乙烯利对菜豆叶枕外植体脱落和离区纤维素酶合成的影响

以乙烯利处理菜豆叶枕外植体,能显著提高对抗的脱落及其离区纤维酶的活力。蛋白质和核酸合成的抑创剂环己酰亚胺和放线菌素Ｄ,对乙烯利促进的脱落与离区纤维素酶活力不仅有明显的抑制作用,而且具有严格的时间顺序。提示乙烯利促进脱落的生理效应与其诱导高区纤维素酶合成时基因表达的转录和翻译过程有密切关系。此外,外植体经乙烯利处理后再分别不同时间加ＩＡＡ,并根据测定其抑制乙烯利诱导的纤维素酶活力变化,与不同时间加放线菌素Ｄ的实验结果相同,推断ＩＡＡ对乙烯利促进脱落的拮抗作用可能是在乙烯利诱导纤维素酶合成的转录过程。     

壳梭霉素(fusicoccin)与吲哚乙酸对离体菜豆叶枕生理活性的比较

应用菜豆叶枕外植体比较壳梭霉素和吲哚乙酸的生理活性。壳梭霉素对菜亘叶枕外植体的生理效应,在许多方面都与吲哚乙酸相似。低浓度的壳梭霉素和吲哚乙酸增加菜豆叶枕外植体离区纤维素酶的活力,加速脱落;而高浓度时,虽然二者都抑制脱落,但壳梭霉素并不象吲哚乙酸那样抑制离区纤维素酶的活力。 壳酸霉素和吲哚乙酸一样,能引起生长弯曲效应和促进乙烯的释放,且随着浓度的增高,其作用也加强。 壳梭霉素和吲哚乙酸促进释放乙烯的作用都能被氨基乙氧基乙烯基甘氨酸和氯化钴所抑制,且二者促进乙烯的释放有加成作用。     

乙烯产生、离区纤维素酶活力与菜豆叶柄脱落的关系

IAA处理菜豆叶柄外植体的远端或近端均显著刺激乙烯产生,但对离区纤维素酶活力和叶柄脱落的影响不同,处理远端时抑制而处理近端时促进纤维素酶的活力和脱落。GA_3处理远端或近端刺激乙烯产生的作用虽没有IAA强,但对离区纤维素酶活力和叶柄脱落却都起促进作用。 1000ppm CoCl_2明显抑制了脱落,而对乙烯产生的抑制作用不很明显;16 ppm AVG已显著抑制了乙烯的产生,但对脱落几乎没有抑制效应,二者对由GA_3所诱导增加的离区纤维素酶活力和脱落均没有明显的抑制作用。     

乙烯利对菜豆叶枕外植体脱落和离区纤维素酶合成的影响

以乙烯利处理菜豆叶枕外植体,能显著提高叶枕的脱落及其离区纤维酶的活力。蛋白质和核酸合成的抑制剂环已酰亚胺和放线菌素Ｄ,对乙烯促进的脱落与离区纤维素酶活力不仅有明显的抑制作用,而且具有严格的时间顺序,提示乙烯利促进脱落的生理效应与其诱导离区纤维素酶合成时基因表达的转录和翻译过程有密切关系。     

植物激素对菜豆下胚轴生长的影响

用黄化菜豆下胚轴切段作材料,研究了五种植物激素对生长的影响。生长素促进切段的伸长,最适浓度为10~(-6)M。浓度过高则有抑制作用。赤霉素亦有促进伸长的效果。激动素和乙烯抑制切段伸长但却促进了它的加粗。脱落酸抑制伸长的作用最明显。高浓度生长素诱导组织产生大量乙烯。赤霉素、激动素和脱落酸对乙烯的产生没有明显的影响;然而,将这几种激素与生长素同时处理则它们可以影响生长素诱导乙烯产生的效果。这种影响与它们对切段伸长的作用呈明显的负相关性。用CO_2和高浓度生长素同时处理可使被抑制的伸长得到部分恢复。本文就高浓度生长素对菜豆下胚轴切段伸长的抑制作用与乙烯释放的关系进行了讨论。     

赤霉酸和吲哚乙酸对器官脱落和离区纤维素酶的影响

赤霉酸(GA_3)处理菜豆叶柄和棉苗子叶柄外植体,离区的纤维素酶活力增加,而吲哚乙酸(IAA)则抑制离区纤维索酶的活力。这与GA_3促进菜豆叶柄和棉苗子叶柄外植体的脱落、IAA延迟脱落的效应成正相关。GA_3促进菜豆叶柄外植体的脱落可被环己酰亚胺(CHI)所阻止,而且离区纤维素酶的活力也显著降低。但在棉铃柄离区并没有观察到GA_3与脱落和离区纤维素酶活力三者之间的相关性。GA_3对棉株上未受精棉铃具有明显的防脱效果,而对棉铃柄外植体有促进脱落的作用,但二者离区纤维素酶活力无明显的差异。     

离体蒜苔衰老过程中乙烯产生和纤维素酶活力的变化

自Horton和Osborne(1967)报道衰老、脱落中激素和纤维素酶活力相关性以来,许多实验证明,乙烯和纤维素酶与衰老和脱落有密切关系。关颖谦等(1981)指明离体水稻叶片衰老时,纤维素酶的活力     

乙烯对苹果果实细胞壁降解效应初探

以陕西主栽苹果品种'秦冠'为试材,研究了不同浓度乙烯利以及加热处理下苹果果实中与细胞壁代谢相关酶的活性变化及其与细胞壁组分降解的关系.结果表明:乙烯对各细胞壁酶活性的促进效应因乙烯利施用浓度不同而异.乙烯利浓度由10 mg/L增至1 000 mg/L时,果胶甲酯酶(PME)、多聚半乳糖醛酸酶(PG)和纤维素酶(CS)的活性先逐渐增强,而后又被抑制;木聚糖(Xyl)没有受到明显影响.加热处理可增进乙烯利的作用,如在60℃时,PME、PG、CS、Xyl活性分别是对照的1.5、2.7、1.1和1.5倍.PG活性的显著增加同时引起了果实可溶性糖含量的显著升高,但其他酶活性变化与可溶性糖含量无直接相关.     

γ-氨基丁酸对烟草MAPK和ACS1基因表达的分叉调节

为探讨γ-氨基丁酸(GABA)在植物生长发育中的调控机理,以含有3种不同浓度的GABA的1/2MS培养基培养烟草(Nicotiana tabacum)品种‘SR1’种子,结果表明:低浓度GABA(1mmol/L)促进了烟草幼苗的生长,主根的长度比对照高30%,同时该浓度处理提高了MAPK基因的表达水平;较高浓度(10~100mmol/L)GABA抑制了主根的伸长,表现出乙烯反应的效应。在叶和根中,ACS1基因表达水平的提高受不同浓度GABA的调节。MAPK和ACS1基因对GABA信号的不同表达模式可能与不同的信号途径有关。     

表油菜素内酯对柑桔幼果外植体脱落的影响(简报)

表油菜素内脂(BR)可抑制离区组织中纤维素酶活力,从而明显控制柑桔幼果外植体幼果的脱落。BR与GA_3,NAA混合处理对控制脱落有加成作用,与BA混合使用时则无,与乙烯利混合时有拮抗乙烯利加速脱落的作用     

Characterization of a Non-abscission Mutant in Lupinus angustifolius L.: Physiological Aspects

A single-gene recessive mutant (Abs^-) of Lupinus angustifoliusL. ‘Danja’ that does not abscise any organs wascompared with its parent during continuous exposure of explantsfrom 14 d old seedlings to 10 µl l^-1ethylene. Both endo-(1,4)-ß- D -glucanase (cellulase) and polygalacturonase(PGA) activities increased significantly and progressively inpetiole-stem abscission zones of the parent before the onsetof abscission, and were reflected in a rapid decline in breakstrengthfrom 300 to 70 g within 32 h. In the mutant there was negligibleincrease in hydrolytic enzyme activity, breakstrength declinedslowly (to 180–200 g by 72 h) and there was no abscission.Isoelectric focusing showed two cellulase isoforms (pI 5.0 andpI 8.5) expressed in abscission zones of the parent; these wereexpressed at much lower levels in the mutant. These data areinterpreted to indicate that expression of at least two formsof cellulase activity is enhanced by ethylene in normal petioleabscission zones of lupin. PGA activity also increased in theabscission zone tissue of the parent but to a lesser extentin that of the mutant. We attribute the Abs^-phenotype to mutationof a gene regulating ethylene-responsive expression of abscission-specifichydrolytic enzymes. Copyright 2001 Annals of Botany Company Lupinus angustifolius, abscission, breakstrength, cellulase, ethylene, legume, lupin, mutant, polygalacturonase     

Endogenous and exogenous ethylene induces needle abscission and cellulase activity in post-harvest balsam fir (Abies balsamea L.)

Post-harvest needle loss is a major problem for balsam fir and other Christmas tree species. Recent evidence has implicated ethylene as a signal responsible for post-harvest needle abscission, but enzymological changes remain unknown. The objective of this study was to identify and quantify cellulase activity associated with endogenous and exogenous ethylene-induced abscission. An experiment was designed with three treatments (control, endogenous ethylene, or exogenous ethylene) with five replicates. Key response variables include needle retention duration, xylem pressure potential, ethylene evolution rate, and cellulase activity. Two complimentary methods were used to assess cellulase activity: a cellulose plate digestion and zymography. The results confirm ethylene as a signal for post-harvest abscission and identify ethylene-induced cellulase. Ethylene evolution was typically between 15 and 16 μL g⁻¹ h⁻¹, but there was no difference among the three treatments. However, exogenous ethylene significantly decreased needle retention by 60% and resulted in a sixfold decrease in xylem pressure potential. In addition, cellulase activity increased by 8- and 12-fold in endogenous and exogenous ethylene-induced abscission, respectively, compared to the control. Identification of ethylene-induced cellulase activity has increased our understanding of the post-harvest needle abscission process and confirms ethylene’s role as a signal molecule.     

Bean abscission cellulase : characterization of a cDNA clone and regulation of gene expression by ethylene and auxin

The physiology and anatomy of abscission has been studied in considerable detail; however, information on the regulation of gene expression in abscission has been limited because of a lack of probes for specific genes. We have identified and sequenced a 595 nucleotide bean (Phaseolus vulgaris cv Red Kidney) abscission cellulase cDNA clone (pBACl). The bean cellulase cDNA has extensive nucleic and amino acid sequence identity with the avocado cellulase cDNA pAV363. The 2.0 kilobase bean mRNA complementary to pBACl codes for a polypeptide of approximately 51 kilodalton (shown by hybrid-selection followed by in vitro translation). Bean cellulase antiserum is shown to immunoprecipitate a 51 kilodalton polypeptide from the in vitro translation products of abscission zone poly(A)⁺ RNA. Ethylene initiates bean leaf abscission and tissue-specific expression of cellulase mRNA. If ethylene treatment of bean explants was discontinued after 31 h and then 2,5-norbornadiene given to inhibit responses resulting from endogenously synthesized ethylene, polysomal cellulase mRNA hybridizing to pBACl decreased. Thus, ethylene is required not only to initiate abscission and cellulase gene expression but also to maintain continued accumulation of cellulase mRNA. Explants treated with auxin 4 hours prior to a 48 hour treatment with ethylene showed no substantial accumulation of RNA hybridizing to pBACl or expression of cellulase activity.     

Abscission of Citrus Leaf Explants: INTERRELATIONSHIPS OF ABSCISIC ACID, ETHYLENE, AND HYDROLYTIC ENZYMES

The question whether abscisic acid (ABA) induces cellulase and polygalacturonase activity and, hence, abscission directly or whether its action is mediated by C₂H₄ was studied in citrus (Osbeck var. Shamouti) leaf explants using aminoethoxyvinyl glycine (AVG), an inhibitor of C₂H₄ biosynthesis. ABA in concentrations of 10 micromolar and higher induced C₂H₄ production and accelerated abscission. AVG inhibited C₂H₄ formation, activity of cellulase and polygalacturonase, and abscission in ABA-treated explants. AVG did not inhibit the increase in the activity of the cell-wall degrading enzymes or abscission in a saturating level of externally supplied C₂H₄. This indicates that the effect of AVG resulted from inhibition of the formation of endogenous ethylene. The data indicate that in citrus leaf explants the induction of the activity of cellulase and polygalacturonase and abscission by ABA is mediated by C₂H₄.     

Activity of pectin esterase and cellulase in the abscission zone of citrus leaf explants

The activity of pectin esterase and cellulase in abscission of citrus explants was studied. No relation was established between pectin esterase and abscission, while cellulase activity was markedly increased before abscission and for a certain period after excision. IAA and cycloheximide delay abscission and cellulase activity, while ethylene and, to a lesser extent, GA₃ accelerate them. Application of cycloheximide during the lag period and before cellulase activity can be measured, inhibits to a certain extent the formation of cellulase. An escape from the inhibitory effect of cycloheximide is detected when inhibitor is supplied at the end of the lag period.     

Abscission: role of abscisic Acid

The effect of abscisic acid on cotton (Gossypium hirsutum L. cv. Acala 4-42) and bean (Phaseolus vulgaris L. cv. Red Kidney) explants was 2-fold. It increased ethylene production from the explants, which was found to account for some of its ability to accelerate abscission. Absci is acid also increased the activity of cellulase. Increased synthesis of cellulase was not du to an increase in aging of the explants but rather was an effect of abscisic acid on the processes that lead to cellulase synthesis or activity.     

Abscission: role of cellulase

Cellulase (β-1,4-glucan-glucanohydrolase EC 3.2.1.4) activity increased during abscission and was localized in the cell separation layer of Phaseolus vulgaris L. cv. Red Kidney (bean), Gossypium hirsutum L. cv. Acala 4-42 (Cotton) and Coleus blumei Benth. Princeton strain (Coleus) abscission zone explants. Cellulase activity was optimum at pH 7, was reduced by one-half after heating to 55° for 10 min, and was associated with the soluble components of the cell. Explants treated with aging retardants (indoleacetic acid, ⁶N-benzyladenine, and coumarin), CO₂, actinomycin D or cycloheximide had less cellulase activity than untreated controls. Ethylene increased cellulase activity of aged explants after a 3-hr lag period but had no effect on cellulase activity of freshly excised explants. It was concluded that 1 of the roles of ethylene in abscission is to regulate the production of cellulase which in turn is required for cell separation.     

Endo‐1,4‐β‐glucanase gene expression and cell wall hydrolase activities during abscission in Valencia orange

The physiological and molecular events of ethylene‐induced abscission in mature fruit calyx, laminar and floral abscission zones of cv. Valencia orange were examined. Continuous exposure of fruit explants to 5 µl 1⁻¹ ethylene for 2 to 40 h resulted in marked increases in endo‐1,4‐β‐glucanase (cellulase) and polygalacturonase (PG) activities in calyx abscission zones. Two abscission‐related cellulases and one PG were found. The major peak of cellulase activity corresponded to a pI of 8.0 and molecular weight of 51 kDa, whereas the minor cellulase peak had a pI of 5.5. The abscission polygalacturonase had a pI of 5.5. Calyx abscission zone RNA was amplified with degenerate primers based on sequence of the purified Valencia orange calyx abscission cellulase, and cloned. The two partial cellulase cDNA clones were 59% identical at the nucleotide level. Genomic Southern analysis suggested that Valencia orange contained two groups of cellulase genes. A full‐length cDNA clone from each group was isolated from a cDNA library prepared from ethylene‐induced calyx abscission zone mRNA. Both genes were expressed in ethylene‐induced calyx, laminar and floral abscission zones, but were not expressed in non‐induced abscission zones or mature leaves treated with or without ethylene, young bark or young fruit of Valencia.     

Changes in Two Forms of Membrane-Associated Cellulase during Ethylene-Induced Abscission

Only one form of membrane-associated cellulase was found previously in the lower petiolar pulvinus of Phaseolus vulgaris (cv Red Kidney). The cellulase has an isoelectric point (pI) of 4.5 (DE Koehler, LN Lewis 1979 Plant Physiol 63: 677-679). This enzyme was detected in abscission zones collected before the onset of abscission (control tissue), and was thought to represent a pre-secretory form of another cellulase, the abscission cellulase, which has a basic pI and is secreted during abscission. We now show that this acidic, membrane-associated cellulase is a glycoprotein, tightly bound to the membrane, with maximum activity at pH 5.1, and that it is not immunologically related to the abscission cellulase. Furthermore, when bean explants are induced to abscise with ethylene, the activity of the acidic cellulase declines rapidly to 50% of control levels in the first day. When abscission is fully developed, the membranes contain a basic form of cellulase with a pI of 8.0 to 9.0 and only trace levels of the acidic cellulase. The basic form is not a high mannose glycoprotein; it has maximum activity in a broad pH range (4.0-8.0) and is antigenically related to the abscission cellulase, which is induced during abscission and transported to the cell wall. Antibody raised against the abscission cellulase recognized two proteins in a crude membrane fraction from abscising tissue. One of those proteins comigrated with the abscission cellulase, and the other was 1 to 2 kilodaltons larger. Thus, during abscission, the acidic membrane-associated cellulase rapidly declines before the appearance of the abscission cellulase. We conclude that there is no conversion from the acidic cellulase to the basic cellulase and suggest that the acidic and basic cellulase isoenzymes are proteins derived from two different genes.