The Effect of Polyethylene Glycol on Proline Accumulation in Rice Leaves

The regulation of proline accumulation in polyethylene glycol (PEG, –1.5 MPa) treated rice leaves was investigated. PEG treatment resulted in a decrease in relative water content, indicating that PEG treatment caused water stress in rice leaves. Proline accumulation caused by PEG was related to protein hydrolysis, an increase in ornithine--amino- transferase activity, an increase in the content of ammonia, and an increase in the contents of the precursors of proline biosynthesis, glutamic acid, ornithine, and arginine. Results also show that abscisic acid accumulation is not required for proline accumulation in PEG-treated rice leaves.     

Changes in Mulberry Leaf Metabolism in Response to Water Stress

A series of experiments were conducted to characterize the water stress-induced changes in the activities of RuBP carboxylase (RuBPCO) and sucrose phosphate synthase (SPS), photosystem 2 activity, and contents of chlorophylls, carotenoids, starch, sucrose, amino acids, free proline, proteins and nucleic acids in mulberry (Morus alba L. cv. K-2) leaves. Water stress progressively reduced the activities of RuBPCO and SPS in the leaf extracts, the chlorophyll content, and PS2 activity in isolated chloroplasts. Plants exposed to drought showed lower content of starch and sucrose but higher total sugar content than control plants. While the soluble protein content decreased under water stress, the amino acid content increased. Proline accumulation (2.5-fold) was noticed in stressed leaves. A reduction in the contents of DNA and RNA was observed. Reduced nitrogen content was associated with the reduction in nitrate reductase activity. SDS-PAGE protein profile showed few additional proteins (78 and 92 kDa) in the water stressed plants compared to control plants.     

Photosynthetic responses and proline content of mature and young leaves of sunflower plants under water deficit

In mature and young leaves of sunflower (Helianthus annuus L. cv. Catissol-01) plants grown in the greenhouse, photosynthetic rate, stomatal conductance, and transpiration rate declined during water stress independently of leaf age and recovered after 24-h rehydration. The intercellular CO₂ concentration, chlorophyll (Chl) content, and photochemical activity were not affected by water stress. However, non-photochemical quenching increased in mature stressed leaves. Rehydration recovered the levels of non-photochemical quenching and increased the F_v/F_m in young leaves. Drought did not alter the total Chl content. However, the accumulation of proline under drought was dependent on leaf age: higher content of proline was found in young leaves. After 24 h of rehydration the content of proline returned to the same contents as in control plants.     

Inhibition of proline oxidation by water stress

The conversion of proline to glutamic acid and hence to other soluble compounds (proline oxidation) proceeds readily in turgid barley (Hordeum vulgare) leaves and is stimulated by higher concentrations of proline. This suggests that proline oxidation could function as a control mechanism for maintaining low cellular levels of proline in turgid tissue. In water-stressed tissue, however, proline oxidation is reduced to negligible rates. These results are consistent with the idea that proline accumulation results from inactivation by water stress of normal control mechanisms. It seems likely that inhibition of proline oxidation is necessary in maintaining the high levels of proline found in stressed barley leaves.     

Regulation of ammonium-induced proline accumulation in detached rice leaves

Accumulation of proline in response to NH₄Cl was studied indetached leaves of rice (Oryza sativa cv. Taichung Native1). Increasing concentrations of NH₄Cl from 50 to 200mMprogressively increased proline content and this was correlated with theincrease in ammonium content. Proline accumulation induced by NH₄Clwas related to proteolysis, an increase in ornithine--aminotransferaseactivity, a decrease in proline dehydrogenase activity, and a decrease inproline utilisation and could not be explained by NH₄Cl-inducedmodification in ¹-pyrroline-5-carboxylate reductase activity.The content of glutamic acid was decreased by NH₄Cl, whereas theincrease in arginine and ornithine contents was found to be associated with theincrease in proline content in NH₄Cl-treated detached rice leaves.     

The Relation between Accumulation of Abscisic Acid and Proline in Detached Rice Leaves

The relation between abscisic acid (ABA) and proline accumulation was investigated in detached rice (Oryza sativa L.) leaves. In darkness, proline content increased about 2-, 2,5- and 6-fold after 24, 48 and 72 h. ABA content reached maximum after 48 h. In the light, proline content remained almost unchanged until 48 h and subsequently increased slightly. ABA content in the light was lower than in darkness, but the maximum was also after 48 h. During 12-h exposure to decreased air humidity, proline content gradually increased, but ABA content increased about 25-fold after 4 h and declined thereafter. Exogenous application of ABA resulted in an increase in proline content in detached rice leaves under both light and darkness.     

Proline accumulation in a barley mutant resistant to trans-4-hydroxy-L-proline

Five proline analogues were tested for inhibition of the growth of mature barley (Hordeum vulgare L.) embryos in sterile culture. Inhibition by all analogues was relieved by proline. Inhibition by trans-4-hydroxy-L-proline was relieved by low amounts of proline. Twenty thousand mature embryos were dissected from M₂ seeds after sodium azide mutagenesis. Four plants (Rothamsted 5201, 6102, 6901, 6902) were selected with good growth on 4 mM trans-4-hydroxyproline. Properties of mutant R5201 were studied in detail. Selfed progeny of R5201 were all resistant to trans-4-hydroxyproline and also to L-thiazolidine-4-carboxylic acid and trans-3-hydroxy-L-proline but not L-azetidine-2-carboxylic acid. The content of soluble proline in progeny of R5201 was higher in leaves by a factor of up to six-fold. Proline content was measured in the soluble fraction of the terminal 20 mm of 4 d old plants subjected to severe water stress in 40% w/v polyethylene glycol. Leaves of the mutant contained more proline initially and accumulated proline morer rapidly than the parental leaves. As mutant leaves were larger and lost water more rapidly the greater increase in proline may have been caused by more severe water stress. Resistance to trans-4-hydroxyproline in R5201 was due to a single partially dominant nuclear gene.Abbreviations AZC L-azetidine-2-carboxylic acid - HYP trans-4-hydroxy-L-proline - ORN L-ornithine - CIT L-citrulline     

PVY侵染后烟草营养成分的变化及其对介体烟蚜生长发育的影响

【目的】明确马铃薯Y病毒(potato virus Y,PVY)侵染后诱导的烟草营养成分的变化及其对烟蚜Myzus persicae生命特性的影响,旨在进一步解析PVY-烟草-烟蚜三者间的互作机制。【方法】通过蒽酮比色法和氨基酸自动分析仪测定了PVY不同侵染时期烟株体内的可溶性糖和游离氨基酸含量的变化;测定和比较了感病与健康烟草植株上烟蚜种群生长发育、成虫寿命、繁殖力和有翅蚜产生量的差异性。【结果】PVY侵染前、中、后期(分别为侵染后5,12和20 d)的烟草叶片中游离氨基酸的总量均显著高于健康烟草叶片。相较于健康烟草叶片,在PVY侵染前期的烟草叶片中,谷氨酸、脯氨酸、天冬氨酸、色氨酸、缬氨酸、赖氨酸和组氨酸的含量显著增加;PVY侵染中期,感病叶片中丝氨酸含量显著下降,谷氨酸、天冬氨酸、色氨酸、缬氨酸、亮氨酸、苯丙氨酸、精氨酸和组氨酸含量显著提高;PVY侵染后期,感病叶片中甘氨酸含量显著下降,谷氨酸、脯氨酸、天冬氨酸、苏氨酸、缬氨酸、亮氨酸、丙氨酸、苯丙氨酸、组氨酸、酪氨酸和精氨酸含量显著提高。在PVY侵染的前期和中期,感病叶片中的可溶性糖含量显著高于健康烟叶,而在侵染后期感病叶片中可溶性糖含量显著低于健康烟草叶片的。PVY侵染前期和中期的烟草叶片中总糖和总游离氨基酸的含量比值显著高于健康烟草叶片中的。在PVY侵染的烟草植株和健康烟草植株上取食的烟蚜其发育历期、若蚜历期、成蚜繁殖期、繁殖后期、寿命、烟蚜种群的内禀增长率、周限增长率和平均世代周期均无显著差异,但在感病烟草植株上取食的烟蚜成蚜繁殖前期显著缩短,其繁殖力和净生殖率显著提高。相较于健康烟草植株,在PVY侵染烟草植株上定殖的烟蚜种群有翅蚜发生的高峰期提前。【结论】PVY侵染前期和中期提高了寄主烟草的营养品质,从而提高了烟蚜的繁殖力。侵染后期烟草营养品质的下降,促使烟蚜种群有翅蚜的产生和扩散,从而有利于PVY自身的传播。     

γ-氨基丁酸对低氧胁迫下甜瓜幼苗多胺代谢的影响

以‘西域一号’甜瓜为试验材料,采用营养液水培法,研究了低氧胁迫下外源添加γ-氨基丁酸(GABA)对甜瓜幼苗多胺代谢的影响.结果表明:与通气对照相比,低氧胁迫处理的甜瓜幼苗谷氨酸脱羧酶(GAD)活性和GABA含量显著提高,同时多胺合成酶活性提高诱导多胺含量显著增加,但二胺氧化酶(DAO)和多胺氧化酶(PAO)活性也显著提高;根系精氨酸脱羧酶(ADC)活性提高幅度较大,导致根系游离态腐胺含量较高,而叶片乌氨酸脱羧酶(ODC)和S-腺苷甲硫氨酸脱羧酶(SAMDC)活性提高幅度较大,导致叶片游离态亚精胺(Spd)含量较高;根系游离态DAO和PAO活性显著低于叶片,其细胞壁结合态PAO活性显著高于叶片.与低氧胁迫处理相比,低氧胁迫下外源添加GABA处理的甜瓜幼苗叶片和根系中GABA和谷氨酸含量均显著提高,而GAD活性显著降低;精氨酸、鸟氨酸、甲硫氨酸含量的提高促使多胺合成酶活性显著提高,从而诱导多胺含量显著增加,DAO和PAO活性显著降低.     

Water stress induced alterations in ornithine aminotransferase of ragi (Eleusine coracana): Protection by proline against heat inactivation and denaturation by urea and guanidinium chloride

Water stress resulted in a specific response leading to a large and significant increase (80-fold) in free proline content of ragi (Eleusine coracana leaves and seedlings. L-Proline protected ornithine aminotransferase, an enzyme in the pathway for proline biosynthesis, isolated from normal and stressed ragi leaves against heat inactivation and denaturation by urea and guanidinium chloride. The protection of the stressed enzyme by L-proline was much more complete than that of the enzyme isolated from normal leaves. While L-ornithine, one of the substrates, protected the stressed enzyme against inactivation, it enhanced the rate of inactivation of the normal enzyme. α-Ketoglutarate protected both the normal and stressed enzyme against inactivation and denaturation. These results support the suggestion that ornithine aminotransferase has undergone a structural alteration during water stress. In view of the causal relationship between elevated temperature and water stress of plants under natural conditions, the protection afforded by proline against inactivation and denaturation of the enzyme from stressed leaves assumes significance. These results provide an explanation for a possible functional importance of proline accumulation during water stress.     

Effect of glutamic acid foliar applications on lettuce under water stress

The yield and quality of leafy vegetables can be compromised by reduced water availability. Glutamic acid is involved in different biological processes and among them it plays an important role in chlorophyll and proline biosynthesis. The aim of this work was to evaluate the possible efficacy of glutamic acid in counteracting water stress in romaine lettuce. Lettuce plants were grown in pots filled with substrate and subjected to water deprivation. A glutamic acid solution (1.9 mM) was applied as foliar treatment, both in stressed and non-stressed plants. The effect of the treatment was evaluated at different time points during the experiment in order to evaluate changes at a molecular, physiological, biochemical and agronomic level. Yield was reduced by 35% in stressed plants, while no significant changes in quality parameters were observed, except for nitrate content, which increased under water stress. At a molecular level, the expression of genes encoding for ROS scavenging enzymes was monitored but, apparently, glutamic acid did not significantly prevent the water stress response. Slightly positive effects deriving from glutamic acid application were found for nitrate and proline contents, suggesting that a possible mode of action of glutamic acid would involve a role for these molecules. Further studies are required, also on other crop species, for confirming these results. Different concentrations and application modes should be also tested.     

The After-Effect of Water Stress on Chlorophyll Formation during Greening and the Levels of Abscisic Acid and Proline in Dark Grown Wheat Seedlings

Cut seedlings of wheat plants (Triticum aestivum L. cv. Starke II Weibull) between 6 and 7 days old were water stressed in darkness by exposing them to air of 35% relative humidity 2.5 to 20 h. This treatment resulted in a water potential of -11 bars in the leaves after 20 h. The leaves were then rewatered and irradiated. The chlorophyll formation that took place in fully turgid leaves during the greening was markedly decreased in the case of the water-stress pretreatmet. and especially the lag phase was prolonged. The longer the stress pretreatment the more evident was the subsequent effect on chlorophyll formation. However, no linear relationship was found between the amount of stress and the chlorophyll content. Protochlorophyllide regeneration from endogenously formed δ-aminolevulinic acid was markedly decreased even after the shortest water-stress period. However, protochlorophyllide accumulation from exogenously supplied δ-aminolevulinic acid was only slightly decreased following the water-stress pretreatment. Further more, the ratio of protochlorophyllide₆₅₀ to protochlorophyllide₆₂₈ was slightly reduced by the same conditions. During the stress period both abscisic acid and proline were accumulated in the leaves. The content of abscisic acid increased up to six times the normal level during water stress lasting for 20 h. The increase of proline was about three-fold for similar treatment. After rewatering the leaves the levels of both abscisic acid and proline rapidly declined and reached. 10 h later, the levels found in unstressed seedlings. The increase in abscisic acid during water stress associated with impaired chlorophyll metabolism suggested that the after-effect of water stress might be linked to chlorophyll metabolism through abscisic acid or some of its metabolites. The changes in proline content open the possibility that this substance could function as a reserve substance for the formation of chlorophyll after the discon tinuation of the stress.     

γ-氨基丁酸对低氧胁迫下甜瓜幼苗多胺代谢的影响

以‘西域一号’甜瓜为试验材料,采用营养液水培法,研究了低氧胁迫下外源添加γ-氨基丁酸(GABA)对甜瓜幼苗多胺代谢的影响.结果表明：与通气对照相比,低氧胁迫处理的甜瓜幼苗谷氨酸脱羧酶(GAD)活性和GABA含量显著提高,同时多胺合成酶活性提高诱导多胺含量显著增加,但二胺氧化酶(DAO)和多胺氧化酶(PAO)活性也显著提高;根系精氨酸脱羧酶(ADC)活性提高幅度较大,导致根系游离态腐胺含量较高,而叶片鸟氨酸脱羧酶(ODC)和S-腺苷甲硫氨酸脱羧酶(SAMDC)活性提高幅度较大,导致叶片游离态亚精胺(Spd)含量较高;根系游离态DAO和PAO活性显著低于叶片,其细胞壁结合态PAO活性显著高于叶片.与低氧胁迫处理相比,低氧胁迫下外源添加GABA处理的甜瓜幼苗叶片和根系中GABA和谷氨酸含量均显著提高,而GAD活性显著降低;精氨酸、鸟氨酸、甲硫氨酸含量的提高促使多胺合成酶活性显著提高,从而诱导多胺含量显著增加,DAO和PAO活性显著降低.     

Does abscisic acid influence proline accumulation in stressed leaves?

Root treatments of barley (Hordeum distichum L.) plants with 10^-7 to 10^-4 M abscisic acid (ABA) caused an increase in proline content, especially at higher concentrations, within 2–3 h. Even 3 h after the removal of ABA from the medium the plants continued to accumulate proline. The higher the concentration of the ABA, the higher was the proline level at 6 h. When the highest ABA concentration, 10^-4 M, was tested with polyethylene glycol (PEG) (-5.0 bars) in the medium, the ABA treatment resulted in a higher proline content than in control plants. The treatments PEG alone and PEG + ABA resulted in heavy accumulation of proline, especially, 3 h after releasing the plants from the stress. The proline content in PEG+ABA-treated plants was always higher than plants treated with PGE or ABA alone. In peas (Pisum sativum L. cv Alaska) the same trend occurred although to a lesser degree. These findings indicate an influence of ABA on proline accumulation in water-stressed plants.Abbreviations ABA abscisic acid - PEG polyethylene glycol - RWC relative water content     

Changes in free amino acids and polyamine levels in Satsuma leaves in response to Asian citrus psyllid infestation and water stress

The effects of biotic and abiotic stresses on changes in amino acids and polyamine levels in Satsuma orange （Citrus unshiu; cultivar Owari） leaves were inves- tigated. Asian citrus psyllids Diaphorina citri （Kuwayama） （ACP） infestation was used to induce biotic stress while a water deficit was imposed to induce abiotic stress. Potted trees were infested by placing 50 psyllids on 3 citrus leaves enclosed in nylon mesh bags for 5 d. A parallel set of plants were kept water stressed by maintaining the soil at 20% water holding capacity for 5 d. Levels of total free amino acids were higher in water stressed and ACP infested leaves. Polyamine putrescine increased in infested leaves but not in water stressed leaves. Proline was the most abundant amino acid and its levels significantly increased by both biotic and abiotic stresses. Proline levels in infested leaves were significantly higher than the water stressed leaves. Histidine, methionine, asparagine, arginine, serine, and leucine levels also increased significantly in infested leaves, but in water stressed leaves only leucine, methionine, and threonine increased. Levels of amino acids, such as tyrosine, isoleucine, phenylalanine, glutamic acid, and alanine, declined in infested leaves. Under water stress asparagine, phenylalanine, serine, and histidine also declined compared to controls. This indicates that while proteolysis occurred under both stresses, metabolic conversion of amino acids was different under the two stresses. In ACP infested leaves some amino acids may be used as feeding material and/or converted into secondary metabolites for defense.     

Light-Dark Changes in Proline Content of Barley Leaves under Salt Stress

Proline accumulation in leaves of barley (Hordeum vulgare L. cv. Alfa) seedlings treated with 150 mM NaCl was promoted in the light and suppressed in the dark. The light/dark changes of proline content was enhanced with each 12 h light/12 h dark cycle and the proline content increased steadily. Root and shoot concentrations of Na⁺ and Cl^– in salt treated plants increased about 10 to 25 times as compared to the control. The content of these ions and the content of malondialdehyde were higher in the shoot of seedlings exposed to salt stress for 4 d in the light in comparison with the seedlings exposed to NaCl for 4 d in darkness. Light stimulated both ions and proline accumulation in the leaves and has no effect in the roots. Oxygen uptake was higher in the seedlings kept 4 d in the light which have higher endogenous free proline content. Chlorophyll fluorescence measurements showed that the photochemical activity of PS 2 slightly decreased as a result of salt stress and was not influenced by light regimes during plant growth.     

Osmotically Induced Proline Accumulation in <Emphasis Type="Italic">Lotus Corniculatus</Emphasis> Leaves is Affected by Light and Nitrogen Source

Proline accumulation in osmotically stressed leaves of Lotus corniculatus was stimulated by increasing light intensity (photon fluence density, PFD). Treatment with propanil limited proline accumulation in response to light and osmotic stress, indicating a dependence of proline synthesis on photosynthetic NADPH. Drought stress induced proline accumulation in L. corniculatus both in nitrate-fed plant (NFP) and ammonium-fed plants (AFP), although higher proline concentration was observed in AFP than in NFP after 24 h of drought stress. Changes in proline accumulation induced by drought stress in plants grown under different nitrogen regimes could not be explained by changes of either total protein or amino acids, consistent with specifically altered regulation of proline synthesis. Under control conditions, alanine, aspartate and glutamate were the predominant amino acids in NFP; conversely, in AFP, arginine and ornithine were the predominant amino acids. Only the NFP regime showed changes in the concentrations of specific amino acids under drought stress a decrease in alanine, aspartate and glutamate and increased gama-aminobutyric acid. In AFP and especially NFP, proline accumulation under osmotic stress was associated with increased ornithine amino transferase activity. An increase of both activity and protein of ferredoxin-dependent glutamate synthase was observed in osmotic-stressed NFP; inversely both decreased in drought-stressed AFP. PFD and nitrogen source are therefore shown to be regulators of proline accumulation in L. corniculatus osmotically stressed plants.     

Diurnal Fluctuations in Relative Water Content, Nitrate Reductase and Proline Content in Water-stressed and Non-stressed Wheat

Diurnal variations in relative water content (RWC), nitrate reductase (NR) and proline content (PC) were studied at 3 h intervals during a 24 h cycle in the flag leaf of wheat (Triticum vulgare, v. Kalyansona) grown under stressed and non-stressed conditions. RWC was lower in stressed plants than in non-stressed ones throughout the 24 h period. Although it was lowest at 12 h, it recovered by 15 h. Non-stressed plants maintained higher NR activity compared to those under stress. The enzyme activity during night was about the same as during day time in both types of plants. Compared to non-stressed plants, stressed ones had lower NO₃^? content. Proline accumulation occurred under stress conditions and had a maximum at 12–15 h. Non-stressed plants exhibited higher PC during night than day time. Changes in temperature and relative humidity were noted during the period and their influence on RWC, NR and proline was discussed.