摘要:

ABSTRACTAt any given time, a vascular or land plant may be a colony of functional sectors, each consisting of a shoot and its associated roots. In most plants, however, the activity of the cambium can change the relative vascular contacts of neighbouring shoots. Vascular tissues can even differentiate along new orientations, forming contacts that change the sectorial structure of the plant. Such reoriented differentiation is induced by the same auxin from developing leaves as are other types of vascular differentiation. The occurrence of vascular reorientation is determined by two criteria: the presence of an auxin flow that exceeds the transport capacity of the tissues that follow the previous, established orientation and the availability of nearby channels that are not fully occupied, not‘protected’ by their own flow of auxin. These controls of vascular orientation suggest that neighbouring shoots (and neighbouring roots) compete with one another, by means of signals indicating their state and their environment, for vascular contacts with the rest of the plant. Such internal competition between genetically equivalent shoots is an adaptation to heterogeneous environments: it is the shoots in the best conditions available to the plant that receive the support of a greater part of the root system. The potential for changes of vascular contacts points to open problems and to neglected aspects of the role of the cambium in plant organizat

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00498.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTThe experiments and simulations reported in this paper show that, for stomata sensitive to both CO2and water vapour concentrations, responses of stomatal conductance (gws) to boundary layer thickness have two components, one resulting from changes in intercellular CO2concentration (χci) and another from changes in leaf surface water vapour saturation deficit (Dws). The experiments and simulations also show that the boundary layer conductance (gwb) can significantly alter the apparent response ofgwsto ambient air CO2mole fraction (χca) and water vapour mole fraction (χwa). Because of the feedback loop involved the responses ofgwsfor χcaand χwaeach include responses to both χciandDws. The boundary layer alters the state of the variables sensed by the guard cells—i.e. χciandDws—and so it is a source of feedback. Thus, when scaling up from responses of stomata to the response ofgwsfor a whole leaf, the effect of the boundary layer must be considered. The results indicate that, for given responses ofgwsto χciandDws, the apparent responses ofgwstoDwaand χcadepend on the size of the leaf and wind speed, showing that this effect of the boundary layer should be considered when comparing data measured under different conditions, or with diffe

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00499.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTThe effects of extreme phosphate (Pi) deficiency during growth on the contents of adenylates and pyridine nucleotides and thein vivophotochemical activity of photosystem II (PSII) were determined in leaves ofHelianthus annuusandZea maysgrown under controlled environmental conditions. Phosphate deficiency decreased the amounts of ATP and ADP per unit leaf area and the adenylate energy charge of leaves. The amounts of oxidized pyridine nucleotides per unit leaf area decreased with Pi deficiency, but not those of reduced pyridine nucleotides. This resulted in an increase in the ratio of reduced to oxidized pyridine nucleotides in Pi‐deficient leaves. Analysis of chlorophyllafluorescence at room temperature showed that Pi deficiency decreased the efficiency of excitation capture by open PSII reaction centres (φe), thein vivoquantum yield of PSII photochemistry (φPSII) and the photochemical quenching co‐efficient (qP), and increased the non‐photochemical quenching co‐efficient (qN) indicating possible photoinhibitory damage to PSII. Supplying Pi to Pi‐deficient sunflower leaves reversed the long‐term effects of Pi‐deficiency on PSII photochemistry. Feeding Pi‐sufficient sunflower leaves with mannose or FCCP rapidly produced effects on chlorophyll a fluorescence similar to long‐term Pi‐deficiency. Our results suggest a direct role of Pi and photophosphorylation on PSII photochemistry in both long‐and short‐term responses of photosynthetic machinery to Pi deficiency. The relationship between φPSIIand the apparent quantum yield of CO2assimilation determined at varying light intensity and 21 kPa O2and 35 Pa CO2partial pressures in the ambient air was linear in Pi‐sufficient and Pi‐deficient leaves of sunflower and maize. Calculations show that there was relatively more PSII activity per mole of CO2assimilated by the Pi‐deficient leaves. This indicates that in these leaves a greater proportion of photosynthetic electrons transported across PSII was used for processes other than CO2reduction. Therefore, we conclude thatin vivophotosynthetic electron transport through PSII did not limit photosynthesis in Pi‐deficient leaves of sunflower and maize and that the decreased CO2assimilation was a consequence of a smaller ATP content and lower energy charge which restricted production of ribulose, 1‐5

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00500.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTResponses of photosynthesis and stomatal conductance were monitored throughout a 3‐year field exposure ofLiriodendron tulipifera(yellow‐poplar) andQuercus alba(white oak) to elevated concentrations of atmospheric CO2. Exposure to atmospheres enriched with +150 and +300 umol mol‐1CO2increased net photosynthesis by 12–144% over the course of the study. Net photosynthesis was consistently higher at +300 than at +150 umol mol‐1CO2. The effect of CO2enrichment on stomatal conductance was limited, but instantaneous leaf‐level water use efficiency increased significantly. No decrease in the responsiveness of photosynthesis to CO2enrichment over time was detected, and the responses were consistent throughout the canopy and across successive growth flushes and seasons. The relationships between internal CO2concentration and photosynthesis (e.g. photosynthetic capacity and carboxylation efficiency) were not altered by growth at elevated concentrations of CO2. No alteration in the timing of leaf senescence or abscission was detected, suggesting that the seasonal duration of effective gas‐exchange was unaffected by CO2treatment. These results are consistent with data previously reported for these species in controlled‐environment studies, and suggest that leaf‐level photosynthesis does not down‐regulate in these species as a result of acclimation to CO2enrichment in the field. This sustained enhancement of photosynthesis provides the opportunity for increased growth and carbon storage by trees as the atmospheric concentration of CO2rises, but many additional factors interact in determining whole‐plant and forest respo

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00501.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTTissue‐specific effects of low growth temperature on maize chloroplast thylakoid protein accumulation were analysed using immunocytology. Sections of leaves from plants grown at 25 and 14°C were probed with antibodies to specific chloroplast thylakoid proteins from the four major protein multisubunit complexes of the thylakoid membrane followed by fluorescein‐conjugated goat anti‐rabbit antibodies. At a normal growth temperature of 25°C, the 32 kDa D1 protein of the photosystem II reaction centre and the 33 kDa protein of the extrinsic oxygen‐evolving complex of photosystem II are both accumulated to a greater degree in the mesophyll than in the bundle sheath chloroplasts. In contrast, subunit II of photosystem I, cytochromefand the α‐ and β‐subunits of ATP synthetase are predominant in the bundle sheath thylakoids at 25°C. A striking difference between the 25°C‐grown and the 14°C‐grown leaf tissue was the presence in the latter of (20–30%) cells whose chloroplasts apparently completely lack several of the thylakoid proteins. In plants grown at 14°C, the accumulation of the 33 kDa protein of the extrinsic oxygen‐evolving complex of photosystem II was apparently unchanged, but other thylakoid proteins showed a significant reduction. The uneven distribution of proteins between the bundle sheath and mesophyll chloroplasts observed at 25°C was also maintained at 14°C. Reduction in the fluorescence at 14°C was manifested either as an overall reduction in the diffuse fluorescence across the chloroplast profiles or less frequently as a reduction to small discrete bodies of intense fluorescence. The significance of these results to low‐temperature‐induced reduction in the photosynthetic

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00502.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTPotato plants (Solanum tuberosumL. cv‘Norland’) were subjected to acute and chronic exposures of ozone (O3). Periodically following or during the exposures, foliage of different physiological ages were sampled for tissue analysis. Measurement of the following parameters were included: ethylene, 1‐aminocyclopropane‐1‐carboxylic acid (ACC), N‐malonyl 1‐aminocyclopropane‐1‐carboxylic acid (MACC), and ACC oxidase activity, putrescine, spermidine, and spermine levels, and ornithine decarboxylase (ODC) activity, and levels of mRNA transcripts for the large and small subunits of ribulose 1,5‐bisphosphate carboxylase/oxygenase (Rubisco) (rbcL andrbcS, respectively). Ozone increased emission of ethylene and the concentration and activity of all associated metabolites and enzymes. Putrescine titre increased in response to O3as did ODC activity. Some increases in spermidine were also detected. Ozone decreased the levels of mRNA forrbcL andrbcS, with the latter transcript exhibiting greater sensitivity. After acute exposures were terminated, therbcL andrbcS transcript in younger leaves returned to levels of nonstressed plants; effects were less likely to be reversed in older tissue. The potential relationship between the changes inrbcL andrbcS and ethylene and polyamines are discussed in the context of O3induction of acc

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00503.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTResponses of individual roots of the widely cultivated cactusOpuntia ficus‐indicato salinity stress were evaluated using a split‐root system. Three roots from a plant with at least 20 roots were isolated from the remainder of the root system and exposed to 0, 30 or 100 mol m‐3NaCl for up to 28 d. Cortical cells became shorter and lateral root development was substantially reduced as salinity increased. Compared with the control, the increase in dry weight for the isolated roots was reduced 40% by 30 mol m‐3NaCl and 93% by 100mol m‐3NaCl. The sodium content of roots increased only two‐fold with increasing salinity. Respiration rates of roots exposed to 30 or 100 mol m‐3NaCl were higher than those of the control. Carbon accumulation in roots measured 2 d after exposing shoots to14CO2was not initially affected by 30 mol m‐3NaCl but was substantially reduced at 100 mol m‐3NaCl. Thus, roots exposed to short periods of moderate salinity stress maintained sufficient carbon sink strength for continued growth of the roots. Moreover, increased salinity led to decreased efficiency of carbon usage for the expansion of

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00504.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTLimitations in carbohydrate supplies have been implicated as a factor responsible for reproductive failure under heat stress. Heat stress affects two stages of reproductive development in cowpea [Vigna unguiculata(L.) Walp.], and genotypes are available with tolerance and sensitivity to heat during these different stages. The objectives of this study were to determine the responses of these cowpea lines to ambient and elevated [CO2], under heat stress and optimal temperature, and test whether differences in carbohydrate supplies due to genotypes, CO2enrichment and heat stress are associated with differences in sensitivity to heat during reproductive development. Plants were grown in reach‐in growth chambers and subjected to day/night temperatures of either 33/20 or 33/30°C, and [CO2] levels of either 350 or 700 μmol mol‐1. Under intermediate night temperature (33/20°C), all lines set substantial numbers of pods. Under high night temperature (33/30°C) with either ambient or elevated [CO2], one heat‐sensitive line produced no flowers and the other set no pods, whereas the heat‐tolerant line abundantly set pods. High night temperature reduced the overall carbohydrate content of the plants, especially peduncle sugars, and caused decreases in photosynthetic rates. The high pod set of the heat‐tolerant line, under high night temperature, was associated with higher levels of sugars in peduncles compared with the heat‐sensitive lines. The heat‐tolerant line accumulated substantial shoot biomass, exhibited less accumulation of starch in leaves, and possibly had less down‐regulation of photosynthesis in response to CO2enrichment and heat stress than the heat‐sensitive lines. Elevated [CO2] resulted in higher overall carbohydrate levels in heat‐sensitive lines (starch in leaves, stems and peduncles), but it did not increase their heat tolerance with respect to flower production or pod set. Heat‐induced damage to floral buds and anthers in the sensitive lines was associated with low sugars levels in peduncles, indicating that heat had greater effects on assimilate demand than on leaf assimilate supply. The heat‐tolerant line was the most responsive genotype to elevated [CO2] with respect to pod production under either high o

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00505.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTA tallgrass prairie ecosystem was exposed to ambient and twice‐ambient CO2concentrations in open‐top chambers and compared to unchambered ambient CO2during the entire growing season from 1989 through 1991. Dominant species wereAndropogon gerardii(C4),A. scoparius(C4),Sorghastrum nutans(C4) andPoa pratensis(C3). Nitrogen and phosphorus concentrations inA. gerardii, P. pratensisand dicotyledonous herbs above ground biomass were estimated by periodic sampling throughout the growing season in 1989 and 1990. In 1991, N and P concentrations in peak biomass were estimated by an early August harvest. N and P concentrations in root production as a function of treatment were estimated using root ingrowth bags that remained in place throughout the growing season. Total N and P in above‐ and belowground biomass were calculated as products of concentration and peak biomass by species groups. N concentration inA. gerardiiand dicotyledonous herb aboveground biomass was lower and total N higher in elevated CO2plots than in ambient CO2plots. N concentration inP. pratensisaboveground biomass was lower in elevated CO2plots than in ambient, but total N did not differ among treatments in 2 out of 3 years. In 1990, N concentration in root ingrowth bag biomass was lower and total N greater in elevated CO2than in ambient CO2plots. Root ingrowth bag biomass N concentration did not differ among treatments in 1991, but total N was greater in elevated CO2plots than in ambient CO2plots. P concentration was lower under elevated CO2compared to ambient in 1989, but did not differ substantially among treatments in 1990 or 1991. In all years, total P in abovegroundA. gerardiiand root ingrowth bag biomass was greater under elevated CO2than ambient. P concentration and total P inP. pratensiswas similar among treat

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00506.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTSensitivity to light quality and pigment composition were analysed and compared in abaxial and adaxial stomata ofGossypium barbadenseL. (Pima cotton). In most plants, abaxial (lower) stomatal conductances are higher than adaxial (upper) ones, and stomatal opening is more sensitive to blue light than to red. In greenhouse‐grown Pima cotton, abaxial stomatal conductances were two to three times higher than adaxial ones. In contrast, adaxial stomatal conductances were 1·5 to two times higher than abaxial ones in leaves from growth chamber‐grown plants. To establish whether light quality was a factor in the regulation of the relationship between abaxial and adaxial stomatal conductances, growth‐chamber‐grown plants were exposed to solar radiation outdoors and to increased red light in the growth chamber. In both cases, the ratios of adaxial to abaxial stomatal conductance reverted to those typical of greenhouse plants. We investigated the hypothesis that adaxial stomata are more sensitive to blue light and abaxial stomata are more sensitive to red light. Measurements of stomatal apertures in mechanically isolated epidermal peels from growth chamber and greenhouse plants showed that adaxial stomata opened more under blue light than under red light, while abaxial stomata had the opposite response. Using HPLC, we quantified the chlorophylls and carotenoids extracted from isolated adaxial and abaxial guard cells. All pigments analysed were more abundant in the adaxial than in the abaxial guard cells. Antheraxanthin and β‐carotene contents were 2·3 times higher in adaxial than in abaxial guard cells, comparing with ad/ab ratios of 1·5–1·9 for the other pigments. We conclude that adaxial and abaxial stomata from Pima cotton have a differential sensitivity to light quality and their distinct responses are correlated with different

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1993.tb00507.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY