Planta

Johnson, Richard

doi: 10.1007/BF00385984pmid: 24420390

Vascular bundles of petioles below wilted leaves of Nymphoides peltata (S.G. Gmel. O. Kuntze) were frozen intact and freeze-fractured for electron microscopy. Cell walls in them appeared drawn in against the helical thickenings of xylem vessels. By contrast, walls round vessels which had been frozen in vascular bundles below turgid leaves, and walls round vessels which had been fixed, embedded and sectioned, were straight or bulged outwards slightly. Walls bulged outwards slightly also from cut vessels filled with sucrose solution before freezing. Movement of vessel walls could produce the clicks audible when water cavitates in vessels, and might explain a variable resistance to the flow of water through plants.

Peumans, W.; Carlier, A.

doi: 10.1007/BF00385985pmid: 24420391

Extracts prepared from dry wheat (Triticum aestivum L.; var. Cama) and rye (Secale cereale L.; var. Celestijner) embryos exhibit relatively high endogenous messenger activities in an in vitro protein synthesizing system: up to 400 pmol leucine are incorporated per 50 μl reaction mixture; the messenger/ribosome ratio is estimated at about 0.03. Sucrose gradient analysis of the incubation mixture during cellfree protein synthesis shows a progressive in vitro polysome formation with the native endogenous mRNPs. The translation of these messengers, although dependent on initiation, follows linear kinetics. The native mRNP particles can be separated on sucrose gradients in 6 distinct size classes with sedimentation values varying from 25 S to 104 S. Their size is strongly reduced after deproteinization so that the naked mRNAs sediment in a range between 8 S and 35 S. The molecular weights of the proteins synthesized under direction of the native RNA particles range from 12,000 to 70,000 as estimated by polyacrylamide gel electrophoresis.

Byrne, Henry; Setterfield, George

doi: 10.1007/BF00385986pmid: 24420392

RNA synthesis was studied in Jerusalem artichoke (Helianthus tuberosus L.) tuber slices immediately following excision and during the early period of aging in water. Incorporation of [3H]adenosine into RNA was detected as early as 20 min after excision. Measurement of the specific activities of RNA (cpm/μg) and of ATP showed that RNA synthesis proceeded at a constant rate for the first several hours of aging and then increased moderately. [3H]adenosine was incorporated into polysomes throughout the aging period examined. Sucrose gradient fractionation of EDTA-dissociated polysomes showed that during the first 2 h of aging most of this incorporation was not into ribosome subunits but into presumed mRNA. Autoradiographic analysis of [3H]adenosine labelled nuclei showed that this was caused, at least in part, by a delay in the onset of rRNA synthesis synthesized during this time chromatographed as poly(A)-RNA on oligo(dT)-cellulose, indicating that a large part of the mRNA was not polyadenylated.

Walk, R.; Michaeli, S.; Hock, B.

doi: 10.1007/BF00385987pmid: 24420393

Molecular properties of the glyoxysomal and mitochondrial isoenzyme of malate dehydrogenase (EC 1.1.1.37; L-malate: NAD+ oxidoreductase) from watermelon cotyledons (Citrullus vulgaris Schrad.) were investigated, using completely purified enzyme preparations. The apparent molecular weights of the glyoxysomal and mitochondrial isoenzymes were found to be 67,000 and 74,000 respectively. Aggregation at high enzyme concentrations was observed with the glyoxysomal but not with the mitochondrial isoenzyme. Using sodium dodecyl sulfate electrophoresis each isoenzyme was found to be composed of two polypeptide chains of identical size (33,500 and 37,000, respectively). The isoenzymes differed in their isoelectric points (gMDH: 8,92, mMDH: 5.39), rate of heat inactivation (gMDH: τ1/2 at 40°C=3.0 min; mMDH: stable at 40°C; τ1/2 at 60°C=4.5 min), adsorption to dextran gels at low ionic strenght, stability against alkaline conditions and their pH optima for oxaloacetate reduction (gMDH: pH 6.6, mMDH: pH 7.5). Very similar pH optima, however, were observed for L-malate oxidation (pH 9.3–9.5). The results indicate that the glyoxysomal and mitochondrial MDH of watermelon cotyledons are distinct proteins of different structural composition.

Walk, R.; Hock, B.

doi: 10.1007/BF00385988pmid: 24420394

Kinetic parameters of the glyoxysomal and mitochondrial malate dehydrogenase (EC 1.1.1.37) of watermelon (Citrullus vulgaris Schrad.) cotyledons were compared. The data were obtained by initial rate experiments at pH 8.5 in both directions of the reaction using homogeneous enzyme preparations. Substrate inhibition at physiologically significant concentrations was observed with reduced nicotinamide adenine dinucleotide (NADH) (50% inhibition at 0.65 mmol·l-1 NADH), but not with oxaloacetate, L-malate or oxidized nicotinamide adenine dinucleotide. The inhibition of both isoenzymes by 5′adenosine monophosphate was studied. Inhibition was found to be competitive with respect to NADH and non-competitive with respect to oxaloacetate. The apparent inhibitor constants at 200 μmol·l-1 of the fixed substrates were 3.2 and 1.6 mmol·1-1 for NADH, and 3.2 and 5.2 mmol·l-1 for oxaloacetate with the glyoxysomal and mitochondrial isoenzymes, respectively. The energy of activation was determined for oxaloacetate reduction by glyoxysomal (E a =3.14×104J×mol-1) and mitochondrial (E a =4.10×104 J x mol-1) MDH from Arrhenius plots, which exhibited constant slopes throughout the range of thermal stability.

Ohta, Yoshimoto; Katoh, Kenji; Miyake, Keiko

doi: 10.1007/BF00385989pmid: 24420395

A green-pigmented cell suspension culture of Marchantia polymorpha was established using the medium of Murashige and Skoog with addition of organic acids of the tricarboxylic-acid cycle, vitamins and sugars plus sugar alcohols, exclusion of kinetin, and replacement of sucrose with glucose. In continuous light, the cells grew exponentially for ca. 10 days; in the dark, they grew only to a slight extent. The light-grown cells contained well-developed chloroplasts, and chlorophyll content reached almost twice that of the intact gametophyte.

Schreiber, Ulrich; Berry, Joseph

doi: 10.1007/BF00385990pmid: 24420396

Methods were developed to measure chlorophyll fluorescence yield of intact leaf tissue during heat treatment under varying conditions of light intensity and photosynthetic activity. Fluorescence yield of a dark-adapted leaf increases by 2- to 3-fold with an increase of temperature into the region where heat-damage occurs. The temperatures of the fluorescence transition correlate well with the temperatures where quantum yield of CO2 fixation is irreversibly depressed. Fluorescence-temperature (F-T) curves allow ranking of different species according to their heat sensitivity. Within a single species acclimation to different growth temperatures is reflected by shifts of the transition temperatures in the F-T curves. When F-T curves are recorded in the steady light states at increasing light intensities, substantial shifts (up to 6°C) of transition temperatures to higher values are observed. Quantum yield measurements of CO2 fixation confirm that hight-light conditions protect from heat-damage. It is suggested that chlorophyll acts as an intrinsic fluorescence probe of the thylakoid membrane and responds to the same changes which cause irreversible denaturation of photosynthetic enzymes.

Cresti, M.; Pacini, E.; Ciampolini, F.; Sarfatti, G.

doi: 10.1007/BF00385991pmid: 24420397

Morphologic changes occurring during pollen grain activation and ultrastructural features of Lycopersicum peruvianum Mill. pollen tube during the first stages of growth in vitro have been studied. The more evident morphologic changes during activation, in comparison to those already described for mature inactive pollen, concern dictyosomes, rough endoplasmic reticulum (RER), and ribosomes. The dictyosomes are very abundant and produce “large” and “small” vesicles. Near the germinative pores both types of vesicles are present, while all along the remaining cell wall only the large type is observed. These latter react weakly to Thiéry's test and probably contain a callose precursor necessary for the deposition of a callosic layer lining at first only the inner side of the functioning pore and occasionally the other two pores, and subsequently the entire inner surface of the cell wall. The small vesicles, highly positive to Thiéry's test, are present only near the pores and could be involved in the formation of the pectocellulosic layer of the tube wall. The setting free of RER cisterns, which in the mature inactive pollen were aggregated in stacks, coinciding with polysome formation and resumption of protein synthesis, is in accord with the hypothesized role of RER cistern stacks as a reserve of synthesizing machinery. The pollen tube reaches a definitive spatial arrangement soon after the generative cell and vegetative nucleus have moved into it. At this stage four different zones that reflect a functional specialization are present. In the apical and subapical zone two types of dictysosome-originated vesicles, similar to those found in the activated pollen grain, are present. Their role in the formation of the callosic and pectocellulosic wall layers seems to be the same as in the activated pollen grain.

Dewsberry, Roland

doi: 10.1007/BF00385992pmid: 24420398

Plant self-thinning of Hellianthus annuus is examined and it is shown that the mean leaf area ratio is equal to the mean plant density ratio to the power-4/3 independent of the mean plant dry weight and independent of the light intensity over the experimental range considered. The constant term of this basic self-thinning equation is identified, in terms of the mean leaf area and mean plant density values (L c and p c respectively) for the plant population in its earliest competing post germination stage and in terms of the derivatives (d log L/d log p)1=(d log L/dt)1/(d log p/dt)1=-4/3 which is independent of light intensity, as L c pc -4/3.

Burgess, J.; Linstead, P.J.

doi: 10.1007/BF00385993pmid: 24420399

The binding of a colloidal gold-Concanavalin A (ConA) complex to the plasmalemma of tobacco leaf protoplasts has been investigated using scanning electron microscopy. At 5° C the particles of gold-ConA appear to be randomly distributed over the surface of the protoplast. If the temperature is raised, the particles associate into clusters. Saturation of the membrane with particles can only occur when the weight of ConA in solution exceeds 1 μg/104 protoplasts in suspension, and when its concentration exceeds 15 μg/ml. These results are discussed in terms of the properties of the ConA binding site and the mobility of such sites within the membrane surface.