Showing papers in "Journal of Experimental Botany in 1990"

An Intermediate Category of Seed Storage Behaviour? I. COFFEE

Abstract: Seeds of four cultivars of arabica coifee (Coffea arabica L.) were tested for germination following hermetic storage for up to 12 months at several different combinations of temperatures between —20 °C and 15 °C and moisture contents between 5% and 10% (wet basis). Most of the seeds from one cultivar withstood desiccation to between 5% and 6% moisture content, a seed water potential of approximately 250 MPa, but those of the remaining three cultivars were much more sensitive to desiccation damage. Moreover, in all four cultivars, seed longevity at cool and sub-zero temperatures, and at low moisture contents did not conform with orthodox seed storage behaviour: viability was lost more rapidly under these conditions than at either warmer temperatures or higher moisture contents. The results confirm that coffee seeds fail to satisfy the definitions of either typical orthodox or recalcitrant seed storage behaviour. These results, therefore, point to the possibility of a third category of storage behaviour intermediate between those of orthodox and recalcitrant seeds. One of the main features of this category is that dry seeds are injured by low temperatures.

A Positive Root-sourced Signal as an Indicator of Soil Drying in Apple, Malus x domestica Borkh.

Abstract: Plants raised from shoot-tip cultures of apple (Malus x domestica Borkh.) were grown in divided pots so that approximately half the root system could be exposed to soil drying whilst the remainder was well watered. Water was withheld from half the root system in this way for 24 d. During this time, the daily increment in leaf area declined to 65% of that of control plants, which had all their roots in well watered soil. Both leaf expansion and, more particularly, leaf initiation were inhibited. Water loss per plant also fell to 70% of the rate exhibited by control plants. No significant differences were detected between the leaf water status of the partially dried plants and that of the well watered ones. After this drying period, the half-dried plants were treated during the night of the 24th day as follows; one group had its roots in dry soil rewatered, another had them excised, and a third continued half dry. Both the rewatered group and the group with roots excised showed significant recoveries in leaf growth rates compared with the group kept half dry. The inhibition of leaf growth by drying soil is discussed with regard to root-to-shoot signalling. The alleviation of this inhibition by the excision of roots in dry soil, is taken as evidence of a positive inhibitor, produced by drying roots, influencing shoot growth.

An intermediate category of seed storage behaviour

Abstract: The effects of endocarp removal either before or after dessication and storage, and of humidification prior to testing the seeds for germination were investigated to determine whether these factors might help to explain the contradictions in the literature regarding the survival of coffee seeds in storage

The Response of Bean Plants to UV-B Radiation Under Different Irradiances of Background Visible Light

Abstract: Investigations show that UV-B radiation may inhibit photosynthesis in many plants, as well as causing visible leaf symptoms, such as glazing, bronzing, and necrosis. The amount of visible light also plays a role with regard to the extent of UV radiation damage to plants. In the present study using bean, three different irradiances of background visible light were applied together with UV-B radiation in order to test the response of bean to different light levels with regard to anatomical and physiological changes

Xylem-Phloem Exchange Via the Rays: The Undervalued Route of Transport

Abstract: This paper aims to link anatomical and physiological aspects of the xylem phloem exchange studied at the cellular, tissue and whole-plant level in plant physiology, horticulture and silviculture and focuses on the mechanisms of radial transport

Does ABA in the Xylem Control the Rate of Leaf Growth in Soil-Dried Maize and Sunflower Plants?

Abstract: Maize (Zea mays L.) and sunflower (Helianthus annuus L.) plants were grown in large volumes of soil and leaf growth rate was monitored on a daily basis. Half the plants were given a soil drying treatment and when they showed a significant restriction of growth rate (compared to both their daily growth rate before drying and the average growth rate of well-watered plants on the same day), leaf water relations were measured and xylem sap was extracted using several techniques. There was a significant negative log-linear relationship between the rate of leaf growth and the concentration of ABA in the xylem for both species. There was no clear relationship between leaf growth rate and leaf water potential or turgor for either species. Assessment of different methods for sampling xylem sap suggests that exudates collected from stem stumps or samples collected by pressurizing the whole root system are suitable for estimating ABA concentration in xylem, at least with large plants of maize or sunflower, provided the first few hundred cubic millimetres of collected sap are used for the assay. Centrifugation of sections of stems resulted in dilution of ABA in the xylem sap with sap squeezed from parenchyma tissue. This is because, at least in plants subjected to mild soil drying, the concentration of the ABA in the xylem is far higher than that in the cell sap of stem tissue. Results support the proposal that ABA plays a major role as a chemical signal involved in the root-to-shoot communication of the effects of soil drying. The non-hydraulic restriction of leaf growth by a chemical signal can be explained by the extra root sourced ABA in the xylem and may be an important component of the modification of growth and development which results from prolonged soil drought.

Changes in N and S Leaf Content, Stomatal Density and Specific Leaf Area of 14 Plant Species during the Last Three Centuries of CO2 Increase

Abstract: Parallel to the increase in atmospheric C02 from 278 /ntnol moP1 in ad 1750 to the current ambient level of 348 fimol mol-1, there have been overall decreases in leaf nitrogen content and stomatal density from 144% and 121%, respectively, in ad 1750 to 100% today of herbarium specimens of 14 trees, shrubs, and herbs collected over the last 240 years in Catalonia, a Mediterranean climate area. These decreases were steeper during the initial slower increases in C02 atmospheric levels as compared with the relatively faster COz increases in recent years. The declines in leaf N content and stomatal density have also been reported in experimental studies on leaves of plants grown under enriched C02 environments. Meanwhile, the stomatal index and overall carbon and sulphur leaf contents have not changed significantly. Leaf S content was higher in the 1940s samples coinciding with the burning of increased quantities of sulphur-rich coal. Consequently, the epidermal cell density has decreased parallel to the stomatal density and the C/N ratio of leaves has increased, implying possible important consequences on herbivores, decomposers, and ecosystems. An overall decrease in the specific leaf area (SLA) from 184% in the 18th century to 100% today has also been found, as would be expected under C02 enrichment, but which might also be an artifact of prolonged storage.

Xylem, Phloem and Transpiration Flows in Developing Apple Fruits

Abstract: Xylem, phloem and transpiration flows were measured in developing fruits of the apples Royal Gala and Cox's Orange Pippin at early, mid and late stages during their development. Fruit volume growth was first computed from measurements of diameter made using a system of sensitive displacement transducers. Xylem, phloem and transpiration flow components (of which fruit volume growth is the integral) were then separated using a scheme of treatments which disabled one or other flow at a time. Changes observed during development in the patterns of the three flows are in general agreement with expectations based on less direct observations (loc. cit. Ferguson and Watkins, 1989). Recognizing the distinctive mineral compositions of xylem and phloem streams, the changes also accommodate, and seem to explain, published observations of mineral accumulation in apple. Significant differences in the pattern of xylem and phloem flow were observed between the varieties examined. These may explain varietal differences in susceptibility to the mineral imbalance disorder bitter-pit. Xylem flows were shown to reverse at times; that is they flowed from fruit to tree. This occurred particularly during periods of high evaporative demand. Xylem reversal is of importance to the overall water economy of a tree but may also have special importance to the mineral composition of the fruit.

Long Distance Transport of Abscisic Acid in NaCI-Treated Intact Plants of Lupinus albus

Abstract: Plants of Lupinus albus were grown for 51 d under control (M mol m-3 NaCl) and saline (40 mol m-3 NaCl) conditions. Plants were harvested and changes of carbon, nitrogen and abscisic acid (ABA) contents of individual organs were determined 41 d and 51 d after germination. In the period between the two harvests xylem and phloem saps were collected and respiration and photosynthesis of individual organs were measured. Using flows of carbon, C/ABA ratios and increments of ABA flows of ABA in phloem and xylem and rates of biosynthesis and degradation of ABA were calculated. Both under control and saline conditions net biosynthesis occurred in the root, the basal strata of leaves and in the inflorescence. Metabolic degradation of ABA took place in the stem internodes and apical leaf strata. Salt stress increased xylem transport of ABA up to 10-fold and phloem transport to the root up to 5-fold relative to that of the controls. A considerable amount of ABA in the xylem sap originated from biosynthesis in the roots, i.e. 55% in salt-treated and smaller than 28% in control plants. The remaining part of ABA in the xylem sap originated from the shoot: it was translocated in the phloem from fully differentiated leaves towards the root and from there it was recirculated back to the aerial parts of the plant. The data suggest that ABA may serve as a hormonal stress signal from the root system.

Effects of Priming and Endosperm Integrity on Seed Germination Rates of Tomato Genotypes II. GERMINATION AT REDUCED WATER POTENTIAL

Abstract: Seed germination rates (GR = inverse of time to germination) are sensitive to genetic, environmental, and physiological factors. We have compared the GR of tomato (Lycopersicon esculentum Mill.) seeds of cultivar T5 to those of rapidly germinating L. esculentum genotypes PI 341988 and PI 120256 over a range of water potential ( were also assessed. Germination time-courses at different 0's were analysed according to a model that identified a base, or minimum, \j> allowing germination of a specific percentage (g) of the seed population (ifib(g)), and a 'hydrotime constant' (9H) indicating the rate of progress toward germination per MPa.h. The distribution of if>b(g) determined by probit analysis was characterized by a mean base b) and the standard deviation in b among seeds ( . A normalized time-scale for comparing germination responses to reduced ij> is introduced. The time to germination at any tp (t g(tfi)) can be normalized to be equivalent to that observed in water (/g(0)) according to the equation fg(0) = (l -^(ip/Ms)))^^)- PI 341988 seeds were more tolerant of reduced > b(g), but did not lower the minimum b between intact and cut seeds incubated at high 0 was much less («0-l MPa), indicating that at the time of radicle protrusion, the endosperm had weakened to the point where it constituted only a small mechanical barrier. In the intact seed, endosperm weakening and the downward adjustment in embryo ifib ceased at

The Greenhouse Effect: Acclimation of Tomato Plants Growing in High CO2, Photosynthesis and Ribulose-1, 5-Bisphosphate Carboxylase Protein

Abstract: Dans cette etude, les effets a long terme d'un enrichissement en CO 2 atmospherique sur la photosynthese sont examines chez des plants de tomate. Des mesures de contenu en ribulose-1,5-bisphosphate carboxylase et de son activite, ainsi que de l'activite photosynthetique sont effectuees au cours du developpement des feuilles

Electrolyte and Pi Leakages and Soluble Sugar Content as Physiological Tests for Screening Resistance to Water Stress in Phaseolus and Vigna Species

Abstract: With the aim of selecting physiological tests for the screening of drought tolerant species, we have studied the behaviour of bean leaf discs treated with PEG 600. The kinetics of electrolyte and Pi leakages and of soluble sugar and starch content were studied during 24 h rehydration of the leaf discs

Induction of Increased Salt Tolerance in Sorghum bicolor by NaCl Pretreatment

Abstract: Following 20 d of exposure to 75 or 150 mol m−3 NaCl Sorghum bicolor (L.) Moench plants become capable of growing in medium containing 300 mol m−3 NaCl. Control plants, which have not been pretreated, or plants pretreated for less than 20 d die within 2 weeks when exposed to 300 mol m−3 NaCl. We consider this induction of a capacity to survive in and tolerate a high NaCl concentration as an adaptation to salinity. We suggest that adaptation to salinity is more than osmotic adjustment and that it takes longer to develop than osmotic adjustment. Concomitantly with the appearance of the ability to grow in high salinity, adaptation also comprises the development of a capacity to regulate internal Na+ and Cl− concentrations, even when external salinity is high. Shoot mean relative growth rates are similar for both control plants and for adapted plants growing in 300 mol m−3 NaCl, although their shoot Na+ and Cl− concentrations are quite different. Based on these data, we propose that adaptation of Sorghum to high salinity results from a modulation of genome expression occurring during extended exposure to non-lethal NaCl concentrations.

Salt Tolerance in the Triticeae: K/Na Discrimination in Synthetic Hexaploid Wheats

Abstract: Les plants hexaploides contiennent le genome d'un tetraploide et celui d'un ble diploide. L'augmentation du rapport K/Na lors de la culture sur milieu sale, caracteristique d'Aegilops squarrosa et du genome BBAADD des plants de ble hexaploides se retrouve chez les diploides et les tetraploides GGAA. On suppose que les tetraploides BBAA ont perdu ce caractere au cours de l'evolution

Transformation of Sugarbeet (Beta vulgaris) by Agrobacterium tumefaciens

Abstract: A method has been developed for the regeneration of transformed plants of the commercially important crop sugarbeet (Beta vulgaris L.), using Agrobacterium tumefaciens. Binary vectors were used, carrying both screenable and selectable genes. Plant regeneration from shoot-base tissues was found to be relatively rapid and frequent compared with petioles or leaf tissue. Inoculation of cultured shoot-base tissues resulted in the production of transformed plants, as determined by (1) introduced resistance to kanamycin, (2) introduced CAT or GUS activity, and (3) Southern blot analysis to show the integration of foreign DNA. The transformation frequency was found to be dependent upon expiant source, plant genotype and selection conditions used.

Afternoon Depression In Photosynthesis in Grapevine Leaves—Evidence for a High Light Stress Effect

Abstract: Recherche des causes de la diminution des echanges gazeux l'apres-midi chez la vigne. Apres avoir verifie que cette diminution de l'activite photosynthetique avait bien lieu dans les feuilles de plantes correctement arrosees et en absence de stress dus a la temperature ou a l'humidite de l'air; les caracteristiques photosynthetiques des feuilles exposees a des densites de flux de photons fortes et moderees ont ete comparees afin de comprendre le role d'une exposition prolongee a une forte luminosite

Response of Soybean Canopy Photosynthesis to CO2 Concentration, Light, and Temperature

Abstract: Etude des effets a long terme de CO 2 sur la photosynthese au niveau de la canopee chez le soja. Les sojas sont plantes en serre avec des concentrations en CO 2 variant de une a trois fois la concentration atmospherique. La reponse de la canopee a la lumiere solaire, a la temperature de l'air et aux effets a court terme du CO 2 est mesuree en fonction des effets a long terme du CO 2 sur la croissance. Les effets du CO 2 et de la temperature sur l'activite de la Rubisco et la concentration en RuBP sont egalement etudies

31P NMR Measurements of the Cytoplasmic and Vacuolar Pi Content of Mature Maize Roots: Relationships with Phosphorus Status and Phosphate Fluxes

Abstract: The vacuolar and cytoplasmic inorganic phosphate (Pi) content of the mature regions of maize roots was measured by a 31P NMR technique which used an external standard to avoid the need for tissue extraction and which exploited the relatively rapid relaxation of cytoplasmic Pi in order to improve the detection of this pool in fully-vacuolated cells.In mature roots of maize growing with abundant external phosphate, the concentration of Pi in the cytoplasm was approximately 6.5 mol m-3. When these plants were deprived of external phosphate, the vacuolar Pi content of the roots decreased rapidly, but the cytoplasmic Pi concentration initially remained constant and did not begin to decline until P-stress became severe. Calculations show that withdrawal of Pi from the vacuoles into the cytoplasm under these conditions would be against an electrochemical gradient.During P-starvation, an increased capacity for Pi influx developed, preceding any detectable change in the cytoplasmic Pi content of the roots. This response is considered in terms of parallel effects on transport sites for phosphate at the plasmalemma and at the tonoplast. Comparisons of simultaneous rates of influx and net uptake implied that phosphate efflux accounted for < 10% of influx in plants of a steady or declining P-status. However, direct measurements of efflux suggested that this process may be temporarily accelerated when plants are recovering from P-stress. © 1990 Oxford University Press.

Exogenous ABA as a Modulator of the Response of Sorghum to High Salinity

Abstract: Treatment of Sorghum bicolor (L.) Moench, cv. 610, with abscisic acid (ABA) during the first week of salinization with 150 mol m"3 NaCl induced enhancement of growth and accelerated adaptation to high salinity (300 mol m ~3 NaCl). Adaptation is defined as the development of the ability of the plant to survive, grow, and set seeds upon exposure to a NaCl concentration which is lethal for the unadapted plant. In the absence of ABA the saline pretreatment requires 20 d for the development of adaptation (Amzallag et al., 1990); with ABA treatment the same result is achieved within approximately one week. The exposure of the plants to non-lethal salinity (150 mol m-3 NaCl) apparently triggers a transient sensitivity to ABA lasting for about 8 to 10 d following the beginning of salinization. This period coincides with an increase in leaf PEP carboxylase activity which seems to occur faster if the plants are treated with ABA. Exogenous ABA-induced enhancement of growth and control of shoot Na + concentration, occur at a lower ABA concentration («10 mmol m~3) than the induction of adaptation to salinity which occurs at «40 mmol irT3 or above. The lowered shoot Na+ concentration which is induced by a low ABA concentration is not sufficient to induce survival of the plants in high salinity (300 mol m'3 NaCl).

Growth and Survival Responses of Rumex Species to Flooded and Submerged Conditions: The Importance of Shoot Elongation, Underwater Photosynthesis and Reserve Carbohydrates

Abstract: Plants of Rumex thyrsiflorus Fingerh., R. crispus L. and R. maritimus L., which are zoned along a gradient of elevation in a river foreland ecosystem, and differ in their flood-tolerance, were subjected to different flooding levels. Under conditions of soil flooding, the growth rates of the flood-tolerant R. crispus and R. maritimus were as high as under drained conditions, but that of the flood-intolerant R. thyrsiflorus was halved. Upon submergence, the low elevation species R. maritimus showed rapid shoot elongation; when elongation resulted in a protrusion of leaves above the water surface, the plants survived. Alternatively, underwater photosynthesis also led to a 100% survival of submerged R. maritimus plants, provided that enough inorganic carbon was made available in the water. This could be attributed in part to the use of photosynthetically-derived oxygen for root respiration; in a hydroculture experiment, with 5 0 mM C02 in the water in the shoot environment, photosynthetically-derived oxygen contributed more than 50% to root oxygen consumption at low oxygen concentrations in the root environment. The intermediately elevated species R. crispus appeared to be much more tolerant towards conditions of prolonged total submergence: older plants survived eight weeks submergence in the, dark. This response was explicable in terms of a dormancy strategy, which is characterized by a slow consumption of carbohydrates stored in the tap-root; The differential responses of R. maritimus and R. crispus to total submergence reveal the limitations, of flood-tbleranee arid reflect the different life-histories of the species.

Effect of Salinity on Growth, Nodulation and Nitrogen Yield of Chickpea (Cicer arietinum L.)

Abstract: Effet de la salinite sur la modulation du pois chiche. Effet d'un apport continu en solution saline sur la croissance, la nodulation et la fixation d'azote chez le pois chiche inocule avec une variete de Rhizobium tolerant la salinite

Invertase Activity and its Relation to Hexose Accumulation in Potato Tubers

Abstract: Utilisation de clones de pomme de terre ayant des capacites tres differentes a accumuler des hexoses afin d'etudier le role de l'invertase et de son inhibiteur dans l'accumulation d'hexoses dans les tubercules stockes a 10°C ou transferres ensuite a 3°C

Salt tolerance in the Triticeae: K/Na discrimination in barley.

Abstract: The experiments described here were designed to compare the ability of T. aestivum, T. durum, H. vulgare, and H. spontaneum to restrict the accumulation of Na (and Cl) in the shoots, and to maintain high K concentrations

Effects of Priming and Endosperm Integrity on Seed Germination Rates of Tomato Genotypes I. GERMINATION AT SUBOPTIMAL TEMPERATURE

Abstract: The bases of differences in germination rates (GR g ) among three cold/salt-tolerant tomato accessions and one cold/salt-sensitive tomato cultivar were investigated. The effects of seed priming (6 d imbibition in aerated −1.2 MPa polyethylene glycol solution at 20°C followed by redrying) and of removing the endosperm/testa cap covering the radicle on the temperature sensitivity of GR g , and the interaction of these treatments with genotypes, were also examined

Comparison of Trunk and Branch Sap Flow with Canopy Transpiration in Pecan

Abstract: The recent development of trunk flow gauges, using the heat balance principle, allows direct measurement of trunk or branch sap flow. When combined with water loss data from precision lysimetry and from leaf transpiration rates obtained by porometry a simultaneous record of water flow through the trunk, branches and canopy can be produced. We obtained such a record to quantify water fluxes through a pecan tree under non-limiting soil moisture conditions, with the purpose of characterizing the water transport system

Investigations of the δ13C Pattern in Leaves of Fagus sylvatica L.

Abstract: The natural abundance of 13C in different parts of beech (Fagus sylvatica L.) leaves was analysed. Values for leaf ribs were consistently higher than those for intercostal tissue. Similar differences occur between petiole and stem, with petiole being less negative. The pattern of results is the same, independent of the position in the tree. However, the absolute values differ by up to 6%o from the bottom to the top of the tree. Values of S13C are in the range of -29 to -32%o for the lower leaf strata; while values between —24 and — 26%o have been measured for the top of the tree. Absolute S13C values of the whole tissue and cellulose differ by about 2%o, but relative S13C trends are almost identical. However, S13C trends are not identical for different leaf parts. A comparison of cellulose and whole tissue S13C data makes it unlikely that the 813C variations are primarily due to different compositions of chemical compounds. No fractionation seems to exist between leaf and wood cellulose. Tissue from different areas of a leaf revealed identical carbon isotope compositions.

Age Dependent Damage and Glutathione Metabolism in Ozone Fumigated Barley: A Leaf Section Approach

Abstract: Chez des feuilles d'orge, l'effet de l'âge sur la reaction a l'exposition a l'ozone est teste a travers l'etude du metabolisme du glutathion. Les proteines solubles, la peroxydation des lipides, le glutathion total, les activites de la glutathion transferase et reductase sont mesures

Dehiscence of Fruit in Oilseed Rape (Brassica napus L.) I. ANATOMY OF POD DEHISCENCE

Abstract: The development sequence of anatomical changes taking place within the pericarp tissues of Brassica napus siliquae have been studied at a fine- and ultra-structural level. Tissue differentiation occurred during the initial 20 d after anthesis (DAA) and allowed the identification of dehiscence zone cells. This descrete tissue was subsequently further delineated by extensive lignification of adjacent valve edge and replar vascular cells. Concomitant with the onset of pericarp lignification, cytoplasmic contents of the thin-walled dehiscence zone cells exhibited progressive senescence and degradation. Wall breakdown, initially evident in pods by 60 DAA, exclusively affected cells within the dehiscence zone, and eventually extended throughout this tissue from the epidermal suture to the locule, thus precipitating valve detachment. Ultrastructural examination confirmed that this loss of cellular cohesion was primarily attributable to middle lamella degradation and, furthermore, the dissolution of wall material was apparently dependent on rupture of the dehiscence zone protoplast. The significance of dehiscence zone cell modifications in relation to autolytic cell wall breakdown, together with possible implications for the regulation of pod shatter, are discussed.