Showing papers in "Plant Cell and Environment in 1982"

Relative addition rate and external concentration; Driving variables used in plant nutrition research

Abstract: An increasing literature accounting for various types of experiments indicates that far lower external nutrient concentrations are required by plants than is usually thought to be the case. It is concluded that the ion uptake capacity of the roots, as described by the carrier concept, is high compared to that required for maintenance of the internal concentration. Serious errors in experimental conclusions are associated with insufficient and constant nutrient addition rates. The main errors are caused by non-steady states of the plants both with regard to the internal nutrient concentrations and the relative growth rate. A dynamic concept has been proposed for direct use as the treatment variable within the range of sub-optimum nutrition. The nutritional factor is expressed as a flow, the relative nutrient addition rate in laboratory studies and the nutrient flux density in the field. The experimental use of the relative addition rate has led to steady-state nutrient status and relative growth rate and the interpretation of plant responses which differ fundamentally from accepted views. Thus, for instance, deficiency symptoms disappear, as in natural conditions, when the internal nitrogen concentration is stable, independent of level. The nutrition/growth relationships are very different from those observed when external concentration is varied. The regression line of relative growth rate on relative addition rate passes near to the origin at an angle close to 45 to the axes, which implies that the obtained relative growth rate approximates closely the treatment variable. A striking example of observed differences is the positive effect on nitrogen fixation exerted by high relative nitrogen addition rates compared to the well-known negative effect of increasing external nitrogen concentration. The application of fertilizer on the basis of the nutrient flux density concept provides the possibility of supplying fertilizers corresponding to the consumption potential of the vegetation and to the natural flux density resulting from mineralization in the soil. Nitrogen utilization is high under such conditions and the resulting feedback of nutrition on the mineralization rate suggests that there will be a long-term increase in fertility.

The adaptive significance of amphistomatic leaves

Abstract: A clear correlation between the presence of stomata on both surfaces and factors such as habitat, growth form, and physiology has yet to emerge in the literature. However, certain loose trends with these factors are evident, and these are reviewed along with evidence for hypostomaty as the primitive form. It is proposed that the effect of developing stomata on the upper surface as well as the lower is to increase maximum leaf conductance to CO2. Plants with a high photosynthetic capacity, living in full-sun environments, and experiencing rapidly fluctuating or continuously available soil water (as opposed to seasonal or long-term soil water depletion), are identified as deriving an adaptive advantage from a high maximum leaf conductance. The correlation between groups of plants fitting the above conditions and those noted to be amphistomatic is remarkable. Plants not fitting the conditions are found to be largely hypostomatic.

The mechanism of bicarbonate assimilation by the polar leaves of Potamogeton and Elodea. CO2 concentrations at the leaf surface

Abstract: Photosynthetic utilization of HCO, in leaves of Poiamogeton and Elodea occurs at the lower leaf side, with subsequent OH∼ release at the upper side. It is accompanied by transport of cations, in the present experiment K +, across the leaf. The resulting pH and K+ concentration changes near the leaf surface were recorded with miniature electrodes. From the pH and K+ concentration the concentrations of the different inorganic carbon species were calculated and compared with photosynthetic O, production. HCO−3 utilization is accompanied by a drastic increase in the free CO2 concentration near the lower epidermis. Experiments with CO2− and HCO3−free solutions showed an oscillating acidification near the lower epidermis and alkalinization near the upper epidermis. It is concluded that the acidification results from the activity of light‐dependent H+ pumps. The finding that an increase in pH at the upper side always coincided with a decrease at the lower in these experiments shows that the H+ pumps and the OH− extruding mechanism are coupled although occurring in different cell layers. Previously we have suggested that the first step in the process of photosynthetic HCO3− utilization is external conversion of HCO3−” by acidification caused by light‐dependent H+ pumps. The present results strongly support this hypothesis. Two possible pathways for the accompanying K + transport are discussed. The model presented here explains the known inhibiting effects of buffers and high pH on photosynlhetic HCO3− utilization.

A portable system for measuring carbon dioxide and water vapour exchange of leaves

Abstract: . The apparatus described here is a fully portable, steady-state gas exchange system for simultaneous measurements of the CO2 exchange and transpiration of single, attached leaves. The leaf cuvette provides temperature, humidity, and CO2-concentration control. The system is suitable for either surveys or detailed studies of photosynthetic and stomatal responses to environmental variables. Representative data demonstrate the response time characteristics of the system and constitute the first field evidence of stomatal behaviour consistent with a recent hypothesis concerning the optimum pattern of stomatal conductance for the maximization of water-use-efficiency.

Relations between water content, potential and permeability in stems of conifers

Abstract: . The influence of sapwood water content on the conductivity of sapwood to water was measured on stem sections of Pinus contorta. A reduction in relative water content from 100 to 90% caused permeability to fall to about 10% of the saturated value. Pressure–volume curves of branchwood and stem sapwood of Pinus contorta and Picea sitchensis have been analysed to define the tissue capacitance and the time constant and resistance for water movement between stored water and the functional xylem as functions of tissue water potential. Three phases in water loss were discernible. In the initial phase at high water potentials (> –0.5 MPa), the capacitance was large, the time constant long and the resistance to flow large in comparison with intermediate water potentials (−0.5 to −1.5 MPa). At still lower water potentials (−1.5 to −3.0 MPa), the time constant and resistance declined still further but the capacitance had a tendency to increase again, especially in the stemwood of Sitka spruce. Typical values in the second phase were for the time constant 5 s, for the resistance 4 × 10−13 N s m−5 and for the capacitance (change in relative water content per unit change in potential) 1×10−11 m3 Pa−1. These parameters define the availability of stored water and are being used in a dynamic model of water transport in trees.

The photoperceptive sites and the function of tissue light‐piping in photomorphogenesis of etiolated oat seedlings

Abstract: . Responses to red light irradiation of discrete areas along the intact, etiolated oat seedling indicate that illumination of the region around the coleoptilar node results in maximal coleoptile growth stimulation and mesocotyl growth suppression. Quantitation of the fibre optic properties of these etiolated tissues shows that the amount of axially transmitted light is log linear as a function of distance for both the mesocotyl and coleoptile (plus primary leaf). Using the fibre optic properties of the tissues to predict the response of the etiolated seedling to defined illumination fields allows one to localize two sites of photoperception: although the mesocotyl response pattern can be explained by the action of a single site found near the top of the mesocotyl itself, the coleoptile response depends on irradiation of both the mesocotyl site and an additional site located just above the node. The very low- and the low-fluence responses of etiolated oats independently predict similar regions of the seedling as sites of photo-perception. The fibre optic properties of the seedling could allow the seedling to increase the effective light signal received by the photosensitive area significantly.

Effect of sowing date on the temperature response of leaf emergence and leaf size in barley

Abstract: Rate of leaf emergence of barley grown in the field in each of 2 years was affected by sowing date and, where direct comparisons were possible, it was found that leaves on late-sown plants emerged more quickly. Rate of leaf emergence fluctuated throughout the season, slowing almost to zero in the winter. Much of this variation in rate was removed when the number of leaves was plotted against accumulated temperature rather than time. When emergence rates for each sowing were calculated using a common base temperature they were found to be well correlated with rate of change of daylength. However, it was (bund that base temperature as well as temperature response was affected by date of sowing. The pattern of change of size of leaves was also affected by date of sowing. It appeared that in low temperatures and short days, there was no increase in leaf size from leaf position to leaf position. The responses of leaf emergence, extension and final size to date of sowing appear to adapt the plant to grow quickly when sown early but to cease growth and possibly frost-harden at low temperatures.

Leaf expansion of four sunflower (Helianthus annuus L.) cultivars in relation to water deficits. II. Diurnal patterns during stress and recovery

Abstract: . Leaf expansion of four sunflower cultivars (Helianthus annuus L. cvs. Hysun 31, Havasupai, Hopi and Seneca) was monitored continuously in a growth cabinet through the final stages of a drying cycle and then throughout the first 2 days after rewatering in order to study the responses of leaf expansion to water deficits. Comparable plants were also measured throughout a diurnal cycle in a glasshouse. In the cabinet, leaf extension was faster in the dark than in the light, but an extended dark period suppressed leaf extension. At similar leaf water potentials, the rate of leaf extension was greater in the light than in the dark, but as the osmotic potential was lower in the light than in the dark, the relationship between turgor pressure and leaf extension rate was similar in both environments. Throughout the drying and recovery cycles turgor and leaf extension rate was positively correlated: no significant differences among cultivars were observed. In the plants grown and measured in the glasshouse, leaf expansion occurred at lower leaf water potentials in stressed than in unstressed plants, but the relationship between leaf expansion and turgor was similar in both stressed and unstressed plants as a result of a lowering of the osmotic potential in the former. Diurnal turgor maintenance resulting from osmotic adjustment was almost half that occurring during a complete drying cycle. During the day, the leaf expansion rate increased linearly with turgor pressure in all cultivars: the expansion rate per unit turgor pressure was greater in the glasshouse than in the growth cabinet. Nocturnal leaf expansion in the stressed and unstressed plants was not, however, correlated with turgor pressure.

Uptake of SO2 in shoots of Scots pine: field measurements of net flux of sulphur in relation to stomatal conductance

Abstract: UPTAKE OF SO2 IN SHOOTS OF SCOTS PINE - FIELD-MEASUREMENTS OF NET FLUX OF SULFUR IN RELATION TO STOMATAL CONDUCTANCE

Experimental systems and a mathematical model for studying temperature effects on pollen-tube growth and fertilization in plum

Abstract: . Cross and self pollen tubes were cultured in ‘Victoria’ plum flowers (Prunus domestica L.) at 5, 10, 15 and 20°C. Pollen-tube lengths measured at intervals were fitted by S-shaped growth curves (logistic function) and the parameters of the curves used to derive a generalized model for pollen-tube growth based on accumulated temperatures. Above the threshold of 2.5°C, maximum growth rate was 0.34 mm per day-degree and the tubes reached half their final length at 16.6 day-degrees above 2.5°C. The model indicates that fertilization of plum flowers requires 16–20 d at a constant temperature of 5°C after pollination, but only 3–4 d at 15°C. Mathematical expressions based on the model are given for estimating pollen-tube penetration and growth rate from values of cumulated temperature since pollination, and for estimating the cumulated temperature necessary for pollen tubes to penetrate a given distance. Pollen-tube growth rates were the same in detached flowers, flowers attached to twigs, and flowers on young, grafted trees in pots. In detached flowers growth stopped before fertilization could occur, but some embryo sacs were fertilized in both the remaining treatments. Accurate pollen-tube growth assessments can therefore be made with detached flowers which are most convenient to use and can be accommodated in small incubators. Studies on fertilization, however, must use flowers on bulky and expensive grafted trees.

Protein accumulation in developing endosperm of a high-protein line of Triticum dicoccoides

Abstract: . Endosperm tissue from developing grains of a line of wheat (Triticum dicoccoides) which accumulates up to 30% protein in the mature grain, was examined by electron microscopy to establish the ontogeny of the storage protein bodies. Ultrastructural evidence suggests that storage proteins of wheat may be transported from their site of synthesis on the rough endoplasmic reticulum (ER) to protein bodies by two different routes within the endomembrane system. The first route, which probably functions throughout protein deposition, involves the transport of protein from the cisternal rough ER to the protein vacuoles via the Golgi apparatus. The second route, observed 20 d after anthesis, appears to lead directly from dilated regions of the rough ER to protein vacuoles, bypassing the dictyosomes. Phytin inclusions are found in protein vacuoles of starchy endosperm cells adjacent to the aleurone layer of developing grain.

Photosynthetic efficiency of Betula pendula acclimated to different quantum flux densities

Abstract: Seedlings of Betula pendula were grown in a controlled environment chamber at quantum flux densities of 50, 250 and 600 μmol m−2 s−1 The relationship between the flux densities of absorbed CC2 and quanta was determined for shoots of whole seedlings Rates of both light-saturated and in situ (measured under the growing conditions) net photosynthesis were determined and the pholosynthetic quantum yields under light-limiting conditions were calculated Anatomical leaf characteristics, chlorophyll contents and sizes and densities of the photosynthetic units (chlorophyll/P700) were determined Chloroplasts were isolated and their rates of 2,6-dichlorophenol indophenol photoreduction were measured together with their pool sizes of the electron transport carriers plastoquinone and cylochrome ƒ Although acclimated to different quantum flux densities, the three birch populations showed the same quantum yield of net photosynthesis This was approximately 0028 in normal air (212 kPa oxygen) and about 0040 when photorespiration was largely inhibited in 20 kPa oxygen In addition, the in situ net photosynthesis rates were limited by the absorbed quantum flux density for low, intermediate and high light grown seedlings It was concluded that birch acclimated to the three light regimes at different levels of organization (metabolic and anatomical) Thus, the quanta which were absorbed in situ could be transferred into chemical equivalents at an optimal and constant efficiency The use of different reference bases for expressing rates of net photosynthesis are also discussed

Stomatal behaviour and water movement through roots of wheat plants treated with abscisic acid

Abstract: Experiments with isolated roots of wheat plants suggested that when water uptake rates are low, low concentrations of abscisic acid (ABA) may increase the flux of water into roots. This increase was recorded despite an ABA-stimulated reduction in the hydraulic conductance of the whole root system. Hydraulic conductances were measured under steady-state conditions. A system is described where the stomatal behaviour and water movement through roots of a single intact plant may be concurrently monitored. Experiments with intact plants confirmed that application of ABA could increase the rate of water movement into roots when uptake rates were low. No such increase was observed at high flux rates. Application of ABA to roots caused partial stomatal closure and caused conductance to oscillate around a reduced mean value. An ABA-stimulated increase in the turgor sensitivity of stomata is postulated and the significance of this effect is discussed.

Early effects of excess cadmium uptake in Phaseolus vulgaris

Abstract: . Seedlings of Phaseolus vulgaris were exposed to solutions containing Cd2+ in the range 0 to 1 molm−3. Ethylene formation started following 3 h of exposure to 10−2, 10−1 and 1 mol m−3 Cd2+, peaked at 18 h and returned to a relatively low rate after 24 h. Cadmium-induced ethylene formation depended on the formation of 1-aminocyclopropane-1-carboxylic acid (ACC). Aminoethoxyvinylglycine (AVG, 0.1 mol m−3) inhibited ACC accumulation and ethylene production during exposure to 0.2 mol m−3 Cd2+. Activity of soluble and ionically-bound peroxidase increased after 18 h of exposure to Cd2+ concentrations above 10−3 mol m−3 due to an increase in activity of cathodic isoperoxidases. Stimulation of soluble and ionically-bound peroxidase by 0.2 mol m−3 Cd2+ was reduced in the presence of 0.1 mol m−3 AVG. Accumulation of soluble and insoluble (‘ligninlike’) phenolics was found in plants exposed to Cd2+ (10−2 mol m−3 or above) in the presence or absence of AVG. Deposition of insoluble (autofluorescing) material occurred in cell walls around vessels and was associated with reduced expansion and water content of leaves.

Osmotic adjustment to water stress in pearl millet (Pennisetum americanum [L.] Leeke) under field conditions

Abstract: . Osmotic adjustment, a mechanism whereby plants maintain positive turgor despite low water potential (ψ), was investigated in pearl millet (Pennisetum americanum [L.] Leeke) in three types of field experiment at Hyderabad, India: 1.Osmotic adjustment during the growing season was evaluated by comparing solute potential (ψs) of leaves taken at midday from irrigated and droughted plots and allowed to rehydrate in the laboratory. The degree of seasonal adjustment was also estimated by comparing observed values of ψs in the field with those expected if ψs decreased solely in proportion to water loss. Both types of assessment indicated the maximum seasonal adjustment to be about 0.2 MPa. The cultivars BJ 104 and Serere 39 differed in their capacity to adjust osmotically over the season; Serere 39 was least able to osmoregulate. 2.Measurements of diurnal variations in ψ and ψs in BJ 104 revealed osmotic adjustment during the afternoon hours. At a given value of ψ, turgor (ψp) was about 0.1 MPa higher in irrigated, and over 0.2 MPa higher in droughted plants, in the afternoon, than in the morning. 3.Osmotic adjustment of different leaves within the canopy was investigated. Upper leaves had lower ψ than basal leaves. Differences in ψ were matched by gradients in ψs, so that turgor was similar for all leaf layers.

Studies on ethylene binding by cell‐free preparations from cotyledons of Phaseolus vulgaris L.: subcellular localization

Abstract: . Studies on the subcellular location of ethylene binding activity from developing cotyledons of Phaseolus vulgaris L. are described. Binding activity has been shown to be predominantly membrane bound. When separated by rate-zonal centrifugation more than 70% of this activity was of low sedimentation rate. The slowly sedimenting band of activity was further fractionated into three bands by isopycnic density gradient centrifugation. The three bands occur at sucrose densities of 1.125 g cm−3, 1.155 g cm−3 and 1.175 g cm−3, corresponding to the distribution of putative marker enzymes for the cell endomembrane system and to protein body membranes. Further circumstantial evidence was obtained by electron microscopy and sucrose step gradient centrifugation.

Stomatal responses of pearl millet (Pennisetum americanum [L.] Leeke) to leaf water status and environmental factors in the field

Abstract: Factors affecting stomatal conductance (g1) of pearl millet (Pennisetum americanum [L.] Leeke), cultivar BJ 104, were examined in the field in India during the dry season. Diurnal changes in g1 were evaluated for upper expanded leaves at flowering on two occasions using plants subjected to varying degrees of water stress. Except for the most severely stressed treatment, diurnal changes in g1 closely matched changes in irradiance (I), the promotive effect of which largely overcame opposing influences on g1 of increasing atmospheric vapour pressure deficit, and decreasing leaf water and turgor potentials (Ψ, Ψp). Two main effects of water stress on g1 were evident: (i) a decrease in the amplitude of the mid-day peak in g1, and (ii) a decrease in the time over which high g1 was maintained, resulting in early (mid-day) closure and hysteresis in the relationship between g1 and I. Leaf conductance was greatest for upper leaves and decreased down the canopy. At equivalent depths in the canopy g1 was higher in flowering than in photoperiodically-retarded plants of the same age. The magnitude of water stress-induced stomatal closure increased down the plant, and was more marked in retarded than in flowering plants. Within individual stress treatments Ψ of upper leaves decreased linearly as transpiration flux increased. It is concluded that stomatal behaviour of upper leaves of pearl millet at flowering largely operates to maximize assimilation rather than to minimize water loss

The lower limit of photon fluence rate for phototrophic growth: the significance of ‘slippage’ reactions

Abstract: . The role of ‘slippage’ reactions, in the form of passive H+ uniport through CF0-CF1, ATP synthetase and breakdown of the S2 and S3 intermediates of O2 evolution, is considered in relation to the growth of phototrophic organisms at low photon fluence rates. Analysis of the limited data available suggests that adaptation (phenotypic or genotypic) to low photon fluence rates is accompanied by an increase in the ratio of light-absorbing pigments to the (potentially slippage-inducing) photosystem two units and CF0-CF1 ATP synthetases. Furthermore, organisms which are genotypically adapted to high photon fluence rates do not, when grown at low photon fluence rates, achieve the same low ratio of reaction centres to total light-harvesting pigments as is found in phototrophs genotypically adapted to low photon fluence rates. The limits to, and energy costs of, such a mechanism of adaptation to low photon fluence rates are also discussed.

Hypocotyl growth in Sinapis alba L: the roles of light quality and quantity

Abstract: . A comparison is made of the relative effectiveness of light quality and light quantity on the elongation growth of Sinapis alba hypocotyls. The results show that hypocotyl extension rate in plants which have not previously been exposed to light is controlled primarily by the prevailing photon fluence rate when the phytochrome photostationary state lies between ∼0.033 and ∼0.81. Below ∼0.033, changes in photostationary state also have a marked effect on extension rate. Elongation growth in light-adapted plants is controlled by both photon fluence rate and the spectral quality of the incident radiation at all photoequilibria. Photosynthesis can modify these responses but is not essential as a prior condition for a green plant to respond to changes in light quality and quantity.

Photoperiodism and rhythmic response to light

Abstract: . Seedlings of Pharhitis nil show a circadian rhythm in the capacity to flower in response to the timing of a second red light pulse given at various times after a first saturating exposure to red when this is given together with a benzyladeninc spray. There are also changes in the photon irradiance required for half maximum response to the second red pulse. The photochemical properties of phytochrome in the photoperiodically sensitive cotyledons were also shown to change rhythmically. Oscillations in both pr→ Pfr and Pfr→ Pr photoconversion characteristics persisted over at least two circadian cycles with a periodicity of about 12 h. There were, however, no significant oscillations in either Pfr peak absorbance or in Δ(ΔA). The changes in sensitivity for the photoconversion of Pr→ Pfr did not parallel the much larger changes in sensitivity of the flowering response to red light. The amplitude of the Pr→ Pfr rhythm was at least as great as that for Pr→ Pfr, but the flowering response to far-red light was not rhythmic, nor was there any large change in sensitivity. The changes in photoconversion properties may reflect a basic biochemical oscillation which affects both photoreceptor properties and sensitivity to photoreceptor input. There was also a marked rhythm in the Pfr/P ratio that would be established by a saturating pulse of red light and this too may have affected the flowering response to such a pulse. Far-red light inhibited flowering when given at any time during the inductive night. After 14 h in darkness, Pfr could still be measured in the cotyledons and it was concluded that far-red light inhibited flowering by removing Pfr As red light also inhibited flowering at this time, there may be two pools of phytochrome with different kinetic properties.