Photocontrol of Hypocotyl Elongation in Light-Grown Cucumis sativus L. : Responses to Phytochrome Photostationary State and Fluence Rate

The effects of the calculated photostationary state of phytochrome (_c) and the photon fluence rate on the elongation growth of the hypocotyl of light-grown seedlings of Cucumis sativus L. are examined. Two threshold responses to _c are found at values of 0.06 and 0.43. At _c = 0.06, there is no response at any fluence rate. In the _c range 0.1 to 0.43, elongation growth does not respond to changes in _c. Above the second threshold (_c = 0.43), there is a strong response to changes in _c. At all values of _c at and above 0.1, there is a response to fluence rate. A linear relationship can be demonstrated between a factor comprised of the logarithm of phytochrome cycling rate (a fluence-rate-dependent process) and _c, and the growth response.     

Photocontrol of hypocotyl elongation in light-grown Cucumis sativus L.

An interaction is demonstrated between the effects of phytochrome and cryptochrome (the specific blue-light photoreceptor) in the inhibition of hypocotyl elongation of light-grown cucumber (Cucumis sativus L.) cv. Ridge Greenline seedlings. At certain fluence rates of blue light the total inhibition response is greater than the sum of the separate responses to each photoreceptor. The threshold for response to blue light is reduced at least 30-fold by additional red-light irradiation. The synergistic effect is demonstrated for two different fluence rates of red light. Synergism is mediated by phytochrome in both the cotyledons and the hypocotyl.Abbreviations and symbols BL blue light - FR far-red light - Pfr far-red-absorbing form of phytochrome - R red light - photostationary state of phytochrome - _c calculated      

Defense Responses in Infected and Elicited Cucumber (Cucumis sativus L.) Hypocotyl Segments Exhibiting Acquired Resistance

Segments from dark-grown cucumber (Cucumis sativus L.) hypocotyls were used to study defense reactions occurring upon fungal infection and induced by elicitors in the same tissue. The segments were rendered resistant to infection by Colletotrichum lagenarium either by growing the seedlings in the presence of dichloroisonicotinic acid (DCIA) or by preincubation of the cut segments with DCIA, salicylic acid (SA), or 5-chlorosalicylic acid (5CSA). This resistance appears to be due mainly to inhibition of fungal penetration into epidermal cells. In the resistant hypocotyl segments, the fungus induced, at the time of attempted penetration, an increased deposition of phenolics, which were visualized by autofluorescence. These phenolics were located mainly in the epidermal cell wall around and in the emerging papillae below appressoria and were quantified either as lignin-like polymers by the thioglycolic acid method or as 4-OH-benzaldehyde, 4-OH-benzoic, or 4-coumaric acid liberated upon treatment with alkali at room temperature. Pretreatment with DCIA, SA, and 5CSA induced little chitinase activity, but this activity greatly increased in resistant tissues upon subsequent infection. These observations indicate that resistance is associated with an improved perception of the pathogen stimulus resulting in the enhanced induction of diverse defense reactions. When the cut segments were pretreated with DCIA, SA, or 5CSA and then split and incubated with chitosan fragments, the deposition of cell wall phenolics was also enhanced. These pretreated and split segments also exhibited an increase in the rapid production of activated oxygen species induced by an elicitor preparation from Phytophthora megasperma f. sp. Glya. Pretreatment of the segments with methyl jasmonate neither induced resistance nor enhanced induction of cell wall phenolics upon fungal infection, although we observed in the corresponding split segments some increase in chitosan-induced cell wall phenolics and in elicitor-induced rapid production of activated oxygen species.     

Similarity between Cytokinin and Blue Light Inhibition of Cucumber Hypocotyl Elongation

The cytokinin benzyladenine inhibited endogenous hypocotyl elongation in intact etiolated seedlings of cucumber (Cucumis sativus L.). In hypocotyl segments, the inhibitory effect of benzyladenine on growth was clearly detectable in the presence of indoleacetic acid. Fusicoccin-induced elongation was unaffected by the presence of cytokinin. The effect of cytokinin on elongation of the segments was determined by measuring changes in fresh weight, a linear function of extension growth. The effect of benzyladenine on hypocotyl growth was at least as large in segments prepared from red-light-grown seedlings as in those from seedlings grown in total darkness. A comparison was made between the inhibitory effects of cytokinin and blue light. The use of the calcium chelator ethyleneglycol-bis(β-aminoethyl ether)-N, N′-tetraacetic acid indicated that calcium ions are required for manifestation of benzyladenine-induced inhibition.     

黄瓜子叶和下胚轴的离体培养

1　植物名称　黄瓜 (Ｃｕｃｕｍｉｓｓａｔｉｖｕｓ)品种“津绿 4号” ,由天津农业科学院黄瓜研究所育成。。2　材料类别　种子萌发的无菌苗子叶和下胚轴切段。3　培养条件　 (1 )种子萌发培养基 :1 /2ＭＳ0 ;(2 )诱导分化培养基 :ＭＳ 6 ＢＡ 1 0ｍｇ·Ｌ- 1 (单位下同 ) ＩＡＡ 0 2～ 0 4;(3 )生根培养基 :ＭＳ ＩＡＡ 0 5。上述培养基内琼脂浓度均为 0 8% ,蔗糖为 3 % ,ｐＨ5 8～ 6 0。培养温度 (2 5± 2 )℃ ,光照时间 1 0ｈ·ｄ- 1 ,光照度 2 0 0 0ｌｘ。4　生长与分化情况4.1　无菌苗的培养　将黄瓜种子去壳后 ,以 75 %乙醇…     

Control by Light of Hypocotyl Elongation and Levels of Endogenous Gibberellins in Seedlings of Lactuca sativa L.

Four 13-hydroxygibberellins, gibberellin A₁ (GA₁), 3-epi-GA₁,GA₁₉ and GA₂₀ were identified by full-scan GC/MS in extractsof lettuce seedlings (Lactuca sativa L. cv. Grand Rapids). Theresults suggest that the early-13-hydroxylation biosyntheticpathway to GA₁ functions in the lettuce seedlings. It was alsofound that GA₁ is active per se in the control of hypocotylelongation in lettuce seedlings. To investigate the relationshipbetween control by light of hypocotyl elongation and levelsof endogenous GAs in lettuce, endogenous levels of GAs werequantified by radioimmunoassay in seedlings that had been grownfor 5 days in the dark (5D) and in those that had been grownfor 4 days in the dark and then under white light for 1 day(4D1L). The endogenous level of GA₁ in the upper and lower partsof hypocotyls in 5D seedlings was about four times higher thanthat in 4D1L seedlings. The response of explants (hypocotylsegments with cotyledons) from dark-grown seedlings to GA₁ isknown to be similar in the dark and under white light when theexplants are treated with inhibitors of the biosynthesis ofGA. Therefore, the above information suggests that the highlevel of GA₁ in hypocotyls of dark-grown seedlings is responsiblefor the rapid elongation of hypocotyl, while irradiation bywhite light decreases the endogenous level of GA₁ in the hypocotylswith a resultant decrease in the rate of hypocotyl elongation. (Received March 13, 1992; Accepted May 21, 1992)     

Metabolic Implications in the Biochemical Responses to Iron Deficiency in Cucumber (Cucumis sativus L.) Roots

Strategy I plants respond to Fe deficiency by inducing morphological and biochemical modifications at the root level that are apt to make iron available for uptake. Cucumber (Cucumis sativus L.) grown in the absence of Fe has been shown to increase the capacity to acidify the rhizosphere and Fe3+ reduction activity. We have determined in these roots some metabolic activities that might be correlated with the increased proton extrusion. Proton efflux from roots may be followed by a mechanism regulating the cytosolic pH according to the pH-stat theory. Roots grown in the absence of Fe showed an increase in dark 14CO2 fixation and organic acid synthesis and a 6-fold increase in the extractable phosphoenolpyruvate carboxylase activity with respect to the control roots. Dehydrogenase activities producing cytosolic NAD(P)H were also increased under Fe deficiency. The presence of Fe2+, but not Fe3+, inhibited dark 14CO2 fixation in a range between 24 and 52% but did not show any effect on the in vitro phosphoenolpyruvate carboxylase activity.     

Cell Elongation and Microtubule Behavior in the Arabidopsis Hypocotyl: Responses to Ethylene and Auxin

During elongation of the Arabidopsis hypocotyl, each cell reacts to light and hormones in a time- and position-dependent manner. Growth in darkness results in the maximal length a wild-type cell can reach. Elongation starts at the base and proceeds in the acropetal direction. Cells in the upper half of the hypocotyl can become the longest of the whole organ. Light strongly inhibits cell elongation all along the hypocotyl, but proportionally more in the upper half. The ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) is known to stimulate hypocotyl elongation in the light. Here we show that this stimulation only occurs in cells of the apical half of the hypocotyl. Moreover, ACC application can partially overcome light inhibition, whereas indole-3-acetic acid (IAA) cannot. On low-nutrient medium (LNM) in the light, elongation is severely reduced as compared to growth on rich medium, and both ACC and IAA can stimulate elongation to the levels reached on a nutrient-rich medium. Furthermore, microtubule orientation was studied in vivo. During elongation in darkness, transverse and longitudinal patterns are clearly related with rates of elongation. In other conditions, except for the association of longitudinally orientated microtubules with growth arrest, microtubule orientation is merely an indicator of developmental age, not of elongation activity. A hypothesis on the relation between microtubules and elongation rate is discussed.     

The Role of DNA Synthesis During Hypocotyl Elongation in Light and Dark

Fluorodeoxyuridine, an inhibitor of DNA synthesis, did not affectgermination and post-germinative growth in the aerial part oflettuce and Haplopappus gracilis seedlings when grown in thelight. In the dark, however, elongation of the hypocotyl wasinhibited by fluorodeoxyuridine, strikingly in lettuce and onlyslightly in Haplopappus gracilis. This could imply that thecontrolling mechanism of hypocotyl elongation is in some casesrelated to DNA synthesis, either because mitotic processes (oftenlittle taken into account in considering hypocotyl growth) areinvolved in the elongation of hypocotyls only when they aregrown in the dark, or because DNA synthesis affects cell elongationdirectly, or through the production of a greater number of endopolyploidcells in the dark. Using mainly autoradiographic and cytofluorimetricmethods, these possibilities were tested. Besides lettuce (Lactucasativa L. var. Great Lakes) and H. gracilis (Nutt.) Gray, radish(Raphanus sativus L. var. Tondo rosso quarantino) and soybean(Soya hyspida Sieb. and Zucc. var. Tokyo) seedlings were alsostudied. Fluorodeoxyuridine drastically inhibits cell elongation onlywhen it is preceded or accompanied by mitotic or endomitoticevents. Need for DNA synthesis during hypocotyl elongation,as well as during early post-germinative growth, seems to beof particular importance when endomitotic processes are involved. DNA synthesis, elongation, endoreduplication, fluorodeoxyuridine, Haplopappus gracilis (Nutt.) Gray, Lactuca sativa L., Raphanus sativus L., Soya hyspida Sieb and Zucc     

The control of food mobilisation in seeds of Cucumis sativus L.

The development of maximal rates of lipid and protein hydrolysis in cucumber cotyledons depends upon the removal of the testa and the presence of the embryonic axis. The testa appears to exert at least part of its inhibitory influence by suppressing the development of enzyme activity associated with lipolysis and proteolysis. There is, however, no evidence to suggest that the presence of the embryonic axis is a pre-requisite for the development of optimal enzyme activity.Abbreviations TLC thin layer chromatography - GC-MS gas chromatography-mass spectrometry - GLC gas-liquid chromatography - TCA trichloroacetic acid     

The control of food mobilization in seeds of Cucumis sativus L.

An analysis of the in vitro activities of proteolytic enzymes from cotyledons of germinating cucumber seeds has been carried out and the effects of protein degradation products on such activities monitored. Aminopeptidase activity is substantially inhibited with either L-leucine or L-phenylalanine and trypsin activity with L-arginine. Aminopeptidase activity was also markedly reduced in the presence of individual di- and tripeptides. Of the peptides tested, however, only L-tryptophyl-L-phenylalanine inhibited the degradation of native cucumber seed protein by the endogenous cucumber seed protease(s) (autodigestive activity).Abbreviations TCA trichloroacetic acid - L-leuglygly L-leucylglycylglycine - L-pheglygly L-phenylalanylglycylglycine - L-phe-L-leu L-phenylalanyl-L-leucine - L-leu-L-phe L-leucyl-L-phenylalanine - L-tryp-L-phe L-tryptophyl-L-phenylalanine - LPA L-leucine-p nitroanilide - BAPNA -N-benzoyl-DL-arginine-p nitroanilide - ADA autodigestive activity     

The control of food mobilisation in seeds of Cucumis sativus L.

The degradation of neutral lipid and the development of lipase activity in cucumber cotyledons is stimulated by white light. Malate synthase and isocitrate lyase activities show no stimulation. Lipase activity and neutral lipid breakdown are also enhanced by red light, far-red light proving ineffective. Far-red light reverses the effect of red light indicating the involvement of phytochrome in the control of lipase activity. Although light stimulates neutral lipid degradation it appears that much of the additional lipid lost is used in the synthesis of polar lipid constituents. Furthermore, the influence of light on lipid degradation appears to be species dependent.Abbreviations WL white light - RL red light - FRL far-red light     

Growth, Pigment Synthesis, and Ultrastructural Responses of Phaseolus vulgaris L. cv. Blue Lake to Intermittent and Flashing Light

Growing bean plants (Phaseolus vulgaris L. cv. Blue Lake) on cycles of 1 minute light-1 minute dark or 5 minutes light-5 minutes dark, providing an integrated 12 hours light-12 hours dark per day for each set of plants, led to production after 21 days of new leaves low or lacking in chloroplast pigments. Subsequently, dry weight increase was sharply cut. Leaf area was affected by the light regimes after the second week of growth. By the fourth week, plants on the 1 minute light-1 minute dark cycle showed about one-half the leaf area of the controls. Shoot growth was favored over root growth to the greatest degree on the 1 minute light-1 minute dark regimes. Chlorophyll a/b ratios were close to 3.0 in all of the intermittent light regimes, but the total amounts of chlorophyll in milligrams per primary leaf were higher from day 9 to day 23 for the 12 hour light-12 hours dark controls than for other plants.

Although they produced chlorophyll, the plants receiving 1 or 2 milliseconds per second of light continued to lose weight at the same rate as the dark controls; thus, it is assumed there was no net photosynthesis. Plants receiving flashing light allocated significantly more food reserves from the seed to roots than did dark controls. Total chlorophyll formation was significantly accelerated by 2 milliseconds per second light. With 1 millisecond per second light, it took 5 days longer to achieve the same level of chlorophyll. After the 18th day, there was a steady decline in chlorophyll, b degrading more rapidly than a.

It is thought that several light-driven reactions are involved in the observed pigment synthesis, photosynthesis, food allocation, and growth of bean. Some of these reactions may be cyclic and others linear. Collectively, they must reach a harmonic point for normal metabolism and development to occur. Because time courses for each of these reactions are different, the intermittent and flashing light technique offers the possibility of individually studying some of the key light-driven reactions.

     

Exposure of Leaves of Cucumis sativus L. to Low Temperatures in the Light Causes Uncoupling of Thylakoids I. Studies with Isolated Thylakoids

Chilling of leaves of cucumber (Cucumis sativus L.) at 5?C inmoderate light for 5 h caused almost complete suppression ofphotosynthetic oxygen evolution in the leaves. Comparison ofelectron transport activities determined in the presence andabsence of an uncoupler, methylamine, indicated that thylakoidsprepared from such treated leaves were uncoupled without anysignificant changes in the capacity for electron transport.Immunoblotting revealed that the amount of coupling factor 1(CF₁) associated with membranes was reduced by the chillingtreatment in the light. Thylakoids prepared from leaves thathad been chilled in moderate light for 5 h and then re-warmedfor 1 h were coupled and capable of synthesising ATP. However,the capacity of leaf photosynthesis was not restored by therewarming. These results indicate that the thylakoids are uncoupledby the dissociation of some CF₁ complexes from the thylakoidmembranes during the chilling treatment of leaves in the lightand that thylakoids are recoupled by reassociation of CF₁ duringthe subsequent rewarming of the treated leaves at 25?C. It alsoappears that chilling in the light causes irreversible damageto reaction(s) other than those involved in electron transportand photophosphorylation. ¹ Present address: Department of Biological Science, Facultyof Science, Himeji Institute of Technology, Kamigori, Ako-gun,Hyogo, 678-12 Japan (Received July 1, 1991; Accepted October 4, 1991)     

Role of phytochrome B in organ formation processes in Cucumis sativus L.

The role of phytochrome B in the organogenesis process in the apical and axillary shoot meristems during early ontogenesis stages in cucumber Cucumis sativus L. at photoperiods (day/night) 10/14, 16/8 h, and continuous light in comparison with wild type plants and phytochrome B-deficient mutant (lh-mutant) was investigated. In mutant phytochrome B, deficiency caused inhibition of initiation of leaves both in the main shoot and lateral shoots and increased the number of flower buds (IV stage of organogenesis). With continuous light, the number of lateral shoots and flowers during stage IV of organogenesis in wild-type plants increased twofold in comparison with the mutant. Short-term temperature drops did not induce floral ontogenesis in mutants but increased the number of off-shoots in both experimental variants during a long photoperiod and continuous lighting. We propose that phytochrome B, by increasing the compactness of chromatin, may facilitate coordination of ontogenesis processes with changing environmental conditions.     

Regulation of Transpiration in Avena. Responses to Red and Blue Light Steps

The transpiration responses of primary Arena leaves to red and blue light steps were investigated. The response to a red light step was a so-called slow response (with a rise time of about 8 min). The response to a blue light step consisted of both a slow, and a rapid response (with a rise time of about 2 min). CO₂-free air outside the leaf eliminated only the slow response, i.e. in CO₂-free ait the plant responded to blue light steps but not to red ones. A short exposure of red light prior to a blue light step enhanced the rapid response. The same enhancement of the rapid response could be achieved by means of a temporary pretreatment with CO₂-free air. The magnitude of the rapid response was dependent on the blue light irradiance and no threshold effects could be detected. — The experimental results are discussed by means of a model, based on stomatal regulation by, ion transport between the subsidiary cells and the guard cells. It is suggested that the slow transpiration response is due to CO₂-regulation of the stomatal aperture and that the rapid response reflect a CO₂-independent blue light sensitive process, which acts directly on the ion transport through the subsidiary and guard cell membranes.     

Characterization of the tonoplast proton pumps in Cucumis sativus L. root cells

Large-scale preparation of highly purified tonoplast from cucumber (Cucumis sativus L.) roots was obtained after centrifugation of microsome pellet (10,000 – 80,000 g) on discontinuous sucrose density gradient (20, 28, 32 and 42 %). Lack of PEP carboxylase (cytosol marker) and cytochrome c oxidase (mitochondrial marker) together with a slight activity of VO₄-ATPase (plasma membrane marker) and NADH-cytochrome c reductase (ER marker) in tonoplast preparation confirmed its high purity. Using latency of nitrate-inhibited ATPase and H⁺ pumping as criteria it was established that the majority of tonoplast vesicles were sealed and oriented right(cytoplasmic)-side-out. Strong acidification of the interior of vesicles observed at the presence of both, ATP and PP_i, confirmed that obtained tonoplast contains two classes of proton pumps: V-ATPase and H⁺PP_iase. To examine and characterise of proton-transport systems in tonoplast, the effect of various inhibitors on H⁺ pumping and hydrolytic activities of ATPase and PP_iase were measured. ATP-dependent activities (H⁺ flux and ATP hydrolysis) were specifically decreased by nitrate and bafilomycin A₁, whereas the PP_iase activities were reduced in the presence of fluoride and Na⁺ ions. Both enzymes showed a similar sensitivity to DCCD and DES. The results of experiments with KCl and NaCl suggested that the vacuolar ATPase was stimulated by Cl⁻, whereas the vacuolar Pp_iase requires K⁺ ions for its activity.     

Exposure of Leaves of Cucumis sativus L. to Low Temperatures in the Light Causes Uncoupling of Thylakoids II. Non-Destructive Measurements with Intact Leaves

To examine the effects of chilling of leaves of cucumber (Cucumissativus L.) in moderate light on the coupling state of thylakoidsin situ, changes in fluorescence, changes in light scatteringand flash-induced changes in absorbance at 518 nm were examinedin intact leaves. After chilling of leaves at 5?C in the lightfor 5 h, the non-photochemical quenching of fluorescence, ameasure of energisation of thylakoids, was largely suppressed.The treatment also caused a suppression of light-induced changesin the light scattering by leaves, which depends on the formationof a pH gradient across thylakoid membranes. When thylakoidswere prepared by very gentle methods from the leaves chilledin the light, through a step of preparation of intact chloro-plasts,the transport of electrons from H₂O to ferricyanide was uncoupled,being insensitive to an uncoupler, methylamine. These data provide consistent evidence that the thylakoids areuncoupled in situ by the chilling of leaves in the light and,as a consequence of the uncoupling, the energisation of themembranes is suppressed. However, the decay of the flash-inducedchange in absorbance at 518 nm in leaves was not markedly acceleratedby the treatment. The thylakoids isolated from leaves chilledin the light, which were in the uncoupled state, also did notshow a rapid decay, unless an efficient uncoupler such as gramicidinwas added. These results suggest that even a considerable uncouplingof thylakoids, brought about by chilling of leaves in the light,is not sufficient to cause a marked acceleration of the decayof the flash-induced change in absorbance at 518 nm. Therefore,analysis at 518 nm is not always a sensitive method for assessingthe coupling state of thylakoids. (Received July 1, 1991; Accepted October 4, 1991)