黄瓜子叶扩张与细胞分裂素的关系

BA(benzyl adenine)专一性地促进离体黄瓜子叶的扩张。为了研究BA的作用机理,我们采用间接EIISA和HPLC的方法测定了子叶扩张过程中内源玉米素 (Z) 和玉米素核苷(ZR)含量的变化。离体黄瓜(Cucumis sativus,津研4号)子叶用100mg／1的BA培养,72小时之后,处理子叶鲜重的增加比对照高70％。Z+ZR在BA处理的子叶中有大量的积累。结果表明BA可能诱发了黄瓜子叶中的细胞分裂素生物合成和代谢的某些基因。     

Inter-organ Control of Greening in Etiolated Cucumber Cotyledons

Inter-organ control of greening in etiolated cucumber (Cucumis sativus L. cv. Aonagajibae) cotyledons was investigated. Four- or six-day-old excised or intact etiolated cucumber cotyledons were illuminated under aerobic conditions. Excised cotyledons without hypocotyl hooks produced chlorophyll without a prolonged lag phase and the rate of chlorophyll formation was not depressed if they were illuminated immediately after excision. If the excised cotyledons were incubated in the dark before illumination, chlorophyll accumulation at the end of 6 h of continuous illumination was remarkably lowered as the dark period lengthened, especially in 6-day-old cotyledons. The rapid loss of chlorophyll-forming capacity of excised cotyledons during dark preincubation suggests a stimulatory effect of hypocotyls on the greening in cotyledons. The treatment of excised cotyledons with bleeding sap in the dark for 18 h resulted in the promotion of chlorophyll formation during subsequent continuous illumination. Partial fractionation of bleeding sap with organic solvents and paper chromatography indicates that the active substances showed the same behavior as cytokinins. These facts add weight to the hypothesis that cytokinins from roots flow into cotyledons and stimulate greening.     

1,4—二取代酰氨基硫脲类化合物(DATCDs)的植物生理效应与应用研究——Ⅴ.DATCD-A对离体黄瓜子叶扩张及核酸代谢的影响

本实验以离体黄瓜子叶为材料,研究了 DATCD—A 对子叶扩张及核酸代谢的影响。结果表明,DATCD—A 可显著地促进离体黄化子叶扩张,使其鲜重明显增加;并且在处理后期逐渐提高子叶干重。在离体子叶扩张变绿的过程中,DATCD—A 促进离体黄化子叶 RNA、DNA 含量和 DNA/RNA 比率明显上升,且 RNA 的增加发生在 DNA 合成增加之前。凝胶电泳证明,RNA 的增加主要是25s 和18s 的 rRNA。     

胚轴对萌发豌豆子叶中淀粉酶活性表达的影响

萌发豌豆的上、下肢轴均能诱导子叶中淀粉酶活性,外源GA和6—BA具有类似胚轴的作用。离体子叶的淀粉酶凝胶电泳只有一条活性极低的酶带,连生子叶中有两条酶带,其中由胚轴诱导新出现了一条活性很高的同工酶带,它的活性受亚胺环己酮的强烈抑制,而受放线菌素D影响不大。推测豌豆子叶中存在淀粉酶的长寿命mRN—A,胚轴和外源激素的作用在于促进mRNA的翻译。     

黄瓜子叶扩张与细胞分裂素的关系

BA(benzyl adenine)专一性地促进离体黄瓜子叶的扩张。为了研究 BA 的作用机理,我们采用间接 EIISA 和 HPLC 的方法测定了子叶扩张过程中内源玉米素(Z)和玉米素核苷(ZR)含量的变化。离体黄瓜(Cucumis sativus,津研4号)子叶用10mg/l 的 BA 培养,72小时之后,处理子叶鲜重的增加比对照高70%。Z+ZR 在 BA 处理的子叶中有大量的积累。结果表明 BA 可能诱发了黄瓜子叶中的细胞分裂素生物合成和代谢的某些基因。     

A double enhancement of greening in the cotyledons of cucumber seedlings by excision and red light

Cotyledons excised without the hypocotyl hook from 6-day-old etiolated cucumber ( Cucumis sativus L. var. Elem) seedlings accumulated a significantly higher amount of chlorophyll than cotyledons excised with hooks or intact cotyledons. It was found that maximum ehancement of greening was achieved after 2 h of dark incubation following excision. Pretreatments with red light effected an additive rise in chlorophyll level in subsequent white light after a dark incubation, suggesting that the effects of excision and phytochrome on greening act independently. Etiolated seedlings were variously dissected before greening and it was found that enhancement occurred only when cotyledons were excised at the level of the hypocotyl hook or above it. Similar results were obtained when the dissected plants were pre-treated with red light.     

Effect of the hypocotyl hook on greening in etiolated cucumber cotyledons

Four-day-old etiolated cucumber cotyledons (Cucumis sativus, L.) were excised and allowed to green in white fluorescent light at 28 C. Cotyledons excised with a full hypocotyl hook exhibited a lag phase of 1 hour before entering the rapid greening phase, whereas cotyledons excised without any hypocotyl hook exhibited a lag phase of 6 hours. Cotyledons excised with varying lengths of hypocotyl hook accumulated chlorophyll roughly in proportion to the hook length. When cotyledons were excised with a full hook and were partially or totally shielded from light with aluminum foil, the samples with the hook covered accumulated more chlorophyll than the wholly exposed samples. The samples with the cotyledons covered showed no net accumulation of chlorophyll irrespective of hook's exposure to light. These data suggest the contribution of some factor or factors by the hypocotyl hook which reduce the lag phase during greening.     

Role of polyamines in the cytokinin-dependent physiological processes II. Modulation of polyamine levels during cytokinin-stimulated expansion of cucumber cotyledons

The cucumber cotyledon expansion test was used as a model system to study a possible relationship between cytokinin and polyamines. When kinetin was applied to excised cotyledons incubated in the dark it caused a marked increase in the activity of arginine decarboxylase. As a result of ADC action, putrescine content also rose markedly, whereas the level of spermidine and spermine decreased. However, inhibition of putrescine biosynthesis with D-arginine did not affect cytokinin promotion growth. Applied alone, putrescine had no significant effect on growth. These results indicate that the large increase in putrescine content that derives from cytokinin treatment cotyledons is not essential for cytokinin-induced expansion of cotyledons. Addition of K⁺ and Ca²⁺ ions to the cotyledons incubated with cytokinin caused a marked reduction in the putrescine level and ADC activity. The higher level of putrescine (35 %) and spermine (62 %) bound to chromatin and the large increase (174 %) in spermidine content bound to ribosomes which derive from cytokinintreated cotyledons in relation to literature data can indicate that these polyamines may play an important role in gene expression during cytokinin-stimulated expansion of cucumber cotyledons. The inhibition of cytokinin effect, viz. enlargement of the cotyledons by inhibitors of spermidine biosynthesis, additionally suggessted a possible involvement of polyamines in cytokinin action.     

The Influence of Atrazine, Benzyladenine, and the Embryonic Axis on Chlorophyll Synthesis in Cucumber and Squash Cotyledons

Excision of the embryonic axis prior to 3 1/2 days of germination in the dark followed by 8-h of light decreased the total chlorophyll content of cucumber cotyledons but not squash cotyledons. Benzyladenine stimulated the accumulation of chlorophyll in the cotyledons of intact embryos and excised cotyledons in both cucumber and squash. Gibberellic acid had no effect. Atrazine inhibited chlorophyll formation in excised squash cotyledons. Benzyladenine also increased the carotenoid and xanthophyll content in the cotyledons from intact squash seedlings. The results suggest that pigment synthesis in cotyledons may be controlled by a number of substances produced in the embryonic axis and that cytokinin-like benzyladenine can simulate the action of one of them.     

Peroxidase and Glucose-6-phosphate Dehydrogenase Levels in Cotyledons of Cucumis sativus (L.)

Peroxidase and glucose-6-phosphate dehydrogenase become increasinglyactive in cucumber cotyledons excised from the plant althoughthere is a fall in total protein content. The increases areinhibited by dinitrophenol, D, and L-threo-chloramphenicol,cycloheximide, puromycinj and actinomycin D, and it is concludedthat the enzymes are synthesized de novo. Disc electrophoresisof cotyledon extracts revealed three bands of peroxidase, oneof which becomes much enhanced in excised cotyledons. Citrullineaccumulates markedly in excised cotyledons. If the shoot ofcucumber plants is cut away above the cotyledons, very largeincreases in peroxidase and glucose-6-phosphate dehydrogenaseare observed although yellowing and protein loss are delayed.     

Exposure to alcohol vapours reduces chilling-induced injury of excised cucumber cotyledons, but not of seedlings or excised hypocotyl segments

Cucumber (Cucumis sativus L. cv. Poinsett 76) seedlings withfully expanded cotyledons, and excised cotyledons, first trueleaves, hypocotyl segments and fruit mesocarp discs were exposedto vapours from a series of aqueous alcohol solutions of 0 to320 mM methanol, ethanol, n-propanol, n-butanol, and n-pentanolduring chilling at 2.5C for 5 d. Certain concentrations ofeach alcohol reduced subsequent chilling-induced ion leakagefrom the cotyledons and leaves. Exposure of cotyledons to certainmethanol or ethanol solutions also reduced chilling-inducedethylene production, but not carbon dioxide production. In contrast,exposing cucumber seedlings with fully expanded cotyledons tothe same series of alcohol concentrations that resulted in reducedchilling-induced ion leakage and ethylene production of excisedcotyledons actually increased chilling injury of the seedlings.The hypocotyl region directly below the cotyledons was the siteof chilling-induced injury and contained the most chilling-sensitivehypocotyl tissue. Exposing hypocotyl segments excised from thissensitive region to alcohol solutions did not significantlyreduce chilling-inducedion leakage. Exposing excised cucumbercotyledons or hypocotyl segments to equivalent osmotic nonvolatilesolutions of mannitol and glycerol at 2.5C or to alcohol solutionsat 12.5C had no significant effect on the rate of ion leakage.For the series of alcohols used, the relationship between thelog of the alcohol concentration that minimized chilling-inducedion leakage from cucumber cotyledon discs held at 2.5C for5 d and the log of the partition coefficient of the alcoholinto olive oil or the log of the molecular weight of the alcoholswas highly significant. The same concentrations of alcoholsthat reduced chilling-inducedion leakage also reduced stomatalaperture as measured as decreased porosity of excised cotyledons.The correlation between reduced chilling injury and stomatalconductance of cotyledons exposed to a series of ethanol solutionswas highly significant. It appears that alcohols may reducechilling injury of cucumber cotyledons by inducing stomata closure.Sufficient endogenously synthesized ethanol accumulated in discsheld in N2 at 10C for 1 d to confer tolerance to chilling at2.5C for 5 d. Key words: Anaerobic, Cucumis sativus, ethanol, ion leakage, stomatal conductance     

Water stress enhances beta-amylase activity in cucumber cotyledons

Cotyledons detached from 4-d-old cucumber (Cucumis sativus L.) seedlings were subjected to water stress (air-drying or PEG-treatment) to examine the effects of the stress on carbohydrate metabolism. Amylolytic activity in the cotyledon was increased about 6-fold by water stress within 1 d. The substrate specificity and the action pattern indicated that beta-amylase is responsible for the activity. Activities of azocaseinase, malate dehydrogenase and triose-phosphate isomerase were not affected by water stress, indicating that the effect of the stress on beta-amylase is rather specific. Cycloheximide-treatment strongly reduced the enhancement of beta-amylase activity. The hypocotyl of cucumber seedlings also exhibited an increase in the enzyme activity when subjected to water stress. The major free sugars in cucumber cotyledons were glucose, fructose, maltose, and sucrose; sucrose being the most abundant. Sucrose content in excised, unstressed cotyledons increased markedly during the incubation. Changes in other free sugars were small compared with that of sucrose. Starch also accumulated in unstressed cotyledons. In stressed cotyledons more sucrose and less starch accumulated than in unstressed ones. Such results were discussed in relation to the enhancement of beta-amylase activity.     

Cytokinin-induced wall extensibility in excised cotyledons of radish and cucumber

The mechanism of cytokinin-induced cell expansion in cotyledons excised from dark-grown seedlings of radish (Raphanus sativus L.) and cucumber (Cucumus sativus L.) was studied. Cotyledons were incubated in dim light with or without 17 micromolar zeatin for periods up to 3 days. Fresh weights and osmotic potentials were measured daily. Cell wall extensibility properties were measured before and after the growth period. Also, experiments in which radish cotyledons were grown in mannitol solutions of various concentrations were performed. Comparisons of growth rates and increases of tissue osmotic potentials (toward zero) during growth without mannitol indicate that wall extensibility increased during the growth period and that this extensibility was enhanced by zeatin.     

Stimulation of cytokinins and chlorophyll synthesis in cucumber cotyledons by triadimefon

Triadimefon [1-(4-chlorophenoxy)-3,3-dimethyl-1-(1,2,4-triazol-1-yl)-2-butanone] changes the morphology and partitioning of dry matter in cucumber ( Cucumis sativus L. cv. National Pickling) seedlings. The dry weights, potassium and cytokinin levels in the cotyledons and roots of the treated seedlings were higher, whereas the hypocotyl weights were lower than the controls. When etiolated intact seedlings or cotyledons excised from triadimefon-pretreated dark-grown seedlings were exposed to light, chlorophyll synthesis in the pretreated cotyledons was stimulated. Triadimefon does not have cytokinin-like activity in the cucumber cotyledon greening bioassay, but appears to induce the plants to produce more cytokinims, probably by stimulating root growth. Hence it is proposed that the stimulation of chlorophyll production by triadimefon in cucumber cotyledons is mediated by maintaining high levels of potassium and cytokinins in the cotyledons.     

ffects of Some Inhibitors on Potassium-and IAA-Induced Adventitious Root Formation of Excised Cucumber Cotyledon

The effects of some inhibitors on potassium- and IAA-induced rooting were studied adopting the root-formation bioassay in the excised cucumber ( Cucumis sativus L. ) cotyledon. 5-fluomuracil at 7 Ï 10-4 – 7 Ï10-1 mmol/L and cycloheximide at 3.5 Ï 10-4 – 1.05 Ï10-2 mmol/L significantly inhibited potassium- and IAA-induced adventitious root formation of the excised cucumber cotyledons, respectively. Na3VO4 at 0.1 – 1.0 mmol/L obviously inhibited potassium and IAA-induced adventitious rooting of the excised cucumber cotyledons, and similar inhibitory effect was found with 2,3,5-triiodobenzoic acid (TIBA) at 2 Ï 10-4 – 2 Ï 10-l mmol/L.There is a close relationship between potassium and IAA-induced adventitious rooting and the promotive effect of potassium on rooting is possibly brought about via affecting the endogenous level of IAA.     

黄瓜毛状根的诱导及细胞分裂素6-BA对其生长和形态的影响

含农杆碱型Ri质粒pRiA4b的发根农杆菌(Agrobacteriumrhizogenes)ATCC15834感染黄瓜子叶外植体5d后产生毛状根,毛状根可直接从叶片外植体叶脉处产生。感染10d后,约90%的子叶外植体产生毛状根。毛状根能在无外源生长调节剂的MS固体和液体培养基上自主生长。PCR扩增结果证实,发根农杆菌Ri质粒的rolB和rolC基因已在黄瓜毛状根基因组中整合并得到表达。挑选一无菌黄瓜毛状根系置于含不同浓度6-BA的MS培养基中悬浮培养来探讨细胞分裂素6-BA对黄瓜毛状根生长及其形态变化的影响。结果表明,细胞分裂素6-BA能促进黄瓜毛状根的生长及改变其生长形态。随着培养基中6-BA浓度的升高,黄瓜毛状根变得越来越短而粗,更少分枝。与对照相比,培养基中添加0·1~3·0mg/L6-BA能推迟毛状根最大生长峰的出现,降低其可溶性蛋白含量、SOD和POD酶活性;而黄瓜毛状根的乙烯释放高峰比其最大生长峰和SOD和POD酶活性高峰提前5天,但6-BA处理能降低毛状根的内源乙烯释放量。该结果表明细胞分裂素6-BA可能通过对乙烯生成和释放的调节来影响黄瓜毛状根的生长和形态并延缓毛状根的衰老。     

Root Formation by Detached White Mustard (Sinapis alba) Cotyledons

Rooting is shown to occur in excised cotyledons of Sinapis alba when grown in petri dishes on moist filter paper. Cotyledons were excised at intervals from 6 hours after the start of imbibition, when they were yellow, unexpanded and enclosed within the testa, to 27 days after sowing when the cotyledons were green and fully expanded and on plants possessing up to 3 foliage leaves. Rooting generally began 5 or 6 days after excision and was completed dining the following 5 days. The age of cotyledons at t ho time of excision had three effects on rooting: the lag period be-fore rooting began and the period during which rooting took place both increased with age: but the most marked effect was on the total number of cotyledons which were able to form roots, which increased until cotyledon expansion was almost complete, then decreased as the mature cotyledons became older. Optimal rooting was shown by cotyledons detached 8 days alter sowing, when they were half expanded. At this age S5 % of them formed roots between 6 days and 8 days after excision.