Involvement of abscisic acid and ethylene in the responses of rice grains to water stress during filling

This study was to test the hypothesis that the interaction between abscisic acid (ABA) and ethylene may be involved in mediating the effects of water stress on grain filling. Two high lodging‐resistant rice (Oryza sativa L.) cultivars were pot‐grown. Three treatments, well‐watered, moderate water‐stressed (MD), and severe water‐stressed (SD), were imposed from 9 d post‐anthesis until maturity. Grain filling rate and grain weight were significantly increased under MD but decreased under SD. The two cultivars behaved the same. ABA concentration in the grains was very low during the grain filling stage, reaching a maximum when the grain filling rate was highest. Both the grain filling rate and ABA concentration were substantially enhanced by water stress. In contrast to ABA, concentrations of ethylene and 1‐aminocylopropane ‐1‐carboxylic acid (ACC) in the grains were very high at early grain filling stage and sharply decreased during the linear period of grain growth. MD reduced, whereas SD remarkably increased, their accumulation. The ratio of ABA to ACC was increased in MD grains but decreased in SD grains, indicating that there was a greater enhancement of ABA concentration than ethylene production in the MD treatment only. Application of cobalt ion (inhibitor of ethylene synthesis) or ABA at the early grain filling stage significantly increased grain filling rate. Spraying with ethephon (ethylene‐releasing agent) or fluridone (inhibitor of ABA synthesis) had the opposite effect. The results suggest that antagonistic interactions between ABA and ethylene mediate the grain filling rate, and a high ratio of ABA to ethylene enhances grain filling rate.     

Abscisic acid in developing grains of wheat and barley genotypes differing in grain weight

Two genetically related wheat lines growing in cabinets were given different temperatures during grain filling, and abscisic acid (ABA) was measured in whole grains by gas chromatography with an electron-capture detector. Three genetically related barley lines grown in the field were assayed for ABA content in endosperm and embryo fractions separately by radiommunoassay.Maximum grain growth rate and final weight per grain of the two wheat lines differed by 50–60% at low temperature and 30–40% at high temperature. During grain development two peaks in ABA level were observed at low temperature but only one at high temperature. At times when differences in grain growth rate between genotypes and between temperature treatments were large, the corresponding differences in ABA concentration were small. In barley, one line (Iabo 14) had 30% heavier grains than the other two (Onice and Opale). Endosperm ABA concentrations showed no clear differences between genotypes until grain filling was nearly complete. Embryo ABA levels were up to 10-times greater than those in the endosperm, with Opale having significantly less ABA in the embryo than the other two cultivars.Our experiments did not provide evidence for a causal relationship between ABA levels during grain filling and grain growth rate or final weight.Abbreviations ABA Abscisic acid - DAA days after anthesis - DW dry weight - FW fresh weight     

Post-anthesis development of inferior and superior spikelets in rice in relation to abscisic acid and ethylene

The purpose of this study was to test the hypothesis that the interaction between abscisic acid (ABA) and ethylene may be involved in mediating the post-anthesis development of spikelets in rice (Oryza sativa L.). Two rice genotypes were field-grown, and the changes of ABA, ethylene, and 1-aminocylopropane-1-carboxylic acid (ACC) levels in spikelets during grain filling and their relationships with endosperm-division and grain-filling rates were investigated. The results showed that earlier-flowering superior spikelets exerted dominance over later-flowering inferior spikelets in endosperm cell-division and grain-filling rates. The two genotypes behaved the same. Later-flowering spikelets had higher levels of ethylene and ACC than earlier-flowering spikelets. The ethylene evolution rate was significantly and negatively correlated with the cell division and grain filling rates. By contrast to ethylene, later-flowering spikelets contained a lower ABA content/concentration and showed a low content ratio of ABA to ACC than earlier-flowering ones. The cell-division and grain-filling rates were significantly and positively correlated with both ABA contents and the ratio of ABA to ACC. Application of cobalt ion (inhibitor of ethylene synthesis) or ABA at an early grain-filling stage significantly increased endosperm cell division rate and cell number, grain-filling rate, and grain weight of inferior spikelets. Application of ethephon (an ethylene-releasing agent) or fluridone (an inhibitor of carotenoid synthesis) had the opposite effect. The results suggest that antagonistic interactions between ABA and ethylene mediate endosperm cell-division and grain-filling in rice. A higher ratio of ABA to ethylene in rice spikelets is required to maintain a faster grain-filling rate.     

Levels of ethylene, ACC, MACC, ABA and proline as indicators of cold hardening and frost resistance in winter wheat

Changes in ethylene production and in the contents of 1-aminocydopropane-1-carboxylic acid (ACC), 1-(malonylamin6)-cyclopropane-1-carboxylic acid (MACC), abscisic acid (ABA) and L-proline were determined after 40 days of cold hardening at 4°C in three wheat cultivars differing in frost resistance. Proline and especially ABA accumulated with hardening in all varieties in parallel with the degree of frost resistance, e.g. proline and ABA increases in the non-resistant cv. Slávia were 2x and 5x, whilst in the resistant cv. Mironovská 808 increases were 4X and 20X. Ethylene production and MACC level showed no significant changes with hardening in any of the cultivars after 40 d, but ACC levels did increase with hardening. The production of ethylene, ACC and MACC was studied during hardening. Ethylene production decreased sharply at low temperature and rose rapidly (within 1 day) on return to normal temperature, while ACC production reacted in the opposite direction. MACC levels rose rapidly during the first 4 days of cold, then more slowly for about 2 weeks, thereafter decreasing again steadily. The only varietal differences occurring at maximum levels were correlated with the degree of frost resistance.     

Ethylene and ACC levels in developing grains are related to the poor appearance and milling quality of rice

The possible relationship between the levels of ethylene and 1-aminocylopropane-1-carboxylic acid (ACC) in the grains and the quality of rice (Oryza sativa L.) were investigated by using 12 rice cultivars. The results showed that both the ethylene evolution rate and ACC content in grains during the grain filling period correlated negatively with head rice production and positively with chalky kernels, chalky size, and chalkiness. The levels of ethylene and ACC were not significantly correlated with alkali spreading value and amylose content. Application of ethephon, an ethylene-releasing agent, or ACC to panicles at the early grain filling stage significantly reduced the rates of brown rice, milled rice, and head rice, and significantly increased the percentage of chalky kernels, chalky size, and chalkiness. Application of aminoethoxyvinylglycine, an inhibitor of ACC synthase, had the opposite effect. Chalkiness appears to be a senescence related phenomenon which is stimulated by ethylene. The results suggest that ethylene and ACC in grains play an important role in regulating rice quality, and that grain appearance and milling quality would be improved though the reduction of ethylene and ACC in grains during grain filling.     

Interactions between polyamines and ethylene during grain filling in wheat grown under water deficit conditions

This study was to test the hypothesis that polyamines (PAs) and ethylene may be involved in mediating the effect of water deficit on grain filling. Two wheat cultivars, drought-tolerant Shannong16 (SN16) and drought-sensitive Jimai22 (JM22), were used and subjected to well-watered and severe water deficit (SD) during grain filling. SD reduced the weight of superior and inferior grains, by 7.38 and 23.54 % in JM22, 13.8 and 2.2 % in SN16, respectively. Higher free-spermidine (Spd) and free-spermine (Spm) concentration and lower free-putrescine (Put) concentration, ethylene evolution rate (EER) and 1-aminocylopropane-1-carboxylic acid (ACC) concentration were found in superior grains than those in inferior ones. Opposite to the variations of Spd and Spm concentration, ACC, Put concentration and EER were significantly increased under SD. The percentage variation of PAs and ACC differed with cultivars and grain types. ACC concentration of superior and inferior grains under SD increased significantly at 21 days post-anthesis, by 90 and 164 % in JM22, 65 and 13.2 % in SN16, respectively. The equivalent value of Put concentration was 1.04 and 7.9 % in JM22, 34.4 and 10.3 % in SN16. Spd concentration of superior grains showed a higher decrease than that of inferior ones in both cultivars, while Spm exhibited an opposite trend between both grain types. These percentage variations were highly consistent with the differed responses of weight of both grain types to SD in JM22 and SN16. Grain filling rate was negatively correlated with EER and ACC concentration, while positively correlated with Spd and Spm concentration as well as the ratio of Spd or Spm to ACC. Exogenous Spd or aminoethoxyvinylglycine (an inhibitor of ethylene synthesis by inhibiting ACC synthesis) obviously reduced ACC concentration and EER and increased Spd and Spm concentration, while exogenous ethephon (an ethylene-releasing agent) or methylglyoxal-bis (an inhibitor of Spd and Spm synthesis) showed the opposite effects. The results suggested that it would be good for wheat to have the physiological traits of higher Spd and Spm, as well as a higher Spd/ACC or Spm/ACC, under SD.     

Activities of key enzymes in sucrose-to-starch conversion in wheat grains subjected to water deficit during grain filling

This study tested the hypothesis that a controlled water deficit during grain filling of wheat (Triticum aestivum) could accelerate grain-filling rate through regulating the key enzymes involved in Suc-to-starch pathway in the grains. Two high lodging-resistant wheat cultivars were field grown. Well-watered and water-deficit (WD) treatments were imposed from 9 DPA until maturity. The WD promoted the reallocation of prefixed 14C from the stems to grains, shortened the grain-filling period, and increased grain-filling rate or starch accumulation rate (SAR) in the grains. Activities of Suc synthase (SuSase), soluble starch synthase (SSS), and starch branching enzyme (SBE) in the grains were substantially enhanced by WD and positively correlated with the SAR. ADP Glc pyrophosphorylase activity was also enhanced in WD grains initially and correlated with SAR with a smaller coefficient. Activities of granule-bound starch synthase and soluble and insoluble acid invertase in the grains were less affected by WD. Abscisic acid (ABA) content in the grains was remarkably enhanced by WD and very significantly correlated with activities of SuSase, SSS, and SBE. Application of ABA on well-watered plants showed similar results as those by WD. Spraying with fluridone, an ABA synthesis inhibitor, had the opposite effect. The results suggest that increased grain-filling rate is mainly attributed to the enhanced sink activity by regulating key enzymes involved in Suc-to-starch conversion, especially SuSase, SSS, and SBE, in wheat grains when subjected to a mild water deficit during grain filling, and ABA plays a vital role in the regulation of this process.     

Post-anthesis alternate wetting and moderate soil drying enhances activities of key enzymes in sucrose-to-starch conversion in inferior spikelets of rice

This study tested the hypothesis that a post-anthesis moderate soil drying can improve grain filling through regulating the key enzymes in the sucrose-to-starch pathway in the grains of rice (Oryza sativa L.). Two rice cultivars were field grown and two irrigation regimes, alternate wetting and moderate soil drying (WMD) and conventional irrigation (CI, continuously flooded), were imposed during the grain-filling period. The grain-filling rate and activities of four key enzymes in sucrose-to-starch conversion, sucrose synthase (SuSase), adenosine diphosphate-glucose pyrophosphorylase (AGPase), starch synthase (StSase), and starch branching enzyme (SBE), showed no significant difference between WMD and CI regimes for the earlier flowering superior spikelets. However, they were significantly enhanced by the WMD for the later flowering inferior spikelets. The activities of both soluble and insoluble acid invertase in the grains were little affected by the WMD. The two cultivars showed the same tendencies. The activities of SuSase, AGPase, StSase, and SBE in grains were very significantly correlated with the grain-filling rate. The abscisic acid (ABA) concentration in inferior spikelets was remarkably increased in the WMD and very significantly correlated with activities of SuSase, AGPase, StSase, and SBE. Application of ABA on plants under CI produced similar results to those seen in plants receiving WMD. Applying fluridone, an indirect inhibitor of ABA synthesis, produced the opposite effect. The results suggest that post-anthesis WMD could enhance sink strength by regulating the key enzymes involved, and consequently, increase the grain-filling rate and grain weight of inferior spikelets. ABA plays an important role in this process.     

喷施ABA对两个穗型不同小麦穗颈节伤流、穗部性状及产量的影响

以冬小麦品种山农8355和山农15为试验材料,研究了不同ABA喷期处理条件下,小麦花后穗颈节伤流变化及其对籽粒穗部性状与产量的影响。结果表明,多穗型品种SN15伤流强度呈现出单峰变化,而大穗型品种SN8355呈现一定的双峰变化趋势,其伤流强度在后期出现一个小高峰。不论是孕穗后期喷施ABA处理(T1)还是花后3d喷施ABA处理(T2),一定程度上均有利于花后穗颈节伤流的增加。各粒位籽粒粒重与体积在不同生育时期表现基本相同,大体上表现为T1处理较对照小,而T2处理则较对照大,即T2＞CK＞T1。施用ABA可改善穗部营养状况,最高增加穗粒数31.31%,平均提高小穗结实率2.79%,增加穗粒重7.90%-19.01%,并最终增加产量4.08%-9.81%。相关分析表明,穗颈节伤流强度在大多数生育时期与穗粒重关系密切,而群体伤流强度则与产量关系相对密切。研究表明,合理施用ABA能够调节小麦穗颈节伤流强度,从而可以优化穗部性状发育,利于产量的提高。     

Polyamines and ethylene in rice young panicles in response to soil drought during panicle differentiation

This study tested the hypothesis that polyamines (PA) and ethylene (ETH) mediate the effects of soil drought on spikelet development in rice (Oryza sativa L.). Two rice cultivars, Yong You-2640 and Yang Dao-6, with vastly different panicle sizes were grown in pots under three soil moisture treatments: well-watered (WW), moderate soil drought (MD) and severe soil drought (SD), from the onset of panicle initiation to the pollen completion stage. MD treatment significantly increased spikelet differentiation, spikelet number per panicle, fully filled grain percentage and grain yield, decreasing the percentage of degenerated spikelets, sterile spikelets and partially filled grains compared to WW treatment. In contrast, SD treatment showed opposite effects. MD also increased the contents of free spermidine (Spd), free spermine (Spm) and the ratios of free putrescine, free-Spd and free-Spm to 1-aminocylopropane-1-carboxylic acid (ACC), decreasing the ETH evolution rate and ACC content in young panicles. In contrast, SD treatment showed opposite effects. Furthermore, free-Spd and free-Spm contents increased significantly, while ETH and ACC levels, and the percentage of degenerated and sterile spikelets decreased significantly under application of Spd or an inhibitor of ETH synthesis. The results were reversed when ACC or an inhibitor of Spd and Spm synthesis was applied. These findings suggest antagonistic interactions between free-PA (Spd and Spm) and ETH in response to soil drought, mediating spikelet development in rice.     

Involvement of abscisic acid and cytokinins in the senescence and remobilization of carbon reserves in wheat subjected to water stress during grain filling

This study investigated the possibility that abscisic acid (ABA) and cytokinins may mediate the effect of water deficit that enhances plant senescence and remobilization of pre‐stored carbon reserves. Two high lodging‐resistant wheat (Triticum aestivum L.) cultivars were field grown and treated with either a normal or high amount of nitrogen at heading. Well‐watered (WW) and water‐stressed (WS) treatments were imposed from 9 d post‐anthesis until maturity. Chlorophyll (Chl) and photosynthetic rate (Pr) of the flag leaves declined faster in WS plants than in WW plants, indicating that the water deficit enhanced senescence. Water stress facilitated the reduction of non‐structural carbohydrate in the stems and promoted the re‐allocation of prefixed ¹⁴C from the stems to grains, shortened the grain filling period and increased the grain filling rate. Water stress substantially increased ABA but reduced zeatin (Z) + zeatin riboside (ZR) concentrations in the stems and leaves. ABA correlated significantly and negatively, whereas Z + ZR correlated positively, with Pr and Chl of the flag leaves. ABA but not Z + ZR, was positively and significantly correlated with remobilization of pre‐stored carbon and grain filling rate. Exogenous ABA reduced Chl in the flag leaves, enhanced the remobilization, and increased grain filling rate. Spraying with kinetin had the opposite effect. The results suggest that both ABA and cytokinins are involved in controlling plant senescence, and an enhanced carbon remobilization and accelerated grain filling rate are attributed to an elevated ABA level in wheat plants when subjected to water stress.     

Grain filling of cereals under soil drying

Monocarpic plants require the initiation of whole-plant senescence to remobilize and transfer assimilates pre-stored in vegetative tissues to grains. Delayed whole-plant senescence caused by either heavy use of nitrogen fertilizer or adoption of lodging-resistant cultivars/hybrids that remain green when the grains are due to ripen results in a low harvest index with much nonstructural carbohydrate (NSC) left in the straw. Usually, water stress during the grain-filling period induces early senescence, reduces photosynthesis, and shortens the grain-filling period; however, it increases the remobilization of NSC from the vegetative tissues to the grain. If mild soil drying is properly controlled during the later grain-filling period in rice (Oryza sativa) and wheat (Triticum aestivum), it can enhance whole-plant senescence, lead to faster and better remobilization of carbon from vegetative tissues to grains, and accelerate the grain-filling rate. In cases where plant senescence is unfavorably delayed, such as by heavy use of nitrogen and the introduction of hybrids with strong heterosis, the gain from the enhanced remobilization and accelerated grain-filling rate can outweigh the loss of reduced photosynthesis and the shortened grain-filling period, leading to an increased grain yield, better harvest index and higher water-use efficiency.     

Hormonal regulation of fruitlet abscission induced by carbohydrate shortage in citrus

 The hormonal signals controlling fruitlet abscission induced by sugar shortage in citrus were identified in Satsuma mandarin, Citrus unshiu (Mak.) Marc, cv. Clausellina and cv. Okitsu. Sugar supply, hormonal responses and fruitlet abscission were manipulated through full, partial or selective leaf removals at anthesis and thereafter. In developing fruitlets, defoliations reduced soluble sugars (up to 98%), but did not induce nitrogen and water deficiencies. Defoliation-induced abscission was preceded by rises (up to 20-fold) in the levels of abscisic acid (ABA) and 1-aminocyclopropane-1-carboxylic acid (ACC) in fruitlets. Applications to defoliated plants showed that ABA increased ACC levels (2-fold) and accelerated fruitlet abscission, whereas norflurazon and 2-aminoethoxyvinyl glycine reduced ACC (up to 65%) and fruitlet abscission (up to 40%). Only the full defoliation treatment reduced endogenous gibberellin A₁ (4-fold), whereas exogenous gibberellins had no effect on abscission. The data indicate that fruitlet abscission induced by carbon shortage in citrus is regulated by ABA and ACC originating in the fruits, while gibberellins are apparently implicated in the maintenance of growth. In this system, ABA may act as a sensor of the intensity of the nutrient shortage that modulates the levels of ACC and ethylene, the activator of abscission. This proposal identifies ABA and ACC as components of the self-regulatory mechanism that adjusts fruit load to carbon supply, and offers a physiological basis for the photoassimilate competition-induced abscission occurring under natural conditions. Received: 19 February 1999 / Accepted: 14 August 1999     

钙对香蕉采后乙烯释放的抑制

本实验用CaCl_2溶液对香蕉(Musa acuminata cf. 'Dwarf Davendish')组织进行真空浸透处理,研究Ca~(2 )对香蕉采后乙烯释放、EFE活性、ACC水平以及ACC/MACC比值的影响。结果表明,Ca~(2 )处理可抑制香蕉果皮和果肉组织乙烯生成,对抑制果皮的乙烯生成尤为明显。Ca~(2 )处理还可降低内源ACC水平,抑制EFE活性。结果还显示,Ca~(2 )处理对组织中ACC/MACC比值有一定影响。     

Changes in duration of developmental phases of durum wheat caused by breeding in Spain and Italy during the 20th century and its impact on yield

Background and Aims

Although the apical development of wheat has been widely described, studies analysing how genetic breeding over the 20th century influenced the developmental phases and its consequences on yield generation are lacking, especially for durum wheat under field conditions in Mediterranean environments. The aims of this study were to analyse the effects of breeding in Spain and Italy on crop development during the last century, to determine whether or not breeding significantly altered the developmental phases between sowing and maturity, and to evaluate the importance of each phase in determining the number of grains per spike of durum wheat (Triticum durum) cultivars representing the germplasm grown throughout the 20th century in Spain and Italy.

Methods

Eight field experiments were carried out during 4 years in two contrasting latitudes (Lleida and Granada, Spain). Plant material consisted of 24 durum wheat cultivars (12 Italian and 12 Spanish) grown throughout the 20th century in Spain and Italy.

Key Results

In Spanish materials, breeding reduced the duration of the period from sowing to anthesis, placing the grain-filling period in better conditions. In those cultivars, the sub-phase sowing–terminal spikelet formation was reduced while the duration of the period from booting to anthesis was increased. The number of grains per spike increased by 23 % from old to modern cultivars, by changes in the number of grains per spikelet in both Spanish and Italian cultivars. Floral abortion from booting to anthesis diminished by 24 % from old to modern cultivars, and grain setting increased by 13 %.

Conclusions

The results suggest that breeding reduced not only plant height, but also the time to anthesis. By extending the duration of the phase from booting to anthesis, which was associated with an increase in spike dry weight and grains per spike, it suggests that future increases in spike fertility could be achieved by enlarging that phase.     

Polyamine and ethylene interactions in grain filling of superior and inferior spikelets of rice

This study was to test the hypothesis that polyamines (PAs) and ethylene and their interactions may be involved in mediating the post-anthesis development of spikelets in rice (Oryza sativa L.). Six rice cultivars differing in grain filling rate were field-grown, and the changing patterns of PAs and ethylene levels in rice spikelets during the filling and their relations with grain filling rates were investigated. The results showed that inferior spikelets had much greater ethylene evolution rate and 1-aminocylopropane-1-carboxylic acid (ACC) concentration than superior spikelets. Opposite to ethylene production, superior spikelets showed much higher free-spermidine (Spd) and free-spermine (Spm) concentrations than inferior spikelets. Grain filling rate was very significantly and negatively correlated with ethylene evolution rate and ACC concentration, whereas positively correlated with free-Spd and free-Spm concentrations and with the ratio of free-Spd or free-Spm to ACC. Application of Spd, Spm, or aminoethoxyvinylglycine (an inhibitor of ethylene synthesis by inhibiting ACC synthesis) to panicles at the early grain filling stage significantly reduced ethylene evolution rate and ACC concentration, while significantly increased Spd and Spm concentrations, grain filling rate and grain weight of inferior spikelets. Application of ACC, ethephon (an ethylene-releasing agent), or methylglyoxal-bis (guanylhydrazone) (an inhibitor of Spd and Spm synthesis) showed the opposite effects. The results suggest that antagonistic interactions between PAs (Spd and Spm) and ethylene may be involved in mediating grain filling. A higher ratio of free-Spd or free-Spm to ethylene in rice spikelets could enhance grain filling.     

Comparison of the Drought Stress Responses of Tolerant and Sensitive Wheat Cultivars During Grain Filling: Changes in Flag Leaf Photosynthetic Activity,ABA Levels,and Grain Yield

Water status parameters, flag leaf photosynthetic activity, abscisic acid (ABA) levels, grain yield, and storage protein contents were investigated in two drought-tolerant (Triticum aestivum L. cv. MV Emese and cv. Plainsman V) and two drought-sensitive (cvs. GK élet and Cappelle Desprez) wheat genotypes subjected to soil water deficit during grain filling to characterize physiological traits related to yield. The leaf water potential decreased earlier and at a higher rate in the sensitive than in the tolerant cultivars. The net CO₂ assimilation rate (P _N) in flag leaves during water deficit did not display a strict correlation with the drought sensitivity of the genotypes. The photosynthetic activity terminated earliest in the tolerant cv. Emese, and the senescence of flag leaves lasted 7 days longer in the sensitive Cappelle Desprez. Soil drought did not induce characteristic differences between sensitive and tolerant cultivars in chlorophyll a fluorescence parameters of flag leaves during post-anthesis. Changes in the effective quantum yield of PSII (Φ_PSII) and the photochemical quenching (qP) depended on the genotypes and not on the sensitivity of cultivars. In contrast, the levels of ABA in the kernels displayed typical fluctuations in the tolerant and in the sensitive cultivars. Tolerant genotypes exhibited an early maximum in the grain ABA content during drought and the sensitive cultivars maintained high ABA levels in the later stages of grain filling. In contrast with other genotypes, the grain number per ear did not decrease in Plainsman and the gliadin/glutenin ratio was higher than in the control in Emese during drought stress. A possible causal relationship between high ABA levels in the kernels during late stages of grain filling and a decreased grain yield was found in the sensitive cultivars during drought stress.     

春小麦水分胁迫响应中的ACC、MACC合成及乙烯的释放

水分胁迫使两个抗旱性不同的春小麦 (TriticumaestivumL .)品种“8139”(抗旱性较弱 )和“5 0 4”(抗旱性较强 )叶片ACC和MACC含量于胁迫初期下降后期升高 ,ACC合酶活性持续升高 ,乙烯释放量在 8139中下降而在5 0 4中先大幅升高而后下降。两种作用效果相反的抑制剂MGBG (抑制SAMDC活性 )和AOA (抑制ACC合酶活性 )均明显影响了两品种春小麦叶片以上各指标的变化。结果表明 ,水分胁迫下作物乙烯的释放量并不与其合成直接前体ACC的量成正相关 ;胁迫乙烯在抗性品种中于胁迫初期的升高可能是植物胁迫信号传导的响应之一 ,是一种干旱适应现象 ,可能与作物的干旱忍耐形成有关 ,而MACC具有调节胁迫乙烯释放的特殊生理作用。     

Changes m Ethylene Production in Relation to l-Aminocyclopropane-l-Carboxylic Acid and Its Malonyl Conjugate in Waterlogged Wheat Plants

When wheat seedlings were subjected to waterlogging, 1-aminocyelopropane-l-carboxylic acid (ACC), an ethylene precursor, accumulated in large quantity in roots. In shoots, ACC and ethylene production also increased, but declined with the prolonged periods of waterlogging. However, ACC content in roots maintained in high level during the whole period of waterlogging. Drainage caused a drastic drop in both ACC content and ethylene production in waterlogged plants to control level. 1-(malonylamino) cyclopropane-l-carboxylic acid (MACC) level in roots subjected to waterlogging showed little changes. However, MACC content in shoots kept increasing during the 9-days period of waterlogging. At later period of waterlogging (longer than 5 days) when ACC and ethylene production bad dropped, the. level of MACC continued to increase. Draining stopped this increasing, but did not reduced its level. When exogenous ACC was introduced into the leaves via transpiration stream, the ability of leaves of waterlogged plant to convert ACC to MACC was much higher than control. The data presented showed that at the later stage of waterlogging, the conversien of a great quantity of ACC to MACC in waterlogged wheat plants is the cause of the reduction of ethylene production and ACC content. It was suggested that the formation of MACC is another way of regulation in ethylene biosynthesis. Among leaves of different ages, the enhancement of ethylene, ACC and MACC content was more pronounced in older leaves than in younger laves during the waterlogging period. The physiological significance of adaptation to waterlogging stress was discussed.