Showing papers in "Physiologia Plantarum in 1974"

Growth and Dormancy in Norway Spruce Ecotypes (Picea abies) I. Interaction of Photoperiod and Temperature

Abstract: Growth and dormancy as affected by photoperiod and temperature have been studied in Norway spruce ecotypes of different latitudinal and altitudinal origin. First-year seedlings were used. In all ecotypes apical growth cessation and terminal bud formation occurred within 2 weeks after exposure to SD at temperatures of 18 to 24°C. At lower temperatures or at near-critical photoperiods the response was delayed. The critical photoperiod for apical growth cessation varied from 21 hours in ecotype Steinkjer, Norway (64°N) to about 15 hours in ecotype Lankowitz, Austria (47°04′N). High-elevation ecotypes also had longer critical pholoperiods than low-elevation ecotypes from the same latitude. A detectable growth depression resulted from as little as 1 or 2 SDs of 10 hours, and with 4 or more SDs apical growth cessation took place. In contrast to the situation in the shoot, root growth was not affected by photoperiod. Accordingly, the top:root ratio is drastically affected by photoperiod. The critical photoperiod for cambial growth was shorter than that for apical growth in all ecotypes and cambial growth cessation was delayed for several weeks compared with cessation of apical growth. A transition to formation of late-wood tracheids with thick walls and narrow lumens took place upon exposure to SD. The photoperiodic effects were significantly modified by temperature, but the critical photoperiods were only slightly changed by temperature in the range of 12 to 24°C. However, a 10-hour “night” at 4°C caused growth cessation in continuous light in four ecotypes tested. Temperature optimum for apical growth under non-limiting photoperiods (24 hours) was 21°C in all ecotypes, but with little difference among 18,21 and 24°C. The Q10 for apical growth was 3.5 in the temperature range 12 to 18°C. The growth potential as determined in 24-hour photoperiods was not significantly different among the various ecotypes except for one northern eco-type which was clearly inferior to the others. However, the growth of ecotype Steinkjer (64°N) was greatly suppressed even by the long midsummer days at 59°40′N, thus demonstrating the misleading impression one gets of the growth potential of northern ecotypes when they are moved southwards.

Effect of Cd on photosynthesis and transpiration of excised leaves of corn and sunflower

Abstract: Detached corn and sunflower leaves exposed to various concentrations of Cd, supplied as CdCl2, exhibit reduced photosynthesis and transpiration. The reduction is dependent on the concentration of CdCl2 solution and generally becomes more pronounced with time. In sunflower, net photosynthesis and transpiration are completely inhibited within 45 min after the introduction of 18 mM Cd. Within two hours net photosynthesis is reduced to 40% and 70% of maximum after the introduction of 9 and 4.5 mM Cd respectively. In corn the trend of photo-synthetic response to Cd is similar to that in sunflower except that the inhibition in corn is more pronounced at all treatment levels. A strong linear relationship between photosynthesis and transpiration inhibition is obtained in both species suggesting that Cd contamination induces stomatal closure.

Iron-stress response in tomato (Lycopersicon esculentum). 1. Sites of Fe reduction, absorption and transport

Abstract: T3238fer (Fe-inefficient) and T3238FER (Fe-efficient) tomato plants differ in their ability to utilize Fe and therefore can be used as test genotypes to locate sites of Fe uptake or to characterize changes that occur in roots in response to Fe stress (Fe deficiency). T3238fer does not respond to Fe stress. Release of hydrogen ions and reduction of Fe3+ to Fe2+ are two primary responses of T3238FER roots to Fe stress. Fe reduction sites were predominately in the young lateral roots, and between the regions of root elongation and maturation of the primary root. The use of BDPS (bathophenanthrolinedisulfonate) to trap Fe2+ did not affect the release of H+ ions or reduction by T3238FER roots. BPDS did not decrease Fe uptake until it exceeded the Fe concentration in the nutrient solution. A sevenfold increase in BPDS caused a threefold decrease in Fe taken up by the plant. Fe3+ is reduced to Fe2+ at root sites accessible to BPDS. Adding Zn decreased the response to Fe stress. Iron stress initiates the development of lateral roots, and we propose that most Fe enters the plant through these roots. The iron moves through protoxylem into the metaxylem of the primary root and then to the top of the plant as Fe citrate. Root environmental factors that are competitive or inhibit Fe-stress response, or genotypes that fail to respond to Fe stress, contribute to the development of Fe deficiency in plants.

Organogenesis in callus from shoot apices of Pisum sativum

Abstract: Shoot formation was observed in callus from apical cells of pea (Pisum sativum L. cv. Century). Shoot apices from 4-day-old plants were macerated and the resulting cell masses grown on agar media. The callus formation and shoot production occurred within 4 to 6 weeks in defined media containing 0.2 to 5.0 μM benzyladenine and 1 μM naphthaleneacetic acid. While most callus produced one or more shoots at high frequency, root formation did not occur regularly. Plants obtained by these procedures were grown to maturity producing flowers and pods.

The water balance of cut rose flowers

Abstract: A sharp decline in water potential of petal tissue associated with wilting of cut rose flowers is described. Such a decline did not develop in senescing intact flowers. A circadian rhythm in water absorption by cut flowers was observed. The decline in fresh weight observed in the last phase of the vase life of cut flowers occurred earlier in a short-lived cultivar than in a longer-lived one. A decline in potential conductivity to water was observed with time in stems of cut roses. Concomitantly cellulase activity increased after cutting. Flowers held in cellulase solution wilted earlier than the controls. However, no difference was found in these two parameters between two cultivars differing in their longevity. The difference in longevity between the two cultivars was large especially under conditions promoting high transpiration rates, and was narrowed when flowers were either held in mild conditions, or the leaves were stripped off. Although stomates were equally open in intact flowers of the two cultivars, in cut flower shoots of the short-lived cultivar stomates were more widely open. In accordance transpiration rates were higher, and wilting occurred earlier in the short-lived cultivar than in the long-lived one. It is concluded that the earlier wilting of cut flowers of the short-lived cultivar is mainly due to lower ability to close stomates in response to water stress conditions, and not to earlier formation of vascular blockage.

Role of Ethylene in Induction of Flooding Damage in Sunflower

Abstract: The possibility that symptoms of flooding damage in plants are primarily caused by an accumulation of ethylene was investigated using pot-grown sunflower (Helianthus annuus) plants. When plants were flooded to the basal pairs of leaves, ethylene in roots and stems below the water line began to increase. This coincided with the start of hypocotyl hypertrophy and new root formation in hypocotyls, which continued for 14-16 days. There were highly significant correlations between ethylene concentration and number of roots and hypocotyl diameter. After approximately 4 days of flooding, ethylene concentrations in stems between nodes for the 1st and 3rd basal pairs of leaves started to increase, coinciding with initiation of chlorophyll breakdown and epinasty of the 2nd basal pairs of leaves. Thus, there were correlations between ethylene concentration and chlorophyll breakdown and epinasty. The lower the leaves, the more chlorophyll breakdown among 1st, 2nd, 3rd, and 4th basal pairs of leaves. The longer the flooding, the more severe the flooding damage; and even when returned to normal condition, plants flooded longer than 3 days were not able to recover from flooding damage. A gas chromatographic study revealed that Ethephon was absorbed by roots and decomposed to ethylene in the plant. Damage symptoms caused by soil application of Ethephon, such as reduced stem height, chlorophyll breakdown, epinasty of the 2nd basal pairs of leaves, and hypocotyl hypertrophy, were almost identical with those caused by soil flooding treatment. Microscopic studies revealed that radially enlarged cells and increased intercellular spaces in the cortex were the major contribution to the increased hypocotyl diameter in both flooded and Ethephon-treated plants. It is concluded that the increase in ethylene concentration in flooded plants is largely, although not exclusively, responsible for flooding damage symptoms.

Growth and dormancy in Norway Spruce ecotypes. II. After-effects of photoperiod and temperature on growth and development in subsequent years

Abstract: Height and radial growth of spruce in years n+ 1, n+ 2, and n+ 3 as affected by photoperiod and temperature in year n have been studied in controlled environments and in the field. In agreement with common opinion apical shoot growth in year n+ 1 was strongly dependent on the temperature conditions prevailing in the period following budset in year n. This was found mainly to be a direct effect upon the differentiation of the shoot and needle primordia for next year's growth. A similar, although less pronounced effect, was found also on radial growth, possibly an indirect effect elicited through the effect on apical growth. A rather wide temperature optimum of 18 to 24°C was found in three Norwegian ecotypes and a somewhat lower optimum (15 to 18 C) in an Austrian high altitude ecotype. The shorter the bud differentiation period, the higher was the temperature optimum in all ecotypes (heat sum effect). Photoperiod which is the main factor controlling the time of budset, thus had a great after-effect. The after-effect was strongly modified by photoperiod and to a lesser extent also by temperature in the current growing season. It is concluded that in second-year or older spruce plants the important effect of photoperiod in the current growing season is to control quantitatively and qualitatively the amount of secondary (lammas) shoot formation, and to modify shoot extension in the main growth flush. Longer photoperiods were needed for continuation or resumption of growth in second-year plants than for maintenance of uninterrupted growth in first-year seedlings. Delayed flushing was observed in plants maturing at high temperatures, indicating that these plants had entered a deeper state of dormancy than those maturing at lower temperatures. Also in years n+ 2 and n+ 3 apical and radical growth was significantly related to photoperiod and temperature conditions in year n. This effect gradually became an indirect one through the effects on general plant size (leaf and root area). The results are discussed in the light of previous work in the field.

In vitro Plant Formation from Stem Explants of Rape (Brassica napus cv. Zephyr)

Abstract: Internodal segments from 6-weeks-old rape plants (Brassica napus L. cv. Zephyr) were induced to differentiate in vitro producing shoots or shoots and roots on synthetic nutrient medium under controlled conditions. Benzyladenine (BA) alone (5 × 10−6 M) induced multiple shoot formation on all stem explants. Roots were induced on shoots when recultured on nutrient medium supplemented with auxins such as naphthalene-acetic acid (NAA) or indoleacetic acid (1AA) or when planted in vermiculite. Complete plant formation was obtained when NAA (2 × 1−6, 5 × 10−6 and 10−5 M) was employed in conjunction with BA at 5 × 10−6M. At higher concentrations (10−5M) NAA retards the shoot development while 1AA suppresses it totally. Lower levels of auxins along with the cytokinin did not retard or inhibit shoot differentiation.

Diurnal Cycling in Root Resistance to Water Movement

Abstract: The occurrence of diurnal changes in root resistance of cotton was studied by measuring the flow of water through 35-to70-day-old root systems under a pressure of 3.10 bars or a vacuum of 0.88 bar. The volume of exudate obtained under constant pressure or constant vacuum was 2 to 3 times greater near midday than near midnight indicating that the root resistance apparently was 2 to 3 times greater at night than during the day. The salt concentration of the exudate also cycled; the concentration was lowest at midday and highest at night, hence there was little diurnal variation in the total amount of salt moved per hour. The cycle for volume of exduate, salt concentration, and apparent root resistance had a period of 22 to 26 hours at 24°C. The cycle gradually died away 2 to 3 days after removal of the shoots. The diurnal variations appeared to be controlled by signals from the shoots because the phase of the cycles could be reset by changing the light-dark cycle under which the plants were grown. Cycling was eliminated by exposure to 8 or more days of continuous light before removing the shoots, and cycling could not be entrained by a 6 hour light-6hour dark cycle. Bubbling nitrogen gas through the nutrient medium stopped cycling. A possible role of ion or growth regulator action is discussed.

Nitrate Reductase Activity of Wheat Seedlings during Exposure to and Recovery from Water Stress and Salinity

Abstract: Nitrate reductase activity was inhibited as a result of reduced soil moisture potentials or application of NaCI to nutrient solutions. The decrease in enzyme activity of wheat seedlings exposed to salinity, was found 24 hours after exposure to stress. The effect of stress on nitrate reductase was found in cell-free extracts as well as in riro in assays of intact leaf sections. A recovery in enzyme activity was found after irrigation or after removal of seedlings from salinity. While relative water content of the leaves was restored within 3 hours after removal of stress, full recovery of enzyme activity occurred only after 24 hours. Cycloheximide and chloramphenicol suppressed the activity of nitrate reductase in non-stressed seedlings, but had no effect on the activity of plants exposed to salinity. However, during removal of stress, cycloheximide prevented completely the recovery of nitrate reductase, while chloramphenicol did not interfere with the recovery of the inhibited enzyme activity. It is concluded that a fraction of nitrate reductase may be located in the cytoplasm and lost activity during stress, probably due to inhibited protein synthesis. Another fraction which may be associated with chloroplasts, was inhibited by stress due to conformational changes or partial denaturation.

A Broad Spectrum Tissue Culture Experiment with Tobacco (Nicotiana tabacum) Pith Tissue Callus

Abstract: The composition and rationale of a broad spectrum tissue culture experiment involving 81 different media are described. Tobacco calluses sub-cultured on media in this experiment were induced to form six main types of callus depending on the concentration levels of minerals, auxins, cytokinins, and sucrose, growth factors and amino acids in the medium. Only nine of the 81 media inhibited callus growth, and growth (increase in mass divided by initial mass of fresh matter) varied considerably reaching a maximum of nearly 200 after eight weeks on a medium high in minerals, cytokinins, sucrose, growth factors and amino acids and low in auxins. Five media induced regeneration from the calluses. This experiment is suggested as a potentially fruitful introductory test for many new or unresolved tissue culture situations.

Growth and Dormancy Cycles in Citrus Bud Cultures and Their Hormonal Control

Abstract: An in vitro bud culture method was devised in order to better understand the control mechanism of Citrus bud development. This technique offers a new approach to the study of hormonal control of growth, dormancy and flowering cycles in perennial plants. Buds were excised from orchard trees throughout the year, cultured on defined media for prolonged periods, and their vegetative growth responses to various growth hormones were determined. The buds proceeded with their vegetative development in vitro and achieved sprouting on a basal medium. The various growth regulators affected both the time required for sprouting (TRS) and the type of growth. In summer buds, IAA delayed sprouting, while GA enhanced it and caused shoot elongation. Cytokinins specifically induced the formation of numerous adventitious buds, whereas ABA completely inhibited sprouting; this inhibition, however, was reversible. A marked decrease in total protein and in the rate of its synthesis was evident during the first 20 days of sprouting induction and early bud growth. The annual growth rhythm was determined in spring buds sampled and cultured throughout the year, and an innate dormancy of citrus buds was revealed. Both the dormancy and the sprouting periods of buds in vitro corresponded to the natural periods occurring under field conditions. The effect of exogenous IAA, GA and cytokinins on the TRS varied at different periods along the season, suggesting the concept of “critical levels” in the endogenous balance of hormones.

The Action of Kinetin in Improving the Water Balance and Delaying Senescence Processes of Cut Rose Flowers

Abstract: Kinetin delays the fading of cut rose (Rosa hyb. cv. Golden Wave) flower shoots exposed to water stress conditions. Using leafless flower shoots (i.e., a plant system devoid of stomates), we demonstrated that the main initial effect of kinetin was on increasing water uptake and petal growth. Later, kinetin slowed down processes associated with both senescence and stress (RNase activity and dry weight reduction), and maintained petal turgidity for an extended period.

Embryogenesis and Organogenesis in Pumpkin Explants

Abstract: Embryogenic callus was induced by culturing explants of pumpkin hypocotyls on Murashige-Skoog-medium with the addition of 3% glucose and one of the following growth substances (or combinations of them): β-indolylbutyric acid, 2,4-dichlorophenoxyacetic acid, β-indolylacetic acid, α-naphthyl-acetic acid, adenine (natural), kinetin, autoclaved water-melon sap and yeast extract (Difco). A large number of embryoids and adventive buds were produced. These were able to develop to normal plants. The 17 strains of embryogenic tissue obtained have maintained their embryogenic characteristics for more than 3 years. The induction of embryogenic callus in pumpkin seems to be strongly dependent on the genetic constitution of each individual plant.

Iron Deficiency in the Blue-Green Alga Anacystis nidulans: Changes in Pigmentation and Photosynthesis

Abstract: Phycocyanin-free photosynthetic lamellae (PSI-particles) were prepared from Anacystis nidulans, grown in complete and iron-deficient media. French press treatment and fractionated centrifugation were used. Absorption studies of the particles revealed an iron deficiency-induced shift of the main red chlorophyll a absorption peak from 679 to 673 nm as reported before for whole cells. The shift may reflect a changed distribution between different chlorophyll a forms. Action spectra for photo-oxidation of mammalian cytochrome c with photosynthetic lamellae revealed an iron deficiency-induced shift, corresponding to that found in the absorption spectra. As photo-oxidation of cytochrome c is mediated by PSI, it is believed that chlorophyll a also after the shift towards shorter wavelengths, is active in PSI. A decreased photosynthetic capacity of PSI, due to iron deficiency, was shown by time course studies of photosynthetic oxygen evolution, by photo-oxidation studies of P700 and mammalian cytochrome c, by photo-reduction studies of NADP and by combined studies of light-induced and chemical oxidation of P700. The ration chlorophyll a/700 was also determined for whole cells, lyophilized cells and PSI-particles. Iron deficiency caused an increased ratio in all studied fractions. The results of this work imply that energy is transferred with less efficiency within the photosynthetic units of PSI in iron-deficient A. nidulans than in iron-supplied algae.

Sorption of Heavy Metal Cations by Corn Mitochondria and the Effects on Electron and Energy Transfer Reactions

Abstract: The passive sorption of Pb+2, Cd+2, Zn+2, Co+2, Ni+2, and Mn+2 by isolated corn mitochondria was determined, and, except for Pb+2, the maximum sorption for each cation was about 58 nmol per milligram of protein. Sorption of Pb+2 was apparently ten times greater, but precipitation may have been the cause of this larger value. The effects of Pb+2, Cd+2, Zn+2, Co+2, and Ni+2 on acceptorless rates of electron transport for three substrates were determined. Greater than 50% inhibitions of oxidation were observed for succinate after additions of >0.1 mM Cd+2, Zn+2, or Pb+2: for NADH after additions of >0.5 mM Cd+2 or Zn+2; and for malate + pyruvate after additions of >0.1 mM Cd+2. Some inhibition of the rate of substrate oxidation was observed for most cations at higher concentrations. Coupling, as measured by ADP/O ratios, was inhibited at lowest concentrations by Cd+2 or Zn+2 and at higher concentrations by Co+2 or Ni+2. Substantial swelling of mitochondria oxidizing succinate was observed following additions of O.1 mM Cd+2 or Pb+2, Correlations are drawn between the effects of Pb+2, Cd+2, Zn+2, Co+2, and Ni+2 and their sorption to mitochondrial membranes.

Effect of Potassium Supply on the Transport of Photosynthates to the Fruits of Tomatoes ( Lycopersicon esculentum )

Abstract: In experiments with intact tomato plants the effect of potassium on the translocation of photosynthates was studied. Four series of plants were grown in nutrient solutions with two different potassium levels (K1 and K2 treatments). When the fruits of the first truss had developed the plants were treated with labelled CO2 for 2 h in a glove box. The plants were then divided in roots, stems, fruits and leaves, which were prepared for chemical analysis. In all experimental series the plants with the higher K supply grew better and therefore assimilated higher amounts of labelled CO2 (cpm/plant). The assimilation rates per g fresh material, however, were not increased in each experimental set by the K2 treatment. The absolute quantities of labelled photosynthates transported from leaves and stems to the fruits were also greater in the plant with the higher potassium supply. In all experimental series the proportion of labelled material found in the fruits was higher in the plants of the K2 treatment (total label of the plant=100%) than in the plants of the K1 treatment. This beneficial effect of potassium was also observed in cases, where potassium had not affected the CO2 assimilation rate. Expressing the distribution of labelled material in relative terms (percentage proportions) means that the effect of CO2 assimilation on the transport of photosynthates was excluded to a high extent. The higher percentage proportions of labelled material found in fruits and roots of the K2 as compared to the K1 treatment is, therefore, predominantly dependent on a specific effect of potassium on the translocation of assimilates. The labelled material found in the soluble fraction of the stems consisted of about 90% sugars, nearly half of which was sucrose, the rest being mainly glucose and fructose. This finding suggests that sucrose is the most important transport form of carbohydrates in tomatoes.

Multiphasic Uptake of Sulfate by Barley Roots I. Effects of Analogues, Phosphate, and pH

Abstract: For sulfate uptake by barley roots, competition studies reveal that uptake and phase transitions are caused by interaction of ions with separate sites on or in the plasmalemma. Uptake is competitively, and unequally, inhibited by sulfate analogues but not by other divalent anions. In contrast, divalent phosphate and di- and trivalent pyrophosphate are equally effective in causing transitions. Phosphate is taken up mainly or entirely as H2PO4− by a similar but separate multiphasic mechanism. At pH 8, sulfate uptake is mediated by fewer phases than at low and intermediate pH.

Promoting Effect of Fusicoccin on Seed Germination

Abstract: The effects of fusicoccin on the germination of dormant, light-requiring or abscisic acid-inhibited seeds has been investigated. (1) Fusicoccin (10−6M) induces germination in dormant wheat seeds (Triticum durum cv. Cappelli; 1972 crop) and stimulates it in seeds already relieved from dormancy (1971 crop), with an effect similar to that of gibberellic acid. (2) Fusicoccin (1.5 × 10−6M) is more active than the two phytohormones gibberellic acid and benzyladenine and than white light in stimulating light-requiring lettuce seeds (Lactuca sativa cv. Grand Rapids) to germinate. Germination of radish seeds (Raphanus sativus) is also accelerated by fusicoccin, while benzyladenine and gibberellic acid are less active in this material. (3) Fusicoccin (1.5 × 10−5M) removes almost completely the inhibitory effect of abscisic acid on germination of radish and lettuce seeds, whereas benzyladenine (10−4M) and gibberellic acid (3 × 10−4M) remove the inhibition only partially. The possible relationship between these results and previous information on growth by cell enlargement is discussed in terms of the mechanism of action of fusicoccin as compared with natural hormones.

Differential Absorption, Translocation and Metabolism of Metribuzin [4‐amino‐6‐tert‐butyl‐3‐(methylthio)‐as‐triazine‐5(4H)one] by Soybean Cultivars

Abstract: Soybean (Glycine max (L.) Merr.) cultivars have been reported to range in tolerance to injury by 4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)one (metribuzin), from tolerant (e.g.‘Bragg’) to susceptible (e.g.‘Coker 102’ and ‘Semmes’). ‘Bragg,’‘Coker 102’, and ‘Semmes’ soybeans were grown in sand subirrigated with nutrient solution containing labelled (14C-carbonyl metribuzin) and nonlabelled metribuzin to determine cultivar variability in absorption, translocation, and metabolism of metribuzin. Plants were periodically harvested, autoradiographed, and radioactivity in tissue extracts quantified. Data indicated that all 3 cultivars readily absorbed and translocated metribuzin. However, ‘Bragg’ tissues accumulated greater quantities of metribuzin metabolites than the other two cultivars. The major 14C-containing metabolite in ‘Semmes’ and ‘Coker’ roots and stems was 6-tert-butyl-as-triazine-3-5-(2H,4H)-dione, whereas the major 14C-metabolite isolated from‘Bragg’ roots and stems was a glucose conjugate. Results indicated that differential-intraspecific responses to metribuzin may result from differential capacities for herbicide detoxification by conjugation.

Iron Deficiency in the Blue‐Green Alga Anacystis nidulans: Fluorescence and Absorption Spectra Recorded at 77°K

Abstract: Low-temperature (77°K) fluorescence and absorption spectra have been determined for whole cells and photosystem I particles of Anacystis nidulans grown in iron-supplied or iron-deficient inorganic media. Iron deficiency induces a decrease of F720 relative to F685 and F695 in the fluorescence spectra of both whole cells and photosystem I particles. This change is correlated to a reduction of preferentially the long wavelength absorbing fraction of chlorophyll a. The relative fluorescence intensity at 755 nm is increased by iron deficiency. No significant effects of culture-age are found in the ratio between the three fluorescence bands (F685: F695: F720) of iron-supplied A. nidulans.

Root Formation of Pea Cuttings in Relation to the Irradiance of the Stock Plants

Abstract: Pea plants were grown at different irradiances for eleven days. At this stage they were used for cuttings. The irradiance during the rooting period (155 mW · dm−2) was the same in all the experiments, Cuttings from stock plants cultivated at the weakest irradiance obtained the highest number of roots, and the poorest rooting appeared in cuttings from stock plants grown at the highest irradiance. The results indicate that the nutritional status of the stock plant is an important factor for root formation in the cutting. Light may influence the production of inhibitors which directly or indirectly affect root formation. The possible role of carbohydrates and growth promoters in the process of root formation is discussed.

Regulation of Leaflet Photosynthesis by Developing Fruit in the Pea

Abstract: Changes in the net photosynthesis of leaflets of Pisum sativum L. (cv. Onward) were found to reflect closely the pattern of assimilate demand in subtended fruit during development. An early peak in leaflet photosynthesis corresponded with the rapid elongation of the fruit; a second peak with the inflation of the pod and initiation of seed growth. However, where the subtended fruit was removed at anthesis, the pattern of fluctuation in leaflet photosynthesis was altered, while leaflets at vegetative nodes maintained a lower photosynthetic rate which fluctuated little. The pattern of net photosynthesis in the fruit appears to reflect the high respiration rates associated with pod elongation and seed growth. This closely coupled system, where fruit assimilate demand modulates the photosynthesis of adjacent leaflets, provides a scope for study of source-sink relationships with the minimum of experimental manipulation.

Agglutinating Effects of Concanavalin A on Isolated Protoplasts of Daucus carota

Abstract: The agglutinating effects of Concanavalin A (Con A) on protoplasts isolated from cell suspensions of Daucus carota were studied. Con A was shown to agglutinate the plant protoplasts in a manner similar to the way some animal cells are agglutinated. The agglutination process is dependent on the Concanavalin A concentration, protoplast density, treatment time, the temperature, and the membrane condition, α-D-Methylgluco-pyranosid completely inhibited Con A induced agglutination. The results are discussed in relation to membrane structure and morphology.

Root Formation in Pea Cuttings

Abstract: Auxin was applied to the upper part of the cuttings, which were both decapitated and disbudded on the same day. The applied auxin was removed by redecapitating the cuttings at different time intervals. In a second experiment, auxin was applied either to the upper or lower part of the decapitated and disbudded cuttings at different time intervals. In cuttings, which were redecapitated after 1 and 2 days, the root formation was reduced considerably. The redecapitation after 3 days had no adverse effect on the root formation. Cuttings treated with auxin at different time intervals showed a weaker root promotion on days 0 and 1 than on the subsequent days. The results emphasize the fact that auxin is active only during the first part of the root initiation phase. A continuous flow of auxin for a period of the first 3 days during the root initiation is of overriding importance. There appears to be at least two different stages of the root initiation phase, (ia) auxin active stage, and (ib) auxin inactive stage. The results also seem to indicate that some other factors, in addition to auxin, are active during the first stage of the root initiation phase.

Role of Silicon in Diatom Metabolism

Abstract: The in vivo uptake of 31Si-silicic acid and 68Ge-germanic acid by cell organelles of Nitzschia alba Lewin and Lewin and Cylindrotheca fusiformis Reimann and Lewin was demonstrated. The organelles were isolated by fractionation of pre-labeled cells by differential centrifugation in 0.4 M sucrose medium. Electron micrographs showed that the isolated organelles were intact, with the exception of the N. alba mitochondria which appeared swollen and the C. fusiformis chloroplasts which had ruptured outer membranes and lacked stroma material. The amount of 31Si or 68Ge per mg protein of the subcellular fractions decreased in the following general order for both organisms: cell wall, mitochondria, chloroplasts, vesicles, and microsomes. A portion of the 31Si or 68Ge in the organelle fractions could be extracted into a distilled water wash. The uptake of silicon by the organelles suggests that silicon may be involved in some processes of the compartmentalized systems of the cell.

Aspects of the Effect of ABA on the Water Status of Barley and Wheat Seedlings

Abstract: The effect of abscisic acid on plant growth and survival during water deprivation was studied in barley and wheat seedlings. Under conditions of both limited and ample water supply, treatment with abscisic acid greatly reduced transpiration and, in addition, suppressed root growth. In water-deprived seedlings, abscisic acid increased the total dry matter, reflecting improved efficiency in water-use. In addition, the growth period and survival of water-deprived seedlings were markedly prolonged. In field trials, however, abscisic acid had no significant effect on waterdeprived seedlings. Possible reasons for this lack of response are discussed.

Ethylene and the Regulation of Apple Stem Growth under Stress

Abstract: Bending stree resulted in an increase in the ethylene concentration in the internal atmosphere of apple stem (Malus domestica Borkh. cv. Winesap). reaching a maximum at about 2 days after bending. The rise in ethylene content was followed by a depression of growth at about 14–21 days. Ethylene content returned to control levels after about 3 weeks. Application of a past naphthaleneacetic acit caused a similar increase in ethylene levels, and the application of ethephon pastes brought about an inhibition of elongation growth. Whereas stress treatment resulted in an inhibition of growth in stem diameter as well as elongation of growth in stem diameter as well as elongation, the ethephon applications resulted in a stimulation of growth in diameter. It is suggested that ethylene may be involved in the growth responses to mechanical stress.

Redistribution of Potassium, Calcium, Magnesium, and Manganese in the Plant

Abstract: The extent of redistribution in apple was described by calculating the fruit/leaf ratio of the cation content. It was found that the redistribution diminishes in the sequence K > Mg > Ca ∼ Mn. These results are more or less in agreement with those found elsewhere. Investigations were made to see whether it was possible to account for the differences in redistribution by the phloem by means of the solubility of these cations in the sieve tube sap. As model plants Yucca flaccida and Ricinus communis were used, plants from which it was possible to obtain phloem sap in a rather pure state. It was found that the addition of potassium and magnesium as a chloride in the usual investigated range of concentrations did not give precipitation. With calcium and manganese, however, a precipitate soon occurred. Manganese was demonstrated to be less soluble than calcium. For Ricinus the maximum amount of calcium and manganese the sieve tube sap could contain before precipitation set in was higher than for Yucca sap. The results confirm the possibility that the redistribution of the different cations in the plant can be related inter alia to their solubility in the sieve tube sap. It was also found that the calcium in the phloem sap is present in ionic condition. Thus the normal laws of solubility should be applicable.