摘要:

Germination of nondormant seeds ofManfreda brachystachya(Agavaceae) was analyzed at temperatures ranging from 11–35°C. Maximum germination (95%) occurred at 25°C. An exponential sigmoid relationship was found between time and cumulative germination. Germination rate for every subpopulation (10–90% germination) was estimated by means of a normal distribution analysis. The kurtosis indicated die amplitude of the range of temperatures where the highest germination rates were concentrated, and the skew indicated sharply inhibitory temperatures in the range of temperatures used. Based on analysis of the normal distribution models for each subpopulation, we calculated a theoretical function which described germination rate over the temperature range considered: F(T,χ) = A × exp[−B(C−1)2], where A is the function that describes germination rate for each subpopulation (characterized by the percentage [χ]at optimal temperature); B is a shape parameter, 1/(σG2); and C is the ratio between each germination temperature (T) and the optimal germination temperature. The Gaussian curves were used to calculate thermal time, and base and ceiling temperatures. Germination thermal time ranged from 1 333 to 2 373°C h, and base and ceiling temperatures were 10.44 ± 0.7°C and 39.54 ± 0.7°C, respectively. There was a linear relationship between thermal time and cumulative percentage of germination of the subpopulations. Based on fitted curves for each subpopulation, the use of a general model for all the subpopulations has been proven: F8 = A × exp[−5.9437(C−1)2], where changes in the curves for each subpopulation depen

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb05696.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Sugar beet cells grown in batch suspension culture have been used to study the regulation of polyamine levels during the transition from a quiescent to a proliferating state. The quiescent state was achieved by maintenance of the phytohormone autonomous cells in the stationary phase of the batch culture cycle. After subculture into fresh medium there was an increase in DNA synthesis which was accompanied by a dramatic increase in cellular polyamine levels. The levels of both free and bound cellular putrescine and spermidine within the cells reached a peak before the onset of the first synchronous division. The levels of putrescine, spermidine and to some extent spermine in the culture medium also increased dramatically shortly after subculture. The increase in polyamines was preceded by a rapid but transient increase in omithine decarboxylase (EC 4.1.1.17) andS‐adenosylmethionine decarboxylase (EC 4.1.1.50). Arginine decarboxylase (EC 4.1.1.19) andS‐adenosylmethionine synthetase (EC 2.5.1.6) activity did not show the same pattern of cell division‐related variation. Inhibition ofS‐adenosylmethionine biosynthesis with methylglyoxal bis‐(guanylhydra‐zone) (MGBG) reduced cell division in the suspension culture. Inhibitors of ornithine decarboxylase and arginine decarboxylase individually had little effect on cell division, but in combination led to a reduction in cell division. Addition of polyamines and their precursors to cells in the stationary phase of a batch culture cycle led to the induction of expression of a mitotic cyclin sequenc

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb05697.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The possible involvement of polyamines during strawberry (Fragaria×ananassaDuch.) fruit development was investigated. Putrescine, spermidine, and spermine were identified in strawberry receptacles and achenes at all stages of development. Total (free) polyamine levels decreased from a maximum of 485 nmol g−1fresh weight at pollination to a minimum of 55 nmol g−1fresh weight in ripe receptacles. Total polyamine concentrations during corresponding stages of development were consistently higher in achenes than in receptacles, and ranged from 891 to 203 nmol g−1fresh weight. Removal of achenes from the surface of developing receptacles 10 days after pollination reduced receptacle growth, and re‐initiation of growth by application of 1 mMα‐naphtaleneacetic acid (α‐NAA) was accompanied by a rapid increase in polyamine concentrations 24 h after treatment. Polyamine content per receptacle increased>3‐fold in normally developing receptacles and in de‐achened, auxin‐treated receptacles 10 days after removal of achenes, but did not increase during this period in de‐achened receptacles not treated with exogenous auxin. α‐NAA increased growth and polyamine levels to a greater extent than the structurally related, but less effective auxin, β‐NAA. Polyamine concentrations in receptacles with intact achenes remained similar to those of auxin depleted (de‐achened) receptacles, implying that the concentration of these compounds may not be lim

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb05698.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

A genuine 1‐SST (sucrose:sucrose 1‐fructosy] transferase, EC 2.4.1.99) was purified and characterized from young chicory roots (Cichorium intybusL. var.foliosumcv. Flash) by a combination of ammonium sulfate precipitation, concanavalin A affinity chromatography, anion and cation exchange chromatography. This protocol produced a 63‐fold purification and a specific activity of 4.75 U (mg protein)−1. The mass of the enzyme was 69 kDa as estimated by gel filtration. On SDS‐PAGE apparent molecular masses of 49 kDa (α‐subunit) and 24 kDa (β‐subunit) were found. Further specification was obtained by MALDI‐TOF MS detecting molecular ions at m/z 40109 and 19 896. These two fragments were also found on a western blot using an SDS‐boiled chicory root extract and chicken‐raised polyclonal antibodies against the purified 1‐SST, indicating that the enzyme is a heterodimer in vivo. The N‐terminus of chicory root 1‐SST α‐subunit was shown to be highly homologous with the cDNA‐derived amino acid sequences from barley 6‐SFT and a number of β‐fructosyl hydrolases (in‐vertases and fructan hydrolases). However, chicory root 1‐SST properties could be clearly differentiated from those of chicory root 1‐FFT (EC 2.4.1.100), chicory root acid invertase (EC 3.2.1.26) and yeast invertase. The enzyme mainly produced 1‐kes‐tose and glucose from physiologically relevant sucrose concentrations, indicating that this 1‐SST is the key enzyme initiating fructan biosynthesis in vivo. However, like chicory root 1‐FFT and barley 6‐SFT, the enzyme also showed some β‐fructofuranosi‐dase activity (fructosyl transfer to water) at very low sucrose concentrations. Although sucrose clearly is the best substrate for the enzyme, some transferase and β‐fructofuranosidase acti

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb05699.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abscisic acid (ABA) has been reported to have diverse effects on photoperiodic flowering. Activity of a natural ABA, (+)‐(S)‐abscisic acid (S‐ABA), was recently suggested to be somewhat different from that of racemic ABA, which has been used in previous work. Use of S‐ABA might enable clarification of the role of ABA in flowering. S‐ABA inhibited flowering of the short‐day plantPharbitis nil(cv. Violet) when given before or 4 h after the start of a 14‐h inductive dark period, and promoted flowering when given 12 h after the start of the dark period or later. The flower‐promoting effect was observed when ABA was applied to the shoot apex. These results indicate that ABA has a dual effect on photoperiodic flowering ofP. nil: it may inhibit the time‐measuring process as well as promote some processes that proceed after generation of the f

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb05700.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

To investigate the possible induction of Crassulacean acid metabolism (CAM) by drought inTalinum paniculatum([Jacq.] Gaertn.), a deciduous herb with succulent leaves and lignified stems, nocturnal acid accumulation and CO2‐exchange were studied in watered and droughted greenhouse‐grown plants. Watered plants had a typical C3 pattern of CO2‐exchange. When plants were subjected to drought, nocturnal acid accumulation increased significantly from 0.9 to 13.4 μmol H+cm−2after 21 days. Water deficit provoked a rapid reduction of daytime CO2assimilation of as much as 92% and a slower increase in night‐time fixation. A maximum of 24% of the diel carbon gain was contributed by dark fixation in droughted plants. After 34 days of drought, only CO2compensation and a small accumulation of acid (idling) was detected during the night. Relative recycling of respiratory CO2was approximately 100% for most of the water deficit treatment, the amount of CO2recycled showing a high positive correlation with nocturnal acid accumulation. A low rate of nocturnal loss of CO2in watered plants did not explain the amount recycled nightly in droughted plants, implying that respiration increased with drought. Leaf lamina area was reduced by 49% during drought due to rolling. Leaf biomass remained unchanged during the water‐deficit treatment. Neither apparent quantum yield nor light‐saturated photosynthetic rate differed significantly between control and 14‐day water‐stressed plants rewatered for 20 h. Chlorophyll content did not change with drought. These results confirm that CAM is induced by drought inT. paniculatum; the carbon acquired through this pathway only contributes to maintain, but not to increase, leaf biomass; also, CAM is responsible for a high recycling of respiratory CO2during the night. Recycling through CAM, plus the reduction of exposed leaf area during drought, may help explain the maintenance of chlorophyll, quantum yield and saturated photosynthetic rates in water‐stressed pla

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb05701.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

We have investigated the effect of aluminum (Al) on the activity of glucose‐6‐phosphate dehydrogenase (G6PDH; EC 1.1.1.49) and 6‐phosphogluconate dehydrogenase (6PGDH; EC 1.1.1.44) isolated from 5‐mm root apices of 4‐day‐old wheat (Triticum aestivum) cultivars differing in resistance to Al. Rapid increases in G6PDH and 6PGDH activities were observed in Al‐resistant cultivars (PT741 and Atlas 66) during the first 10 h of treatment with 100 μMAl, while no change in the activity of either enzyme was observed in Al‐sensitive cultivars (Katepwa and Neepawa) during a 24‐h exposure to Al. The Al‐induced increases in enzyme activities observed in the Al‐resistant PT741 appear to reflect an induction of protein synthesis since the increases were completely abolished by 1 mMcycloheximide. No differences in G6PDH and 6PGDH activities were observed between the Al‐sensitive and the Al‐resistant genotypes when Al was supplied in vitro. Under these conditions, an increase in Al concentration from 0 to 1.4 mMcaused a gradual decrease in activity of both enzymes, irrespective of the Al‐resistance of whole seedlings. Aluminum‐sensitive and aluminum‐resistant cultivars also differed in the rate and extent of accumulation of slowly‐exchanging Al in 5‐mm root apices. During the first 6 h of Al treatment, Al accumulation was only 10% more rapid in Katepwa than in PT741. After 24‐h exposure, accumulation in the Al‐sensitive Katepwa, was two‐fold higher. A decline in Al accumulation in a slowly‐exchanging compartment as well as a decrease in activities of G6PDH and 6PGDH were found in the Al‐resistant PT741, when seedlings were transferred to Al‐free treatment solutions after 16‐h exposure to 100 μMAl. These results suggest that rapid induction of G6PDH and 6PGDH in the Al‐resistant line PT741 by Al may play a role in the mechanism of Al resistance, po

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb05702.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Drought responses of diurnal gas exchange, malic acid accumulation and water status were examined inDelosperma tradescantioides, a succulent that grows in drought‐prone microenvironments in summer rainfall and all‐year rainfall regions of southern Africa. When well‐watered, this species exhibited Crassulacean acid metabolism (CAM)‐cycling, but its carbon fixation pattern changed during the development of drought, shifting to either low‐level CAM or to CAM‐idling. The rate and pattern of this change depended on environmental conditions, duration of water stress and leaf age. At the onset of drought, diurnal malate fluctuation increased, but was strongly depressed (by ca 70%) as drought continued, and when leaf water content and water potential were low (ca 35 and 50% of the initial levels, respectively). When rewatered, rates of growth and photosynthesis, gas exchange and water status recovered fully to pre‐stressed values within two days. Whole‐shoot carbon uptake rates suggested that leaf growth had continued unabated during a short‐term (≅ one week) drought. This emphasises that CAM‐idling allows the maintenance of active metabolism with negligible gas exchange when soil water is limiting. It is possible that old or senescent leaves may provide water for the expansion of developing leaves during initial periods of drought. Regardless of the water regime and environmental conditions, leaf nocturnal malate accumulation and water content were positively correlated and increased with leaf age. Thus the gradual loss of water from older mature leaves may induce CAM‐idling, which reduces water loss. An important ecological consequence of this combination of CAM modes is the potential to switch rapidly between fast growth via C3gas exchanges when well‐watered to water‐conservin

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb05703.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

We have investigated the water use efficiency of whole plants and selected leaves and allocation patterns of three wheat cultivars (Mexipak, Nesser and Katya) to explore how variation in these traits can contribute to the ability to grow in dry environments. The cultivars exhibited considerable differences in biomass allocation and water use efficiency. Cultivars with higher growth rates of roots and higher proportions of biomass in roots (Nesser and Katya) also had higher leaf growth rates, higher proportions of their biomass as leaves and higher leaf area ratios. These same cultivars had lower rates of transpiration per unit leaf area or unit root weight and higher biomass production per unit water use. They also had higher ratios of photosynthesis to transpiration, and lower ratios of intercellular to external CO2partial pressure. The latter resulted from large differences in stomatal conductance associated with relatively small differences in rates of photosynthesis. There was little variation between cultivars in response to drought, and differences in allocation pattern and plant water use efficiency between cultivars as found under well‐watered conditions persisted under dry conditions. At the end of the non‐watered treatment, relative growth rates and transpiration rates decreased to similar values for all cultivars. High ratios of photosynthesis to transpiration, and accordingly high biomass production per unit of transpiration, is regarded as a favourable trait for dry environments, since more efficient use of water postpones the decrease in plant water sta

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb05704.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Cultured tobacco cells (Nicotiana tabacumL. cv. Wisconsin 38) adapted to NaCl exhibited significant morphological and physiological changes. Adapted cells remained smaller and more isodiametric at maturity than unadapted cells. The vacuole increased in size relative to the cytoplasm and an extensive network of transvacuolar membrane strands developed. These changes altered the surface contact area between the cytoplasm and the vacuole substantially. In addition, the network of Hechtian strands that anchor the cortical structure to the cell wall became more extensively branched possibly facilitating surface contact of the cytoplasm to the extracellular matrix. Many changes in membrane proteins could also be identified after NaCl adaptation. In particular, a 50‐kDa protein that is associated with the plasma membrane and tonoplast was induced during adaptation. Immunocytochemical localization indicated that this 50‐kDa protein is associated with Golgi vesicles. By immunoscreening using anti‐50‐kDa antibody, a 1.71‐kb cDNA clone (p50C) was isolated from a λ‐ZAP cDNA expression library. The sequence of p50C did not show any significant identity with other genes. Because of the very low abundance of the p50C message, quantitative reverse transcription‐polymerase chain reaction (RT‐PCR) was used to analyze p50C gene expression. Immunoblot and quantitative RT‐PCR analyses indicated that the expression of this gene is regulated developmentally since the mRNA and protein increased with age in salt‐adapted cells but decreased with age in unadapted cells. Also in tobacco plants, p50C mRNA was more abundant in younger leaves than in older leaves. The gene was responsive to NaCl in tobacco cells and to ABA

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb05705.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY