摘要:

AbstractStomatal behaviour, transpiration and nitrogen fixation were investigated inMedicago sativaL. (cvs. Tierra de Campos and Aragon, Hidalgo‐Maynar 1966),Trifolium repensL. (cv. Aberystwyth S‐184) andTrifolium subterraneumL. (cv. Clare) subjected to drought by withholding water and then to three days’ recovery after rewatering. Dawn leaf water potential was measured with pressure chamber, stomatal response with a diffusion porometer and nitrogen fixation by using acetylene reduction technique.At low water potentials, the leaf resistance was higher inMedicagothan inTrifolium. As water stress developed all species decreased their transpiration,T. subterraneumbeing the one most affected by moderate deficits. During water stress ‘Tierra de Campos’ always maintained higher acetylene reduction levels than ‘Aragon’ and theTrifoliumspecies, except for the lowest water potentials.During recovery from water stress only ‘Tierra de Campos’ reached predeficit transpiration rates. In ‘Tierra de Campos’ acetylene reduction recovery after rewatering was more rapid and intense than in ‘Aragon’. It is concluded that, of the plants investigated, ‘Tierra de Campos’ was b

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1980.tb03209.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractIn vitrocultivated pear,Pyrus communisL. cv. Beurré Hardy, pedicels cut above their primary abscission layer can form a secondary abscission layer, especially under the influence of auxins or cytokinins in the culture medium. The maximum percentage of abscission reached by auxin application was always higher than that by cytokinin. The presence of the flower was of no consequence to the abscission. Characteristic differences in abscission were observed between pear and apple pedicels. In contrast to apple (1) secondary abscission in pear could also be induced by cytokinins, and (2) the site of abscission in pear was dependent on the auxin concentration. At lower auxin concentrations abscission was induced in the basal parts of the pedicels inserted in the medium, whereas at higher auxin concentrations the abscission layer was formed in the terminal parts of the pedicels above the culture medium. A clear effect of gibberellins, ABA and CEPA could not be detected

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1980.tb03210.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractThe effects of DCMU and NaN3were studied on menadione‐mediated photophosphorylation in broken spinach chloroplasts kept in low oxygen tension in Tricine or HEPES buffers at either high or reduced irradiances. – (A) At high irradiance (131 W. m−2) andabsenceof NaN3the ATP formation was inhibited by DCMU regardless of the type of buffer used. – (B) At high irradiance andpresenceof NaN3some concentrations of DCMU stimulated, whilst others inhibited the ATP formation in a HEPES buffer. The ATP formation was predominantly inhibited by DCMU in a Tricine buffer. – (C) At reduced irradiance (57 W. m−2) the chloroplasts in a HEPES buffer were almost insensitive towards DCMU both in the presence and absence of NaN3. – (D) Chloroplasts in a Tricine buffer were slightly stimulated in their ATP formation by DCMU at reduced irradiance either with or without the presence of NaN3in the experimental medium. When menadione acts as a terminal electron acceptor, oxygen is consumed on its reoxidation. The results indicate that this process may occur with oxygen released by the splitting of water as the main oxidant. – The data also demonstrate the importance of caution when selecting buffering substances as well as when choosing light intensities for experiments on photophosphorylation

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1980.tb03211.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractSustained divisions of protoplast‐derived cells obtained from cell suspension cultures ofRosa‘Paul's Scarlet’ leading to colony and callus formation was achieved. The rather low plating efficiencies observed for agar‐plated protoplasts were partly due to early arrests in further development of dividing protoplast‐derived cells and cell clusters. Successful cultivation of dividing protoplast‐derived cells was particularly dependent upon frequent subculturing of the precultures and on an efficient procedure for viable protoplast isolation. Colony formation was largely independent of medium

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1980.tb03212.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractThe intensity of the process of redistribution of the elements potassium, boron, iron, magnesium and calcium was determined by following the rate of accumulation of these elements into the fruits of apple (Malus domesticaBorkh.) trees. The determination is based on the assumption that the process of primary distribution via the xylem becomes relatively unimportant with respect to supply along the phloem during the period of fruit growth. Thus a decreasing rate of accumulation for a phloem‐immobile and xylem‐mobile element will be seen during this period of growth, while an element which is mobile in both pathways will give a linear rate of accumulation when the supply by the root does not alter too much.In addition, the ratios of the contents in fruits and leaves were used as an indicator of the relative mobility in redistribution.In these experiments with apple, potassium and boron showed a high mobility. Magnesium and especially calcium showed a much lower mobility in redistribution than in the primary rate of supply. Iron was intermediary. The results, especially for boron and magnesium, are in contradiction to some of the data in the literature. Further studies are needed before these contrasting results can be explai

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1980.tb03213.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractCytokinin activity in sap collected under vacuum from field grown oaks (Quercus roburL.) was determined at monthly intervals throughout the year. A very low level in January was followed by an increase in February and March which reached its maximum 20–25 days before bud‐break. Levels decreased through April and May during leaf expansion, rising once more in June, 10–15 days before a second shoot growth flush. The levels then progressively decreased to reach a minimum in November and December.Cytokinin activity in roots, 24 h and one week after root‐tip removal did not differ significantly from that in intact control plants. Cytokinin activity in roots and shoots determined in relation to shoot growth flushes revealed no differences in the shoot while the activity in root extracts was lowered after a single flush of shoot growth.The effects of applying growth regulators at the time of transplanting were investigated by soaking entire transplants in hormone solution. Gibberellin promoted shoot growth at the expense of root growth, but root growth could be restored to normal levels by a simultaneous application of auxin. Cytokinin treatment increased leaf number, but resulted in small bushy plants.The seasonal changes in cytokinin activity are discussed with regard to successful transp

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1980.tb03214.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractKinetics of fluorescence at room temperature, electron transport and photooxidation of P700 and cytochromefhave been studied in chloroplasts isolated from active and winter stressedPinus silvestris. The winter stress induced block in the electron transport chain between the two photosystems is close to the site of plastoquinone, since winter stress and DCMU caused the same type of inhibition of the reoxidation of the primary electron acceptor Q of photosystem II. No winter inhibition of the electron transport between cytochromefand P700 was observed.Time course studies of P700 photooxidation in chloroplasts of active and winter stressed pine have shown that the photosynthetic unit size must be about equal in the two types of chloroplasts. An apparent increase of the photosynthetic unit size was induced by winter stress, as revealed by the high chlorophyll/P700 ratio of winter stressed pine. The phenomenon is explained by the formation of photosynthetically inactive chlorophyll.Low‐temperature fluorescence emission spectra were recorded when either chlorophylla(433 nm) or chlorophyllb(477 nm) were preferentially excited. Winter stress induced the formation of a chlorophyllafraction emitting at 673 nm. This chlorophyll is most likely derived from the chlorophyllaantennae of the two photosystems, and it probably contributes to the photosynthetically inactive pool of chlorophyll in winter stressed pine. The light harvesting chlorophylla/bcomplex is relatively resistant to winter stres

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1980.tb03215.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractThe light dependent chloroplast development of dark grown seedlings ofPinus silvestrisL. was followed by analyses of chlorophyll content, chlorophylla/bratios, chlorophyll/P700 ratios, chlorophyll‐protein complexes and structural changes.Low‐temperature fluorescence emission spectra of isolated chloroplasts and separation of sodium dodecyl sulphate solubilized chlorophyll‐protein complexes by gel electrophoresis showed that the chlorophyll‐protein complexes of photosystem 1 (P700‐CPa), photosystem II (PS II‐CPa) and the light‐harvesting complex LH–CPa/bwere present in dark grown seedlings. The low‐temperature fuoorescence emission maxima of isolated P700–CPaand PS II–CPashifted towards longer wavelengths during greening in light, indicating a light induced change of the chlorophyll organisation in the two photosystems. Illumination caused LH–CPa/bto increase relative to P700–CPa, whereas the ratio between LH–CPa/band PS II–CParemained essentially constant. Analyses of low‐temperature fluorescence spectra with or without 0.01 M Mg2+showed that the Mg2+controlled distribution of excitation energy into PS I was activated upon illumination of the seedlings.The photosynthetic unit size, as defined by the chlorophyll/P700 ratio, did not change over a 96 h illumination period, although the chlorophyll content increased about 6–fold during that time. This result and the constant electron transport rate per unit chlorophyll and time during chlorophyll accumulation provided evidence for a sequential development of the photosynthetic units when illuminating dark grown pine cotyledons. Electron micrographs showed that exposure of dark grown seedlings to light for 2 h caused the prolamellar body to disappear and grana to form. These changes occurred prior to substantial accumulation of chlorophyll or change in the ratio between LH–CPa/band P700–CPa. However, both the water‐splitting system of photosystem II and the Mg2+controlled redistribution of excitation

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1980.tb03216.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractPhosphate‐rich yeast cells (Saccharomyces cerevisiae) take up more calcium and strontium than phosphate‐deficient cells. The divalent cations appear to be tightly bound in phosphate‐rich cells. Electron microscopical investigations, combined with energy‐dispersive X‐ray microanalysis, showed that divalent cations were sequestered in cytoplasmic granules, together with a large amount of phosphorus. The major part of the divalent cations is retrieved in the polyphosphate fraction, a minor part is bound to lipids. The results suggest that polyphosphate granules may serve as an important store for divalen

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1980.tb03217.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractGeoperception and georeaction in Asparagus officinalis epicotylsThe location and the role of the statenchyma were investigated inAsparagus officinalisepicotyls 1, 2 or 3 cm in length. The statocytes represent a monocellular sheath which comprises the outer layer of the pericycle. Three phases of differentiation (S1, S2, S3) of the statocytes may be distinguished by criteria of cell length, the state of vacuolisation and the sedimentation of amyloplasts and nuclei with respect to gravity. The statenchyma was found to be located only in the first 10 mm of the epicotyl 1, 2 or 3 cm in length; in effect the oldest statocytes (S3) differentiate into sclerenchyma beneath this level.The geotropic curvature of the epicotyls begins with a positive (downward) curvature and the negative (upward) response is only realized after 15–30 min of geotropic stimulation. The upper limit of the bending is located in the zone containing the mature statocytes (S3), while the lower limit is located much closer to the base of the epicotyl.Experiments on decapitation of the epicotyls have indicated that the S1and S2statocytes do not play an important role in the perception of gravity. However, with S3statocytes, it has been demonstrated that there is a statistical correlation between the initial rate of curvature of the epicotyls and the length of their sheaths. Thus, the longer the sheath, the more the epicotyls curve.From the results obtained it is proposed that the statocytes are responsible for the geotropic perception ofAsparagus officinalisepicotyl

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1980.tb03218.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY