摘要:

Abstract.This article continues the discussion on sensitivity prompted by the publication of an earlier paper by the author in 1981. It is indicated that appropriate measurements of sensitivity can help uncover the function of growth substances in development. The experimental constraints which are necessary for unambiguous measurements of sensitivity are outlined and it is shown that a specific sensitivity measurement, termed control strength, would most readily clarify function and help obviate controversy. Methods for measuring control strength which deal with the problem of compartmentalization are considered and it is suggested that stochastic variation in single cell biochemistry might provide a constraint on the accuracy of control strength determinations.

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01366.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Apart from its impact on global warming, the annually increasing atmospheric [CO2] is of interest to plant scientists primarily because of its direct influence on photosynthesis and photorespiration in C3species. But in addition, ‘dark’ respiration, another major component of the carbon budget of higher plants, may be affected by a change in [CO2] independent of an increase in temperature. Literature pertaining to an impact of [CO2] on respiration rate is reviewed. With an increase in [CO2], respiration rate is increased in some cases, but decreased in others. The effects of [CO2] on respiration rate may be direct or indirect. Mechanisms responsible for various observations are proposed. Theseproposedmechanisms relate to changes in: (1) levels of nonstructural carbohydrates, (2) growth rate and structural phytomass accumulation, (3) composition of phytomass, (4) direct chemical interactions between CO2and respiratory enzymes, (5) direct chemical interactions between CO2and other cellular components, (6) dark CO2fixation rate, and (7) ethylene biosynthesis rate. Because a range‐of (possibly interactive) effects exist, and present knowledge is limited, the impact of future [CO2] on respiration rate cannot be predicted. Theoretical considerations and types of experiments that can lead to an increase in the understanding of this issue are out

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01367.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.The effects of a change in the distribution of nitrate within the root zone on N uptake and growth were studied using young lettuce plants after reducing the proportion of their root systems supplied with nitrate from 100 to ca 10% in split‐root experiments in the glasshouse. The main effects of the localized nitrate supply were concentrated in a 2‐week period immediately after the treatment was imposed, when a temporary reduction in nitrate uptake caused the gradual development of N deficiency and a decline in plant growth rate. The plants adapted to the change in nitrate distribution, initially by increasing unit absorption rates (uptake rates per unit weight of root) and more gradually by increasing production of new roots in the high‐nitrate zone. As a result, relative N uptake rates and relative growth rates were restored to the same levels as for control plants (given a spatially uniform N supply throughout) after ca 12d, even though only ca 12–15% of their roots were exposed to nitrate at this time. Thereafter, the plants continued to adapt by concentrating new root growth in the nitrate‐containing zone, ultimately allowing unit absorption rates to return to normal. There was no evidence of any significant N deficiency in the plants after the initial adaptive response was complete, even though the total‐N concentrations of the plants given the localized supply were consistently less than those given the uniform N treatment, and nitrate concentrations in the petiole sap were generally lower in leaves on one side of the plant (because of limited lateral movement of nitrate between xylem vessels during its transport to the shoot).The delay in the initiation of an adaptive response caused a significant check in growth, and the resulting relative weight differences were maintained throughout the subsequent life of the plant. Plants in all treatments matured on the same date, so yields for those grown with the localized supply were less than those of the control, and could not be recovered by delaying final harvest without unacceptable loss of quality. The pattern of the changes in N uptake and plant growth, and the effect on final yield, were similar to those exhibited by young lettuce plants subjected to a temporary interruption in nitrate supply, suggesting that the reduction in final yield for plants grown with the localized supply was largely the effect of the check in growth which occurred whilst the Plants were adapting to the change in nitrate distribution during the early part of the experiment. This implies that the rate of dry matter production of young lettuce plants can be altered by N treatment without affecting their rate of physiological

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01368.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Red spruce (Picea rubensSarg.) seedlings were overwintered in two controlled environment chambers designed to simulate sub‐zero winter conditions. One of the chambers was fumigated throughout the 5‐month period with low concentrations of SO2+ NO2. Extracts of extracellular fluid from trees in this treatment revealed accumulations of sulphite and nitrite, but not of sulphate or nitrate. Analysis of the chloroplast membrane lipid monogalactosyl diglyceride (MGDG) indicated a large increase in fatty acid saturation in both treatments during mid‐winter, with a subsequent recovery to earlier levels. Although at the end of the experiment the MGDG of polluted trees contained significantly less linolenic acid, there was no overall treatment effect on fatty, acid content. In the following spring, there was some indication that flushing of leader buds began earlier and proceeded at a slower rate in polluted trees compared to controls, but no other growth parameters were affected by the winter treatment. The absorption of SO2and NO2and the accumulation of their products during dormancy is discussed as a potential mechanism for metabolic disruption, resulting in changes to seasonal responses which could be critical to the survival of the

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01369.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.Changes in gene expression induced by salinity were investigated in a suspension culture of the tropical, graminaceous plant sugarcane (Sacchammspp.). Three cell lines tolerant to 5, 10 and 15kg m−3NaCl were adapted and the expression of newly synthesized proteins and translatable mRNAs in these cell lines were compared with those in unadapted cells on high‐resolution, two‐dimensional gels. Specific proteins and mRNAs altered by salinity were identified. At the protein level, the expression of 15 proteins was induced or enhanced, and that of three others was repressed or abolished. At the translatable mRNA level, the expression of 18 mRNAs was induced or enhanced, and that of eight others was repressed or abolished. The expression of some of these was also regulated, depending on the salt‐adapted cell line. The above changes were characteristic of salt‐adapted cells and were not found in unadapted cells undergoing a short‐term salt stress. Overall, 29 sugarcane proteins were regulated by salinity: for 15, translatable mRNAs were found; for three, no translatable mRNA was detected; and for six of the remaining 11,in vivoequivalents were not observed. These data suggest that a multitude of mechanisms at the transcriptional, post‐transcriptional and post‐translational levels may contribute to the control of gene expression in the sail‐adapte

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01370.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.We investigated the effects of photon fluence rate on internode elongation in fully de‐etiolated plants growing under sunlight. Our goal was to find out whether perception by the stems of fluence rate changes related to canopy density may be involved in the modulation of internode growth in canopies formed by plants of similar stature (e.g. crop stands). UsingDatura feroxL. andSinapis albaL. seedlings growing under natural radiation, we found that internode elongation is promoted by localized shading. This effect was observed with internodes receiving light with a high (>0.9) or a low (0.3) red (R) to far‐red (FR) photon ratio. Selective removal of the different wavebands from the light impinging on the internodes showed that part of the response to fluence rate is due to photons in the R + FR range. The blue (B) component, most likely acting through a specific photoreceptor, also inhibited elongation. However, changes in the fluence rate of B light did not have detectable effects on the response of the internodes to R:FR ratio. Fibre‐optic studies and measurements with integrating‐cylinder sensors in even‐aged populations of seedlings showed that both the quality and quantity of radiation received by the stems are profoundly influenced by changes in canopy density. When density is very low (leaf area index = LAI ≥ 1) only the R:FR ratio is reduced, due to FR reflected from nearby leaves. In the LAI range of 1 to 2, though a large proportion of the leaf area is still receiving full sunlight, the photon fluence rate at the stem level drops dramatically. These results suggest that in even‐aged populations of LAI>1 elongation growth is promoted by the low R:FR ratioandthe reduced fluence rate. Perception of these two factors at the stem level may elicit morphological adaptations in the canopy before the onset of severe competition among neighbours for the reso

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01371.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.The levels of particular mRNAs in tomato leaves are altered in response to water stress. Certain transcripts appear as a consequence of the stress whereas others diminish in abundance. These changes were analysed by cell‐free translation of leaf RNA followed by two‐dimensional polyacrylamide gel electrophoresis of the translation products. Within 20 min of the onset of reduced leaf water potential in detached leaflets, stress‐induced mRNAs appear in the transcript population. Other mRNAs accumulate more slowly and include among theirin vitrotranslation products a prominently labelled group of polypeptides of about 18–19 kD. These transcripts are recovered from detached leaflets incubated for 2 and 8h at low water potential and from leaflets of intact plants that were stressedin situfor 10d. An additional water stress‐induced mRNA that encodes a 64‐kD polypeptide is detected in the transcript population from detached leaflets when [3H]glycine is used in place of [35S]methionine in the cell‐free translations. Among the transcripts that decline in abundance as a consequence of water stress is an mRNA that encodes the small subunit of ribulose‐1,5‐bisphosphate carboxylase. Within 2h of rewatering stressed plants, certain mRNAs that were lost from the population return and those in the 18–19 kD range that are associated with the stress

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01372.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.An accepted view, that unless nitrate concentrations in the soil solution are very low (e.g. below 0.1–0.2 mol m−3) the growth of high‐yielding crops is not limited by the availability of nitrogen, is challenged. Conventional analyses of nutrient supply and demand, based on calculations of apparent inflow rates (uptake rates per unit total root length) are invalid. Apparent inflow rates are inversely proportional to root length. The convention of using total root length grossly overestimates the fraction of the root system active in nutrient uptake. Consequently, inflow rates based on total root lengths underestimate the true values, indicating unrealistically low nutrient concentration differentials between bulk soil and root surfaces required to drive uptake. An alternative method of analysis is suggested. This is based on total nutrient uptake rather than on inflow rate. Measurements of the former do not depend on estimates of active root length and can be made directly and reliably. The method was applied to data obtained from a pot experiment using spring wheat (Triticum aestivumL., cv. Wembley) grown in soil without nitrogen fertilizer (N0) or with nitrogen fertilizer equivalent to 200kg N ha−1(N+). Soil nitrate concentrations calculated using the conventional method based on total root length, suggested that any increases in concentration above those measured in the N0treatment should not have resulted in increased uptake and growth. However, the N+plants were always bigger than those in the No treatment, refuting this suggestion. Theoretical uptakes of nitrogen (calculated initially on the basis of a fully active root system) were adjusted, by reducing the effective root length incrementally, until the theoretical uptake matched the measured net uptake of nitrogen. The mean fractions of the root systems likely to have been involved in nitrate uptake were 11% and 3.5% of the total lengths of root in the N0and N+treatments, respe

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01373.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.The water sorption by cuticular membranes (CM) isolated from both leaves and fruit and representing different structural and chemical cuticular types, was measured over the whole range of relative humidities using a magnetic suspension microbalance. The sorption isotherms were generally not linear and sorption increased more rapidly at the highest values of relative humidity. The highest values of water content, at 80–99% r.h., measured for the seven species ranged from 1.1 to 7.7% of the dehydrated weight. Extraction of the soluble cuticular lipids did not result in a decrease of sorption, but only in a lower interspecific dispersion. There was a drastic reduction (63%) in water sorption when polymer matrix membranes (MX) were partially acid‐hydrolysed; but methylation or charging with iron of (MX) did not have any significant effect on water sorption. The data obtained are discussed in relation to cuticular permeability. Two determinants of water permeability were determined: the partition coefficient (K) relating the equilibrium Water concentration of the cuticle to that of the surrounding atmosphere; and the diffusion coefficient (D), calculated from the half‐times of the sorption process in kinetic measure

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01374.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract.The activities of five active‐oxygen scavenging enzymes were compared for cold‐lability and three were compared for chilling induction in twoZeagenotypes of contrasting susceptibility to photoinhibition during chilling. Activities of superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11), monodehydroascorbate reductase (MDHAR, EC 1.6.5.4), dehydroascorbate reductase (DHAR, EC 1.8.5.1), and glutathione reductase (GTR, EC 1.6.4.2) in leaf extracts from plants grown without chilling stress were assayed at 19°C and 5°C. Enzymes from the chilling‐susceptibleZ. Mayscv. LG11 had lower specific activities at 5°C than did enzymes from the chilling‐tolerantZ. diploperennis, except for MDHAR where no significant differences were observed. The activities of SOD and APX fromZ. diploperenniswere double those ofZ. maysat both assay temperatures. Monodehydroa‐scrobate reductase and glutathione reductase activities in both species were reduced by 63–78% at a 5°C assay temperature. The dehydroascorbate reductase (DHAR) showed the greatest low‐temperature lability losing 96% (Z. diploperennis) and 100% (Z. mays) of its activity at 5°C. To examine possible chilling‐induced changes in levels of enzyme activity, plants of bothZeagenotypes were transferred to growth chambers at 10°C at moderate light intensities. Glutathione reductase activity was found to increase within 24h inZ. diploperennis, but it decreased slightly inZ. mays.MDHAR activity decreased by 50% inZ. diploperennisbut showed only a transient increase

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1991.tb01375.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY