摘要:

Genetically modified potato (Solanum tuberosumL. cv. Desiree) and tobacco (Nicotiana tabacumcv. Samsun N.N.) plants were used to analyze the effects exerted by the chloroplastic (cp) fructose‐ 1,6‐bisphosphatase (FBPase) on the regulation of light energy discrimination at the level of photosystem II. The cp‐FBPase activity was progressively inhibited by an mRNA antisense to this FBPase. The chlorophyll fluorescence quenching parameters of these transgenic plants were compared to those of wild‐type and transgenic plants that were acclimated to low temperatures. In particular various lines of the transgenic potato and tobacco plants were exposed to a temperature treatment of 10 and 20°C for 10 days. Light intensities were kept low to reduce photoinhibition so that we could analyze exclusively the effects of a modification in the carbon fixation cycle on the chlorophyll fluorescence quenching parameters. The photon flux densities (PFDs) employed at the level of the middle leaves of all plants were set to two different values of 10 μmol m−2s−1and 50 μmol m−2s−1. Subsequent to this 10‐day acclimation the chlorophyll‐fluorescence parameters of all plants were measured. Photoinhibition as expressed by the Fy/Fmratio was minor in plants subjected to a PFD of 10 μmol m−2s−1. Higher photon fluence rates of 50 μmol m−2s−1at temperatures of 10°C gave rise to a significant reduction in the Fy/Fmratios obtained from the transgenic plants which were characterized by a restriction in cp‐FBPase capacity to 20% of normal activity. Furthermore, a progressive inhibition of the cp‐FBPase activity induced an amplified nonphotochemical quenching of chlorophyll fluorescence with in the genetically manipulated species (except at 10°C and 50 μmol m−2s−1). The increase in nonphotochemical quenching depended upon light and temperature. Photochemical quenching of light quanta within the antisense plants declined relative to that in the wild type. To further characterize the mechanisms producing higher levels of nonphotochemical fluorescence quenching. we analyzed several of the xanthophyll cycle pigments. The deepoxidation state of the xanthophyll cycle pigments in potato plants increased with attenuating FBPase activities under all conditions. For tobacco plants, this elevation of the deepoxidation state w

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00800.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The effects of varied boron (B) supply (0.01–50 μMand light intensity (100–580 μpmol m−2s−1) on plant growth, leaf symptoms and membrane permeability of leaves were studied in sunflower plants over a 10‐day‐period of growth in nutrient solution. Membrane permeability was measured by incubating isolated young leaves in aerated distilled water. Additional experiments showed the effect of short‐term supply (20 min to 2 h) of B and germanium (Ge) on membrane permeability of B‐deficient leaves incubated in distilled water. Low supply of B decreased shoot and root growth and caused brown‐purple pigmentation of young leaves, particularly under high light intensities. Leakage of K‐ from leaves increased with severity of B deficiency whereas, in B‐sufficient leaves, leakage of solutes was low. Also leakage of phenolics, amino acids and sucrose was enhanced by B deficiency. Compared to B‐sufficient leaves, the leakage from B‐deficient leaves was 35‐fold higher for K+, 45‐fold higher for sucrose and 7‐fold higher for phenolics and amino acids. Increases in solute leakage were marked in leaf areas with brown‐purple pigmentation and particularly pronounced by increasing light intensity or by exposure of leaves to continuous light. In severely B‐deficient leaves grown under high light intensity, treatment with B and Ge up to 1 000 μMMfor 20 min resulted in an immediate decrease in K+efflux to about the same levels as in B‐sufficient leaves. Similar rapid decreases in K+efflux were also found in B‐deficient leaves when exposed to darkness for 16 h or 30 h before the leakage measurement.The results demonstrate a particular role for B in maintaining the integrity of plasma membranes. Boron presumably stabilizes the structure of the plasma membrane by complexing membrane constituents. It also has a protective effect on membrane constituents by complexing phenolics, so that oxidation of phenolics to highly toxic quinones and oxygen free radicals is prevented or limited. In these functions, boron seems to be

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00801.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Removal of the peripheral subunits PSI‐C, ‐D and ‐E from the photosystem I (PSI) complex of barley requires a urea treatment much harsher than required to remove the similar subunits from cyanobacterial PSI. The resulting PSI barley core was reconstituted by addition of theE. coliexpressed subunits PSI‐C and ‐D, and PSI‐E isolated from barley. Western blotting, flash photolysis and NADP+photoreduction measurements demonstrated complete and specific removal of the three subunits from the core and efficient reconstitution of the complex after addition of PSI‐C, ‐D and ‐E. Flash photolysis reveals that PSI‐D is essential for binding of functional PSI‐C to the PSI core. An N‐terminally truncated barley PSI‐D lacking 24 amino acid residues and thus being without the N‐terminal extension characteristic for higher plant PSI‐D proteins reconstitutes the PSI core to 50% of the level obtained with intact PSI‐D as demonstrated by flash photolysis and NADP+photoreduction measurements. Cyanobacterial PSI‐D is functionally equivalent to truncated barley PSI‐D with respect to its activity to reconstitute the PSI core. This shows that the N‐terminal extension of plant PSI‐D plays a key role in binding PSI‐C to the core. The plant‐specific N‐terminus of PSI‐D is hypothesized to execute its function through interaction with a plant‐specific PSI subunit, possibly PSI‐H. An anchoring function of the N‐terminus of PSI‐D would also explain the harsh treatment needed to obtain a plant PSI core. PSI‐E is important for efficient NADP+reduction but does not influence electron transfer to iron‐sulphur centres A/B nor binding of PSI‐C. The enhancing effect of PSI‐E on NADP+redu

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00802.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

We conducted a series of gravitropic experiments on Avena coleoptiles in the weightlessness environment of Spacelab. The purpose was to test the threshold stimulus, reciprocity rule and autotropic reactions to a range of g‐force stimulations of different intensities and durations The tests avoided the potentially complicating effects of earth's gravity and the interference from clinostat ambiguities. Using slow‐speed centrifuges, coleoptiles received transversal accelerations in the hypogravity range between 0.1 and 1.0 g over periods that ranged from 2 to 130 min. All responses that occurred in weightlessness were compared to clinostal experiments on earth using the same apparatus.Characteristic gravitropistic response patterns ofAvenawere not substantially different from those observed in ground‐based experiments. Gravitropic presentation times were extrapolated. The threshold at 1.0 g was less than 1 min (shortest stimulation time 2 min), in agreement with values obtained on the ground. The least stimulus tested, 0.1 g for 130 min, produced a significant response. Therefore the absolute threshold for a gravitropic response is less than

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00803.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Experiments were undertaken to determine if the reciprocity rule is valid for gravitropic responses of oat coleoptiles in the acceleration region below 1 g. The rule predicts that the gravitropic response should be proportional to the product of the applied acceleration and the stimulation time.Seedlings were cultivated on 1 g centrifuges and transferred to test centrifuges to apply a transverse g‐stimulation. Since responses occurred in microgravity, the uncertainties about the validity of clinostat simulation of weightlessness was avoided Plants at two stages of coleoptile development were tested. Plant responses were obtained using time‐lapse video recordings that were analyzed after the flight. Stimulus intensities and durations were varied and ranged from 0.1 to 1.0gand from 2 to 130 min, respectively. For threshold g‐doses the reciprocity rule was obeyed. The threshold dose was of the order of 55gs and 120gs, respectively, for two groups of plants investigated. Reciprocity was studied also at bending responses which are from just above the detectable level to about 10 degrees. The validity of the rule could not be confirmed for higher g‐doses, chiefly because the data were more variable.It was investigated whether the uniformity of the overall response data increased when the gravitropic dose was defined as (gm× 1), with m‐values different from unity. This was not the case and the reciprocity concept is, therefore, valid also in the hypogravity region. The concept of gravitropic dose, the product of the transverse acceleration and the stimulation time, is also well‐defined in the acceleration region studied. With the same hardware, tests were done on earth where responses occurred on clinostats. The results did not contradict the reciprocity rule but scatter in the da

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00804.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The effect of the nitrogen source on carbohydrate and protein contents and on several enzymatic activities involved in the carbon and nitrogen metabolism was studied inAnabaena variabilisATCC 29413 cells grown under a constant supply of either N, NO−3or NH+4at different concentrations. An enhancement of protein content accompanied by a parallel decrease of carbohydrates was observed with increasing NO−3or NH+4concentrations in the medium. In cultures containing 0.1 mMNO−3or 0.1 mMNH+4nitrogenase (EC 1.18.6.1) activity was 74 and 66%, respectively, of that found in N2‐grown cells. This activity was still present with 1 mMNO−3or 1 mMNH+4in the medium and even with 10 mMNO−3, but it was completely inhibited by 5 mMNH+4. Ferredoxin‐nitrate reductase (EC 1.7.7.2) activity was detected only in NO−3grown cells and simultaneously with nitrogenase activity. Increasing concentrations of combined nitrogen in the medium, especially NH+4, promoted a concomitant decline of glutamine synthetase (EC 6.3.1.2), NADP+‐isocitrate dehydrogenase (EC 1.1.1.42), and NAD+‐malate dehydrogenase (EC 1.1.1.37) activities, suggesting that these enzymes play an important role in the regulation of carbon‐nitrogen metabo

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00805.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

When fruits of Hopea odorata are shed, seed water content is high. These seeds are not tolerant to desiccation and germination usually occurs within the first week after abscission. To determine the factors involved in the control of germination, isolated embryos were cultured in vitro and their sensitivity to abscisic acid (ABA), water potential and inhibitors of gibberellin biosynthesis was determined. Moreover, free ABA content was quantified by radioimmunoassay and ABA metabolism was studied by feeding [3H]‐ABA to embryos. Reproductive units of the desiccation‐sensitive seeds ofHopea odoratacontain several embryos, all of which are germinable and may give, according to their developmental stages, plantlets that range from those that are prematurely developed as a result of precocious germination to those that are normal. Whatever the developmental stage, the free abscisic acid (ABA) content of the embryo was low. This low endogenous ABA and the inability of high levels of exogenously applied ABA to inhibit germination could be explained by an active ABA metabolism as demonstrated by both a rapid [3H]‐ABA turnover and the existence of high levels of endogenous conjugates. Moreover, both a decrease in the water potential of the culture medium, alone or in addition with ABA, and an inhibition of gibberellin biosynthesis, could induce a reversible inhibition of germination. Such an interaction between ABA, GA and water potential is discussed in the light of results recently reported in hormone‐deficient or hormone‐insensitiv

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00806.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Changes in various nitrogen compounds during senescence of the fourth leaf were studied in two cultivars of spring wheat (Triticum aestivumL.). One of the cultivars (Yecora) was supplied with two N levels; the other (Tauro) was grown with the high N level and pruned above the fourth leaf, whereas the control was left intact. In both cultivars grown with high N supply, net nitrogen export from the fourth leaf did not occur until 35 days after sowing (DAS). Loss of leaf soluble proteins started earlier than that of chlorophylis, and coincided initially with an increase in insoluble protein. In N deficient plants the level of total N, soluble protein, and the activity of nitrate reductase (NRA. EC 1.6.6.1) started to decrease about 5 days earlier, and along with chlorophyll, continued to decrease at a faster rate, than in high N plants. Also, with low N supply, the large subunit (LSU, 58 kDa) of ribulose‐1.5‐bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) decreased in greater proportion than other soluble proteins, while with high N supply the decrease in Rubisco LSU was similar to that of other soluble proteins. Nitrogen deficiency caused a greater decrease in soluble proteins than in insoluble proteins, and NRA relative to soluble proteins. The faster senescing Tauro cultivar had lower levels of most parameters, especially NRA, soluble protein and, after 35 DAS. Rubisco LSU as a proportion of soluble protein. The decrease in sink strength due to shoot pruning did generally not affect the level of the various nitrogenous compounds until 35 DAS; thereafter the levels of most parameters, especially soluble protein, Rubisco LSU and, at late stages of senescence, insoluble protein, were higher in pruned than in control shoots. Thus, shoot pruning slows down senescence. The 56‐ and 78‐kDa polypeptides increased, rather than decreased, with leaf age; the level of these two polypeptides showed a negative relationship with Rubisco LSU (r = ‐0.933 and r = ‐0.758, re

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00807.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The objective of this study was to determine the effect of short‐term (4 days) and long‐term (8 days) heat stress (35°C) on sink activity of maize (Zea maysL.) kernels. Beginning at 3 days after pollination (DAP) kernels were grown in vitro at 25°C and 24 h later were transferred to 35°C for either 4 or 8 days. Each treatment had a control that was maintained continously at 25°C. Two experiments were designed to examine the uptake and distribution of14C among hexoses, sucrose and starch in the pedicel placento‐chalazal (pedicel/p‐c). endosperm, and pericarp tissues of kernels exposed to heat stress for 4 or 8 days. Kernels cultured in vitro were placed in14C‐sucrose medium either during the period of heat stress (experiment 1; 5 to 13 DAP) or immediately following heat‐stress treatments (experiment 2; 10 to 22 DAP). In both experiments no significant effect of heat stress was observed on the total radioactivity accumulated in the kernels until about 17 DAP, after which heat‐stressed kernels accumulated less14C than the control. During the linear fill period, the endosperm of kernels exposed to heat stress accumulated more radioactivity associated with hexoses and sucrose and less radioactivity incorporated into starch, as compared to the control. Kernels heat stressed for 4 days showed a partial recovery in starch synthesis by 21 DAP, but to levels of only 65% of that of the control. Kernels heat stressed for 8 days did not recover. When14C‐sucrose was supplied during the heat stress period (5–13 DAP). kernels from all treatments accumulated more hexoses that sucrose in the pedicel/p‐c. However, during the period following heat stress (10–22 DAP), pedicel/p‐c accumulated sucrose, but only in kernels exposed to long‐term heat stress. Soluble invertase activity was inhibited by both short‐term and long‐term heat stress, whereas the activity of insoluble invertase was affected only by long‐term heat stress. These results support the hypothesis that the disruption of kernel growth and more particularly endosperm starch biosynthesis, in response to heat stress, is mainly associated with changes in carbon utilization and partitioning between the different nonstructural carbohydrates within the endosperm rather than with a limitation in carbon supply to the kernel. Therefore, the effect on sink activity does not seem to be attributable to a thermal disruption of kernel uptake of sugars, but rather it is a consequence of heat perturbation of other physiological processes such as endosperm sugar

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00808.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Short photoperiod induces growth cessation in seedlings of Norway spruce (Picea abies(L.] Karst.). Application of different gibberellins (GAS) to seedlings growing under a short photoperiod show that GA9and GA20can not induce growth. In contrast application of GA, and GA4induced shoot elongation. The results indicate that 3β‐hydroxylation of GA9to GA4and of GA20to GA1is under photoperiodic control. To confirm that conclusion, both qualitative and quantitative analyses of endogenous GAs were performed. GA1, GA3, GA4, GA7, GA9, GA12, GA15, GA15, GA20, GA29, GA34and GA51were identified by combined gas chromatography‐mass spectrometry in shoots of Norway spruce seedlings. The effect of photoperiod on GA levels was determined by using deuterated and14C‐labelled GAs as intermal standards. In short days, the amounts of GA9, GA4and GA1are less than in plants grown in continuous light. There is no significant difference in the amounts of GA3, GA12,andGA20between the different photoperiods. The lack of accumulation of GA9and GA20under short days is dis

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00809.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY