Showing papers in "Physiologia Plantarum in 1979"

Mineral Nutrient Requirements of Pinus silvestris and Picea abies Seedlings

Abstract: The mineral nutrient requirements of Pinus silvestris L. and Picea abies Karst. were studied according to previously published methods applied to a series of various plant species. The optimum nutrient proportions are similar to those of Vaccinium, with a lower relative potassium requirement than birch and other broad-leaf species. Various ratios between ammonium and nitrate nitrogen were about equally efficient except for a minor growth reduction with pure nitrate, which gave a comparatively low nitrogen content and a high cation/nitrogen ratio. The rate of ammonium uptake was much higher than that of nitrate when both sources were supplied. The required total concentration in the nutrient solution for maximum growth is lower in pine than in spruce, but both fall within the low salt range. Both species, especially pine, are sensitive to high salt concentrations. Although pine and spruce grow on the same type of soils as Vaccinium— leached soils with low base saturation – accumulation of calcium or other cations is not as pronounced as in Vaccinium, especially not in pine. The results are compared with results from similar experiments with a series of other conifers. All the conifers have more flexible cation uptake mechanisms than Vaccinium but the results indicate tendencies to accumulation of anions, nitrate and phosphate. Recommended fertilizer compositions for forest fertilization and nurseries are discussed.

Nitrogen stress in birch seedlings. II. N, K, P, Ca, and Mg nutrition

Abstract: In a series of experiments with nitrogen stress, optimum and supra-optimum nitrogen supply, N, K, P, Ca, and Mg have been analysed in leaves, stems and roots of birch seedlings (Betula oerrucosa Ehrh.). Growth rate was strongly and linearly correlated with the nitrogen status of the seedlings within the whole sub-optimum range. Seedling weight was equally strongly correlated with nitrogen status, although exponentially. Various expressions for growth rate and nitrogen status give similar results. Nitrogen efficiency (dry matter produced per unit nitrogen) decreased with increasing nitrogen status, but nitrogen productivity (dry matter produced per unit nitrogen and time) increased up to optimum. The maintenance of a stable nitrogen status in the seedlings and a stable growth rate requires an accurate and closely controlled technique of nitrogen addition. Because of the exponential relation between seedling weight and sub-optimum nitrogen status and a rapid decrease in the supra-optimum range, a strict control of the optimum status is necessary to maintain maximum growth.

Uptake of nitrate by mutants of arabidopsis-thaliana, disturbed in uptake or reduction of nitrate .2. kinetics

Abstract: The uptake of nitrate by wildtype plants and chlorate-resistant mutants of Arabidopsis thaliana (L.) Heynh. was studied by intermittent or continuous measurement of the nitrate concentration of the ambient solution. The uptake rate in the wildtype and the nitrate reductase-less mutant B 25 showed a dual-phase relation ship with concentration. Each phase showed Michaelis-Menten kinetics although multiphasic patterns within each phase could not be excluded. A dual-phase relationship was also found in the uptake mutant B I. Here, however, phase II did not follow Michaelis-Menten kinetics and uptake rate of nitrate in the phase II concentration range was considerably lower in the B 1 mutant than in the wildtype. It is concluded that the mutation in B I has disturbed phase II of the nitrate uptake, without affecting phase I, which leads to the suggestion that uptake of nitrate in Arabidopsis is mediated by at least two independent uptake mechanisms. The nitrate uptake rate showed an optimum at pH 8, and it was not stimulated by the presence of calcium. Ammonium had different effects on nitrate uptake: a direct effect, when it was present during the uptake of nitrate, resulting in a release of nitrate and a reduced rate of uptake, and an indirect inhibitory effect, possibly caused by assimilation products of ammonium, which is most pronounced after growth on ammonium as the sole nitrogen source or in long-lasting uptake experiments in the presence of ammonium. Chlorate also showed a multiple effect, an inhibiting one which proved to be competitive and, at very low concentrations of chlorate, a stimulating one. Evidence was obtained that chlorate and nitrate arc taken up by the same carrier.

The Influence of Light and Temperature on Isoprene Emission Rates from Live Oak

Abstract: There is a growing awareness of the role of vegetation as a source of reactive hydrocarbons that may serve as photochemical oxidant precursors. A study was designed to assess independently the influence of variable light and temperature on isoprene emissions from live oak (Quercus virginiana Mill.). Plants were conditioned in a growth chamber and then transferred to an environmentally controlled gas-exchange chamber. Samples of the chamber atmosphere were collected; isoprene was concentrated cryogenically and measured by gas chromatography. A logistic function was used to model isoprene emission rates. Under regimes of low temperature (20°C) or darkness, isoprene emissions were lowest. With increasing temperature or light intensity, the rate of isoprene emission increased, reaching maxima at 800 μE m-2 s-1 and 40–44°C, respectively. Higher temperatures caused a large decrease in emissions. Since the emissions of isoprene were light-saturated at moderate intensities, temperature appeared to be the main factor controlling emissions during most of the day. Carbon lost through isoprene emissions accounted for 0.1 to 2% of the carbon fixed during photosynthesis depending on light intensity and temperature.

Starch Measurement in Plant Tissue Using Enzymatic Hydrolysis

Abstract: This work explored completeness of starch hydrolysis in situ in relation to degree of gelatinization, starch content of tissue, evailable enzyme activity, and time allowed for hydrolysis. Maximum hydrolysis of starch in lyophilized red oak (Quercus rubra L.) root tissue with purified Diazyme (amyloglucosidase) or Clarase (Takadiastase) required high enzyme activity (2.4 U Diazyme or 48 U Clarase per mg starch). Results suggested that at least 70 U Clarase or 5 U Diazyme should be used per mg starch in routine analyses. Neither prolonging gelatinization (more than 15 min) nor hydrolysis (more than 24 to 48 lh) offset inadequate starch hydrolysis caused by insufficient enzyme activity. Starch was completely hydrolyzed in situ after 48 h without gelatinization by 5 U of Diazyme per mg starch. Tissue weight (5 to 100 mg) had no effect on starch hydrolysis by sufficient enzyme. Methanol: chloroform: water (12:5:3 by volume) freed tissues of solubles before starch hydrolysis. No interference with the glucose oxidase analysis of hydrolysates was encountered. In addition, the pigment free methanol–water fractions (soluble sugars, amino acids, organic acids) and chloroform fractions (lipids and pigments) were available or further analysis. Results obtained with red oak were verified with issue from other species such as jack pine (Pinus banksiana lamb.) and white spruce (Picea glauca (Moench) Voss). The resulting technique simply and reliably measured less than 5% starch in 5 mg lyophilized tissue, with a minimum of sample manipulation.

Influence of Rate of Development of Leaf Water Deficits upon Photosynthesis, Leaf Conductance, Water Use Efficiency, and Osmotic Potential in Sorghum

Abstract: This study reports the effect of rate of development of leaf water deficits in soil-grown sorghum (Sorghum bicolor) on the relationship of net photosynthesis, leaf conductance, and water use efficiency to leaf water potential, and on the degree of solute accumulation (osmotic adjustment). Recovery of these processes on rewatering, and responses during a second stress cycle were also studied. The most rapid rate of stress (1.2 MPa day−1) resulted in no solute accumulation and the lowest rate of net photosynthesis and leaf conductance for any given leaf water potential during stress. Stress at 0.7 and 0.15 MPa day−1 led to equal solute accumulations of approximately 0.6 MPa, but net photosynthesis, leaf conductance, and water use efficiency at a given leaf water potential were lower with the faster rate of stress (0.7 MPa day−1). Additionally, leaf conductance at a given leaf turgor potential was lowest at the 1.2 MPa day−1 stress rate, slightly higher at the intermediate rate of stress, and clearly highest at the slowest rate of stress. Recovery of both net photosynthesis and leaf conductance upon rewatering was rapid, taking less than 3 days, but full recovery of osmotic potential took between 6 and 11 days. One slow stress cycle had no influence on relationships during a second cycle. The concept of a threshold leaf water potential for stomatal closure is discussed and the conclusion reached that stomatal closure occurs slowly over a wide range of leaf water potential (> 1.0 MPa), the range being greater for slower rates of stress.

Plant Regeneration from Mesophyll Protoplasts of Several Nicotiana Species

Abstract: In a search for model systems in plant cell genetics studies mesophyll protoplasts from eleven species of Nicotiana with low chromosome number (N. acuminata, N. alata, N. glauca, N. glutinosa, N. langsdorffii, N. longiflora, N. otophora, N. paniculata, N. plumbaginifolia, N. suaveolens, N. sylvestris) were shown to divide in a liquid culture medium. Plants were recovered from calli originating from protoplasts of all these species except N. glutinosa.

Osmotic Requirement for Shoot Formation in Tobacco Callus

Abstract: Tobacco callus grown on medium containing 3% sucrose (w/v) shows optimum growth and produces the highest number of shoots; whereas cultures grown on medium with lower or higher sucrose levels show a reduced growth rate and capacity to form shoots. Cultures grown on a low sucrose containing medium produce a high number of shoots only if the medium is supplemented with mannitol to give the same water potential as that of the 3% sucrose medium. Mannitol cannot replace the sucrose requirement for growth. Increased levels of Bacto Agar, tricarboxylic acid cycle intermediates and amino acids added to the medium do not promote shoot formation or replace the carbohydrate requirement for that process. The success in partially replacing the sucrose requirement for shoot formation with mannitol supports the view that part of the tissue carbohydrate is acting in an osmoregulatory role. This finding is further interpreted in terms of the hypothesis of turgor-driven growth and cell expansion.

Analytical Procedures for the Sequential Extraction of 14C‐Labeled Constituents from Leaves, Bark and Wood of Cottonwood Plants

Abstract: A procedure for the extraction, separation, and measurement of photosynthetically fixed 14C in up to 8 chemical fractions (CHCl), amino acids, organic acids, sugars, protein, starch, hemicellulose, and residue) from small samples (1 to 100 mg) of cottonwood (Populus deltoides Bartr.) leaf material is described. The different chemical fractions are extracted in a sequence of chemical, ion exchange, and enzymatic steps. The 14C-activity in these major fractions is then determined with liquid scintillation spectrometry. These major fractions (e.g., sugars, amino acids, organic acids) can be further separated into their individual chemical components by standard thin-layer or gas- chromatographic methods for quantitative analysis if specific activities are desired. The major advantage of the procedure is that many chemical fractions can be sequentially separated with good reproducibility from a small amount of plant material without transfer of the material from the original homogenizer or centrifuge tube.

Effects of Fertilization and Irrigation on the Seasonal Changes of Carbohydrate Reserves in Different Age‐Classes of Needle on 20‐Year‐Old Scots Pine Trees (Pinus silvestris)

Abstract: The effects of fertilization, irrigation or both on the seasonal changes of starch and soluble carbohydrates (glucose, fructose, myo-inositol, pinitol and sucrose) in needles of 20-year-old Scots pine trees (Pinus silvestris L.) were studied during three consecutive years. The starch content of the mature needles increased during spring and early summer to about 25% of dry weight. Neither fertilization nor irrigation affected the general pattern of starch accumulation during the spring. The starch reserves were mobilized when the shoot started to grow. Starch content decreased more rapidly in needles from fertilized than in those from unfertilized trees. The current needles from the control trees accumulated starch while they were still growing. The current needles of the fertilized trees did so to a lesser extent. The amount of starch was closely correlated to the air temperature and to the growth rate. Large amounts were found at low temperatures and low growth rates. The concentrations of soluble carbohydrates showed the well-known seasonal variation, with the highest value during the winter. The levels of sugars were nearly similar, irrespective of fertilization. An exception was sucrose, which was found in small quantities in needles from fertilized plots. Small amounts of sucrose were also found in growing current needles. The results are discussed in relation to growth limitation by assimilate availability and indicate that the ‘sink demand’ is the limiting factor.

Differentiation in Lilium Bulbscales Grown in vitro. Effect of Various Cultural Conditions

Abstract: Tissue cultures of Lilium auratum Lindl and L speciosum Thunb, which were derived from bulbscales, all appeared to differentiate organs The effect of cultural conditions on the differentiation of bulblets and roots was examined The best material for bulblet formation was bulbscales of intact or in vitro produced bulblets The optimum temperature was 20°C and optimum pH was 6 Effect of irradiance on organ formation was not obvious but leaf emergence was stimulated Higher kinetin concentrations stimulate the formation of numerous bulbscalcs High NAA concentrations induce roots On the other hand kinetin inhibits the NAA effect on root formation A high sucrose concentration stimulated organ formation, but the number of bulblets was at a constant level in the medium containing between 10 and 90 g/l of sucrose The formation of bulblets and their growth were stimulated at increasing strength of Murashige-Skoog's (MS) medium, but the length of roots was inhibited Inter action of strength of MS medium and sucrose concentration was examined High concentration of both components stimulated bulb lei growth, but the second strength of MS medium containing 90 or 120 g/l sucrose stimulated callus induction and inhibited the growth of bulblets Maximum growth took 100 days for bulblets and about 50 days for roots The change of fresh weight/dry weight ratio during differentiation is also discussed

Epicuticular Wax and Cuticular Resistance in Rice

Abstract: High leaf cuticular resistance has been reported as a component adaptation of plants to drought prone regions, Experiments were conducted to evaluate and characterize the role of epicuticular wax as a component of cuticular resistance to water vapor loss from rice (Oryza sativa L.) leaves. This information is necessary to determine the applicability of including higher cuticular resistance in an upland rice breeding program and to evaluate potential selection methods. Diffusion porometry, electron microscopy, and gas liquid chromatography were employed. Measurement of cuticular resistance by leaf diffusive resistance porometry after stomatal closure by exposure of rice leaves to pure CO2 for 15 min was found sufficient to induce complete stomatal closure regardless of light level, and was superior to dark acclimation for this purpose. Removal of epicuticular wax from rice leaves by chloroform dip significantly reduced the cuticular resistance. Stressed plants were observed to increase cuticular resistance, illustrating the responsive nature of this characteristic. Gas liquid chromatography (GLC) of the chloroform leaf dip proved to be an expedient method of characterizing both quantitative and qualitative differences in the epicuticular wax of rice cullivars. The porometry and GLC techniques may be useful in selecting parents, spot checking in a pedigree program, or checking lines reaching the yield testing stage, but ate not well suited lor mass screening early generation progeny. Significant differences were found in the two rice cultivurs, ‘63–83′, an upland adapted rice from West Africa, and “IR20′, bred and selected in submerged paddy culture in ihc Philippines, by tlie above methods of characterizing cuticular resistance and epicuticular wax. These results are of ecological significance to plant breeders.

The Role of Endogenous Auxins and Ethylene in the Formation of Adventitious Roots and Hypocotyl Hypertrophy in Flooded Sunflower Plants (Helianthus annuus)

Abstract: The role of ethylene and auxins in flood-induced adventitious root formation and hypocotyl hypertrophy in sunflower (Helianthus annuus L. cv. Russian) plants was studied. Flooding without aeration (F) resulted in a steady increase in ethylene in hypocotyls, and flooding with aeration (FA) caused a transient increase. Low light intensity increased ethylene levels but decreased adventitious root formation. Treatment of shoots with benzyladenine (BA) increased ethylene content in non-flooded (NF) but not in F or FA shoots. Twenty-four hours of flooding brought about a rise of endogenous indole-acetic acid (IAA) in hypocotyls. 14C-IAA applied to the shoot accumulated more in F and FA hypocotyls than in NF hypocotyls, and BA reduced this accumulation. There was less IAA metabolism in F and FA than in NF hypocotyls. Tri-iodo benzoic acid (TIBA) applied to the hypocotyls of F plants inhibited root production. Benzyladenine (BA) applied to the leaves had similar effect but was not effective when supplied to the shoot apex. BA did not inhibit flood-induced hypocotyl hypertrophy. Ethrel did not affect adventitious root formation in NF plants but did increase hypocotyl thickening. It is concluded that flood-induced adventitious root formation is stimulated primarily by an accumulation of auxins in the hypocotyls. Increases in ethylene might cause this auxin build up. Hypocotyl hypertrophy is presently thought to be the result of an interaction of auxin and ethylene with ethylene being the major factor.

Effects of Sulphur Dioxide on Sugar and Free Amino Acid Content of Pine Seedlings

Abstract: Treatment of jack pine (Pinus banksiana Lamb.) seedlings with gaseous SO, resulted in a shift between the reducing and nonreducing sugars. Increasing concentrations of gaseous S02 caused an increase in reducing sugars and a decline in the non-reducing sugars, suggesting a conversion from the latter to the former at high S02 concentrations. The total amino acid content of the intact tissues also increased with increasing concentrations of gaseous S02. Gas-liquid chromatographic analyses of the amino acids

Starch Synthesis in Developing Potato Tubers

Abstract: The activities of enzymes involved in starch metabolism were measured at intervals during tuberization and the early stages of tuber growth in Solanum tubersum grown in water culture under controlled environmental conditions. Starch synthase, ADPglucose pyrophosphorylase, UDPglucose pyrophosphorylase and phosphorylase activities all increased during tuber development, the most pronounced increases occurring in the activities of ADP-glucose pyrophosphorylase and phosphorylase. The activity ratio ADPglucose pyrophosphorylase/phosphorylase was lowest in slow growing tubers and hightest in fast growing tubers. In addition, high sugar concentrations in fast growing tubers and low sugar concentrations in slow growing tubers suggested that enzyme levels might be influenced by sugar concentration. The activities of starch synthase, phosphorylase and ADPglucose pyrophosphorylase were increased 2–2.5 fold by the presence of 100 mM K+. It is concluded that the major enzyme changes occur as a consequence of tuber initiation and that starch accumulation is controlled, at least in part, by the activities of ADPglucose pyrophosphorylase and phosphorylase.

Effects of Glyphosate on Metabolism of Phenolic Compounds

Abstract: Amounts of extractable phenylalanine ammonia-lyase (PAL; E.C. 4.3.1.5) activity increased in the axes of 3–day-old, dark-grown soybean seedlings [Glycine max (L.) Merr.] shortly after the seedlings were transferred to glyphosate [N-(phosphonomethyl)-glycine] solutions. The stimulation of PAL activity in herbicide-treated tissue (as compared to control tissue) was detectable as early as 12 h after treatment, whereas growth inhibition (length, fresh weight and dry weight) was not significantly affected until 24 h on a fresh-weight basis and at 48 h on a dry-weight basis. PAL activity increased with time (12–72 h) in herbicide-treated axes when expressed as activity per gram fresh weight, specific activity, and on a per axis basis. PAL activity stimulation correlated positively with glyphosate concentration from 10–4 to 10–3M. PAL activity in control tissues remained nearly constant over the sampling period (12–72 h). Total alcohol-soluble hydroxyphenolic compound levels in treated axes were not significantly different from the control at any sampling period. The total soluble amino acid pool showed a general decrease with time in glyphosate-treated tissues. The phenylalanine pool was lowered with treatment time and the ammonia concentration (per g fr. wt. basis) was increased after treatment. No significant differences were noted in the concentration of soluble protein of glyphosate-treated tissue when compared to controls. Visual effects (stunting, lack of secondary root formation, and necrotic areas) of glyphosate were more obvious in the root than in the hypocotyl. Analysis of various chemical constituents substantiated that other glyphosate effects were more clearly demonstrable in the root than in the hypocotyl or in the intact axis. On a per root basis glyphosate markedly increased PAL activity while reducing free phenylalanine, free tyrosine, soluble hydroxyphenolics, total free amino acids and ammonia content. The effect of glyphosate in the root was greatest on phenylalanine content, reducing it five-fold. The results indicate that glyphosate could exert its effect through either induction of PAL activity and/or inhibition of aromatic amino acid synthesis.

Translocation of 14C‐Assimilates in Roses

Abstract: Movement of 14C-assimilates from young and mature leaves to young rose shoots (Rosa hybrida cv. Marimba) was examined in two developmental stages. In the first stage after bud breaking the young shoot, especially its tip, depends for its supply of assimilates mainly on the mature foliage. At this stage young leaves are powerful sinks and retain 97% of their own photosynthates. The translocated 3% move mainly to the roots. At a later stage, just after the appearance of the flower bud, most of the leaves on the shoot become a source. The upper leaves supply assimilates to the flower bud and to the upper part of the stem. The 14C-assimilates from the lower leaves move in two directions, the larger part being directed downward.

The Effect of Salinity on Growth, Cation Content, Na+‐Uptake and Translocation in Salt‐Sensitive and Salt‐Tolerant Plantago Species

Abstract: Growth of salt-sensitive Plantago media L. and salt-tolerant P. coronopus L. and P. maritima L. was followed under saline conditions. Growth was reduced according to the ecological features of these species: P. media was sensitive to 25 mM NaCl, while P, coronopus and P. maritima could grow in 150 mM and 300 mM NaCl, respectively. The three Plantago species accumulated Na+ in the shoot and maintained a relatively low Na+ level in the root. K+. Mg2+ and Ca2+ levels of both shoots and roots decreased with increasing salinity. The results suggest that the difference between salt-resistant and salt-sensitive species is located in the ion secretory system which is involved in the ion translocation from the root to the shoot rather than in the primary uptake process through the plasmalemma of the cortical cells.

Diurnal and Seasonal Changes in Leaf Water Potential Components and Elastic Properties in Response to Water Stress in Apple Trees

Abstract: Apple trees are very drought tolerant, having the capability to grow and carry on photosynthesis even at low water potentials. Much of the tolerance is due to the ability of apple leaves to maintain turgor potentials at levels conducive to growth and stomatal opening. Diurnally, leaf turgor is maintained through decreases in osmotic potentials (due to active solute accumulation), osmotic adjustment, or to concentration of solutes via tissue water loss. These two processes combined may decrease osmotic potentials by as much as 1.65 MPn during the day. Seasonally, osmotic potentials remain fairly constant, but leaf elasticity increases, allowing growth to continue and stomata to remain open us water and turgor potentials become progressively lower. Release of stored water from plant tissues to the transpiration stream is another means of preventing water potentials from reaching critical values for stomatal closure. A combination of a number of these physiological adaptations may account for much of the drought tolerance in apple trees.

Hydraulic Resistance of Rough Lemon Roots

Abstract: A pressure chamber technique was used to estimate hydraulic root resistance in rough lemon (Citrus jambhiri Lush.) seedlings. The effect of previous water stress on hydraulic root resistance was evaluated. A factorial 3 × 3 design with four replications was established with potted rough lemon seedlings in a growth chamber. Three water-stress treatments were applied by watering at intervals of 1, 2 and 3 days, and root resistance measurements were made after 6, 12 and 18 days of treatment. Plants that had experienced mild and severe water stress (irrigation interval of 2 and 3 days, respectively) had higher hydraulic root resistances after several drying cycles than those plants irrigated daily. Additional cycles had no significant effect. The increase in root resistance was not due to decreased root growth but apparently to changes in the permeability of the root cell membranes or to increased suberin deposition in the cell walls of the cortical cells. In a short-term experiment (1 h), temperature strongly affected water flow through rough lemon roots in the range 5 to 35°C. Temperature influenced root membrane permeability, since reduced blow could not be explained by changes in water viscosity.

Activities of Enzymes Relating to Starch Synthesis and Endogenous Levels of Growth Regulators in Potato Stolon Tips During Tuberization

Abstract: Changes in contents of starch and protein, and activities of enzymes involved in starch synthesis were studied during tubcrization of stolon tips of Solanum tuberosum L. cv. Irish Cobbler. Starch content and activities of phosphorylase and granule-bound starch synthctase based on fresh weight increased rapidly in the early phase (stage I, the stolon tips just before swelling; stage 2, the swelling tips; stage 3, young tubers of 0.2–0.5 cm diameter), and they all remained nearly unchanged in the later phase (stage 3 to stage 6, young tubers of 3.5 cm diameter). The content of soluble protein based on fresh weight remained unchanged. Activities of soluble starch snythetase and ADP-glucose pyrophosphorylase were not detected at stage 1 and 2, but increased at later stages. Endogenous levels of auxin, cytokinin and gibberellin were assayed for the materials at the corresponding developmental stages. Auxin content was high at stages 1 and 2, and lowered at later stages. Cytokinin content increased abruptly at stage 6. Gibberellin content was low at all stages. The internal conditions for starch deposition and tuberization in potato were discussed in regard to regulation of enzyme activities by growth regulators.

Isolation and Mobilization of Storage Proteins from Apple Shoot Bark

Abstract: Separation of the bark storage protein into three groups was achieved with minimal contamination from interfering cbromophores, using diethylaminoethyl cellulose column chromatography. Two of these groups were shown 10 contain neutral sugars in close association with the proteins. All three groups disappeared rapidly after the onset of growth. Polyacrylamide gel electrophoresis of the storage proteins showed the presence of eight prominent proteins. Ammo acid analysis of hydrolyzates of the proteins indicated that a large percentage of the protein nitrogen was in the form of basic amino acids.

Stomatal Responses of Fraxinus pennsylvanica Seedlings during and after Flooding

Abstract: Effects of flooding for 10, 20, 30, or 40 days on leaf diffusion resistance (r1) of fraxinus pennsylvanica seedlings were studied during the period of flooding and continuing for 17 days after flooding. All Flooding treatments induced stomatal closure, as indicated by increased r1. There was some evidence of stomatal adaptation to flooding, with stomata beginning to reopen after a critical period of flooding. After termination of flooding, stomata opened further within 6 to 10 days to near preflooding levels. The degree of stomatal opening was only slightly higher after 10 days than after 40 days of flooding. Some stomata may have been permanently damaged by flooding. The stomatal adaptation to flooding as well as rapid recovery of stomatal opening, even after prolonged flooding, appeared to be important factors in the flooding tolerance of Fraxinus petmsylvanica and are consistent with its distribution on wet sites.

Freeze-Preservation of Rice Cells Grown in Suspension Culture

Abstract: A simple procedure has been worked out for the freeze-preservation of rice (Oryza sativa L.) cells grown in suspension culture. The protocol differs in some interesting aspects from those established for other organisms. A peculiar feature of this procedure is that growth of freeze-recovered rice cells resumes after an extremely short lag period of 2–8 days and proceeds with a growth rate identical to that of untreated cells. This, together with data obtained with viability tests, rules out the possibility that selection of freeze-resistant mutant cells may occur, as postulated with other plant cells where growth resumption was considerably delayed in time. The viability of freeze-recovered rice cells, when assessed at time zero after thawing by measuring the mitochondrial respiratory efficiency, was 60–65% of that of untreated cells. However, the limits of this and other viability tests in determining the efficiency of the freeze preservation methods and the percentage of surviving cells were shown by experiments in which cell viability and cell growth were followed in cultures initiated with freeze-recovered rice cells.

Nitrogen Fixation Associated with Sand Grain Root Sheaths (Rhizosheaths) of Certain Xeric Grasses

Abstract: Nitrogen fixation (acetylene reduction) was found to be associated with sand grain root sheaths (rhizoseaths) occurring on the following xeric grasses: Oryzopsis hymenoides (Roem. and Shult.) Ricker, Agropyron dasystachyum (Hook.) Scrib., Stipa comata Trin. and Rupr., and Aristida purpurea Nutt. Acetylene reduction rates associated with whole plant specimens of these species varied from 515 to 920 nmol C2H4/(g dry wt.) × (6 days). Nitrogenase activity was shown to be associated with the rhizosheaths. Bacillus polymyxa-like nitrogen fixers were isolated from the rhizosheaths of each grass. The isolates reduced acetylene and assimilated 15N2.

Relationship between Position on the Parent Plant and Dormancy Characteristics of Seeds of Three Cultivars of Celery (Apium graveolens)

Abstract: Germination and seedling emergence studies were made on seeds harvested from four different umbel positions of three cultivars of celery (Apium graveolens L.). Although heavier seeds were produced from primary umbels than from other umbels, these were less viable as measured by the germination percentage at 18°C in the light. However, germination of viable seeds from quaternary umhels was lower than that of seeds from primary umbels at 18'^C in the dark when incubated with GA^^, (2 x 10""* M) and seeds from secondary and tertiary umbels tended to be intermediate in response. All viable seeds germinated when N^-benzyladenine (10"^ M) was used in combination with GA^^.,. Seeds from quaternary umbels of two of the cultivars had a lower high-temperature limit for germination in the dark than did seeds from other umbels. In glasshouse experiments the emergence of viable 'quaternary' seeds of these cultivars was higher than that of 'primary" seeds. Under these conditions the time to 50% of the final emergence as determined after 42 days was similar for seeds from all umbel positions within each cultivar. In two vaneties seedling weights were greater from seeds of primary as compared to quaternary umbels, and in general, the largest seedlings arose from the heaviest seeds and the smallest from the lightest seeds in all three cultivars.

The Effect of 2,3.5 Triiodobenzoic Acid on Caulogenesis in Callus Cultures of Tomato and Pelargonium

Abstract: Stem explants from winter grown tomatoes cultured on a cytokinin, auxin-free medium, developed one or two adventitious shoots at the top end of the explant. Addition of the auxin transport inhibitor. 2,3,5-triiodobenzoic acid (TIBA) to the medium stimulated caulogenesis with loss of polarity. Callus, initiation in pelargonium and ‘geranium’ petiole explants requires both auxin and cytokinin. On transfer, after callus induction to an auxin-free medium, rhizogenesis occurs in pelargonium cultures followed by caulogenesis. Few shoots develop and unless these are removed, further caulogenesis is suppressed. Bud-like structures were formed in the callus. Subculture on auxin-free medium containing cytokinin and TIBA resulted in shoot formation from these bud-like organs. An analogy with apical dominance is suggested. In ‘geranium’ callus, shoots developed with a low frequency (c. in 2% of the cultures): caulogenesis was increased to 80% when calli were subcultured from auxin-free, cytokinin medium after green nodule formation to cytokinin-TIBA medium. Histological studies of green nodules in ‘geranium’ callus indicated a variation in morphological development within and between nodules. It is suggested that auxin synthesis may occur at some microscopic stage in morphogenesis in ‘geranium’ cultures which suppresses further caulogenesis. This may be overcome by the addition of TIBA to the medium at the appropriate stage in morphogenesis. The possible interaction of endogenous auxin in morphogenesis is discussed.

Ethylene Production by Tobacco (Nicotiana tabacum) Callus

Abstract: Tobacco callus cultures grown on defined agar-solidified media produced ethylene in differing amounts, which were related to cultural treatment and age of the callus. There was a close correlation between the rate of ethylene production and growth. In darkness, maximal rates occurred in the third week of growth with ethylene production in the range of 750 nl (callus piece)−1 d−1 (fr. wt. = 1.5 g), and in the light, maximal rates occurred in the first week of growth, 200 nl (callus piece)−1 d−1 (fr. wt. = 200 mg). Growth was also correlated with ethylene production when the latter was altered by exposure of the callus to inhibitors of ethylene synthesis, L-canaline, benzyl isothiocyanate, and 3,5-diiodo-4-hydroxy-benzoic acid. No correlation was found following treatment with AgNO3, a presumptive inhibitor of ethylene action. The inhibition of growth and ethylene production by L-canaline was partially reversed by gassing the cultures with ethylene (1 μl/1). A mercuric perchlorate sink had no significant effect on growth. A possible relationship between ethylene evolution and growth is discussed.