Root apoplastic barriers block Na+ transport to shoots in rice (Oryza sativa L.) (original) (raw)
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The role of root apoplastic transport barriers in salt tolerance of rice (Oryza sativa L.)
Planta, 2009
Increasing soil salinity reduces crop yields worldwide, with rice being particularly aVected. We have examined the correlation between apoplastic barrier formation in roots, Na + uptake into shoots and plant survival for three rice (Oryza sativa L.) cultivars of varying salt sensitivity: the salt-tolerant Pokkali, moderately tolerant Jaya and sensitive IR20. Rice plants grown hydroponically or in soil for 1 month were subjected to both severe and moderate salinity stress. Apoplastic barriers in roots were visualized using Xuorescence microscopy and their chemical composition determined by gas chromatography and mass spectrometry. Na + content was estimated by Xame photometry. Suberization of apoplastic barriers in roots of Pokkali was the most extensive of the three cultivars, while Na + accumulation in the shoots was the least. Saline stress induced the strengthening of these barriers in both sensitive and tolerant cultivars, with increase in mRNAs encoding suberin biosynthetic enzymes being detectable within 30 min of stress. Enhanced barriers were detected after several days of moderate stress. Overall, more extensive apoplastic barriers in roots correlated with reduced Na + uptake and enhanced survival when challenged with high salinity.
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.
Root-to-shoot signal transduction in rice under salt stress
Pakistan Journal of Botany, 2010
This paper describes the impact of salt stress on changes in the level of Abscisic acid (ABA) and cytokinins as signal molecules communicated through root-to-shoot in rice. The study focus to investigate the time related changes in the salt induced ABA and cytokinins accumulation concomitant with the changes in water potential and stomatal conductance of salt stressed plants. Seeds of 3 rice varieties were grown in plastic pots in phytotron. The changes in the level of abscisic acid (ABA), transzeatin riboside (t-zr) and 2-isopentyl adenine (2-ipa) were monitored in xylem sap and leaves of three rice varieties viz. BAS-385 (salt-sensitive), BG-402 (moderately tolerant) and NIAB-6 (tolerant). The salt solution (NaCl,1.2 dSm -1 ) was added to the rooting medium after transplanting when plants were 50 d old. There was delay in response of stomata to salt treatment in BAS-385 as opposed to earlier increase in leaf resistance in BG-402 and NIAB-6. The stem water potential increased sharp...
Response to Salinity in Rice: Comparative Effects of Osmotic and Ionic Stresses
Plant Production Science, 2007
The effects of the osmotic component of salt stress on rice cultivar IR64 were examined. Treatments were four combinations of two levels of osmotic stress at two developmental stages: medium-and highlevel stress applied at the vegetative and reproductive stages using salt (NaCl) and polyethylene glycol-6000 (PEG) as sources of osmotic stress. Both PEG and NaCl reduced the total above ground biomass and delayed flowering and maturity, with a longer delay observed with the high-level stress. The reduction in number of filled spikelets, 1,000-grain weight, and hence grain yield was significantly greater when they were applied during the reproductive stage than during the vegetative stage. The sodium concentration in plant tissues also increased in plants treated with NaCl, indicating that besides osmotic stress, plants were also subjected to ionic stress. Treatment with NaCl decreased the potassium concentration in plant tissues but did not cause significant differences in phenology, biomass accumulation, yield or N uptake compared with PEG. We concluded that the response of IR64 to NaCl was attributed to the osmotic component. These findings may be specific to IR64, which has a medium tolerance to salinity stress. Further studies are needed with longer stress durations to achieve a higher Na + concentration in plant tissues in several varieties with contrasting tolerance to salt stress to further establish the relative importance of osmotic versus ionic components of salt stress in rice.
Some aspects of mechanisms of NaCl stress tolerance in the seedlings of four rice genotypes
Bangladesh Journal of Botany, 2008
Biomass production under salt stress decreased with the sequence: IRATOM -24 > BR 9 > Nonabokra > Pokkali. In Pokkali root-shoot dry wt. was less affected and it maintained high root to shoot ratio (R/S) and their tolerance indices (TI). Salinity stress increased Na + , Cland decreased K + and Ca + contents and consequently their ratios in both root and shoot of the seedlings. Under stress proline level was increased in both root and shoot of the s eedlings in all genotypes, the highest was observed in the root of Pokkali and in the shoot of IRATOM -24. Excepting BR 9 salinity increased protein content in other genotypes and among them Nonabokra maintained the highest protein level. Salinity inhibited the root ATPase activity in all except Pokkali. Efficiency of the maintenance of relatively high dry matter, R/S ratio, essential ions, K + -Ca 2+ / Na + ion ratios, proline and protein contents in the seedlings including the root ATPase activity may be imp ortant aspects of NaCl stress tolerance mechanism as found in one or another rice genotype of the present work.
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.
Plant Soil and Environment, 2011
In order to investigate the solutes accumulation associated with salt tolerance of rice (Oryza sativa L.), two rice genotypes including IR651 (salt-tolerant) and IR29 (salt-sensitive) were grown hydroponically in the Youshida nutrient solution. Salinity treatment was imposed 3 weeks after sowing using NaCl in two levels 0 and 100 mmol. Samples were separately collected from the youngest (sixth) leaves, leaf sheaths and roots at 72 and 240 h after salinization; then Na + , K + , Ca 2+ , Mg 2+ , P, Mn 2+ , Cland total soluble sugars concentration and Na + /K + ratio were determined. Total dry weight of both genotypes decreased with the application of NaCl. Salinity caused higher accumulation of Na + and Clin the sixth leaf and leaf sheath of IR29 than in IR651 while their concentration in root of IR651 was higher. K + concentration was decreased in the sixth leaf and leaf sheath of IR29 under NaCl stress. Reduction in Ca 2+ and Mg 2+ concentrations were observed in sixth leaves of both genotypes. P concentration was increased in leaf sheath and root of IR29 under saline conditions while it showed no changes in IR651. Our results indicated that the tolerant genotype had mechanisms to prevent high Na + and Claccumulation in the sixth leaf. High total soluble sugars concentration in shoot of IR651 is probably for adjusting osmotic potential and better water uptake under salinity. These mechanisms help plant to avoid tissue death and enable to continue its growth and development under saline conditions.
PLoS ONE, 2013
Sudden elevations in external sodium chloride (NaCl) accelerate potassium (K +) efflux across the plasma membrane of plant root cells. It has been proposed that the extent of this acceleration can predict salt tolerance among contrasting cultivars. However, this proposal has not been considered in the context of plant nutritional history, nor has it been explored in rice (Oryza sativa L.), which stands among the world's most important and salt-sensitive crop species. Using efflux analysis with 42 K, coupled with growth and tissue K + analyses, we examined the short-and long-term effects of NaCl exposure to plant performance within a nutritional matrix that significantly altered tissue-K + set points in three rice cultivars that differ in salt tolerance: IR29 (sensitive), IR72 (moderate), and Pokkali (tolerant). We show that total short-term K + release from roots in response to NaCl stress is small (no more than 26% over 45 min) in rice. Despite strong varietal differences, the extent of efflux is shown to be a poor predictor of plant performance on long-term NaCl stress. In fact, no measure of K + status was found to correlate with plant performance among cultivars either in the presence or absence of NaCl stress. By contrast, shoot Na + accumulation showed the strongest correlation (a negative one) with biomass, under long-term salinity. Pharmacological evidence suggests that NaCl-induced K + efflux is a result of membrane disintegrity, possibly as result of osmotic shock, and not due to ion-channel mediation. Taken together, we conclude that, in rice, K + status (including efflux) is a poor predictor of salt tolerance and overall plant performance and, instead, shoot Na + accumulation is the key factor in performance decline on NaCl stress.
Hydroponic experiments were conducted to investigate the possible role of abscisic acid (ABA) and silicate (Si) on inducing salinity tolerance in wheat seedlings. Caryopses of two wheat genotypes Kharchia-65 (salt tolerant) and Punjab-85 (salt sensitive) were pretreated with ABA (10 m M) for 24 h. Ten-day-old seedlings were exposed to 100 mM NaCl solution containing either 0 mM or 3 mM of sodium silicate for 16 days. We employed a fluorescent tracer trisodium salt of 8-hydroxy-1, 3, 6-pyrenetrisulphonic acid (PTS) for estimating Na + transport pathway to shoot. Exogenously applied Si as alone or with ABA significantly improved seedling growth by inhibiting Na + transport and the Na/ + K + ratio in both wheat genotypes. The genotype Punjab-85 maintained higher apoplastic Na + concentration compared to Kharchia-65 under NaCl treatment. Moreover, Si and ABA application improved leaf chlorophyll contents and consequently net assimilation rate of NaCl-stressed wheat seedlings through up-regulation of antioxidative enzyme activities. The results suggested that application of Si alone or in combination with ABA can significantly limit Na + bypass flow in both salt sensitive and tolerant wheat genotypes; however, ABA alone was effective in sensitive genotype only (Punjab-85). It is inferred from the results that Si had a more prominent role than ABA on plants in increasing biomass accumulation, proline contents and antioxidant enzyme activities, and inhibiting Na + accumulation and bypass flow. Nevertheless, ABA assisted Si in the amelioration of salt stressed in much better way than Si alone.