The role of root apoplastic transport barriers in salt tolerance of rice (Oryza sativa L.) (original) (raw)
Related papers
Root apoplastic barriers block Na+ transport to shoots in rice (Oryza sativa L.)
Journal of Experimental Botany, 2011
Rice is an important crop that is very sensitive to salinity. However, some varieties differ greatly in this feature, making investigations of salinity tolerance mechanisms possible. The cultivar Pokkali is salinity tolerant and is known to have more extensive hydrophobic barriers in its roots than does IR20, a more sensitive cultivar. These barriers located in the root endodermis and exodermis prevent the direct entry of external fluid into the stele. However, it is known that in the case of rice, these barriers are bypassed by most of the Na + that enters the shoot. Exposing plants to a moderate stress of 100 mM NaCl resulted in deposition of additional hydrophobic aliphatic suberin in both cultivars. The present study demonstrated that Pokkali roots have a lower permeability to water (measured using a pressure chamber) than those of IR20. Conditioning plants with 100 mM NaCl effectively reduced Na + accumulation in the shoot and improved survival of the plants when they were subsequently subjected to a lethal stress of 200 mM NaCl. The Na + accumulated during the conditioning period was rapidly released when the plants were returned to the control medium. It has been suggested that the location of the bypass flow is around young lateral roots, the early development of which disrupts the continuity of the endodermal and exodermal Casparian bands. However, in the present study, the observed increase in lateral root densities during stress in both cultivars did not correlate with bypass flow. Overall the data suggest that in rice roots Na + bypass flow is reduced by the deposition of apoplastic barriers, leading to improved plant survival under salt stress.
Journal of Experimental Botany, 2009
Salinity tolerance in rice, like in other glycophytes, is a function of cellular ion homeostasis. The large divergence in ion homeostasis between the salt-tolerant FL478 and salt-sensitive IR29 rice varieties can be exploited to understand mechanisms of salinity tolerance. Physiological studies indicate that FL478 shows a lower Na + influx, a reduced Na + translocation to the shoot, and maintains a lower Na + :K + ratio. To understand the basis of these differences, a comparative investigation of transcript regulation in roots of the two cultivars was undertaken. This analysis revealed that genes encoding aquaporins, a silicon transporter, and N transporters are induced in both cultivars. However, transcripts for cation transport proteins including OsCHX11, OsCNGC1, OsCAX, and OsTPC1 showed differential regulation between the cultivars. The encoded proteins are likely to participate in reducing Na + influx, lowering the tissue Na + :K + ratio and limiting the apoplastic bypass flow in roots of FL478 and are therefore important new targets to improve salt tolerance in rice.
The Crop Journal, 2020
Rice, a major staple, is the most salt-sensitive cereal. High salinity triggers several adaptive responses in rice to cope with osmotic and ionic stress at the physiological, cellular, and molecular levels. A major QTL for salinity tolerance, named Saltol, is present on chromosome 1 of Indian landraces such as Pokkali and Nona Bokra. The early proteomic and physiological responses to salinity in roots and shoots of FL478, an inbred rice line harboring the Saltol QTL, were characterized. Plantlets were cultured in hydroponic cultures with 100 mmol L À1 NaCl and evaluated at 6, 24, and 48 h. At the physiological level, root length significantly increased at 48 h, whereas shoot length was reduced. The Na + /K + ratio was maintained at lower levels in shoots than in roots, suggesting that roots play a protective role. More than 2000 proteins were detected in both tissues. Roots showed a faster and more coordinated proteomic response than shoots, evident after only 6 h of treatment. These responses showed clear correspondence with those of proteins involved in transcription and translation. Maintenance of mitochondrial activity and amino acid metabolism in roots, and activation of stress-responsive proteins such as dehydrins and PLAT in shoots, may play a key role during the response of the plant to salinity stress. Proteomic and physiological responses showed that roots respond in a more highly adaptive manner than shoots to salinity stress, suggesting that this tissue is critical to the tolerance observed in cultivars harboring Saltol.
Frontiers in Plant Science, 2019
Rice (Oryza sativa) is a staple food that feeds more than half the world population. As rice is highly sensitive to soil salinity, current trends in soil salinization threaten global food security. To better understand the mechanistic basis of salinity tolerance in rice, three contrasting rice cultivars-Reiziq (tolerant), Doongara (moderately tolerant), and Koshihikari (sensitive)were examined and the differences in operation of key ion transporters mediating ionic homeostasis in these genotypes were evaluated. Tolerant varieties had reduced Na + translocation from roots to shoots. Electrophysiological and quantitative reverse transcription PCR experiments showed that tolerant genotypes possessed 2-fold higher net Na + efflux capacity in the root elongation zone. Interestingly, this efflux was only partially mediated by the plasma membrane Na + /H + antiporter (OsSOS1), suggesting involvement of some other exclusion mechanisms. No significant difference in Na + exclusion from the mature root zones was found between cultivars, and the transcriptional changes in the salt overly sensitive signaling pathway genes in the elongation zone were not correlated with the genetic variability in salinity tolerance amongst genotypes. The most important hallmark of differential salinity tolerance was in the ability of the plant to retain K + in both root zones. This trait was conferred by at least three complementary mechanisms: (1) its superior ability to activate H +-ATPase pump operation, both at transcriptional and functional levels; (2) reduced sensitivity of K + efflux channels to reactive oxygen species; and (3) smaller upregulation in OsGORK and higher upregulation of OsAKT1 in tolerant cultivars in response to salt stress. These traits should be targeted in breeding programs aimed to improve salinity tolerance in commercial rice cultivars.
Differences in 22 Na uptake was determined in contrasting rice cultivars differing in salt tolerance. Selection for contrasting cultivars with significant differences in salt tolerance was based on a preliminary screening and included varietal differences in Na ? exclusion capacity, K/Na selectivity based on K ? , Na ? content of roots and shoots and a few other physiological traits. Almost 80 percent of the 22 Na uptake, into roots occurred during the first 1 h after salt stress imposition in both varieties. However 22 Na uptake was significantly higher in the salt susceptible KMP-175 as compared to Pokkali—in the first hour after salt stress imposition. After 6 and 24 h, the 22 Na uptake differences tapered off in the roots while these differences remained up to 6 h in the shoot. Overall the results broadly suggested that plants of the salt tolerant Pokkali were able to regulate Na ? transport into roots, more effectively than the salt susceptible variety immediately upon salt stress imposition but only for short periods.
2006
Rice marks second among the agricultural crop plants in the world (FAO, 2004). This work aimed at identifying the molecular mechanisms implicated in tolerance to salt. Salinity is a major environmental threat for agricultural production that affects ionic and osmotic as well as nutritional relation of plants. Ion channels are key players in maintaining ion homeostasis also under salinity. Clcontent was very low in control conditions but under 150 mM NaCl, Clwas abundantly accumulated in leaves of the salt sensitive rice line IR29, whereas the salt tolerant line Pokkali excluded it from the leaves. Transcript of OsCLC1 i.e. voltagedependent Clchannels was found in both lines in roots and leaves under normal growth conditions and was repressed in IR29 and induced transiently in Pokkali upon salt treatment. Simultaneous, transcript amounts of the Na + /H + antiporter OsNHX1 and the vacuolar H +-ATPase subunit OsVHA-B decreased in IR29, whereas Pokkali showed transient increase of OsVHA-B. Subsequent analysis of the water channel aquaporin OsPIP2;1 and the cellspecificity of OsCLC1 transcript distribution by in situ PCR showed coordinated regulation of OsCLC1, OsVHA-B, OsNHX1 and OsPIP2;1 on the one hand and suggest that OsCLC1 functions in osmotic adjustment at high salinity on the second hand. Transcript of the K + transporter OsHAK7 that belongs to the HAK/KT/KUP family were also analysed in relation to K + homeostasis. K + content was high in plant tissues under normal conditions, however salt stress decreased root levels and strongly increased its accumulation in leaf cells in both IR29 and Pokkali. OsHAK7 showed high transcript abundance only during the first 6 h of the salt treatment in leaves, whereas in roots the induction was maintained up to 48 h in both lines. Tissue and cell-specificity distribution of OsHAK7 transcript by in situ PCR revealed expression in plant tissues under normal conditions. Strong signals in the mesophyll of both rice lines were detected in leaves, whereas expression in the vasculature cells was specific to Pokkali. In response to salt stress, transcript amounts were reduced in the mesophyll and were detectable in phloem and xylem parenchyma cells of both lines. Analyses of these results demonstrated transcriptional regulation of OsHAK7 under salinity stress and suggest that the K + transporter functions in salt-dependent K + homeostasis in rice. A comparative analysis of salt stress responses in the monocotyledonous halophyte Festuca rubra ssp littoralis and the salt sensitive crop species wheat (Triticum aestivum) were investigated for better understanding strategies of salt tolerance. Ion accumulation was similar in both species except for Ca, Mg, Fe and Na, whose contents were higher in Festuca Summary ii than in wheat in control conditions. In response to 125 mM NaCl (which characterised severe stress for wheat), the crop species (Triticum aestivum) limited the uptake of Na + in leaves whereas Festuca significantly accumulated it in root and leaves. In addition, Mg and Fe content increased in Festuca. At 500 mM NaCl, Festuca accumulated Na + in both tissues. Expression of genes with important function in the regulation of ion homeostasis was also analysed. In root tissue treatment of 125 mM NaCl improved the transcript level of Festuca FrPIP2;1, FrVHA-B and FrNHX, whereas in wheat the expression of TaPIP2;1 and TaVHA-B was down regulated. FrPIP2;1, FrVHA-B and FrNHX cell-specificity analysis indicated expression in root epidermis, cortex cells, endodermis and in the vasculature tissue. Treatment of 500 mM NaCl showed repression in the epidermis and the outer cortex cells whereas strong signals were observed in the endodermis and the vasculature. These results indicated divergent transcriptional regulation of the aquaporin PIP2;1, V-ATPase and the Na + /H + antiporter NHX and seems to be correlated with salt tolerance and salt sensitivity in Festuca, in the rice lines Pokkali, IR29 and wheat and suggested coordinated control of ion homeostasis and water status at high salinity in plants. As reported in many studies, salinity is a complex constraint that induced the regulation of many of other genes with significant function in the mechanism of salt tolerance. Identification of probable salt induced genes was investigated by using rice and Festuca cDNA-arrays to identify 192 and 480 salt responsive expressed sequence tags (ESTs) from a rice and Festuca salt stress-cDNA-library. The rice cDNA-array hybridizations compared between the salt sensitive line IR29 and the salt tolerant line Pokkali showed no significant difference. Considering the number of salt regulated genes, more induced genes could be showed in Pokkali leaf than in IR29 under 150 mM NaCl 6 h. IR29 recovered slowly according to the duration of the treatment and at 48 h, more genes were regulated in IR29 than in Pokkali. While more genes were up and down-regulated under NaCl and LiCl stress, salt stress under K + starvation induced more regulated genes in Pokkali than in IR29. Saltinduced gene expression was compared between the salt sensitive line IR29 and the halotolerant Festuca using Festuca cDNA-arrays. Treatment of 125mM NaCl during 6 h indicated no significant difference in the number of upregulated genes in both species, however, several genes were repressed in Festuca. Festuca showed only a high rate of upregulated genes at high salt concentration (500 mM NaCl). Functional classification of salt-induced genes identified gene products related to metabolism such as the NADPdependent oxidoreductase that is a component of the antioxidative system. Second large Summary iii group corresponded to genes with unknown function. In these groups as well as in the group of defence, many of the induced genes were only observed at 500 mM NaCl. These results suggest a small rate of genes were needed to maintain normal growth under low salinity in the halophyte Festuca. This number increased and reached the maximum at 500 mM NaCl, whereas in the salt sensitive rice line IR29 the maximum was reached at low salt concentration. Transcription factors, translation and signal transduction constituted a small group with a slight increase in Festuca treated for 6 h with 125 mM NaCl and 500 mM NaCl. The expression of the translation initiation factor SUI1 as well as the signalling tanscduction element protein kinase SPK3 seemed to be moderate in the Festuca-cDNA-array. However Northern blot expression of the rice translation initiation factor OsTIF (SUI1) and the rice serine-theonine proteine kinase OsSPK3 showed clear improvement in the halophythe Festuca at 500 mM NaCl. In IR29, Northern blot analysis showed a decrease in the transcript abundance of the genes. According to their induced expression in Festuca to high salinity, sequences of OsTIF as well as the sequence of OsSPK3 inserted and analyzed in the salt sensitive rice IR29. Under salt stress conditions, transgenic plants overexpressing OsTIF or OsSPK3 increased the transcript level of both genes and improved the tolerance to salinity compared to the wild-type. In addition, expression of the V-ATPase in transgenic plants was significantly induced under salt stress. These results suggest that the translation initiation factor OsTIF and the protein Kinase OsSPK3 are useful for improvement of salt tolerance in rice. Liste of publications: Diedhiou CJ and Golldack D (2005) Salt-dependent regulation of chloride channel transcripts in rice. Plant Science, in press Diedhiou CJ and Golldack D (2006) Wheat and a salt-tolerant relative, Festuca rubra ssp. litoralis, regulate a plasma membrane aquaporin, the vacuolar H +-ATPase and Na + /H + antiporter differently. Physiologia Plantarium, in revision Diedhiou CJ and Golldack D (2006) Salt stress regulates expression of the HAK-type K +transporter OsHAK7 in rice, Submitted Contents I 4-Discussion 4-1 Salt-dependent regulation of chloride channel transcripts in rice 4-1.1 Consequences of salt stress in IR29 and Pokkali 4-1.2 Transcriptional regulation of OsCL1 4-1.3 Correlated expression changes of OsCLC1 and genes involved in maintenance of cellular Na + homeosthesis 4-1.4 OsCLC1 and water channel OsPIP2;1 4-1.5 Tissue-specificity of OsCLC1 expression is regulated in response to salinity 4-2 Salt stress regulates expression of the HAK-type K +-transporter OsHAK7 in rice 4-2.1 Photosynthesis and osmotic stress Contents V 4-2.2 Importance and localisation of K + and control of Na + uptake in IR29 and Pokkali 4-1.3 Regulation of K + transport in the mechanism of salt tolerance by rice 93 4-3 Wheat and a salt-tolerant relative, Festuca rubra ssp. litoralis, regulate a plasma membrane aquaporin, the vacuolar H +-ATPase and Na + /H + antiporter differently 96 4-3.1 Two different modes of ion regulation in response to salinity in Festuca and Triticum aestivum 96 4-3.2 Expression of PIP2;1 aquaporins under salt stress in Festuca and wheat 97 4-3.3 Expression of VHA-B and NHX1 is coordinated to the regulation of water and Na + homeostasis 98 4-4 Salt-responsive genes in rice and Festuca rubra ssp litoralis and induction of salt tolerance in the line IR29, rice sensitive 4-4.1 Molecular mechanisms of salt stress in the rice lines IR29 and Pokkali 4-4.2 Festuca cDNA-arrays 4-5 Transgenic plants carrying a rice translation initiation factor (OsTIF) 4-5.1 Interactions of inserted gene OsTIF with other genes 4-6 Transgenic plants carrying the protein kinase OsSPK3 References Appendix Abbreviations Acknowledgements Alkalinity Alkaline soils are a type The high pH is caused by High pH of sodic soil with a high pH. They are defined carbonate salts in parent material. affects nutrient uptake as having an ESP = 15% with a pH of 8.5-10. Salinity is an environmental factor that greatly affects plant growth and development and is a major constraint for crop production. This stress is complex and causes a number of determinant effects. Among them ionic...
Salinity resistance of the African rice species (Oryza glaberrima) is poorly documented and the specific responses of the plant to Na+ and Cl-toxic ions remain unknown. Moreover, the roles of Na+/H+ antiport and cation-chloride-cotransporter in salt stresses still remain unclear. In 1st experiment, two distinct cultivars TOG5307 and TOG5949 were maintained for 15 days on iso-osmotic nutrient solutions containing 50 mM NaCl, or a combination of Cl-salts (Cl-dominant) or Na+ salts (Na+-dominant). Plant water status, ion accumulation, gas exchange and fluorescence related parameters; carbon (∆13C) and nitrogen (δ15N) isotope discrimination were analyzed. But Only ion content results were displayed in this paper. TOG5307 exhibited a higher level of resistance than TOG5949 in terms of growth and photosynthesis maintenance and control of Cl-and Na+ accumulation. NaCl was the most detrimental treatment, followed by Na+-dominant treatment while Cl-treatment had the lowest effect. Impact of Na+ and Cl-on considered parameters are additive. In 2nd experiment, the two contrasted cultivars (TOG5307 and TOG5949) were exposed during 3 days in nutrient solutions to 75 mM NaCl containing 100 µ M amiloride (inhibitor of Na+-H+ antiporters) or 200 µ M bumetanide (inhibitor cation-chloride-cotransporters). Amiloride increased Na+ accumulation in roots and leaves to a higher extent in salt-resistant TOG5307 than in salt-sensitive TOG5949. Bumetanide reduced Cl-accumulation in both cultivars as well as K+ accumulation in TOG5307 and Na+ accumulation in TOG5949. Cultivars exhibiting contrasting levels of salinity resistance are available in Oryza glaberrima and salt-tolerant genotypes may constitute a valuable source of gene for classical rice improvement.
Protoplasma, 2018
The understanding of physio-biochemical and molecular attributes along with morphological traits contributing to the salinity tolerance is important for developing salt-tolerant rice (Oryza sativa L.) varieties. To explore these facts, rice genotypes CSR10 and MI48 with contrasting salt tolerance were characterized under salt stress (control, 75 and 150 mM NaCl) conditions. CSR10 expressed higher rate of physio-biochemical parameters, maintained lower Na/K ratio in shoots, and restricted Na translocation from roots to shoots than MI48. The higher expression of genes related to the osmotic module (DREB2A and LEA3) and ionic module (HKT2;1 and SOS1) in roots of CSR10 suppresses the stress, enhances electrolyte leakage, promotes the higher compatible solute accumulation, and maintains cellular ionic homeostasis leading to better salt stress tolerance than MI48. This study further adds on the importance of these genes in salt tolerance by comparing their behaviour in contrasting rice ge...
International Journal of Agronomy, 2012
Rice is an important produced cereal in the world. We evaluated the effect of salt compositions including NaCl and Na 2 SO 4 on suberin lamellae as a major barrier to radial ion and water movements in two rice genotypes representing contrasting salt tolerance levels under salinity stress. Two rice genotypes, Fajr as salt tolerant and Khazar as salt sensitive, were transplanted in sand culture under glasshouse condition. Rice seedlings were treated with five salt compositions including NaCl, Na 2 SO 4 , 1 : 1, 1 : 2, and 2 : 1 molar ratios for 40 days. It was proven that suberin lamellae in endodermis of root cell wall were thickened with Na 2 SO 4 treatment. The results demonstrated that the number of passage cells was higher in Fajr genotype than that in Khazar genotype under saline condition. Calcium concentration in root tissue decreased as the SO 4 2− concentration in root media increased. It can be concluded that Fajr genotype is able to keep some passage cells open to maintain Ca 2+ uptake. The Ca 2+ /Na + ratio in shoot tissue can be also a reliable index for the early recognition of salt stress in these rice genotypes.