Proline Accumulation In Barley Research Articles

Proline and agronomic production responses of different barley cultivars to salinity stress : A correlation analysis

Salinity affects crop growth and development, and markedly leads to observable losses in agronomic yield. Barley is considered as an excellent model crop for the prediction of crop response to climate change and as a salt tolerance crop. The main objective of this study was to identify the correlation magnitude (r) between salt stress level and both agronomic parameters and proline accumulation in barley leaves. Twenty-eight barley genotypes were exposed to salt stress, ranging from 0.85 to 16 dS/m. This simple approach will help agronomist and farmers to predict plant response under different soil salinity levels. The following agronomic parameters were recorded: proline accumulation (mg/kg), plant height (cm), grain yield (g/plant), harvest index (%), biological yield (g/plant) and straw yield (g/plant). For the purpose of data fitting and simplicity, a simple linear regression analysis was used. The results of this study showed that agronomic parameters in barley had moderate to strong correlation coefficients ranging from 0.67 to 0.98. Reduction rates in agronomic parameters were 0.799 cm, 0.079 g/plant, 0.007%, 0.67 g/plant and 0.036 g/plant per one dS/m increment of salt stress on plant height, grain yield, harvest index (%), biological yield and straw yield, respectively. This study also showed that per one unit increase of water salinity, proline accumulation increased by 1.49 mg/kg. It can be concluded from this study and under the current growing conditions, agronomic parameters and proline accumulation in examined barley genotypes are well correlated with increasing the level of salt stress.

Influence of water stress and abscisic acid on free proline accumulation in barley leaves

Rapid accumulation of free proline was found in barley leaves under conditions of osmotic stress at the level of -8.3 bars, but not before 9 days of its duration. The threshold value of osmotic stress for the start of a rapid accumulation of proline was about -6 bars. The excised leaves of barley subjected to water stress by wilting accumulated free proline more rapidly. In the course of 24 hours free proline content increased about 30-fold, while the water content in the leaves decreased 3-fold only. We found also that excised barley leaves with full turgor treated with abscisic acid (10<sup>-4</sup> M) accumulated free proline as early as after 3 hours and subsequently after 24 hours free proline content increased 10-fold.

Differences in Physiological Traits Among Salt‐Stressed Barley Genotypes

The effect of salinity on some physiological parameters in 16 barley genotypes with different salt tolerance was investigated. The results showed 50 mM NaCl treatment increased Na+/K+ ratio, malondialdehyde (MDA) and proline contents, and decreased cell membrane stability index (CMSI) and fresh shoot biomass (FSB) of all tested genotypes. Salt stress also resulted in a decreased chlorophyll (Chl) content and net photosynthesis (Pn) for most genotypes. Under higher salt stress (300 mM NaCl), the marked increase for Na+/K+, MDA, and proline content, and decrease for other parameters were found for all genotypes. The affected extent of these parameters by salt stress varied with genotypes. Proline accumulation in barley was associated with injured extent under salt stress, indicating it is not a defensive reaction to the stress. K+ uptake was less affected, whereas Na+ accumulation in plants was enhanced under high salt stress. The correlation analysis showed that MDA and proline content, Na+ concentration and Na+/K+ were negatively correlated with FSB, whereas other parameters examined in the study were positively correlated with FSB.

Is Photosynthetic Activity Responsible for the Stimulating Effect of Light on ABA-Induced Proline Accumulation in Barley Leaves?

Summary In hydrated barley leaf segments incubated in solution for 7 h, the accumulation of proline induced by 100 µmol/L ABA with the synergistic interaction of KCl was stimulated by white, blue. (460 nm) and red. (660 nm) light. With 30 mmol/L KCl concentration, the stimulating effect of light reached a plateau at a photon fluence of 120, 40 and 10 gmol sec -1 m -2 for white, blue and red light, respectively. The contents of proline at the plateau level were similar with the different lights. DCMU effectively inhibited the hormonal process both in the light and in the dark. Experiments with etiolated barley leaves showed that also in these leaves the hormonal process occurred in the dark. The light stimulated, as in the case of green leaves, ABA-induced proline accumulation in the leaves without differentiated chloroplasts and the effect of white, blue and red light showed a considerable effectiveness at low light intensity. The stimulation of the three lights reached a plateau in the presence of 30 µmol/L KCl and at the same photon irradiance as that for green leaves. In etiolated, light-incubated leaves, ABA inhibited chlorophyll synthesis as a function of its concentration and the inhibition was almost complete at 100 µmol/L concentration. The comparison of chlorophyll content and accumulated proline content in green and etiolated leaves showed that the capability of proline accumulation in the light is independent of chlorophyll content. The results indicated that photosynthesis cannot be responsible for light-stimulation of proline accumulation induced by exogenously supplied ABA in hydrated barley leaves.

Glucose Mimics the Enhancing Effect of Light on ABA-Induced Proline Accumulation in Hydrated Barley and Wheat Leaves

Summary The effect of some possible precursors of proline, such as arginine, pyruvate, malate, citrate, α-ketoglutarate and glutamate, on the accumulation of proline induced by exogenous ABA was tested in nonstarved, hydrated leaves of barley ( Hordeum vulgare L. cv. Georgie) and wheat ( Triticutn durum L. cv. Valnova). Glutamate and, to a lesser extent, α-ketoglutarate increased proline accumulation in barley, both in the dark and in the light. In wheat, where the effect of ABA occurs only in the light, glutamate and α-ketoglutarate were effective when the treatment was applied in the light. Other compounds, such as ribose, ribulose, glucose and the non-metabolized glucose-analogues deoxy-D-glucose and 3-O-methylglucose, were tested. In wheat, glucose and to a lesser extent ribose allowed ABA-induced proline accumulation to occur in the dark; they also stimulated the process in barley. It is shown that in wheat, glutamate and α-ketoglutarate increased the ABA effect allowed by glucose equally in light and in darkness. The possible role of glucose in inducing the permissive condition for the expression of the hormonal process in wheat, as light does, is discussed. The possibility that glucose supplies the reducing power needed for ABA-induced proline accumulation in non-stressed leaves of wheat in the dark is suggested.

ABA‐induced proline accumulation in barley leaf segments: Dependence on protein synthesis

The kinetics of proline accumulation in barley (Hordeum vulgare L. cv. Georgie) leaf segments showed a lag phase of ca 3 h when the increase was induced by abscisic acid (ABA), but not when the accumulation of the imino acid was promoted by isobutyric acid (IBA). Cycloheximide (CHI) supplied together with ABA, either from the beginning of the treatment or some time before the end of the lag phase, completely abolished ABA‐induced proline accumulation, whereas no block was observed when the inhibitor was supplied after the lag phase. Cordycepin (COR) exibited a similar effect. The IBA‐induced increase in proline was not influenced by CHI for at least 5 h.When segments were pretreated with ABA for a period longer than the lag phase in the absence of salts in the external medium, there was no significant increase in proline. If KCI was added to the incubation medium after such a pretreatment, however, proline increased even after removal of the hormone from the external medium. This increase in proline occurred without any lag phase, and was only partially inbibited by CHI and rapidly and totally blocked by fusicoccin (FC). These results suggest that some protein, characterized by a fast turnover and possibly conferring the sensitivity to KCI, is synthesized during the early hours (lag phase) of the ABA treatment.The synthesis of this protein(s) does not seem to be involved in the increase in proline induced by IBA and is thus a peculiar aspect of that mediated by ABA.

Abscisic Acid Accumulation Is Not Required for Proline Accumulation in Wilted Leaves

Leaves from dark-grown barley (Hordeum vulgare L. var Larker) seedlings grown in the presence and absence of fluridone were used to determine whether or not abscisic acid (ABA) accumulation was necessary for proline to accumulate in wilted tissue. Wilted tissue (polyethylene glycol-treated) leaves from fluridone-grown seedlings did not accumulate ABA but did accumulate proline at a rate that was not different from the non-fluridone-treated leaves. Thus ABA accumulation is not required for wilting-induced proline accumulation in barley leaves. Proline accumulation in wilted leaves from the wilty tomato (Lycopersicon esculentum) mutant, flacca, was compared to that in the wild type, Rheinlands Ruhm. Proline accumulated in wilted leaves from flacca. The rate of accumulation was faster in flacca compared to the rate in the wild type because the wilty mutant wilted faster. ABA accumulated in wilted leaves from the wild type but not in the wilty mutant. This result is a further confirmation that ABA accumulation is not required for wilting-induced proline accumulation. These results are significant in that proline accumulation in barley leaves can be induced independently by any one of three treatments: wilting, ABA, or salt.

The Effects of Benzyladenine, Cycloheximide, and Cordycepin on Wilting-Induced Abscisic Acid and Proline Accumulations and Abscisic Acid- and Salt-Induced Proline Accumulation in Barley Leaves

Benzyladenine inhibits proline accumulation in wilted, abscisic acid (ABA)-treated, and salt-shocked barley leaves. It does not affect ABA accumulation or disappearance in wilted leaves. Inhibition of proline accumulation in salt-shocked leaves was observed both when benzyladenine was added at the beginning of or after salt treatment. Cycloheximide (CHX) and cordycepin inhibited both ABA and proline accumulations in wilted barley leaves and proline accumulation in ABA-treated leaves. In salt-shocked leaves, cordycepin inhibited proline accumulation when added after salt treatment but before proline began to accumulate but not when added after the onset of proline accumulation. CHX delayed the accumulation of proline in salt-shocked leaves but, after a period of time, proline accumulated in the CHX-treated leaves at rates comparable to the salt-treated control. This delay and subsequent accumulation was observed when CHX was added before, during, and after salt treatment. However, the earlier in the salt treatment period that CHX was given, the longer was the observed delay. These results are interpreted to indicate that gene activation is involved in proline accumulation in response to wilting, to ABA, and to salt in barley leaves. This gene activation is in addition to the gene activation that is required for ABA accumulation in wilted leaves. If ABA accumulation is required for proline accumulation in wilted barley leaves, then two sets of gene activation are involved in wilting-induced proline accumulation. All of our results are consistent with this possibility but do not prove it. The inhibition of proline accumulation by benzyladenine is probably neither due to an effect on gene activation nor to an effect on the ABA level.

Effects of weak acids on proline accumulation in barley leaves: a comparison between abscisic acid and isobutyric acid

Abstract. When isobutyric acid (IBA) or abscisic acid (ABA) are supplied to leaf sections a similar rapid and marked decrease in the intracellular pH is observed. This acidification is accompanied by an increase in proline level which is about the same for both 3 mol m−3 IBA and 1 mol m−3 ABA treatments.Fusicoccin (FC), known to act at the proton pump level, almost completely suppresses the ABA‐induced acidification of the cell sap, whereas it only partially counteracts the acidifying effect of IBA, in particular during short periods of treatment. This effect of FC is paralleled by a similar inhibition of the induced proline accumulation: in fact, FC completely suppresses the ABA‐induced increase in proline during short treatment periods, whereas it is only effective in inhibiting the IBA‐induced proline accumulation after long treatment periods.These data seem to suggest that the ABA‐ and IBA‐induced changes in proline level might be mediated by changes in the intracellular pH.

Inhibiting effect of fusicoccin on abscisic acid-induced proline accumulation in barley leaves

Abscisic acid (ABA) treatments induce in barley leaf fragments an increase in proline with a maximum at 10 −4 M ABA. This effect is suppressed by the presence of fusicoccin (FC). FC induces an acidification on the incubation medium paralleled by an increase in cell sap pH; both of these effects of FC are significantly antagonized by the simultaneous addition of ABA. The antagonism between FC and ABA on the proline accumulation process and on the external pH changes suggests that both of these substances can influence H + secretion, presumably by acting on the proton pump, and that the consequent changes in intracellular pH might affect some metabolic process and thus influence proline metabolism.

The Mechanism of Abscisic Acid-induced Proline Accumulation in Barley Leaves

When leaf blades of fully expanded second leaves of barley (cv. Prior) were excised and incubated with the cut end in a 20 milligram per liter solution of abscisic acid, they accumulated proline at the rate of about 1 micromole per hour per gram fresh weight after a 3- to 4-hour lag. This accumulation occurred reproducibly only if leaves were pretreated by placing the cut end in a solution consisting of 50 millimolar sucrose and 1 millimolar glutamate. Treated leaves were taken from plants which had been in the light for 24 hours.Abscisic acid caused a stimulation of proline synthesis from glutamic acid. Proline oxidation rates were similar in leaves incubated in abscisic acid and in water even though the proline level in abscisic acid-treated leaves was 2.5 times the level in the water-treated controls. The incorporation of proline into protein was not affected by abscisic acid.These results are interpreted to indicate that the metabolic cause of abscisic acid-induced proline accumulation is a stimulation of proline synthesis from glutamic acid. Inhibition of the utilization of proline by oxidation and protein synthesis does not contribute to proline accumulation the way it does in drought-stressed leaves.

Free proline accumulation in cereals in relation to salt tolerance

In a micro-plot experiment it was observed that free proline accumulation in barley and wheat crops increased with the salt stress. But in sensitive strains of both the crops it did not accumulate in accordance with the preceding values after their tolerance limit and at this point yield of barley was reduced by 25.8% and wheat by 23.2% over control while significant yield reductions were not observed with tolerant strains. Proline accumulation was also found to be related to tissue K/Na ratio and the critical limits of this ratio were observed between 0.60 and 0.34 for barley and 4.2 and 1.4 for wheat.

Stress Metabolism. VII. Salinity and Proline Accumulation in Barley

Barley plants (cv. Prior) were grown in nutrient culture and subjected to a variety of salinity stress treatments when 10-12 days old. Salinity stress was either imposed abruptly by transferring plants to a solution containing NaCl of - 5.7 or - 10.7 bar osmotic potential, or gradually by transferring plants daily to solutions of successively lower osmotic potential (- 1 bar per day). Prolonged exposure to salinity stress was achieved by holding plants in a - 10.7 bar osmotic potential solution for 6 days. Proline accumulated rapidly in plants subjected to a salinity stress greater than - 5.7 bar osmotic potential. Accumulation appeared to be controlled by tissue osmotic potential rather than by turgor, and continued for 24 h after the saline solution was removed from the root medium. Proline accumulation continued for at least 3 days in plants held at - 10.7 bar osmotic potential, during which time the plants continued to grow slowly. The accumulated proline made only a minor contribution to osmotic regulation in the plant,

Stress Metabolism. VIII. Specific Ion Effects on Proline Accumulation in Barley

Intact 12-day-old barley (cv. Prior) plants or first-leaf sections were grown on iso-osmotic solutions of polyethylene glycol or a variety of inorganic salts for 24 h. All solutions caused a similar decline in leaf water potential with external osmotic potential in the intact plant, but the decline in internal osmotic potential was least on solutions of polyethylene glycol, causing a loss of turgor in plants growing on that osmoticurn. Plants growing on solutions of NaCl, KCl, Na2SO4 or CaCl, accumulated less proline than plants on iso-osmotic solutions of polyethylene glycol, but plants on MgCl2, solutions accumulated as much or more. With leaf sections, no proline accumulated on solutions containing the monovalent cations, whereas tissue floated on salt solutions containing Mg2+ or Ca2+ accumulated as much or more proline as that on iso-osmotic solutions of polyethylene glycol. NaCl was found to inhibit the proline accumulation caused by a reduction in external osmotic potential.