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1.
The relationship between ammonium accumulation and senescence of detached rice leaves was investigated. Ammonium accumulation in detached rice leaves coincided closely with dark-induced senescence. Exogenous NH4Cl and methionine sulfoximine, which caused an accumulation of ammonium in detached rice leaves, promoted senescence. Treatments such as light and benzyladenine, which retarded senescence, decreased ammonium level in detached rice leaves. Abscisic acid, which promoted senescence, increased ammonium level in detached rice leaves. The current results suggest that ammonium accumulation may be involved in regulating senescence. Evidence was presented to show that ammonium accumulated in detached rice leaves increases tissue sensitivity to ethylene. The accumulation of ammonium in detached rice leaves during dark-induced senescence is attributed to a decrease in glutamine synthetase activity and an increase in reduction of nitrate. 相似文献
2.
Ammonium accumulation in relation to prolineaccumulation in detached rice leaves under stressconditions was investigated. Ammonium accumulation indark-treated detached rice leaves preceded prolineaccumulation. Ammonium accumulation caused by waterstress coincided closely with proline accumulation indetached rice leaves. Exogenous NH4Cl andmethionine sulfoximine (MSO), which caused anaccumulation of ammonium in detached rice leaves,increased proline content. It was found that prolinein NH4Cl- or MSO-treated rice leaves is lessutilized than in water-treated rice leaves (controls). These results are in agreement with the observationthat a decrease in proline utilization contributes tothe accumulation of proline in dark-treated and waterstressed rice leaves. Although ammonium contentincreased in Cd- and Cu-treated rice leaves, theincrease in ammonium content was only observed afterthe increase in proline content. 相似文献
3.
The activities of catalase, peroxidase, and polyphenoloxidase were studied in attached and detached rice (Oryza sativa L. cv. Ratna) leaves. Catalase activity decreased while peroxidase and polyphenoloxidase activities increased during senescence of both attached and detached rice leaves. Kinetic (5 mum) and benzimidazole (1 mm), which are known to delay the senescence of detached rice leaves, retarded the decrease of catalase activity during detached leaf senescence. On the other hand, these chemicals accelerated the increase of peroxidase and polyphenoloxidase activities over the water control. Total phenolics accumulated in detached and darkened rice leaves, but in attached leaf senescence in light no accumulation of phenolics was observed. 相似文献
4.
The regulation of proline accumulation in detached rice leaves exposed to excess NiSO4 was investigated. NiSO4 treatment increased proline and Ni contents but had no effect on relative water content, indicating that proline accumulation
in Ni-exposed detached rice leaves was due to Ni uptake per se, rather than to water stress. Proline accumulation caused by
NiSO4 was related to protein hydrolysis, a decrease in proline dehydrogenase activity, and a decrease in proline utilization. It
seems that an increase in the content of ammonia and an increase in the activities of Δ1-pyrroline-5-carboxylate reductase and ornithine-δ-aminotransferase play minor if any role in Ni-induced proline accumulation
in detached rice leaves. 相似文献
5.
The relationship of cellulase to detached leaf senescence of rice seedlings was investigated by examining the effect of ABA and 6-BA on changes in the level of cellulase of leaf segments during senescence. It was shown that the rise in cellulase activity increased with declining chlorophyll content, which was used as the senescence indicator during the senescence of detached rice leaves caused by ABA. The action of ABA took place only after a 48h lag period. ABA enhanced the cellulase secretion and increased the permeability of plasma membrane. A high level of cellulase activity in cell wall closely related to membrane permeability changes. The action of cellulase in the cell wall may cause depolymerization of β-1, 4-glucan in situ, thus speeding senescence. The 6-BA reverses completely or partly the increase in cellulase activity and tile permeability caused by ABA during the first two day, }) ut it antagonized hardly any of the ABA effect from the third day on, suggesting the onset of an irreversible stage in the senescence of detached rice leaves. 相似文献
6.
Both abscisic acid (ABA) and jasmonates are known to promote leaf senescence. Since ABA and jasmonates have both chemical and physiological similarities, we are interested to know whether senescence of detached rice leaves induced by methyl jasmonate (MJ) is mediated through an increase in endogenous ABA levels. In darkness, the endogenous level of ABA in detached rice leaves remained unchanged in the first day of incubation in water and increased about 5 times its initial value in the second day. However, the pattern of senescence, as judged by protein loss, was rapid during the first day. MJ significantly promoted senescence of detached rice leaves. Contrary to our expectation, endogenous ABA levels decreased in MJ-treated detached rice leaves. Similar to the effect of MJ, endogenous ABA levels decreased in detached rice leaves which were induced to senesce by treatment with NH4Cl. These results suggest that endogenous ABA levels are not linked to MJ-induced senescence of detached rice leaves. 相似文献
7.
Ammonium accumulation in relation to water stress-promoted senescence of detached rice leaves was investigated. The effect of water stress on the senescence of detached rice leaves is associated with the accumulation of ammonium. The accumulation of ammonium in detached rice leaves by water stress is attributed to a decrease in glutamine synthetase activity. Ammonium accumulation in detached rice leaves, induced by water stress, was accompanied by an increase in tissue sensitivity to ethylene which, in turn, accelerated leaf senescence. 相似文献
8.
The possibility that ammonium (NH
4
+
) accumulation is linked to the senescence of detached rice (Oryza sativa) leaves induced by copper (Cu) was investigated. CuSO4 was effective in promoting senescence of detached rice leaves. Both CuSO4 and CuCl2 induced NH
4
+
accumulation in detached rice leaves, indicating that NH
4
+
accumulation is induced by copper. Sulfate salts of Mg, Mn, Zn, and Fe were ineffective in inducing NH
4
+
accumulation in detached rice leaves. The senescence of detached rice leaves induced by Cu was found to be prior to NH
4
+
accumulation. Free radical scavengers, such as glutathione and thiourea, inhibited senescence caused by Cu and at the same time inhibited Cu-induced NH
4
+
accumulation. The current results suggest that NH
4
+
accumulation is not associated with senescence induced by Cu, but is part of the overall expression of oxidative damage caused by an excess of Cu. Evidence was presented to show that copper-induced ammonium accumulation in detached rice leaves is attributed to a decrease in glutamine synthetase activity and an increase in reduction of nitrate. 相似文献
9.
The Relation between Accumulation of Abscisic Acid and Proline in Detached Rice Leaves 总被引:4,自引:0,他引:4
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. 相似文献
10.
Tungro virus infection stimulates proline accumulation in leaves of rice ( Oryza sativa L.), especially in a sensitive cultivar, Taichung Native 1. Disease-induced proline accumulation increases with the severity of the disease. Proline also accumulates in senescing, detached healthy rice leaves. The magnitude of proline accumulation in these leaves was further accentuated by ABA and retarded by kinetin. In the absence of drought stress, virus infection induces severe symptoms (stunting) in a drought tolerant cultivar (Lalnakanda 41) when compared to cultivars with intermediate (MW 10) and high sensitivity (Cauvery) to drought. Thus tungro virus mimics water stress in inducing proline accumulation in rice leaves. In both cases a common factor, ABA, may mediate proline accumulation. In drought stress, proline accumulation is associated with tolerance, while in virus stress, proline accumulation is connected with sensitivity. It is, therefore, clear that proline cannot always act to relieve physiological stress. 相似文献
11.
The chlorophyll and protein contents of the flag, second and third leaves gradually decreased during the reproductive development of rice (Oryza sativa L. cv. Rasi) and wheat (Triticum aestivum L. cv. Sonalika) plants, whereas proline accumulation increased up to the grain maturation stage and slightly decreased thereafter. In rice plant, the rate of decrease in chlorophyll and protein and increase in proline level were higher in the flag leaf than in the second leaf. It was opposite in wheat plant. The export of [32P]-phosphate from leaves to grains gradually increased reaching a maximal stage at the grain development stage, and then declined. The export of this radioisotope was greater in rice than in wheat. Removal of panicle at the anthesis and grainfilling stages delayed leaf senescence of rice plant, while in wheat the ponicle removal at any stage did not have a marked effect on delaying leaf senescence. The contents of chlorophyll and protein of glumes were higher in wheat than in rice. The variation of such source-sink relationship might be one of the possible reasons for the above effect on leaf senescence. 相似文献
12.
Proline is synthesized either from glutamate or from ornithine in plants. Relatively little is known about the contribution of the pathway from ornithine to proline biosynthesis. In this paper we investigated the contribution of ornithine--aminotransterase (OAT), an enzyme responsible for ornithine pathway, to proline accumulation in water-stressed detached rice leaves. Although OAT activity increased with the increase of water stress duration, a pattern similar to that obtained for proline accumulation, the ornithine pathway in rice leaves seems to contribute little, if any, to proline accumulation under water stress condition. This conclusion was based on the observations that (a) gabaculine (50 M), an inhibitor of OAT, inhibited about 75% OAT activity caused by water stress but reduced only 20% of proline content and (b) cycloheximide, a protein synthesis inhibitor, had no effect on OAT activity induced by water stress but significantly reduced proline accumulation. 相似文献
13.
Effects of compounds that influenced calcium uptake and calmodulininhibitors on the senescence of detached rice leaves were examined.Chelators, ethyleneglycol-bis-(ß-aminoethyl ether)-N,N,N',N'-tetraaceticacid (EGTA) and l,2-bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetraaceticacid (BAPTA), significantly promoted senescence of detachedrice leaves in the dark and light. The effect of EGTA can bereversed by treating detached rice leaves with calcium. Verapamil,a calcium channel blocker, and lanthanum chloride, a calciumantagonist, promoted dark-induced, and suppressed BA- and light-retardedsenescence of detached rice leaves. Calcium ionophore A23187
[GenBank]
and ruthenium red, believed to raise cytosolic level of Ca2+,were quite effective in retarding dark-induced and ABA-promotedsenescence of detached rice leaves. Calmodulin inhibitors, W-7,compound 48/80, chlorpromazine and trifluoperazine, significantlypromoted dark-induced, and suppressed BA- and light-retardedsenescence of detached rice leaves. It is concluded that cytosoliclevel of Ca2+ may regulate senescence of detached rice leavesthrough a calmodulin-dependent mechanism. (Received June 13, 1990; Accepted August 3, 1990) 相似文献
14.
Characteristics of the Induction of the Accumulation of Proline by Abscisic Acid and Isobutyric Acid in Detached Rice Leaves 总被引:1,自引:0,他引:1
The effects of abscisic acid and isobutyric acid on levels ofproline in detached rice leaves were compared. The lowest concentrationof abscisic acid that induces accumulation of proline in detachedrice leaves was much lower than that of isobutyric acid. Theaccumulation of porline induced by isobutyric acid was associatedwith acidification of the cell sap, whereas abscisic acid increasedlevels of proline without decreasing the pH of the cell sap.Potassium chloride enhanced the accumulation of proline thatwas induced by abscisic acid, but it did not stimulate thatinduced by isobutyric acid. Of particular interest is the findingthat detached rice leaves treated with fusicoccin showed anincrease in levels of proline and a decrease in the pH of thecell sap. A synergistic increase in levels of proline was observedwhen fusicoccin and abscisic acid applied simultaneously. However,fusicoccin had no effect on the induction of the accumulationof pro-line by isobutyric acid. Benzyladenine inhibited theinduction by abscisic acid of the accumulation of proline, butit did not inhibit the induction by isobutyric acid. It is concludedthat the mode of action of abscisic acid in inducing the accumulationof proline differs from that of isobutyric acid. Our resultsalso indicate that factors other than acidification of the cellsap are involved in regulation of the accumulation of proline. (Received September 25, 1990; Accepted December 20, 1990) 相似文献
15.
A protease activity was detected in rice (Oryza sativa L. cv. Ratna) leaves that hydrolysed hemoglobin more efficiently than bovine serum albumin. The activity was high when the enzyme was extracted and assayed with tris-maleate buffer [tris (hydroxymethyl) methyl amino-maleate] pH 7.0 rather than with water or with citrate-phosphate buffer pH 7.0. The enzyme had a strong dependence on sulfhydryl groups for its activity without which it was inaotive. The pH optimum was 7.0 and the temperature optimum was 40 °C. Protease activity expressed per unit leaf fresh weight (absolute activity) increased only little during senescence of detached rice leaves while the same activity expressed per unit soluble protein content (specific activity) increased by a greater factor (about 5 times) than absolute activity. Total and soluble protein content decreased during the senescence of detached leaves. Benzimidazole (10-3M) and kinetin (0.5xl0-5M) treatment arrested the increase of the protease activity and the deorease in the protein content during detached leaf senescence. It was indicative that protease protein was more stable than the bulk of other proteins in senescing leaves. 相似文献
16.
The effect of NaCl on proline accumulation in rice leaves 总被引:1,自引:0,他引:1
The regulation of proline accumulation in detached leaves of rice(Oryza sativa cv. Taichung Native 1) was investigated.Increasing concentrations of NaCl from 50 to 200 mM progressivelyincreased proline content in detached rice leaves. NaCl induced prolineaccumulation was mainly due to the effect of both Na+ andCl– ions. Proline accumulation caused by NaCl was related toprotein proteolysis, an increase in ornithine--aminotransferaseactivity,a decrease in proline dehydrogenase activity, a decrease in prolineutilisation,and an increase in the content of the precursors of proline biosynthesis,ornithine and arginine. Results also show that proline accumulation caused byNaCl was associated with ammonium ion accumulation. 相似文献
17.
The possibility that NH4
+ accumulation is linkedto the senescence of detached rice (Oryza sativa) leavesinduced by NaCl was investigated. NaCl was effective in promoting senescenceandin increasing NH4
+ content of detached rice leaves.NaCl-promoted senescence is mainly due to the effect of both Na+ andCl- ions. NaCl had no or slight effect on relative water content,suggesting that an osmotic effect is unlikely to be a major factor contributingto senescence of these leaves. NaCl-induced NH4
+accumulation was due to enhanced nitrate reduction and decreased glutaminesynthetase activity. Exogenous NH4Cl, which caused an accumulationofNH4
+ in detached rice leaves, also promoted senescence.Itwas found that an increase in NH4
+ content preceded theoccurrence of senescence caused by NaCl. Results also show that NaCl-promotedsenescence is unlikely to be due to the lack of glutamate, glutamine,aspartate,and asparagine. The current results suggest that NH4
+accumulation is linked to NaCl-induced rice leaf senescence. Since ethylene isknown to be a potent promoter of leaf senescence, we also investigated the roleof ethylene in the regulation of NH4
+-promoted senescenceof detached rice leaves. NaCl or NH4Cl treatment resulted in adecrease of ethylene production. Evidence was presented to show thatNH4
+ accumulation in detached rice leaves does not changetissue sensitivity to ethylene. Clearly, the possible involvement of ethyleneinNH4
+-promoted senescence is excluded. 相似文献
18.
The role of H2O2 in the senescence of detached rice leaves induced by methyl jasmonate (MJ) was investigated. MJ treatment resulted in H2O2 production in detached rice leaves, which was prior to the occurrence of leaf senescence. Dimethylthiourea, a chemical trap of H2O2, was observed to be effective in inhibiting MJ‐induced senescence and MJ‐increased malondialdehyde (MDA) content in detached rice leaves. Diphenyleneiodonium chloride (DPI) and imidazole (IMD), inhibitors of NADPH oxidase, prevented MJ‐induced H2O2 production, suggesting that NADPH oxidase is a H2O2‐generating enzyme in MJ‐treated detached rice leaves. DPI and IMD also inhibited MJ‐promoted senescence and MJ‐increased MDA content in detached rice leaves. Phosphatidylinositol 3‐kinase inhibitors wortmannin (WM) or LY 294002 (LY) inhibited MJ‐induced H2O2 production and senescence of detached rice leaves. Exogenous H2O2 reversed the inhibitory effect of WM or LY. In terms of leaf senescence, it was observed that rice seedlings of cultivar Taichung Native 1 (TN1) are jasmonic acid (JA)‐sensitive and those of cultivar Tainung 67 (TNG67) are JA‐insensitive. On treatment with JA, H2O2 accumulated in the leaves of TN1 seedlings but not in the leaves of TNG67. Evidence was also provided to show that MJ‐induced H2O2 production in detached rice leaves is abscisic acid (ABA)‐independent. Ethylene action inhibitor, silver thiosulfate, was observed to inhibit MJ‐ and ABA‐induced H2O2 production and senescence of detached rice leaves, suggesting that the action of MJ and ABA is ethylene‐dependent. 相似文献
19.
H2O2 metabolism during senescence of rice leaves: changes in enzyme activities in light and darkness
The possible role of H2O2 metabolism on light-regulated senescence of detached rice leaves was investigated. Light retards senescence but at the same time accumulates more H2O2. Light treatment resulted in an increase in malondialdehyde level in detached rice leaves but no membrane leakage was observed in light-treated detached leaves. It seems that there was no direct relationship between lipid peroxidation and deterioration in membrane integrity. The results obtained suggest that retardation of senescence by light is closely related to high activities of superoxide dismutase and ascorbate peroxidase. 相似文献
20.
The role of proteolytic enzymes in protein degradation during senescence of rice leaves 总被引:2,自引:0,他引:2
The role of proteolytic enzymes in protein degradation of detached and intact leaves of rice seedling ( Oryza sativa L. cv. Taiching Native 1) during senescence and of mature leaves during reproductive development was investigated. The amount of soluble protein decreased by about 50% in 2, 4, and 15 days for detached, intact and mature leaves, respectively. Three proteolytic enzyme activities were monitored with pH optima of 4.5 for hemoglobin-digesting proteinase, 5.5 for carboxypeptidase and 8.0 for aminopeptidase. No azocoll-digesting proteinase activity could be detected in rice leaves. Dialysis did not alter the activities of any of the three proteolytic enzymes. Acid proteinase activity and aminopeptidase activity were highly unstable during storage of the enzyme extracts at 4°C. Proteolysis was stimulated by inclusion of meroaptoethanal either in the extraction medium or the assay medium.
Acid proteinase, carboxypeptidase and aminopeptidase were all present in detached, intact and mature leaves throughout senescence. There seems to be a direct correlation between protein degradation and increases of acid proteinase and carboxypeptidase activity in seedling leaves (detached and intact) during senescence. In senescing (detached and intact) leaves of seedlings the acid proteinase activity developed first, while that of carboxypeptidase developed later. Acid proteinase and carboxypeptidase may play major roles in protein degradation of leaves from seedlings during senscence. During reproductive development, protein degradation was associated with decreases in the activities of acid proteinase, carboxypeptidase and aminopeptidase in mature leaves suggesting that the enzymes were less important for protein degradation in this system. Hence, the role of protelytic enzymes in protein degradation during senescence of rice leaves appears to depend largely on the leaf system used. 相似文献
Acid proteinase, carboxypeptidase and aminopeptidase were all present in detached, intact and mature leaves throughout senescence. There seems to be a direct correlation between protein degradation and increases of acid proteinase and carboxypeptidase activity in seedling leaves (detached and intact) during senescence. In senescing (detached and intact) leaves of seedlings the acid proteinase activity developed first, while that of carboxypeptidase developed later. Acid proteinase and carboxypeptidase may play major roles in protein degradation of leaves from seedlings during senscence. During reproductive development, protein degradation was associated with decreases in the activities of acid proteinase, carboxypeptidase and aminopeptidase in mature leaves suggesting that the enzymes were less important for protein degradation in this system. Hence, the role of protelytic enzymes in protein degradation during senescence of rice leaves appears to depend largely on the leaf system used. 相似文献