摘要:

The model presented takes into account the interaction between the negatively charged membranes and macromolecules and the cations. A central postulate is that a constant average surface charge density (σ) as well as a constant average surface potential (Ψ) is conserved under different ionic conditions. The model makes it possible to predict the size of σ and Ψ from measurements of Na, K, Mg and Ca content in plant tissues of the same age but grown under two different ionic conditions (e.g. high and low K+). Assumptions were made about the relative amounts of free and bound Ca2+and σ and Ψ were calculated from values in the literature. In all cases σ (and Ψ) are predicted to be higher for shoot (−29 to −96 mC m−2) than for root membranes (−14 to −27 mC m−2). In most cases the predicted σ falls within the range determined experimentally for

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1984.tb05165.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Seedlings of winter wheat (Triticum aestivumL. cv. Hildur) were grown at 18°C for 7 days in darkness in a complete growth medium in the presence or absence of 1 mMKCl to produce roots with different ion contents (high and low K+respectively). The roots were homogenized, the 3 000 g, 10 000 g, 30 000 g (further fractionated by two phase partitioning) and 100 000 g pellets isolated, and their surface charge densities (σ) determined by the use of 9‐aminoacridine fluorescence. The average σ for all membrane fractions weighted for protein content was the same (−18 mC m−2) for low and high K+roots. The K+, Na+, Mg2+and Ca2+content of roots was determined and used to calculate an average σ following the procedure of Bérczi et al. [Physiol. Plant. 61: 529–534 (1984)]. The predicted value (−11 mC m−2) does not deviate much from the experimentally determined value. It is concluded as a useful working hypothesis that the average surface charge density is constant and that the ionic content of plant cells is regulated such that the average surface poten

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1984.tb05166.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Cycling of stomatal conductance in three hybrid poplar (Populussp.) cultivars was observed under a variety of conditions. Illumination of plants kept previously in the dark induced very large oscillations with a period of about 40 min and large oscillations with a shorter period (<10 min) were superimposed on the longer cycles. During these oscillations, large changes in conductance could occur very rapidly (1.0 cm s−1in 3 min). Plants in constant light also displayed both long and short term cycles in conductance, but these were smaller in amplitude than those induced by sudden illumination. Stomatal oscillations were also observed in darkness and after darkening of previously illuminated plants. These oscillations had shorter (<30 min) and less regular periods than those observed in the light. Such cycling in the dark is rare. Cycling of the two leaf surfaces was sometimes in synchrony in the light, and more so after a perturbation. Little synchrony between the two surfaces was observed in the dark. Stomatal movements of different leaves on a plant were usually relatively independent. Transient stomatal opening occurred following leaf excision in the light or dark, and often after sudden darkening of intact leaves. Also, stomata of intact leaves sometimes transiently closed following illuminatio

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1984.tb05167.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

The influence of row orientation on spectral distribution of light received by growing soybean [Glycine max(L.) Merr. (cv. Coker 338)] plants was measured under field conditions, and light spectrum effects on photosynthate partitioning were studied under controlled environments. Light received by leaves under field conditions differed among those grown in north‐south vs east‐west oriented rows. In morning and late afternoon, the far‐red/ red ratio received by leaves at the surface of the canopy differed about 3‐fold from the east to west sides of north‐south rows, but only 1.3‐fold from the south to north sides of east‐west rows.In controlled environments, brief exposures to red or far‐red light at the end of the photosynthetic period influenced partitioning of photosynthate among leaves, stems and roots. The top/root ratios differed significantly between the red and far‐red treated plants. Red treated plants partitioned less photosynthate to stems and more to roots than did those treated with far‐red. Also, plants with larger root systems developed more nodules. Phytochrome effects on photosynthate partitioning between tops and roots may influence yield of soybean plants grown in soils with low wat

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1984.tb05168.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Brassinosteroid (BR) stimulation of auxin‐induced ethylene production and the particular step at which BR acts to promote such synthesis were studied in mung bean (Vigna radiataL. Rwilcz cv. Berken) hypocotyl segments. Increasing concentrations of methionine alone and in combination with 3 μMBR and 10 μMIAA had a minimal effect on ethylene production. With increasing concentrations of 1‐aminocyclopro‐pane‐1‐carboxylic acid (ACC), however, ethylene production increased. BR or IAA further enhanced ethylene production with maximum rates occurring when these compounds were added together with ACC. The addition of 10 μMCoCl2in conjunction with BR and/or IAA resulted in 85–97% inhibition of ethylene production. When 20 μMcycloheximide was used in conjunction with BR and/or IAA there was a complete inhibition of ethylene production. Total inhibition also resulted when 1.0 μMaminoethoxy‐vinylglycine (AVG) was used in combination with BR and/or IAA. AVG alone had no effect on ACC conv

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1984.tb05169.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Experiments were carried out with barley cultivars (Hordeum vulgareL.) grown in both pot‐ and water‐culture. Net uptake of NO3−and K+in the roots was followed in two barley cultivars grown on water‐culture for 85 days. After an initial period of low net uptake of both ions, uptake increased until a maximum was reached after 30 to 45 days. Thereafter, net uptake of NO3−and K+steadily decreased. In the pot experiments, effects of different mineral supply on day 4 to 18 upon the development of five barley cultivars of various earliness were investigated. The effect of earliness on fresh weight production was largest when mineral supply on day 4 to 18 was limited. The influence of limited mineral supply on day 4 to 18 on K‐economy was independent of earliness of the cultivars. The maximal N‐content was reached at the same time as maximal fresh and dry weight in fairly late cultivars; in early cultivars maximum N‐level was reached later than maximum fresh and dry weight. Overall, maximal N‐content was higher in the fairly late cultivars than in the early cultivars. The highest rate of15N‐transport was attained later in two of three fairly late cultivars than in early cultivars. Partitioning of dry weight, N and K in the shoots changed during ageing, ears being an important sink. Varietal differences in partitioning depended on the earliness of the cultivars. The largest fraction of recently supplied15N, supplied as nitrate, and K+(86Rb) were found in the stems. In the oldest plants of the early cultivars the transport to the ears of these isotopes was gradually impaired, reflecting the decreasing function of the long distan

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1984.tb05170.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Detailed dose‐response curves were obtained for cytokinin‐induced retention of chlorophyll in detached leaves of barley,Hordeum vulgareL. cv. Møyar, over a wide range, 10−10– 2.5 × 10−4M, of external concentrations of benzyladeninc or kinetin. The over‐all shape of the curves was log‐linear and the response was subsensitive. Benzyladenine was somewhat more effective than kinetin. In the curves there were pronounced local minima and maxima both at low, intermediate (10−7– 10−5M) and high concentrations. At low and high concentrations these deviations from the best smooth curves were reproducible, statistically significant and occurred at the same concentrations for benzyladenine and kinetin. In the intermediate range the deviations from the log‐linear line were marked and statistically highly significant in some but not all experiments. The cause of the complexities in the dose response curve is not known, but multiphasic uptake of the cyt

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1984.tb05171.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Uptake of [U‐14C]‐sucrose (40 mM) by fresh and aged peeled leaf discs of broad bean (Vicia fabaL. cv. Aguadulce) has been studied. In fresh discs, uptake was nearly insensitive to external pH, whereas the pH response of absorption in discs aged for 12 h was bell‐shaped, with an optimum between pH 5 and 6. At this pH, uptake was nearly twice that in fresh tissue. The passive (insensitive to carbonyl cyanidem‐chlorophenylhydrazone and to cold treatment) uptake was the same in fresh or aged discs. The development of pH sensitivity of absorption did not appear when ageing was performed in the presence of 10−HMcycloheximide or 5.7 × 10−5Mactinomycin D. Similarly, when the tissues were treated with 10−3Mspermidine for 2 h after excision and then aged for 10 h, the development of the pH‐sensitive uptake system was inhibited. Ca2+(10−2M) supplied together with spermidine prevented the inhibiting effect of spermidine. The appearance of the pH‐sensitive system was also markedly reduced if ageing took place in the presence of 10−3Maminoethoxyvinylglycine. Autoradiographs from fresh discs and from discs aged with or without the inhibitors suggest that pH sensitivity developed more intensively in the parenchyma than in the veins.The results suggest some caution when using excised leaf discs for studies on sucrose uptake and phloem loading. Development of pH sensitivity of uptake may require the synthesis of both DNA‐dependent RNA and protein and could be relate

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1984.tb05172.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Schjørring, J. K. and Jensén, P. 1984. Phosphorus nutrition of barley, buckwheat and rape seedlings. I. Influence of seed‐borne P and external P levels on growth, P content and32P/31P‐fractionation in shoots and roots.Seedlings of barly (Hordeum vulgareL. cvs Salka and Zita), buckwheat (Fagopyrum esculentumMoench) and rape (Brassica napusL. ssp.napusev. Line) were grown at 8 or 10 different external P levels in the range 0‐2000 μM. Apart from P, the nutrient solutions were complete. In some experiments with barley and rape,32P‐labelled phosphate was used. Root fresh weights of buckwheat and rape decreased when the external P supply exceeded the level required for maximal root development. In all three species, the roots constituted a decreasing proportion of the total plant fresh weight as the external P level increased. The shoot/root fresh weight ratio increased linearly with the P concentration of the roots. The ratio between the P concentration in shoots and roots increased with the P status of the seedlings grown at low to intermediate external P levels, but decreased at higher P levels. The proportion of total seedling‐P held in roots consequently reached a minimum value and thereafter increased as the P status of the seedlings increased. This indicates that some control mechanism counteracted the accumulation of harmful P levels in the shoots.32P‐Phosphate uptake by seedlings of barley and rape grown in solutions with 2 μMP overestimated the actual net phosphorus uptake by a factor of 6 to 7, indicating a marked fractionation of32P and31P. For seedlings grown in solutions with 25 μMP (barley) or 50 μM(rape) no fractionation occurred. The relative excess of32P in high P seedlings accumulated in the roots. It is suggested that the fracionation was caused by efflux of low specific activity phosphorus and by diffusion of free phosphate ions across the plasmalemma of the root cells in response to a difference in the concentration gradient between t

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1984.tb05173.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Seedlings of barley (Hordeum vulgareL. cvs Salka and Zita), buckwheat (Fagopyrum esculentumMoench) and rape (Brassica napusL. ssp.napuscv. Line) were raised at 8 or 10 different extenral P concentrations in the range 0–2000 μM. Apart from P, the nutrient solutions were complete. Phosphate influx in roots of different P status was determined by use of a nutrient solution containing 0.1 mM32P‐labelled phosphate. A double labelling technique was used for simultaneous determination of influx (33P) and efflux (32P) of phosphorus by roots of barley and rape with three selected P levels. Flux determinations were also done in presence of a metabolic uncoupler (2,4‐dinitrophenol) and a protein synthesis inhibitor (cycloheximide). Influx of phosphate was maximal at a certin optimal P level of the roots and decreased at both lower and higher P levels. Maximum phosphate influex [μmol (g root)‐−1h−1] were: rape 4,4, buckwheat 2.2, barley cv. Salka 1.6, barley cv. Zita 1.5. Both Hill plots and plots of the untransformed decreasing phosphate influx vs root P concentrations above the optimal were linear and had high correlation coefficients. The Hill coefficient varied between ‐3.1 and ‐4.2. The decrease of phosphate influx from the maximum to the lowest value at the highest P concentration of the root was 60–70%. Hence, phosphate influex appeared to be regulated through negative feedback by the internal level of phosphorous in the roots. The regulation mechanism seems bascially similar for the three species and may be of an allosteric type. P efflux from roots of low and optimal (with regard to P influx) P status was 15–20% of the simultaneous P influx. Contary to P influx, P efflux increased at high P status and almost eliminated (barley) or halved (rape) net P uptake. 2,4‐Dinitrophenol reduced both P influx and P efflux by low P roots and gave linearly increasing P efflux with increasing root P status. This indicates that P efflux partly occurred by counter transport and ion exchange at the uptake sites, partly by passive P efflux along an electrochemical potential gradient. Phosphate influx was not affected by inhibition of barley root growth with cycloheximide, but P efflux

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1984.tb05174.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY