摘要:

Water relations, desiccation tolerance and longevity ofTaxus brevifolia(Nutt.) seeds were studied to determine the optimal stage of development and storage conditions for seeds of this species. Seeds equilibrated to a range of relative humidities (RHs) had unusually low water contents which can be accounted for by the high lipid content of gametophyte tissues (71% of the dry mass). Water relations of embryonic tissue were more typical of those reported for other seed species. The water content below which freezing transitions were not observable in the embryo was ca 0.24 g H2O (g dry weight)−1(g g−1) for all maturity classes studied. Embryos did not achieve significant levels of desiccation tolerance (survival to water contents less than 0.5 g g−1) until the latter stages of development when dry matter was maximal. Mature embryos could be dried to 0.025 g g−1(seed water content of 0.010 g g−1) with no loss of viability. Thus, at the latter stages of development, embryo water content could be optimized to avoid both desiccation and freezing damage. Survival of mature seeds declined over a 2‐year period when seeds were stored at temperatures between 5 and 35°C and RHs between 14 and 75%, corresponding to seed water contents between 0.015 and 0.07 g g−1. The deterioration rate was slowest for seeds stored at the lowest RH and temperature. Our data indicate that seeds ofTaxus brevifoliashow orthodox rather than recalcitrant storage characteristics, but that the optimum water content for storage was extremely low. The results suggest that even if stored at optimal water contents and low temperatures,T. brevifoliaseeds will be relatively short lived. The high quantity of lipids or reducing sugars may be contributing factors in the poor storage c

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb00669.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The activity of NADP+‐dependent isocitrate dehydrogenase (ICDH, EC 1.1.1.42) was investigated during the post‐germinative growth of cucumber (Cucumis sativusL. cv. Marketmore) seedlings. Isoelectric focusing showed the presence of several isoenzymes, two of which represented 70–80% of the total NADP+‐ICDH activity in cotyledons of seedlings grown in the dark. They had pI values between 4.8 and 5.8. The isoenzyme with higher pI was purified to homogeneity by hydrophobic interaction, affinity, hydroxylapatite and anion exchange chromatography. The purified isoenzyme is a dimeric protein, consisting of two apparently identical 43‐kDa subunits. It is specific for NADP+, inhibited by ATP and by 2‐oxoglutarate, whereas it is not inhibited by citrate, succinate, and glyoxylate. The data indicate that NADP+‐ICDH from cucumber is structurally similar to ICDHs from other plants, but it shows some peculiar biochemical ch

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb00670.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Electroporation was used to introduce DNA into excised scutella of immature embryos ofHordeum vulgareL. cvs Golden Promise and Delita. Using the firefly luciferase gene as reporter, parameters were analyzed for high transient gene expression while maintaining tissue viability. Enzymatic wounding was necessary for DNA uptake. The optimized protocol involves use of linearized DNA and addition of 15% (w/v) polyethylene glycol at a field strength of 950 V cm−1and approximately 56 ms pulse length. A one‐day preculture was required for obtaining callus after electroporation. Transient gene expression was further demonstrated using the β‐glucuronidase gene. Blue spots were detected at the abaxial scutellar surface, indicating that cells competent for somatic embryogenesis are also amenable to transfection by electropo

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb00671.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Light is recognized as crucial in determining high quality of fleshy fruits, for example, kiwifruit [Actinidia deliciosavar.deliciosa(A. Chev.) C. F. Liang et A. R. Ferguson]. Among the possible mechanisms through which light improves the quality of kiwifruit berry, there may be a direct morphogenic role on the differentiation of the fruit's vascular system, though this has not yet been investigated.The present study's aim was to determine (1) whether light positively affects the differentiation of the vascular system of the fruit and/or the pedicel, and, if so, (2) which component (xylem, phloem, or both) is more affected, and (3) in which period of the berry's development the improvement of the vascular differentiation (if any) occurs. To this end, fruit morphogenesis of kiwifruit was studied in two developmental environments (i.e., in full sunlight and in paper bags that reduced the full sunlight to 10%), and in two phases of fruit development (i.e., 1 and 5 months [harvest] after anthesis). During the growth period, the type of environment did not affect the differentiation pattern of the vascular system in the three types of bundles present in the fruit. However, in comparison with shade, light improved the vasculature in the fruit pericarp and pedicel, inducing a consistently higher extent of the xylary component in the main bundles of the fruit and pedicel, principally due to an increase in the number of xylem elements. The phloic component was also increased by light, but to a much lesser extent than that of the xylary. During the entire period of development, light‐grown fruits contained higher concentrations of calcium and magnesium, as compared with shade‐grown fruits.In conclusion, in the berry ofActinidia deliciosa, light enhances the differentiation of the vascular system, in particular the xylary component. The hypothesis that fruit quality is improved through a more efficient translocation of specific mineral nutrients (e.g., calcium) via the xylem is presen

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb00672.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Irradiation with blue light resulted in acidification of the suspension medium of a colorless mutant ofChlorella kessleri(Fott et Novákóva, no. 9.80). Qualitatively red light gave the same result, although to a much lower extent than blue, whereas far‐red had little effect. A pulse of blue light led to a transient acidification of the medium. The light‐induced acidification was particularly pronounced if nitrate‐starved cells were used. Acidification was inhibited by vanadate (V2O5, Na3VO4), so that the phenomenon appears due to proton extrusion from the mutant. The light‐induced acidification was also observed in a yellow mutant and the wild‐type ofChlorella kessleri. The role of light in the acidification of the medium of algal cells is discussed in relation to the earlier findings that blue light enhances the uptake of nitrate in the colorless mutant; and that inChlorellacells the transport process of nitrate is connected with a pro

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb00673.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Leaf epidermal cells from a wide variety of plants focus light to surprisingly high levels. Using image analysis, the concentration and distribution of light was measured after it passed through epidermal cells within peels and epidermal cells attached to palisade cells in partially dissected leaves. In peels taken fromMedicago sativa, Zea mays, andImpatienssp., light was concentrated 15‐ to 20‐fold by individual epidermal cells. When left attached to the mesophyll, which attenuated focusing by absorption and scattering, light was focused up to 5 times. The position of the focal spot beneath each epidermal cell was affected by the direction at which the light struck the cell. When the light was perpendicular to the leaf surface, individual focal spots fell beneath each epidermal cell. When the incident light was oblique, the focal spot shifted laterally and was positioned closer to the anticlinal cell wall. Focusing was observed when leaves were irradiated with collimated light but not with diffuse light. Focal lengths were relatively independent of wavelength within the visible region of the spectrum and there were only slight differences between focusing of blue vs red light. Epidermal lens properties can affect chlorophyll fluorescence and the photosynthetic performance of leaves. A survey of 47 species collected from a wide variety of habitats indicates that many plants have leaf epidermal cells with lens properties. The ability to measure epidermal focusing makes it possible to examine the adaptive and physiological significance of epidermal lens effects in pla

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb00674.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The effects of drought acclimation on CO2assimilation and light utilization were investigated in two sunflower genotypes (Helianthus annuusL., T32 and Viki) in relation to water deficit and/or high light conditions. Drought interaction with PSII efficiency was observed in the genotype T32 with a sustained decrease in the potential photochemical efficiency of PSII, Fn/Fm. In response to drought acclimation, T32 displayed some tendency to accumulate closed PSII traps (higher value of 1‐qp) without an enhancement of thermal deactivation (Stem‐Volmer non‐photochemical quenching, NPQ). Irrespective of the growth conditions (growth chamber or greenhouse), only Viki was responsive to drought acclimation, with (1) increased net photosynthesis in well‐watered plants, (2) higher maintenance of photochemical electron transfer under water deficit and/or high light, (3) limited PSII inactivation (lower value of 1‐qp) through increased non‐photochemical energy dissipation (Stern‐Volmer NPQ) which was readily reversible even at low leaf water potentials, and (4) higher Fv/Fmrecovery after high light treatment. Additionally, drought acclimation delayed turgor loss during subsequent water stress in Viki. Thus, the response to drought acclimation, with an adjustment of water relations and of energy utilization by PSII, was observed under both growth conditions and was mainly genot

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb00675.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The effects of cytoplasmic protein synthesis and protein phosphatase activity on NADH:nitrate reductase (NR) activity, protein and transcript were examined in maize (Zea maysL.) seedling leaves. A rapid increase in NR activity, measured in the presence of 5 mMMg2+, was found upon exposure of excised leaves to light. Inhibitors of protein phosphatase activity (okadaic acid [OKA] and microcystin [MC]‐LR) completely prevented the increase in NR activity. The cytoplasmic protein synthesis inhibitor, cycloheximide (CHX), did not affect Mg2+inhibition of NR activity during the dark‐to‐light transition. VmaxNR activity, measured in the presence of 5mMMg2+, was found upon exposure of excised leaves to light. Inhibitors of protein phosphatase activity (okadaic acid [OKA] and microcystin [MC]‐LR) completely prevented the increase in NR activity. The cytoplasmic protein synthesis inhibitor, cycloheximide (CHX), did not affect Mg2+inhibition of NR activity during the dark‐to‐light transition. VmaxNR activity, measured in the presence of Piand EDTA, remained constant or increased slightly in maize leaves during the first 2 h of the light period. OKA, MC‐LR or CHX treatment caused a 40 to 50% reduction in VmaxNR activity during this time. Incorporation of35S‐Met into NR protein was reduced more than 90% by CHX and 80% by OKA. The inhibition of NR protein synthesis by CHX and OKA correlated with a 50 to 60% decrease in35S‐Met incorporation into total soluble protein over the treatment period. The increase in NR mRNA levels early in the light period was prevented by OKA and MC‐LR, but not by CHX. OKA had a similar effect on sucrose phosphate synthase mRNA levels, but did not affectCatalaselorCatalase3mRNA accumulation. The data suggest that light‐induced decreases in Mg2+inhibition of NR activity and transcript levels are independent of new protein synthesis. The effects of OKA and MC‐LR indicate that protein phosphatase activities could be involved, directly or indirectly, in the regulation of NR activity, protein synthesis and

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb00676.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Doubling the atmospheric CO2concentration from 350 to 700 μ1 1−1increased the relative growth rate (RGR) of hydroponically grownUrtica dioicaL. andPlantago majorssp.pleiospermaPilger only for the first 10–14 days. Previous experiments withP. majorled to the conclusion that RGR did not respond in proportion to the rate of photosynthesis. The present paper is focussed on the analysis of the impact of changes in leaf morphology, dry matter partitioning, dry matter chemical composition and ontogenetic drift on this discrepancy.Soon after the start of the treatment, carbohydrate concentrations were higher at elevated CO2: a reaction that was largely due to starch accumulation. An increase in the percentage of leaf dry matter and decreases in the specific leaf area (SLA) and the shoot nitrogen concentration were correlated with an increase in the total nonstructural carbohydrate concentration (TNC). A combination of accumulation of soluble sugars and starch and ontogenetic drift explains the decrease in SLA at the elevated CO2level. A similar ontogenetic effect of elevated CO2was observed on the specific root length (SRL). Other variables such as shoot nitrogen concentration and percentage leaf dry matter were not affected by correction of data for TNC levels. The net diurnal fluctuation of the carbohydrate pool inP. majorwas equal for both CO2concentrations, indicating that the growth response to elevated CO2may be ruled by variables other than photosynthesis, as for instance sink strength.Elevated CO2did not greatly influence the partitioning of nitrogen between soluble and insoluble, reduced N and nitrate, nor the allocation of dry matter between leaf. stem and root. The finding that the root to shoot ratio (R/S) was not affected by elevated CO2implies that, in order to maintain a balanced activity between roots and shoot, no shift in partitioning of dry matter upon doubling of the atmospheric CO2concentration is required. Our data on R/S are in good agreement with the response of R/S to high CO2predicted by models based on such a the

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb00677.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

We assessed the effects of doubling atmospheric CO2concentration, [CO2], on C and N allocation within pedunculate oak plants (Quercus roburL.) grown in containers under optimal water supply. A short‐term dual13CO2and15NO3−labelling experiment was carried out when the plants had formed their third growing flush. The 22‐week exposure to 700 μl l−1[CO2] stimulated plant growth and biomass accumulation (+53% as compared with the 350 μl l−1[CO2] treatment) but decreased the root/shoot biomass ratio (‐23%) and specific leaf area (‐18%). Moreover, there was an increase in net CO2assimilation rate (+37% on a leaf dry weight basis; +71% on a leaf area basis), and a decrease in both above‐ and below‐ground CO2respiration rates (‐32 and ‐26%, respectively, on a dry mass basis) under elevated [CO2].13C acquisition, expressed on a plant mass basis or on a plant leaf area basis, was also markedly stimulated under elevated [CO2] both after the 12‐h13CO2pulse phase and after the 60‐h chase phase. Plant N content was increased under elevated CO2(+36%), but not enough to compensate for the increase in plant C content (+53%). Thus, the plant C/N ratio was increased (+13%) and plant N concentration was decreased (‐11%). There was no effect of elevated [CO2] on fine root‐specific15N uptake (amount of recently assimilated15N per unit fine root dry mass), suggesting that modifications of plant N pools were merely linked to root size and not to root function. N concentration was decreased in the leaves of the first and second growing flushes and in the coarse roots, whereas it was unaffected by [CO2] in the stem and in the actively growing organs (fine roots and leaves of the third growth flush). Furthermore, leaf N content per unit area was unaffected by [CO2]. These results are consistent with the short‐term optimization of N distribution within the plants with respect to growth and photosynthesis. Such an optimization might be achieved at the expense of the N pools in storage compartments (coarse roots, leaves of the first and second growth flushes). After the 60‐h13C chase phase, leaves of the first and second growth flushes were almost completely depleted in recent13C under ambient [CO2], whereas these leaves retained important amounts of recently assimilated13C (carbohydr

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb00678.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY