Cell Cycle Responses to Red or Far-red Light, or Darkness, in the Shoot Apex of Silene coeli-rosa L. During Floral Induction

Twenty-eight-day-old plants of Silene coeli-rosa L. were maintainedin short days (SD) for 9 d (0–8) or exposed to 7 longdays (LD), or 7 SD with a 5 min exposure at 1700 h of each dayto far-red (FR), red (R) or 5 min FR/5 min R, or 7 dark-interrupted(di = 1700–1720 h) LD. Treatments were followed by twofurther SD. The mitotic index and G1 and G2 proportions weremeasured in the shoot apices of plants sampled at 2000 h ofeach day of each replicated treatment. Exposure to 7 LD (= 100per cent flowering) resulted in significant increases, relativeto the SD controls, in both the G2 proportion and the mitoticindex on d 0 to 3, 7 and 8. Five minute FR (= 0 per cent flowering)resulted in cell cycle responses similar to those in LD onlyfrom d 0 to 2. R and FR/R (both = 0 per cent flowering) didnot result in any increases in the G2 proportion in the apexapart from d 3 of FR/R. However 5 min FR/5 min R, and to a lesserextent 5 min R, did result in significant increases in the mitoticindex on d 0, 1, 7, and 8. diLD (= 8–10 per cent flowering)also prevented any significant increases in the G2 proportionon d 0 to 3, and 5 to 8 but the mitotic index was again higheron these days compared with control data. Thus the transitionto floral growth for 90 per cent of the plants is associatedwith changes in the cell cycle in the shoot apex measured asincreases in the G2 proportion at 2000 h of LD 0 to 3 and 7to 8. Silene coeli-rosa L., cell cycle, flowering, phytochrome, shoot apex     

Changes to Proteins in the Shoot Meristem of Silene coeli-rosa during the Transition to Flowering

Changes in proteins were measured to test whether they werelinked to flowering, the cell cycle or both in Silene coeli-rosashoot apices. Seeds were germinated and grown at 20?C in shortdays (SD) of 8 h light from fluorescent and tungsten (F + T)/16hdarkness for 28 days (day 0). Plants were then exposed to: 7long days (LD)+2 SD (inductive), 7 LD + 48 h darkness (inductive)or 7 dark-interrupted (di) LD + 2SD (non-inductive), where eachLD and diLD comprised 8 h F + T/16 h T, 8 h F+T/l h darkness/15h T, respectively. There were no qualitative differences inpolypeptide composition in the LD and SD treatments on days0, 5, 6 and 7 but 60 new polypeptides were detected on LD₈ andsome modifications in the intensity of common spots also occurred.These qualitative and quantitative changes were not alteredfollowing 7 LD + 48 h darkness, which is known to suppress synchronisationof the cell cycle but not flowering. Thus, changes on day 8are linked to flowering. Transient increases in protein perunit area were detected in prophase cells on days 0, 3, 4 whilesustained increases occurred on days 7 and 8. The changes ondays O, 3 and 4 were suppressed by the diLD treatment. Thus,quantitative changes to proteins, co-inciding with known LD-inducedchanges to the cell cycle, are linked to flowering. (Received April 2, 1990; Accepted September 12, 1990)     

Location of cell cycle changes in relation to morphological changes in the shoot apex ofSilene coeli-rosa immediately before sepal initiation

Summary Changes in morphology, the mitotic index and the proportions of cells in G₁ and G₂ were measured in shoot meristems ofSilene coeli-rosa immediately before floral morphogenesis in order to determine whether the known changes to the cell cycle at this time are restricted to a particular region of the apex. Twenty-eight day-old plants were given either 7 long days (LD) plus 2 short days (SD) (day 8 of the LD treatment) or 9 SD [day 8 of the SD control (SDC) treatment]. Plants were sampled on day 8 every 2 h for 12 h and the various cell cycle measurements were performed on sections of the apical meristem. In the inductive LD treatment there was a peak in the mitotic index at 13.00 h and, possibly, the start of another at 19.00 h. At 21.00 h all meristems in this treatment initiated sepals. The mitotic activity at 13.00 and 19.00 h in the LD treatment was a result of significant increases in the mitotic index in the axial, lateral and central sub-axial areas of the apex compared with the corresponding zones in the SDC treatment. At 13.00 h of day 8, 80% of cells were in G₂ phase in the axial region in the LD treatment whilst 85% of cells were in G₁ in the axial zone in the SDC treatment. In the other zones significantly more cells were in G₂ in the LD compared with the SDC treatment as was the case at 19.00 h although not to the same extent as the axial zone at 13.00 h. Thus these data emphasize, for the first time, the mitotic activation and predominance of the G₂ population of cells particularly in the axial zone of shoot meristems in the LD treatment. These data are discussed in relation to the synchronisation of cell division which could occur in the prefloral shoot meristem at this time, affecting each shoot apical zone.Abbreviations LD long day - SD short day - SDC short day control     

Synchronization of Cell Division During Flower Initiation in Third-Order Buds of Silene

Plants of Silene coeli-rosa were induced to flower with sevenlong days and then returned to non-inductive short days. Third-orderbuds were formed more than three weeks after the beginning ofinduction and third-order flowers were initiated about one weeklater. Comparison of the mitotic index with the ratio of cellsin the G2 and G1 phases of the cell cycle for each third-orderapex provided evidence for synchronization of cell divisionjust before flower initiation. It is suggested that this resultsfrom changes of competence of the apical cells to react to theirinternal environment rather than because of the arrival of afloral stimulus at the shoot apex. Silene, cell division synchrony, flowering, evocation, mitotic index, cell cycle, competence     

Activation of latent origins of DNA replication in florally determined shoot meristems of long-day and short-day plants: Silene coeli-rosa and Pharbitis nil

Replicon spacing was measured during the S-phase of the cell cycle in shoot meristems of Silene coeli-rosa L., a long-day (LD) plant, and Pharbitis nil Chois, a short-day (SD) plant to examine the hypothesis that activation of latent origins of DNA replication is a feature of floral determination. Silene coeli-rosa was germinated and grown in SD for 28 d and then exposed to either a florally inductive combination of 7 LD + 2 SD, the last day of which coincides with determination of the sepal and stamen whorls, or was germinated and grown in 37 non-inductive SD. Pharbitis nil was germinated and grown in continuous light (CL) for 5 d and then given either 48 h of inductive darkness followed by 1 d of CL, the last day of which coincides with determination of the sepal, petal and stamen whorls, or given one of two independent non-inductive treatments: 48 h dark interrupted by red light (R) + 1 d of CL, or 8 d of CL. Following these treatments, each batch of plants was exposed to tritiated [methyl-³H]thymidine for 30, 60, 90 or 120 min. Apical domes were dissected, nuclei lysed and prepared as fibre autoradiographs from which replicon size was recorded. In S. coeli-rosa, replicon size was in the range 10–15 μm in SD (non-inductive) and 0–5 μm in LD (inductive) while in P. nil it was 10–15 μm in the 48 h dark interrupted by R, 5–10 μm in CL (both non-inductive) but was reduced to 0–5 μm in the 48 h dark treatment (inductive). Therefore, the recruitment of additional initiation points for DNA replication occurred in both a LD and a SD plant immediately before the appearance of floral organs. The data are consistent in showing that a shortening of S-phase, which is a characteristic feature of florally determined shoot meristems for both species, is brought about by the activation of latent origins of DNA replication. Received: 14 May 1998 / Accepted: 20 August 1998     

Lung endothelial cell proliferation with decreased shear stress is mediated by reactive oxygen species

Acute cessation of flow (ischemia) leads to depolarization of the endothelial cell (EC) membrane mediated by K_ATP channels and followed by production of reactive oxygen species (ROS) from NADPH oxidase. We postulated that ROS are a signal for initiating EC proliferation associated with the loss of shear stress. Flow cytometry was used to identify proliferating CD31-positive pulmonary microvascular endothelial cells (mPMVECs) from wild-type, Kir6.2^–/–, and gp91^phox–/– mice. mPMVECs were labeled with PKH26 and cultured in artificial capillaries for 72 h at 5 dyn/cm² (flow adaptation), followed by 24 h of stop flow or continued flow. ROS production during the first hour of ischemia was markedly diminished compared with wild-type mice in both types of gene-targeted mPMVECs. Cell proliferation was defined as the proliferation index (PI). After 72 h of flow, >98% of PKH26-labeled wild-type mPMVECs were at a single peak (PI 1.0) and the proportion of cells in the S+G₂/M phases were at 5.8% on the basis of cell cycle analysis. With ischemia (24 h), PI increased to 2.5 and the ratio of cells in S+G₂/M phases were at 35%. Catalase, diphenyleneiodonium, and cromakalim markedly inhibited ROS production and cell proliferation in flow-adapted wild-type mPMVECs. Significant effects of ischemia were not observed in Kir6.2^–/– and gp91^phox–/– cells. ANG II activation of NADPH oxidase was unaffected by K_ATP gene deletion. Thus loss of shear stress in flow-adapted mPMVECs results in cell division associated with ROS generated by NADPH oxidase. This effect requires a functioning cell membrane K_ATP channel. cell signaling; ischemia; mechanotransduction; K_ATP channels; NADPH oxidase     

Mitotic Activities and Levels of Nuclear DNA in the Apical Meristem of Silene armeria (strain SI.2) Following Application of Gibberellin A3

Strain S1.2 of Silene armeria was grown under an 8h-photoperiodand treated with GA₃ every day for 20 days. This growth substancecaused stem elongation, but no flowering in this long-day plant.Changes in the mitotic index and DNA content of cells in thevarious zones of the apical meristem before, during and afterGA₃ treatment were described. Mitotic activity and increasein the proportion of nuclei at the 4C level (S+G₂ phase of thecell cycle) were strongly stimulated in the rib-meristem, andto a lesser extent in the lateral zone, but not in the axialzone. This stimulation of apical activity reached a peak aftertwo GA₃ treatments and then declined gradually, so that after20 days the activity in GA₃-treated meristems was lower thanthat in untreated controls; at this point most cells were inthe G₁ phase. When the GA₃ treatment was discontinued, there was a gradualincrease in the mitotic activity which ultimately reached thesame level as that in controls. Stem elongation ceased and leavesformed aerial rosettes. It is concluded that in vegetative plants of strain S1.2 ofSilene armeria GA₃ acts mainly on the rib-meristem cells whichresults in stem elongation. Lack of response in the axial cellsexplains why GA₃ fails to induce flowering in this strain ofSilene armeria. (Received June 18, 1983; Accepted August 3, 1983)     

Early effects of floral induction on cell division in the shoot apex of Silene

The changes in cell number, the relative proportions of interphase nuclei with different amounts of DNA, mitotic index and labelling index have been investigated in the shoot apex of Silene coeli-rosa L. (a long-day plant) during the first long day of photoinduction, and compared with the corresponding changes in plants in short days. 3 h after the start of induction the proportion of nuclei in the G2 phase of the cell cycle had increased, the mitotic index tended to be higher, and the labelling index was lower than in plants in short days. 8–9 h later the values for plants in the long day had become similar to those for plants in short days. No evidence was obtained for a synchronisation of cells in one phase of the cell cycle as a result of photoinduction. The results obtained were consistent with a temporary shortening of the cell cycle in the induced apices over the first long day which resulted in a greater increase in cell number by the end of the first day of photoinduction than in plants in short days.Abbreviations LD long day - SD short day     

The Effects of Cell Cycle Parameters on Cell Wall Regeneration and Cell Division of Cotton Protoplasts (Gossypium hirsutum L.)

Protoplasts of cotton cotyledons were isolated and culturedto undergo cell wall regeneration and cell division. DNA contentand cell cycle parameters of nuclei from cotyledons and/or protoplastswere determined by flow cytometry. The DNA content of cotton,Gossypium hirsutum L., was estimated to be 4·34±0·12pg DNA per nucleus. There was a strong positive correlation between G₂ or Sand G₂,and cell wall regeneration and cell division and a strong negativecorrelation between G₁, and cell wall regeneration and celldivision of cotton cotyledon protoplasts. The cell cycle statusof cotyledons changes during their development; as the cotyledonsenlarge, the proportion of cells in G₀ and G₁ phases of thecell cycle increases. The implication of these results in relationto protoplast growth and development is discussed. Key words: Cell cycle parameters, cell wall regeneration, cell division, flow cytometry, Gossypium     

The cell cycle in the shoot apex ofSilene during the first day of floral induction

Summary The length of the cell cycle was measured in the shoot apical meristem ofSilene coeli-rosa during the first day of an inductive photoperiod. The length of the cell cycle in the shoot apex of vegetative controls (those in short days) was about 18–20 hours. Exposure of plants to the long day resulted in an immediate shortening of the cell cycle to about 13 hours, roughly two thirds of that in short days. Measurements of the component phases of the cell cycle revealed that the shortened cycle in long days was the result of a decrease in the length of G 1 and perhaps S, whilst G 2 and M remained constant.     

Growth and development of Neocalanus flemingeri/plumchrus in the northern Gulf of Alaska: validation of the artificial-cohort method in cold waters

In situ growth and development of Neocalanus flemingeri/plumchrusstage C1–C4 copepodites were estimated by both the artificial-cohortand the single-stage incubation methods in March, April andMay of 2001–2005 at 5–6°C. Results from thesetwo methods were comparable and consistent. In the field, C1–C4stage durations ranged from 7 to >100 days, dependent ontemperature and chlorophyll a (Chl a) concentration. Averagestage durations were 12.4–14.1 days, yielding an averageof 56 days to reach C5, but under optimal conditions stage durationswere closer to 10 days, shortening the time to reach C5 (fromC1) to 46 days. Generally, growth rates decreased with increasingstage, ranging from 0.28 day^–1 to close to zero but weretypically between 0.20 and 0.05 day^–1, averaging 0.110± 0.006 day^–1 (mean ± SE) for single-stageand 0.107 ± 0.005 day^–1 (mean ± SE) forartificial-cohort methods. Growth was well described by equationsof Michaelis–Menten form, with maximum growth rates (G_max)of 0.17–0.18 day^–1 and half saturation Chl a concentrations(K_chl) of 0.45–0.46 mg m^–3 for combined C1–3,while G_max dropped to 0.08–0.09 day^–1 but K_chl remainedat 0.38–0.93 mg m^–3 for C4. In this study, in situgrowth of N. flemingeri/plumchrus was frequently food limitedto some degree, particularly during March. A comparison withglobal models of copepod growth rates suggests that these modelsstill require considerable refinement. We suggest that the artificial-cohortmethod is the most practical approach to generating the multispeciesdata required to address these deficiencies.     

Synchronisation of cell division in the shoot apex of Silene in relation to flower initiation

In plants of Silene coeli-rosa, induced to flower by 7 LD, synchronisation of cell division in 20 per cent or more of the cells in the shoot apical dome was found on the 8th and 9th days after the beginning of induction, during the plastochron before sepal initiation. Synchronisation was inferred from the changes in the proportions of cells with the 2C and 4C amounts of DNA, and changes in mitotic index and labelling index. From the peaks of mitotic index a cell cycle of 10 h was measured for the synchronised cells, half that of cells in the apices of uninduced plants in short days. The faster cell cycle and synchronisation in the induced plants was associated with a shortening, of both G1 and G2, suggesting two control points, while S and M remained unchanged. These results are compared with those from other plants in which synchronisation occurs at the beginning rather than the end of evocation.Abbreviations LD long day(s) - SD short day(s) - S DNA synthesis phase of cell cycle - G1 pre-S interphase - G2 post-S interphase - M mitosis     

Sugar Accumulation in Barley and Rice Grown in Solutions with low Concentrations of Oxygen

Barley and rice, at the early tillering stage, were grown inaerated nutrient solutions (> 7 mg O₂ l^–1) and transferredto solutions of low O₂ concentrations (< 0.5 mg l ^–1). For barley, low O₂ concentrations during the first 5 days severelyinhibited growth of seminal roots had less effect on nodal roots,and did not reduce shoot growth. Longer exposure to low O₂ concentrationsreduced shoot as well as root growth. Sugar concentrations inroots and shoots increased within 7 h after transfer of plantsto low O₂ concentrations. After 5 days at low O₂ concentrationssugar concentrations were very high in fast growing nodal rootsand in shoots, as well as in the slower growing seminal roots. In rice, low O₂ concentrations increased sugar levels of rootsduring summer, but not during winter. In summer, the highersugar levels at low O₂ concentrations persisted throughout adiurnal cycle. In root apices, sugar concentrations were increasedby low O₂ concentrations, even though the experiment was donein winter and the bulk of the root system showed no differencein sugar levels. The data indicate that sugar accumulation, at low O₂ concentrations,is caused by reduced growth and also that even apices of rootsgrown at low O₂ concentrations have sufficient substrates forrespiration. Hordeum vulgare L, barley, Oryza sativa L, rice, sugar accumulation, oxygen concentration     

The Interactive Effects of Carbon Dioxide Enrichment and Daylength on Growth and Development inPetunia hybrida

Plants were grown at either 350 or 1000 µl l^-1CO₂and inone of three photoperiod treatments: continuous short days (SD),continuous long days (LD), or short switched to long days atday 41 (SD–LD). All plants received 9 h of light at 450µmol m^-2s^-1and LD plants received an additional 4 h oflight at 8 µmol m^-2s^-1. Growth of SD plants respondedmore positively to elevated CO₂than did LD plants, due largelyto differences in the effect of CO₂on unit leaf rate. High CO₂increasedheight and decreased branching under SD conditions, but hadno effect under LD conditions. Elevated CO₂also increased thenumber of buds and open flowers, the effect for flower numberbeing greater in short than in long days. The specific leafarea of plants grown at 1000 µl l^-1CO₂was reduced regardlessof daylength. High CO₂also decreased leaf and increased reproductiveallocation, the magnitude of these effects being greater underSD conditions. Bud formation and flower opening was advancedunder high CO₂conditions in SD plants but bud formation wasdelayed and there was no effect on flower opening under LD conditions.The effects of CO₂on plants switched from SD to LD conditionswere largely intermediate between the two continuous treatments,but for some parameters, more closely resembled one or the other.The results illustrate that daylength is an important factorcontrolling response of plants to elevated CO₂. Petunia hybridaHort. ex Vilm; carbon dioxide; photoperiod; functional growth analysis; daylength; global change; development; phenology     

UV-induced mortality of zoea I larvae of brown shrimp Crangon crangon (Linnaeus, 1758)

Zoea I larvae of the brown shrimp Crangon crangon (Decapoda)were exposed to varying levels of UV radiation in a sunshinesimulator. ‘Short-term exposures’ (0–8 h)were used to determine the highest UV dose with no significanteffect (NOEC; defined by limit of detection) and the lethaldose of 10 and 50% mortality (LD₁₀ and LD₅₀). Crangon crangonshowed a relatively high sensitivity to UVB radiation (NOEC= 10 kJ m^–2, LD₁₀ = 15 kJ m^–2, LD₅₀ = 24 kJ m^–2)compared to other crust-acean species. LD values (1997–1998)showed no adaptation to seasonal light regimes. ‘Long-termexposures’ (0–10 days) were carried out to assessthe range where the ‘law of reciprocity’ is valid.The larvae were exposed to UV levels of 0.2, 0.4 and 0.7 J m^–2for appropriate time intervals, always cumulating in a sublethaldose of 5 kJ m^–2 day^–1. Results reflect a possiblethreshold (0.2–0.4 J m^–2 UVB) in the effect of thedifferent UVB doses used; thus, a proportional relationshipof intensity and exposure time can only be shown at UVB levelsabove this threshold intensity.     

Freezing tolerance, protein composition, and abscisic acid localization and content of pea epicotyl, shoot, and root tissue 3

The freezing tolerance of many plants, such as pea (Pisum sativum),is increased by exposure to low temperature or abscisic acidtreatment, although the physiological basis of this phenomenonis poorly understood. The freezing tolerance of pea shoot tips,root tips, and epicotyl tissue was tested after cold acclimationat 2C, dehydration/rehydration, applications of 10^–4M abscisic acid (ABA), and deacclimation at 25C. Tests wereconducted using the cultivar ‘Alaska’, an ABA-deficientmutant ‘wil’, and its ‘wildtype’. Freezinginjury was determined graphically as the temperature that caused50% injury (T₅₀) from electrical conductivity. Endogenous ABAwas measured using an indirect enzyme-linked immunosorbant assay,and novel proteins were detected using 2-dimensional polyacrylamidegel electrophoresis. The maximum decrease in T₅₀ for root tissuewas 1C for all genotypes, regardless of treatment. For ‘Alaska’shoot tips and epicotyl tissue, exogenous ABA increased thefreezing tolerance by –1.5 to –4.0C, while coldtreatment increased the freezing tolerance by –7.5 to–14.8C. Cold treatment increased the freezing toleranceof shoot tips by –9 and –15C for ‘wil’and ‘wild-type’, respectively. Cold acclimationincreased endogenous ABA concentrations in ‘Alaska’shoot tips and epicotyls 3- to 4-fold. Immunogold labeling increasednoticeably in the nucleus and cytoplasm of the epicotyl after7 d at 2C and was greatest after 30 d at the time of maximumfreezing tolerance and soluble ABA concentration. Cold treatmentinduced the production of seven, three, and two proteins inshoot, epicotyl, and root tissue of ‘Alaska’, respectively.In ‘Alaska’ shoot tissue, five out of seven novelproteins accumulated in response to both ABA and cold treatment.However, only a 24 kDa protein was produced in ‘wil’and ‘wild-type’ shoot and epicotyl tissues aftercold treatment. Abscisic acid and cold treatment additivelyincreased the freezing tolerance of pea epicotyl and shoot tissuesthrough apparently independent mechanisms that both resultedin the production of a 24 kDa protein. Key words: Pisum sativum, cold acclimation, immuno-localization     

Salt Tolerance in the Halophyte Suaeda maritima L. Dum. Growth, Ion and Water Relations and Gas Exchange in Response to Altered Salinity

Clipson, N. J. W. 1987. Salt tolerance in the halophyte Suaedamaritima L. Dum. Growth, ion and water relations and gas exchangein response to altered salinity.—J. exp. Bot. 38: 1996–2004. Shoot and root fresh and dry weights and shoot sodium, chlorideand potassium contents were measured and shoot relative growthrates calculated in seedlings of Suaeda maritima over a periodof 11 d following a raising of culture solution salinity from0 to 200 mol m₃– NaCl. Growth, growth rates and sodiumand chloride contents, as compared to plants growing in theabsence of salt were increased whilst potassium contents declined.Shoot sodium accumulation rate and the rate of transport ofsodium from root to shoot, osmotic potential, and rates of photosynthesisand transpiration were also measured for up to 72 h after transferof plants originally growing at 0 and 200 mol₃– NaCl to200 and 400 mol m₃– NaCl respectively. Ion uptake andtransport rates were maximal 6-12 h after transfer and thendeclined to new steady-state levels within 48 h; osmotic potentialswere lowered over a 72 h period on average by approximately1·0 MPa; and after 9 h photosynthetic and transpirationrates were reduced by about 20percnt; and 30% respectively.Results are discussed in terms of the ability of halophytesto adjust to fluctuating salinity and to salt tolerance mechanismsin general. Key words: Suaeda maritima, salinity, gas exchange, growth, ion and water relations     

Developmental control of xylem hydraulic resistances and vulnerability to embolism in Fraxinus excelsior L.: impacts on water relations

The freezing tolerance of many plants, such as pea (Pisum sativum),is increased by exposure to low temperature or abscisic acidtreatment, although the physiological basis of this phenomenonis poorly understood. The freezing tolerance of pea shoot tips,root tips, and epicotyl tissue was tested after cold acclimationat 2C, dehydration/rehydration, applications of 10^–4M abscisic acid (ABA), and deacclimation at 25C. Tests wereconducted using the cultivar ‘Alaska’, an ABA-deficientmutant ‘wil’, and its ‘wildtype’. Freezinginjury was determined graphically as the temperature that caused50% injury (T₅₀) from electrical conductivity. Endogenous ABAwas measured using an indirect enzyme-linked immunosorbant assay,and novel proteins were detected using 2-dimensional polyacrylamidegel electrophoresis. The maximum decrease in T₅₀ for root tissuewas 1C for all genotypes, regardless of treatment. For ‘Alaska’shoot tips and epicotyl tissue, exogenous ABA increased thefreezing tolerance by –1.5 to –4.0C, while coldtreatment increased the freezing tolerance by –7.5 to–14.8C. Cold treatment increased the freezing toleranceof shoot tips by –9 and –15C for ‘wil’and ‘wild-type’, respectively. Cold acclimationincreased endogenous ABA concentrations in ‘Alaska’shoot tips and epicotyls 3- to 4-fold. Immunogold labeling increasednoticeably in the nucleus and cytoplasm of the epicotyl after7 d at 2C and was greatest after 30 d at the time of maximumfreezing tolerance and soluble ABA concentration. Cold treatmentinduced the production of seven, three, and two proteins inshoot, epicotyl, and root tissue of ‘Alaska’, respectively.In ‘Alaska’ shoot tissue, five out of seven novelproteins accumulated in response to both ABA and cold treatment.However, only a 24 kDa protein was produced in ‘wil’and ‘wild-type’ shoot and epicotyl tissues aftercold treatment. Abscisic acid and cold treatment additivelyincreased the freezing tolerance of pea epicotyl and shoot tissuesthrough apparently independent mechanisms that both resultedin the production of a 24 kDa protein. Key words: Pisum sativum, cold acclimation, immuno-localization     

The Partitioning of Nitrate Assimilation Between Root and Shoot of a Range of Temperate Cereals and Pasture Grasses

Nitrate reductase activity (NRA, in vivo assay) and nitrate(NO^-₃) content of root and shoot and NO^-₃ and reduced nitrogencontent of xylem sap were measured in five temperate cerealssupplied with a range of NO^-₃ concentrations (0·1–20mol m^–3) and three temperate pasture grasses suppliedwith 0·5 or 5 0 mol m^–3 NO^-₃ For one cereal (Hordeumvulgare L ), in vitro NRA was also determined The effect ofexternal NO^-₃ concentration on the partitioning of NO^-₃ assimilationbetween root and shoot was assessed All measurements indicatedthat the root was the major site of NO3 assimilation in Avenasatwa L, Hordeum vulgare L, Secale cereale L, Tnticum aestivumL and x Triticosecale Wittm supplied with 0·1 to 1·0mol m^–3 NO^-₃ and that for all cereals, shoot assimilationincreased in importance as applied NO^-₃ concentration increasedfrom 1.0 to 20 mol m^–3 At 5.0–20 mol m^–3 NO3,the data indicated that the shoot played an important if notmajor role in NO^-₃ assimilation in all cereals studied Measurementson Lolium multiflorum Lam and L perenne L indicated that theroot was the main site of NO^-₃ assimilation at 0.5 mol m^–3NO^-₃ but shoot assimilation was predominant at 5.0 mol m^–3NO^-₃ Both NRA distribution data and xylem sap analysis indicatedthat shoot assimilation was predominant in Dactylis glomerataL supplied with 0.5 or 5.0 mol m^–3 NO^-₃ Avena sativa L., oats, Hordeum vulgare L., barley, Secale cereale L., rye, x Triticosecale Wittm., triticale, Triticum aestivum L., wheat, Dactylis glomerata L., cocksfoot, Lolium multiflorum Lam., Italian ryegrass, Lolium perenne L., perennial ryegrass, nitrate, nitrate assimilation, nitrate reductase activity, xylem sap