摘要:

Bean (Phaseolus vulgarisL. cv. Golden Saxa) plants were grown under low artificial light or under natural daylight. The rate of net photosynthesis (PN) was measured at: CO2partial pressure, p(CO2), of 0.03, 0.09 or 0.15 kPa; O2partial pressure, p(O2), of 2, 21 or 31 kPa and at light intensities of 350 or 1000 μmol m−2s−1(photosynthetically active radiation). In plants which had been grown under natural light, stimulation of PNat 21 kPa p(O2) was found only at elevated p(CO2) and high light. It is proposed that this phenomenon is dependent on a high capacity of the photosynthetic apparatus to regenerate ribulose 1.5‐bispho

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb00624.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Microtubule organization in the course of the interphase‐mitosis transition, karyokinesis and cytokinesis in cultured mesophyll protoplasts ofMedicago sativaL. cv. Regen S andNicotiana tabacumL. cv. Wisconsin 38 was investigated during the early culture stages. A prominent circular band of microtubules, the prophase band of microtubules (PB) was seen in the cell cortex during prophase in most cells. The band appeared during very early prophase and disappeared during late prophase. Other prophase microtubule arrays were nuclear‐envelope associated microtubule fluorescence (perinuclear fluorescence, PNF) and groups of microtubules radiating from the nuclear envelope into the cytoplasm. These radiating microtubutes (perinuclear radiating microtubules, PNR) were particularly long and prominent in the PB plane appearing to link the PNF with the PB network. The possible functions of the PNR are discussed. The role of the PB is discussed in the light of the unorganized nature of these ce

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb00625.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Karyokinetic and cytokinetic irregularities were examined in cultured mesophyll protoplasts ofMedicago sativaL. cv. Regen S andNicotiana tabacumL. cv. Wisconsin 38 during the early cell divisions. Spindle anomalies, laggine chromalids during anaphase, displaced phragmoplasts during telophase and incomplete cross‐walls following the completion of cytokinesis were scored in these cultures. The abnormalities, however, occurred at low frequencies when compared to those found in suspension culture‐derived protoplasts ofVicia hajastana. It is suggested that abnormalities are reduced because the mesophyll protoplasts regenerate a substantial cell wall prior to the onset of the first division.An entirely different class of cytological aberration occurring in 40–50% of the cells was caused by localized protruding of the cytoplasm (budding). The nucleus was often positioned at the site of constriction of the bud. The association of budding with mitosis has led us to postulate a mechanism which may be a cause of budding and to suggest a possible way to preve

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb00626.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The in vitro conversion of [14C]‐tryptophan to [14C]‐indole‐3‐acetaldoxime (IAOX) by microsomal membranes of Chinese cabbage(Brassica campestrisssp.pekinensiscv. Granat) has been studied. The reaction product was identified by thin‐layer chromatography (TLC) and high performance liquid chromatography (HPLC). Furthermore. IAOX was identified as an endogenous compound of Chinese cabbage by mass spectroscopy. The tryptophan‐oxidizing enzyme (TrpOxE) was characterized. MnCl2was required as cofactor, H2O2, and 2,4‐dichlorophenol (DCP) stimulated the reaction. The enzyme showed a pH optimum at pH 8–9 and a Kmforl‐tryptophan of 20 μM. The membranes containing TrpOxE activity were identified as plasma membranes by means of aqueous polymer two‐phase partitioning. The TrpOxE from Chinese cabbage was purified 3‐fold from plasma membranes by solubilization followed by (NH4)2SO4‐fractionation, affinity‐chromatography with concanavalin A, and native gel electrophoresis. Enzyme activity was reduced by a tunicamycin pretreatment. Several other plant species, e.g. maize(Zea maysL. Inrakorn), sunflower(Helianthus annuusL. cv. Hohes Sonnengold), tobacco(Nicotiana tabacumL. cv. White Burley), and pea(Pisum sativumL. cv. Krombeck) showed a similar conversion of [14C]‐tryptophan to [14C]‐IAOX by phas

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb00627.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Net rates of NO3−and K+uptake were compared for oilseed rape (Brassica napusL. cv. Jet neuf), perennial ryegrass (Lolium perenneL. cv. S23), Italian ryegrass (Lolium multiflorumLam. cv. Augusta) and wheat (Triticum aestivumL. cv. Fen‐man) in flowing solution culture during a 4‐day sequence of low‐low‐high‐high natural irradiance. Concentrations of NO3−(10 μM) and K+(2.5 μM) in solutions were maintained automatically and hourly variation in net uptake of these ions was measured. During the 2 days of low irradiance (<1 MJ m−2day−1) the uptake rates of both ions by all species were low at<1 mmol NO3−, m−2h−1and1.4 mmol K+m−1h−1. These higher rates were maintained throughout the following night. The lag‐time between maximum irradiance and the onset of the highest acceleration in uptake was greater for NO3−(5–8 h) than for K+(≤1 h) in rape, wheat and Italian ryegrass. Uptake of NO3−, by perennial ryegrass showed an almost constant acceleration for 18 h following maximum irradiance. In all species the measured maximum inflows (uptake rate per unit root length) of both ions were greater than theoretical maximum potential inflows to a non‐competing infinite‐sink root in soil, by factors of 7 and 36

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb00628.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Temperature‐induced changes in Hill activity of glutaraldehyde‐fixed pea (Pisum sativumL. cv. Alaska) thylakoids have been examined. Using ferricyanide as electron acceptor, a temperature‐induced change occurred at ca 12–14°C for both control and fixed thylakoids. In contrast to the controls, fixed thylakoids not only showed a change in slope of the Arrhenius plots but also a discontinuity which has not been observed in previous studies. A drop in activity coincided with the decrease in slope: the extent of the reduction depended on the concentration of glutaraldehyde used for fixation. Using a lipophilic electron acceptor, a temperature‐induced change also occurred at 12–14°C, but there was no reduction in activities of fixed thylakoids at temperatures above the change in slope.The results indicate that a temperature‐induced change in fixed thylakoids restricts the access of ferricyanide to its reductant(s) in the membrane but that fixation does not affect the temperature‐induced change per se. The results confirm that temperature has a general effect on the functioning of thylakoid membranes. The data demonstrate that calculations of the extent of inhibition by glutaraldehyde of Hill activity with ferricyanide should take into account the temperature at which ass

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb00629.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

In contrast to the data reported for developing seeds of pea and broad bean, assimilate transport into empty kernels of maize is not reduced by a low osmolality of the substitute medium. Therefore, additional data were collected from representatives of other taxonomical groups. In pulse‐labelling experiments withLunaria annuaL. andAcer pseudoplatanusL., sucrose and amino acid transport into empty ovules was strongly reduced by a low osmolality of the medium filling an empty ovule, compared to that seen with high osmolality. In experiments of 8 h without radioiso‐topes, a very low osmolality of the medium (about 0 mM) reduced the rate of sugar and amino acid release from attached seed coats of soybean [Glycine max(L.) Merr. cv. Fiskeby V], in comparison with a 300 mMmannitol medium. It can be concluded that in all dicotyledonous plants studied (five species), a low osmotic potential of the seed apoplast is one of the most important factors controlling the rate of assimilate transport into developing seeds. At this moment, the data reported for maize have an isolated posit

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb00630.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Spruce seedlings [Picea abies(L.) Karst.] were exposed in nutrient solutions to a range of concentrations of HgCl2and CH3HgCl for 7 weeks. The mineral, chlorophyll and water contents of the needles, and dry weights of root and needles were then estimated. The rates of photosynthesis, transpiration and dark respiration of the intact plants were determined using a Li‐cor portable photosynthesis‐measuring system. CO2uptake decreased as the supply of both forms of Hg increased. Rates of transpiration were significantly reduced only after exposure to CH3HgCl. Similar concentrations of Hg were found in needles independent of the form of Hg supplied. Decreased rates of CO2uptake at 100 nMHgCl2and 1 nMCH3HgCl could be explained by lower levels of chlorophyll, and by lower levels of chlorophyll and closed stomata at all other CH3HgCl concentrations. Only at 1000 nMHgCl2were other photosynthetic parameters affected.Decreased rates of transpiration and the lower chlorophyll levels in the needles did not appear to be due to the direct action of Hg, but rather to root damage that leads to a decrease in water supply and nutrient levels in the need

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb00631.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Vulnerability of xylem conduits to cavitation and embolism was compared in two species of Rhizophoraceae, the mangroveRhizophora mangleL. and the tropical moist‐forestCassipourea elliptica(Sw.) Poir. Cavitation (water column breakage preceeding embolism) was monitored by ultrasonic detection; embolism was quantified by its reduction of xylem hydraulic conductivity. Acoustic data were not predictive of loss in hydraulic conductivity, probably because signals from cavitating vessels were swamped by more numerous ones from cavitating fibers.Rhizophora manglewas the less vulnerable to embolism of the two species, losing 80% of its hydraulic conductivity between – 6.0 and – 7.0 MPa.Cassipourea ellipticalost conductivity in linear proportion to decreasing xylem pressure from – 0.5 to – 7.0 MPa. Species vulnerability correlated closely with physiological demands of habitat; the mangroveRhizophora manglehad field xylem pressures between – 2.5 and – 4.0 MPa. whereas the minimum forCassipourea ellipticawas – 1.6 MPa. Differences in vulnerability between species could be accounted for by differences in the measured air permeability of intervessel pit membranes. According to this explanation, embolism occurs when air enters a water‐filled vessel from a neighboring air‐filled one via pores in s

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb00632.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Effects of contrasting temperatures of an expanding leaf (source) and of remaining plant parts (sink) on diurnal export and distribution of carbon were studied in seedlings ofCucumis sativusL., cv. Farbio. The time course of the rate of export was calculated by measuring simultaneously the exchange of14CO2and the amount of14C in the source leaf by means of a Geiger‐Müller detector using a steady‐state labelling technique.In all treatments average export rate during the night (16 h) was maximally 50% of the average rate during the 8‐h day. Temperature affected the diurnal course of export via the source leaf and the sink in different ways. At a source leaf temperature of 25 or 30°C export stopped 12 h after start of the night, whereas at 20°C export continued throughout the night. However, the total amount of carbon exported during a 24 h cycle, expressed as a proportion of the amount of carbon assimilated, was the same at source leaf temperatures of 20 or 30°C. Thus source leaf temperature did not affect the distribution of assimilates between source and sink, in contrast to sink temperature. After 24 h at a sink temperature of 30°C, 20% more14C was exported to plant parts below the source leaf than with a sink temperature of 20°C, at the expense of carbon remaining in the source.During the day less starch and more structural dry matter was formed at a source leaf temperature of 30°C than at 20°C. After a complete day/night cycle, however, there was no difference between the treatments. Starch was the primary carbon source during the night, and the decline in the rate of export coincided with the depletion of starch. Thus the decline in the rate of export at a source leaf temperature of 25 or 30°C at 12 h after the start of the night was due to the depletion of starch at that time. Similarly, at 20°C export could continue until the end of the night as the starch degradation supplied assimilates during

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb00633.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY