much more tolerant to alkaline stress than its wild type (G19).

Proline accumulation is a common physiological response to various abiotic stresses in plants. In this study, we show that rice seedlings accumulate proline to different levels in response to different saline-alkaline stress factors including osmotic, saline and alkaline stresses. Expression analysis of genes for proline biosynthesis (OsP5CS1, OsP5CS2 and OsP5CR) and catabolism (OsPDH1 and OsP5CDH) revealed up-regulation of the proline synthesis genes under osmotic and alkaline stresses. In comparison, under the salt stress, a decrease in catabolic enzyme gene expressions was observed. Our results suggest that rice seedlings employ different gene regulation in proline accumulation in response to different saline-alkaline stress factors.