摘要:

Three‐week‐old seedlings of carob (Ceratonia siliquaL. cv. Mulata) were grown for 9 weeks under different root temperatures (20, 30 and 40°C) at pH values of 5, 7 and 9 with nitrate or ammonium as nitrogen source. Nitrogen uptake rates were determined by depletion from the medium and decreased with distance from the apex. The decline of nitrogen uptake rates along the roots depended on the form of inorganic nitrogen in the medium as well as on pH and temperature, such that the NO−3and NH+4ions were taken up essentially by the root tips (0–2 cm) through processes requiring energy. The uncharged NH3species entered passively, through the mature parts of the root (2–10 cm). Root zone temperature and pH affect the NH+4/NH3equilibrium in the nutrient solution and, consequently, the uptake areas of the root for these ions. Furthermore. while root tip uptake of nitrogen is energy dependent, uptake through mature root areas is essentially passive and seems to depend on a well developed apparent

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00824.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The aim of the present work was to investigate the relationship between theBtlgene(Btl)and the major 39–44 kDa amyloplast membrane polypeptides which were deficient in amyloplast membranes ofbrittlel (btl)kernels of maize (Zea maysL.). A rapid yet gentle procedure for the isolation of amyloplasts from immature kernels is described. These amyloplasts were relatively free of contamination by other cellular components, and immunological studies showed that they contained polypeptides which reacted with antibodies to maize starch branching enzyme and ADP‐Gle pyrophosphorylase. Purified membranes isolated from the amyloplast contained a poly‐peptide which reacted with antibodies to the Pi‐translocator from spinach chloroplasts. However, a cluster of 39–44 kDa polypeptides accounted for about 40% of the total amyloplast membrane protein from W64A kernels. These polypeptides were specifically recognized by antibodies raised against a fusion protein consisting of 56 amino acids of the carboxyl terminus of the BTI protein and glutathione S‐transferase. The BT1 antibodies also reacted with the abundant polypeptides in amyloplast membranes from hybrid kernels (Doebler 66XP and Pioneer 3780), and theshrunkenlandshrunken2mutant genotypes, but no BTl reacting polypeptides were present in amyloplast membranes frombtlmutant kernels. We were unable to detect BTl by the immunoblot procedure in microsomal membranes from embryo and pericarp tissues from the kernel, from seedling roots and shoots, or in membranes from mitochondria and chloroplasts. The same BTl immunoblot pattern was obtained for proteins extracted from microsomal membranes from developing endosperm and from purified amyloplast membranes. A linear relationship between the number of copies ofBtlalleles and the levels of BTl in endosperm microsomal membranes was demonstrated in a gene dosage series. BTl was not extracted from amyloplast membranes by chloroform/methanol or by alkaline buffer at pH 11.5, but was partially extracted by 0.1MNaOH. These lines of evidence support the conclusion thatBtl is the structural genefor the major 39–44 kDa amyloplast membrane polypeptides and that these polypeptides are integral proteins specific to amyloplast membranes from

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00825.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Gibberellin A4/7(GA4/7) was applied in lanolin or ethanol around the circumference at the midpoint of the previous‐year terminal of dormantPinus sylvestrisseedlings. After cultivating the seedlings under environmental conditions favorable for growth for up to 10 weeks, cambial growth was measured as the radial widths of xylem and phloem, and the level of indole‐3‐acetic acid (IAA) was determined by combined gas chromatography‐mass spectrometry using [136](IAA) as the internal standard. In intact seedlings, both 1 mg GA4/7g−1lanolin and 50 mg GA4/7I−1ethanol increased phloem production and the cambial region IAA level in the current‐year terminal, without significantly altering its longitudinal growth. In the previous‐year terminal, 1 mg GA4/7g−1lanolin promoted phloem production at the application point and increased the cambial region IAA level above this point, whereas 50 mg GA4/7I−1ethanol stimulated the production of both xylem and phloem at the treatment site and elevated the cambial region IAA level beneath it. Laterally applied GA4/7at 50 mg I−1ethanol stimulated xylem and phloem production in debudded previous‐year terminals treated at the apical cut surface with 1 mg IAA g−1lanolin, but not in those treated with plain lanolin. However, the promotion of cambial growth in debudded terminals treated apically with 1 mg IAA g−1lanolin and laterally with 50 mg GA4/7I−1ethanol was not associated with an elevated IAA content in the cambial region. The results indicate that exogenous GA4/7can promote xylem and phloem production provided an IAA source is present, and that it or a metabolic product acts directly, rather than indirectly by stimulating longitudinal growth and/or raising

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00826.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The effect of 24‐epibrassinolide (EBS), a brassinosteroid, on the response of smooth bromegrass (Bromus inermisLeyss) cell suspension cultures under low and high temperature stress was evaluated. EBS minimally increased freezing tolerance of bromegrass cells by 3–5°C, but markedly enhanced cell viability following exposure to high temperature stress. The net effect on hardening was, however, less than that obtained with abscisic acid (ABA). Treatment of cells with EBS increased the accumulation of a subset of ABA‐inducible heat‐stable proteins, but unlike ABA, EBS did not induce the expression of dehydrin transcripts which hybridized to a barley dehydrin clone. EBS slightly increased the hsp90 transcript levels, while ABA reduced the level of expression. These results confirm that brassinosteroids confer some stress tolerance to plant cells and further suggest that the mechanisms by which these compounds exert anti‐stress effects may only in part be similar to t

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00827.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Olive (Olea europaeaL. cv. Frantoio) plants grown hydroponically in a glasshouse were supplied with half‐strength Hoagland solutions containing 0, 50, 100, and 200 mMNaCl for 4 weeks and subsequently supplied with the standard solution without NaCl to relieve salinity stress. Two complete stress‐relief cycles were repeated on the same plant material during one growing season. Growth was inhibited at all salt levels, but most growth parameters of plants treated with 50 or 100 mMNaCl returned to control levels after 4 weeks of relief. More severely stressed plants (200 mMNaCl) recovered to only 60% of the growth of the controls after 4 weeks. During relief, plants treated with 50 and 100 mMNaCl had net photosynthetic rates and stomatal conductances higher than the controls. Increasing the NaCl concentration of the external solution from 0 to 200 mMdecreased both leaf pre‐dawn water potential (from ‐0.3 to ‐1.0 MPa) and osmotic potential (from ‐2.1 to ‐2.7 MPa). The sodium concentration in the leaves of plants treated with 200 mMNaCl reached maximum levels of 211 and 388 mM(expressed on a tissue water basis) at the end of the first salinity and relief periods, respectively. Leaf chloride concentrations were 359 and 223 mMat the same sampling dates. These data indicate that the inhibitory effects of salinization on growth and gas exchange of the salt‐tolerant olive cv. Frantoio can be readily reversed when salinity is relieved, despite the marked accumulation of potentially toxic ions (Na+.

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00828.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

I considered the possibility that changes in fruit photosynthesis obscure the occurrence of the climacteric rise in respiration in tomato fruits attached to the plant. Internal CO2and ethylene concentrations in tomatoes (Lycopersicon esculentumMill. cv. OH 7814) were analyzed after direct sampling through polyethylene tubes implanted in the external pericarp. Fruits which were shaded with aluminium foil contained up to 60 ml 1−1CO2, until the internal ethylene concentration exceeded 1 μl l−1, when CO2concentration declined to below 40 ml l−1; the CO2concentration in fruits exposed to light only occasionally exceeded 40 ml 1−1. The internal CO2concentration of detached fruits first declined and then increased along with ethylene concentration, as expected for the climacteric. Detached green fruits under continuous low photosynthetic photon flux density (100 μmol m−2s−1) contained almost no internal CO2and produced no CO2. Changes in photosynthesis and an associated CO2‐generating system in green fruits are thought to obscure the climacteric rise in tomato fruits developi

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00829.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Field‐grown roots of maize, oats, barley and crabgrass collected at different times of day and night have been examined by cryo‐scanning electron microscopy. Droplets and blobs (their high water content confirmed by X‐ray microanalysis) were observed on the young root surfaces and within interstices of the rhizosheaths of guttating plants, particularly in the early morning. Plants collected at midday and in the afternoon had very few or none of these watery deposits. I propose that water released from the root surface during the night allows the expansion of root‐cap mucilage into the surrounding soil. When transpiration resumes, the mucilage is dried and binds tightly to the surrounding soil particles, thus stabilizing the coherent rhizosheath. This nocturnal water effflux may also facilitate nutrient uptake into the root when transpiration resumes. The water efflux to the rhizosheaths may be driven by root pressure and thus differs from the passive water loss from the root thought to occur during hydraul

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00830.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Previous findings indicated that leaf conductance and net photosynthesis were positively correlated with water status (relative water content) of tissue‐cultured shoots and plantlets, and that acclimatization was associated with a reduction in leaf conductance and transpiration. In the present study, the effect of acclimatization on plant water status after plants were removed from culture and transplanted in soil, as well as the relation of water status with survival and growth after acclimatization were determined. Tissue‐cultured plantlets (Malus pumilacv. Greensleaves) were acclimatized by exposure to a 4‐day gradual reduction in humidity before they were transplanted. Once plants were transplanted, acclimatized plants maintained a higher relative water content than nonacclimatized plants, probably because of a lower initial stomatal conductance and less transpiration. High plant water status, as indicated by high relative water content, appeared to be an important factor for both plant survival and growth after the plants were transplanted. Higher water status was associated with higher growth rates and net assimilation rates. The differences in gas exchange, water relations and growth characteristics between plantlets in vitro and at 4 weeks after they were transplanted were also studied. Compared to in vitro plants, transplanted plants had a higher water status and higher leaf conductance and net photosynthesis. There was also an increase in the leaf area ratio (leaf area to plant biomass ratio) after they were transplanted which might have contributed to the higher net assimilation rate in transplanted compared to in vitro p

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00831.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The effects of postharvest storage duration, and storage and incubation temperatures on the loss of innate tuber dormancy, endogenous levels of free and conjugated abscisic acid (ABA) and the metabolism of (+)‐[3H]ABA were examined over three growing seasons in tubers of potato (Solanum tuberosumL. cv. Russet Burbank). The storage and incubation temperatures used were chosen in order to differentiate between events relating solely to dormancy status vs those relating to the resumption of sprout growth following the termination of dormancy. In tubers stored at 20°C, dormancy was lost and sprout growth began after 35 to 50 days of storage. In contrast, dormancy was lost after 50 to 80 days of storage at 3°C but subsequent sprout growth was initiated only after transfer to 20°C. After 35 days of storage, endogenous levels of free ABA were highest (860 ± 35 pmol g−1fresh weight) in tubers held at 3°C, intermediate (659 ± 78 pmol g−1fresh weight) in tubers transferred from 3 to 20°C 7 days prior to analysis and lowest (471°18 pmol g−1fresh weight) in tubers stored at 20°C. Regardless of temperature, free ABA levels declined with increasing duration of storage. The onset of sprouting was not associated with any threshold level of free ABA. Base‐labile, conjugated ABA was present in lower and more variable amounts than free ABA. The decline in free ABA was not accompanied by a commensurate increase in conjugated ABA. (+)‐[3H]ABA was readily taken up and metabolized by both dormant and nondormant tubers. In short‐term (≤ 7 days) studies, (+)‐[3H]ABA was metabolized to phaseic acid and dihydrophaseic acid. In tubers held at 20°C, dihydrophaseic acid was the major metabolite while in tubers held at 3°C there was a transient accumulation of phaseic acid with dihydrophaseic acid predominating only after 7 days. During postharvest storage, there was no change in the rate of ABA metabolism regardless of the dormancy status and/or growth potential of the tubers. These results demonstrate that ABA is readily metabolized by potato tubers and that the principal route of catabolism consists of the oxidative metabolism of ABA to phaseic and dihydrophaseic acids with minimal esterification to conjugated ABA. These results also suggest that a decline in endogenous ABA below a threshold level is not a prerequisite for the loss of potato tuber dormancy an

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00832.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

A short‐term study linked directly to our previous long‐term experiments was conducted to clarify whether or not benzyladenine (BA) acts directly or through endogenous cytokinins in the development of kiwifruit explants. The uptake and metabolism of BA were characterized in kiwifruit explants after 0.5, 1, 2, 8 and 16 h exposure to 8‐[14C]BA on both solidified and liquid Murashige and Skoog media. Endogenous cytokinins were measured by enzyme‐linked immunosorbent assay (ELISA) using polyclonal antibodies. The kinetics of BA uptake by explants cultured under these conditions were different, being higher in explants cultured in liquid medium. The glucosylation rate of BA was faster in explants cultured on solid medium. The levels of active forms of BA (BA and [9R]BA) were higher in explants cultured on liquid medium due to its higher uptake and lower glucosylation. The levels of zeatin‐type cytokinins were influenced by the culture conditions. A direct correlation was observed between morphogenic response and proportion of active forms of BA, but not with zeatin‐type

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00833.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY