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991.
Low growth temperature-induced changes to pigment composition and photosynthesis in Zea mays genotypes differing in chilling sensitivity 总被引:1,自引:1,他引:0
P. Haldimann 《Plant, cell & environment》1998,21(2):200-208
The effects on pigment composition and photosynthesis of low temperature during growth were examined in the third leaf of three chilling-tolerant and three chilling-sensitive genotypes of Zea mays L. The plants were grown under a controlled environment at 24 or 14 °C at a photon flux density (PFD) of 200 or 600 μ mol m–2 s–1 . At 24 °C, the two classes of genotypes showed little differences in their photosynthetic activity and their composition of pigments. At 14 °C, photosynthetic activity was considerably reduced but the chilling-tolerant genotypes displayed higher photosynthetic rates than the chilling-sensitive ones. Plants grown at 14 °C showed a reduced chlorophyll (Chl) a + b content and a reduced Chl a / b ratio but an increased ratio of total carotenoids to Chl a + b . These changes in pigment composition in plants grown at low temperature were generally more pronounced in the chilling-sensitive genotypes than in the tolerant ones, particularly at high PFD. Furthermore, at 14 °C, all the genotypes showed increased ratios of lutein, neoxanthin and xanthophyll-cycle carotenoids to Chl a + b but a reduced ratio of β -carotene to Chl a + b , especially at high PFD. At 14 °C, the chilling-tolerant genotypes, when compared with the sensitive ones, were characterized by higher contents of β -carotene and neoxanthin, a lower content of xanthophyll-cycle carotenoids, a lower ratio of xanthophylls to β -carotene, and less of their xanthophyll-cycle carotenoid pool in the form of zeaxanthin. These differences between the two classes of genotypes were more pronounced at high PFD than at low PFD. The results are discussed in terms of the relationship that may exist in maize between pigment composition and the capacity to form an efficient photosynthetic apparatus at low growth temperature. 相似文献
992.
Embryogenic and non-embryogenic callus lines derived from the same diploid Cyclamen persicum genotype (`Purple Flamed') were analyzed by flow cytometry and compared to the initial plant material. The DNA content of
the diploid plant in the greenhouse was 1.12 pg DNA/2C as estimated in relation to the internal standards tomato nuclei and
chicken erythrocytes. In both callus lines the majority of cells contained the same amount of DNA as the initial plant, indicating
that no polyploidization has taken place after 5 years of culture on medium containing 2.0 mg/l 2,4-dichlorophenoxyacetic
acid (2,4-D) and 0.8 mg/l 6-(γ-γ-dimethylallylamino)purine(zip). Thus, our data suggest that in Cyclamen callus lines there was no strict correlation between the ploidy level and the ability to produce somatic embryos. Furthermore,
following the proportion of cells in the three phases of the cell cycle (G0/G1, S, G2/M) during one subculture period of 4
weeks revealed high division activity within the first 2 weeks for both callus lines cultured on the 2,4-D-containing medium.
However, when transferred to hormone-free medium, the division activity of the embryogenic cell line decreased markedly, corresponding
to the differentiation of somatic embryos. In contrast, for the non-embryogenic callus an increase in cells in the G2/M phase
was observed.
Received: 22 November 1996 / Revision received: 6 January 1997 / Accepted: 20 February 1997 相似文献
993.
Stem elongation in Fuchsia × hybrida was influenced by cultivation at different day and night temperatures or in different light qualities. Internode elongation
of plants grown at a day (25°C) to night (15°C) temperature difference (DIF+10) in white light was almost twofold that of
plants grown at the opposite temperature regime (DIF−10). Orange light resulted in a threefold stimulation of internode elongation
compared with white light DIF−10. Surprisingly, internode elongation in orange light was similar for plants grown at DIF−10
and DIF+10. Flower development was accelerated at DIF−10 compared with DIF+10 in both white and orange light. To examine whether
the effects of DIF and light quality on shoot elongation were related to changes in gibberellin metabolism or plant sensitivity
to gibberellins (GAs), the stem elongation responses of paclobutrazol-treated plants to applied gibberellins were determined.
In the absence of applied gibberellins paclobutrazol (>0.32 μmol plant−1) strongly retarded shoot elongation. This inhibition was nullified by the application of about 10–32 nmol of GA1, GA4, GA9, GA15, GA19, GA20, GA24, or GA44. The results are discussed in relation to possible effects of DIF and light quality on endogenous gibberellin levels and
gibberellin sensitivity of fuchsia and their effects on stem elongation.
Received October 4, 1997; accepted December 17, 1997 相似文献
994.
The nucleotide analogue 9-[2-(phosphonomethoxy)ethyl]guanine (PMEG) has been identified as a powerful antiproliferative substance
when acting on hybridoma cells. In the range of 10 nM to 100 nM concentrations this agent reduces cell growth rate, while
its apoptosis-inducing activity is marginal. Marked induction of apoptosis can be observed at micromolar and higher order
concentrations. In PMEG-supplemented media the cell cycle progression is perturbed, the flow-cytometric DNA profile shows
a higher proportion of cells in the S and G2/M phases of the cell cycle. Concomitantly with the reduction of the growth rate,
the specific monoclonal antibody production rate may rise by 20–27%. Addition of PMEG at the end of the exponential phase
of a batch culture results in an enhancement of the final monoclonal antibody concentration.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
995.
Bruno Chauffert Marie-Thérèse Dimanche-Boitrel Carmen Garrido Mikael Ivarsson Monique Martin François Martin Eric Solary 《Cytotechnology》1998,27(1-3):225-235
Kinetic resistance plays a major role in the failure of chemotherapy towards many solid tumors. Kinetic resistance to cytotoxic
drugs can be reproduced in vitro by growing the cells as multicellular spheroids (Multicellular Resistance) or as hyperconfluent
cultures (Confluence-Dependent Resistance). Recent findings on the cell cycle regulation have permitted a better understanding
why cancer cells which arrest in long quiescent phases are poorly sensitive to cell-cycle specific anticancer drugs. Two cyclin-dependent
kinase inhibitors (CDKI) seem particularly involved in the cell cycle arrest at the G1 to S transition checkpoint: the p53-dependent
p21cip1 protein which is activated by DNA damage and the p27kip1 which is a mediator of the contact inhibition signal. Cell quiescence could alter drug-induced apoptosis which is partly
dependent on an active progression in the cell cycle and which is facilitated by overexpression of oncogenes such as c-Myc
or cyclins. Investigations are yet necessary to determine the influence of the cell cycle on the balance between antagonizing
(bcl-2, bcl-XL...) or stimulating (Bax, Bcl-XS, Fas...) factors in chemotherapy-induced apoptosis. Quiescent cells could also be protected from toxic agents by an enhanced
expression of stress proteins, such as HSP27 which is induced by confluence. New strategies are required to circumvent kinetic
resistance of solid tumors: adequate choice of anticancer agents whose activity is not altered by quiescence (radiation, cisplatin),
recruitment from G1 to S/G2 phases by cell pretreatment with alkylating drugs or attenuation of CDKI activity by specific
inhibitors.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
996.
Janet H. Parham Marie A. Iannone Laurie K. Overton Jeff T. Hutchins 《Cytotechnology》1998,28(1-3):147-155
The goals of this study were to identify mammalian cell lines which could be efficiently transiently-transfected and scaled-up
for protein production. The transfection efficiencies of eight cell lines (NSO, NSO-TAg, CV-1, COS-7, CHO, CHO-TAg, HEK 293,
and 293-EBNA) were measured using electroporation for DNA delivery and green fluorescent protein (Evans, 1996) as the reporter
gene. In addition, we have evaluated the effects of stable expression of viral proteins, cell cycle manipulation, and butyrate
post-treatment in small scale experiments. The cell lines varied widely in their GFP transfection efficiencies. Stable expression
of simian virus 40 large T-antigen or Epstein Barr nuclear antigen failed to significantly increase transfection efficiency
above that seen in the parental lines. Aphidicolin (a DNA polymerase inhibitor), which blocked cells from S or G2/M, brought
about an increase in transfection efficiency in two cell lines. The primary effect of butyrate (a histone deacetylase inhibitor)
post-treatment was an increased intensity of the fluorescent signal of green fluorescent protein, as measured by flow cytometry
(1.0 to 4.2-fold, depending on the cell line). The combined use of aphidicolin pretreatment followed by butyrate treatment
post- electroporation yielded increases in fluorescence intensities ranging from 0.9 to 6.8-fold. Based on their high transfection
efficiencies in small scale experiments, rapid growth, and ability to grow in suspension culture, CHO, CHO-TAg, and 293-EBNA
were selected to assess the feasibility of using flow electroporation for large-scale transfections. Using secreted placental
alkaline phosphatase as a reporter, 293-EBNA cells produced the highest protein levels in both the presence and absence of
butyrate. These data indicate that flow electroporation provides an efficient method of DNA delivery into large numbers of
cells for mammalian protein production.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
997.
Masaki Uchida Takayuki Nakatsubo Takao Horikoshi Kaneyuki Nakane 《Ecological Research》1998,13(1):17-26
In order to clarify the role of micro-organisms in the carbon cycle of the boreal forest ecosystem, the vertical distribution of soil carbon, soil microbial biomass and respiratory activity was studied in a black spruce forest near Candle Lake in Saskatchewan, Canada. The total amount of carbon contained in moss and soil layers (to the depth of 50cm beneath the mineral soil surface) was 7.2kgm–2, about 47% of which was in the L and FH horizons of the soil. Soil microbial biomass per dry weight of soil was largest in the L horizon, while the biomass per ground area was largest in the FH horizon. Soil respiration rate, measured using a portable infrared gas analyzer, was highest in the FH horizon, exceeding 50% of the total soil respiration. Low but significant CO2 emission was detected even in deeper soil horizon (E horizon). We also examined the respiration rate of cut roots and the effect of root excision on respiration. The contribution of root respiration to total soil respiration, calculated from root biomass and respiration rate of cut roots, was about 54%. The amount of carbon evolved through microbial respiration during the snow-free season (June–October) was estimated as 221gCm–2. Micro-organisms in the L horizon showed high respiratory activity as compared with those in deeper soil horizons. 相似文献
998.
Yasunori Machida Marina Nakashima Kayoko Morikiyo Hiroharu Banno Masaki Ishikawa Takashi Soyano Ryuichi Nishihama 《Journal of plant research》1998,111(2):243-246
The tobaccoNPK1 gene encodes a homolog of mitogenactivated protein kinase kinase kinases. We have recently identified tobacco kinesin-like
proteins (NACK1/2) as activators for NPK1. Immunochemical analyses of NPK1 and NACK1 proteins suggest that NPK1 is involved
in the regulation of some process in the M phase of the plant cell cycle.
The extended abstract of a paper presented at the 13th International Symposium in Conjugation with Award of the International
Prize for Biology “Frontier of Plant Biology” 相似文献
999.
An analytical link is proposed between branchwood volume and branchiness. A segmented linear model with one parameter is
used to describe the branch basal area density along the tree bole and integrated to find a function describing the cumulative
branch basal area. It appears that the bases of insertion of the branches defining the base of the light crown correspond
to the maximum branch basal area density along the bole. This function is then used together with an individual branch volume
equation to find a model that estimates branchwood volume. This model is calibrated with data gathered in 15 stands dominated
by sugar maple (Acer saccharum Marsh.) in southern Quebec. A comparison is made with other models of branchwood volume found in the literature.
Received: 22 August 1997 / Accepted: 9 February 1998 相似文献
1000.
Ülo Niinemets 《Trees - Structure and Function》1998,12(7):446-451
Foliar inclination angles, petiole morphology and dry matter partitioning between assimilative and support biomass were studied
in shade-intolerant Populus tremula L. and shade-tolerant Tilia cordata Mill. along a natural light gradient across the canopy. The leaves of sub-canopy species T. cordata were on average exposed to lower irradiances, and they were also more horizontal with greater blade inclination angles (ϕB, defined as the angle between the leaf fall-line and the horizon; ϕB was positive for the leaves inclined upwards, and negative for the leaves inclined downwards) than those in P. tremula. Seasonal average daily integrated quantum flux density (Q
int, mol m–2 day–1) and ϕB were not related in T. cordata, and only a weak negative effect of Q
int on ϕB was detected in P. tremula. Nevertheless, when both species were pooled, there was a strong negative relationship between Q
int and ϕB, implying that the leaves became progressively vertical with increasing height in the canopy. Interspecific differences in
foliage inclination were mainly related to petiole morphology, in particular to petiole length, rather than to contrasting
biomass investment patterns between assimilative and support tissues within the leaf. It was suggested that more horizontal
leaves, resulting from the species-specific structure of petioles, partly explain the superior performance of shade-tolerant
T. cordata in the understory and the sub-canopy.
Received: 13 November 1997 / Accepted: 6 March 1998 相似文献