摘要:

AbstractAccumulation of nitrogen (N) by plants in response to N supply outstripping demand is contrasted with storage of N, which implies that N in one tissue can be reused for the growth or maintenance of another. Storage can, therefore, occur in N‐deficient plants; accumulation can not. The consequence of accumulation and storage of N is considered, particularly in relation to the reproductive growth of annual plants, which can often use a great deal of stored N. Nitrate and proteins are the forms of N most often stored in vegetative tissues and, quantitatively, ribulose 1,5‐bisphosphate carboxylase/oxygenase is often the most important protein store. While storing nitrate will be less costly to the plant in terms of energy, protein stores offer several possible advantages. These advantages are (i) maximizing the potential for carbon assimilation, (ii) avoiding problems with the regulation of leaf turgor and (iii) allowing the reduction on nitrate to occur in the young, fully illuminated l

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01769.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractDepending on the applied concentration, nitrate can either stimulate or inhibit germination of dormant seeds ofSinapis arvensisL. (wild mustard). Seed NO−3levels that corresponded to the maximal germination frequencies recorded, ranged from 0.3 to 4.4 nmol seed−1for applied NO−3concentrations between 2.5 and 20 mol m−3. Germination was significantly lower in seeds containing more than 5 nmol NO−3. Although the presence of NO−3within the seed was required to promote germination, seed NO−3levels were 5 to 15 times less than levels calculated from the volume of solution taken up by the seeds. Seed NO−3levels also responded in a passive fashion to the external NO3−concentration when the seeds were incubated on filter paper or in soil. In a representative soil containing 26 mg NO−3‐N per kg dry weight and 8 to 16% water by weight, the amount of NO−3taken up by the seeds reached inhibitory levels. Our results suggest that levels of inorganic nitrogen (NO−3, NH+4) in managed soils may play an important role in regulating germination o

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01770.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractSeedlings ofPinus radiata, 10–20 weeks old and hitherto fully watered, responded rapidly when water was withheld. Wilting occurred 9d later, at which time soil matric water potential at dawn (Ψm) was –1.06MPa and shoot water potential (Ψ) was –1.9 MPa. Small reductions in Ψmelicited large responses in assimilation rate (A) and leaf conductance to water vapour (g). Seedlings appear to be more sensitive to small water deficits than are older Plants ofP. radiata.After rewatering, significant increases ofAandgoccurred within one day, but neither regained the values measured prior to the imposition of a single drying cycle. This residual effect of drought onA, after one or six drying cycles, was partially caused by a decrease in photosynthetic capacity.In plants wilted for the first time, the concentration of abscisic acid (ABA) in the bulk foliage increased 3.4 times as Ψ decreased to –1.77 MPa. In comparison, pretreatment with six drying cycles significantly reduced Ψ to –2.13 MPa (indicating some osmotic adjustment) and induced only a doubling of ABA concentration. However, these differences in Ψ and ABA concentration did not Persist after the plants of all pretreatments had been watered for 7 d, althoughgof drought‐pretreatment Plants remained approximately half that of continuous

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01771.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractGrowing roots ofNicotiana tabacumvar.Havanagenerate transcellular ion currents which traverse developing and wounded tissues. Positive current of around 10 mA m−2enters meristematic and elongating cells at the tip of primary roots. The growing tips of first order laterals are also traversed by a similar positive current with a density of around 2.0 mA m−2, as are immature laterals emerging at the primary root surface. These self‐generated ion currents flow basipetally through developing tissues and leave from mature non‐elongating tissue. A large positive current of around 70 mA m−2also enters induced wound sites on the primary root surface. Motile zoospores of the fungal pathogenPhytophthora parasiticavar.nicotianaehave been reported to associate preferentially with these regions of the root. This might suggest that electrotaxis may be part of the mechanism by which zoospores locate root regions susceptable to fungal

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01772.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractThe aquatic vascular plantNelumbo nuciferaGaertn. is able to improve its oxygen supply to the submerged and buried organs by a thermo‐osmotic gas transport. Investigations with tracer gas and oxygen measurements have shown that thermo‐osmotic gas transport exists inN. nuciferawhen there is a temperature difference between the lacunar air of the leaves and the surrounding atmosphere. The gas transport was increased by up to 935% when a temperature difference of 2.9 ± 1.0 K was detected. Lacunar pressure of up to 166 ± 44 Pa was measured in both young and old leaves. In contrast to the flow‐through ventilation system recently described forNuphar luteaandNymphoides peltata, a two‐way flow in separate air canals in the petioles of both young and oldNelumboleaves may carry oxygen‐rich air down to the rhizome and excess air back to the atmosphere. Anatomical investigations have shown that, inNelumbo, the two largest air canals of the petiole end directly under the mesh system of the centre plate. These large air canals are proposed to be predominant in the upward flow of air in sunlight. The other air canals of the petiole veer into the leaf blade well below the centre plate. The gas flow system through fresh leaves may carry as much as 10.3 ± 4.5 cm3air per minute to the bu

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01773.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractHydraulic conductivity of the xylem is computed as the quotient of mass flow rate and pressure gradient. Measurements on excised plant stems can be difficult to interpret because of time‐dependent reductions in flow rate, and because of variable degrees of embolism. UsingAcer saccharumMarsh. stems, we found that certain perfusing solutions including dilute fixatives (e.g. 0.05% formaldehyde) and acids with pH below 3 (e.g. 10 mol m−3oxalic) prevent long‐term decline in conductivity. Xylem embolism can be quantified by expressing the initial conductivity as a percentage of the maximum obtained after flow‐impeding air emboli have been removed by repeated high‐pressure (175 kPa) flushes. Correlation between microbial contamination and declining conductivity suggests that long‐term (>4h) declines are caused by microbial growth within the vessels. Unpredictable trends in short‐term (<4h) measurements may be caused by movements of air emboli in vessels and/or parti

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01774.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractFreeze‐thaw damage to thylakoids in spinach leaves has been simulatedin vitro, using a complex, defined artificial stroma medium. The resulting mechanical damage was quantified by measuring the loss of the marker protein plastocyanin from the thylakoid lumen, which is released as a result of membrane rupture. Loss of plastocyanin was already apparent at 0°C and became more severe at subzero temperatures. The time course of plastocyanin loss during freezing was biphasic: after an initial rapid loss, plastocyanin release was linearly dependent on incubation time. In short‐term experiments a linear dependence on freezing temperature was observed. Solute diffusion into the thylakoids, leading to influx of water and eventually membrane rupture, has been observedin vitroas well as after freezing of le

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01775.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractThylakoids isolated from cold‐acclimated spinach (Spinacia oleracea L.) leaves were more resistant against mechanical freeze‐thaw injury measured as plastocyanin release, than thylakoids from non‐acclimated leaves. They were more resistant against solute influx during freezing and they were able to re‐expand to a larger volume in comparison to non‐hardy controls. Likewise, plastocyanin was released from thylakoids of non‐acclimated but not of frost‐hardy leaves under conditions of mildin situfreezing stress for

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01776.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractExperiments were conducted withEchinochloa crus‐gallito partition the effects of chilling the leafvs.chilling the whole plant on subsequent11C translocation. The results clearly demonstrated that whole plant chilling was very detrimental whereas chilling only the leaf had no effect on subsequent translocation nor on11C uptake. The inhibition of translocation was due to a reduced rate and percentage of export while11C fixation rate was not significantly altered. When the leaf of a chilled plant was maintained at 22 °C, there was no impairment of the transport system nor of photosynthesis. The decrease in export with whole plant chilling may have been due to carbon movement into storage carbohydrates, resulting in a low sucrose gradie

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01777.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractChara vulgarisL. growing in a brackish water lake was investigated in a field study during the main growth season (May to October 1985). Sucrose content and the ionic concentrations of the cations Na+, K+, Mg2+and Ca2+and the anions Cl−and SO42‐of the vacuolar sap were estimated. Sucrose concentration in the vacuolar sap of vegetative growing plants was negligible, but with the beginning of the sexual reproduction period (fructification) the sucrose content increased from about 2 mol m−3to 110 mol m−3. This level remained constant until the end of the fructification period. In spite of the increase of the sucrose concentration the osmotic potential of the vacuolar sap was constant. This was achieved by changing the ionic concentrations accordingly; in old or vegetative growing plants the ionic content accounted for about 80% of the vacuolar osmotic potential, but was about 63% during fructification. Sucrose is considered as a major photosynthate to supply the developing antheridia and oogonia and to serve as a precursor for the starch stored in t

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1988.tb01778.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY