bluuebunny/crossref_metadata_2025_split huggingface dataset:
Physiological changes in, and phosphate uptake by potato plants during development of, and recovery from phosphate deficiency
Authors: Cogliatti Daniel H. , Clarkson David T. 
Published: April 2006

The development of phosphate deficiency (P‐stress) was observed in rooted sprouts of Solanum tuberosum L. cv. Desiree growing in solutions without phosphate. Shoot growth was inhibited by P‐stress within 3 to 5 days of terminating the phosphate supply, while significant effects on root growth were not recorded until 7 to 9 days. Thus, the shoot:root dry weight ratio decreased from 4.3 to 2.6 over a 10‐day period. Growth in the absence of an exogenous phosphate supply progressively diluted the phosphorus in the plant. The proportional decrease in concentration was similar in roots and shoots over a 7‐day period, even though the former were growing more quickly.The potential for phosphate uptake per unit weight of root increased rapidly during the first 3 days of P‐stress. When the plants were provided subsequently with a labelled, 1 mol m−3 phosphate solution, the absorption rate was 3 to 4‐fold greater than that of control plants which had received a continuous phosphate supply. The increased rate of uptake by P‐stressed plants was accounted for by an increase (3‐fold) in the Vmax of system 1 for phosphate transport and by a marked increase in the affinity of the system for phosphate (decrease in Km). In the early stages of P‐stress, before marked changes in growth were measured, the proportion of labelled phosphate translocated to the shoots increased slightly relative to the controls when a phosphate supply was restored. In the later stages of stress a greater proportion was retained in the root system of P‐stressed plants than in that of controls.In plants with roots divided between solutions containing or lacking a phosphate supply, the increased absorption rate was determined by the general demand for phosphate in the plant and not by the P‐status of the particular root where uptake was measured. By contrast, the poportion translocated was strongly dependent on the P‐status of the root.The restoration of a phosphate supply to P‐stressed plants was marked by a rapid increase in the P concentration in snoots and roots which returned to levels similar to unstressed controls within 24 h. The enhanced uptake rate persisted for at least 5 days, resulting in supra‐normal concentrations of P in both shoots and roots, and in the formation of extensive necrotic areas between the veins of mature leaves. Autoradiographs showed accumulations of 32P in these lesions and at the points where guttation droplets formed on leaves.
Comparative study of the action of ultraviolet‐C and ultraviolet‐ B radiation on photosynthetic electron transport
Authors: Kulandaivelu G. , Noorudeen A. M. 
Published: April 2006

The effect of ultraviolet‐C (UV‐C, mainly 254 nm radiation) and ultraviolet‐B (UV‐B, 290‐320 nm) radiation on the photosynthetic electron transport reactions has been investigated. The rates of Hill activity mediated by ferricyanide and dichlorodimethoxy‐p‐benzoquinone (DCDMQ) were differently sensitive to UV‐C but equally inhibited by UV‐B. Replacement of water with diphenylcarbazide was ineffective in restoring the activity of dichlorophenol indophenol (DCPIP) Hill reaction in UV‐B treated chloroplasts, but had significant effect in UV‐C treated chloroplasts.Photobleaching of carotenoids in the presence of carbonyl cyanide‐m‐chlorophenyl‐hydrazone, an indicator of the photochemical reaction associated with the reaction centre of photosystem II, was suppressed and is paralleled by the changes in Hill activity only in UV‐B‐treated chloroplasts. Carotenoid photobleaching occurred even in UV‐C treated chloroplasts showing no measurable Hill activity. UV‐C and UV‐B irradiation diminished variable fluorescence. With UV‐B treated, but not with UV‐C treated chloroplasts, an increase in the fluorescence yield was observed upon the addition of 3‐(3,4‐dichIorophenyl)‐l,l‐dimethylurea (DCMU) and/or Na dithionite.Photosystem I activity was found to be unaffected by both UV‐C and UV‐B radiation at the fluences tested. Kinetics of P700 photooxidation and dark reversal in UV treated chloroplasts indicate that only the electron flow from photosystem II to photosystem I is impaired. It is concluded that while UV‐B radiation inactivates specifically the photosystem II reaction centre, UV‐C radiation acts at plastoquinone, the quencher Q, and the water oxidizing enzyme system.
Action of UV‐B radiation on photosynthetic primary reactions in spinach chloroplasts
Authors: Iwanzik W. , Tevini M. , Dohnt G. , Voss M. , Weiss W. , Gräber P. , Renger G. 
Published: April 2006

Spinach (Spinacia oleracea L. cv. Matador) chloroplasts were irradiated with several levels of UV‐B radiation. Measurements which reflect characteristic steps of photosynthetic electron transport were made to localize the site of impairment of photosynthesis by UV‐B radiation.Variable fluorescence, the μs‐kinetics of the 320 nm absorption changes and also oxygen evolution were substantially reduced in chloroplasts irradiated with UV‐B. It was not possible to restore the amplitude of the 320 nm absorption changes nor the signal of the transmembrane electric field measured at 520 nm by adding the photo‐system II donor couple hydroquinone/ascorbate to UV‐B treated chloroplast samples. This indicates that impairment of photosystem II activity is not caused by selective inhibition of the water‐splitting enzyme system Y, but rather is due to blockage of photosystem II reaction centers. Photosystem 1 is inferred to be highly resistant to UV‐B radiation.These results suggest that the reaction centers of photosystem II are transformed into dissipative sinks for excitation energy by action of UV‐B radiation.
Effects of ultraviolet‐B radiation on the growth and yield of crop plants
Authors: Teramura Alan H. 
Published: April 2006

This paper reviews growth chamber, greenhouse, and field studies on the effects of ultraviolet‐B (UV‐B. between 280 and 320 nm) radiation on agricultural crop plants. Our understanding of the physiological effects of UV‐B radiation comes primarily from growth chamber studies, where UV‐B is artificially supplied via filtered lamps. Both photosystems I and II, as well as carboxylating enzymes, are sensitive to UV‐B radiation. Ultraviolet‐B radiation also affects stomatal resistance, chlorophyll concentration, soluble leaf proteins, lipids, and carbohydrate pools. In general, the effects of UV‐B radiation are accentuated by the low levels of visible radiation typically found inside growth chambers.Ultraviolet‐B radiation has also been shown to affect anatomical and morphological plant characteristics. Commonly observed UV‐B induced changes include plant stunting, reductions in leaf area and total biomass, and alterations in the pattern of biomass partitioning into various plant organs. In sensitive plants, evidence of cell and tissue damage often appears on the upper leaf epidermis as bronzing, glazing, and chlorosis. Epidermal transmission in the UV region decreases in irradiated leaves. This decrease is primarily associated with a stimulation in flavonoid biosynthesis and is thought to be a protective, screening response to the deleterious effects of UV‐B. A considerable degree of variability exists in sensitivity to UV‐B radiation between different species. Approximately 30% of the species tested were resistant, another 20% were extremely sensitive, and the remainder were of intermediate sensitivity, in terms of reductions in total dry weight. In addition to this sizable interspecific variability, there appears to be a similarly wide intraspecific variability in UV‐B response.The effects of UV‐B radiation on crop yield have only been examined in a limited number of field studies, with ambient levels of UV‐B radiation being supplemented with fluorescent sun lamps. Due to various deficiencies, all these field experiments to date have only limited utility for assessing the potential impact of enhanced levels of UV‐B on crop productivity.
Simulation of marked root hair curling in Rhizobium‐legume symbiosis
Authors: van Batenburg F. H. D. , Kijne J. W. , van Iren F. , Libbenga K. R. 
Published: April 2006

The soil bacterium Rhizobium infects its leguminous host plants in temperate regions of the world mostly by way of the growing root hairs. Root hair curling is a prerequisite for root hair infection, although sidelong root hair infections occasionally have been observed. The processes underlying Rhizobium‐induced root hair curling are unknown.Computer simulation of root hair growth indicates that one‐sided tip growth inhibition by Rhizobium can result in root hair curling when three conditions are simultaneously fulfilled: 1) rhizobial growth inhibition is strong enough to prevent removal out of the tip growth range: 2) root hair surface growth between the attached Rhizobium and the root hair top is inhibited; 3) rhizobial growth inhibition is limited to one side of the root hair.The results predict that root hair curling by stimulation of tip growth is improbable. This study accentuates the need for information about the growth processes contributing to tip growth in leguminous root hairs.
Effects of activated charcoal in anther cultures
Authors: Johansson Lars 
Published: April 2006

Embryogenesis in anther cultures of Anemone Canadensis L., Anemone hupehensis Lemoine and Nicotiana tabacum L. was shown to be inhibited by abscisic acid added to the medium. However, this inhibition was reduced in the presence of activated charcoal (AC).The presence of AC in the culture medium strongly promoted embryogenesis in anther cultures of Anemone Canadensis compared with other media combinations. Treatment of the agar medium with AC, which was removed before inoculation of the anthers, also stimulated embryogenesis, but treatment of the water constituent did not.The number of embryos produced in anther cultures of Anemone Canadensis and Nicotiana tabacum was shown to be positively related to the length of lime of incubation on medium supplemented with AC. In the case of Anemone Canadensis the stimulating effect of AC was most pronounced when the first visible embryos had emerged.The presence of anther‐derived embryos from Anemone Canadensis in anther cultures of Anemone Canadensis and Nicotiana tabacum was shown to inhibit embryogenesis. It was also demonstrated that embryos from anther cultures of Anemone canadensis, Papaver setigerum DC and Clematis viticella L. produced phenolic substances, and that the concentration of these substances was higher in culture medium lacking AC. Treatment of such medium with AC could reduce the concentration of phenolic substances by more than 80%.
The pathway of betalain biosynthesis: Effect of cytokinin on enzymic oxidation and hydroxylation of tyrosine in Amaranthus tricolor seedlings
Authors: Elliott Daphne C. 
Published: April 2006

The effect of exogenously added tyrosine or l‐3‐(3,4‐dihydroxyphenyl) alanine on the accumulation of betacyanin in response to cytokinin in Amaranthus tricolor (L.) var. tricolor half‐seedlings depends on the age of the seedlings and the treatment of the seedlings prior to induction of pigment by benzyladenine. Neither extracted polyphenol oxidase, peroxidase or tyrosine hydroxylase activity, nor in vivo tyrosine hydroxylation is increased in response to exposure of seedlings to cytokinin. However a small percentage of the polyphenol oxidase activated or unmasked by Triton X‐100 treatment of membrane fractions is increased after cytokinin treatment of half‐seedlings for 22 h. It is concluded that cytokinin control may be on a multi‐enzyme membrane‐located complex involving part of the polyphenol oxidase activity of the tissue (possibly an isoenzyme), and that the majority of the polyphenol oxidase activity in Amaranthus is a constitutive membrane enzyme which is not involved in betacyanin synthesis.Although cytokinins do not affect in vivo tyrosine hydroxylation, this activity follows closely the accumulation of betacyanin which is first detectable about 6.5 h after the application of cytokinin. Only a very low level of in vivo hydroxylation can be demonstrated in half‐seedlings treated for 6 h either with or without cytokinin but it begins to increase shortly after this time. A large increase in this activity by 16 h (independent of cytokinin) can be almost completely (79%) prevented by chloramphenicol (300 μM) although the drug increases accumulation of betacyanin. At this concentration about 30% of the protein synthesis in inhibited. In vitro tyrosine hydroxylation is, however, not reduced in half‐seedlings treated with chloramphenicol during 16 h induction nor is extractable polyphenol oxidase reduced. It is concluded that chloramphenicol is inhibiting the synthesis of some protein essential for in vivo hydroxylation other than the activity measured during in vitro hydroxylation and that the inhibition of synthesis of 79% in vivo hydroxylation still leaves enough activity for maximum betacyanin synthesis.
Isolation from sugarcane cultures of variants resistant to antimetabolites
Authors: King John , Maretzki Andrew 
Published: April 2006

Variants resistant to antimetabolites are useful for investigating metabolic regulation and biochemical genetics in organisms. In this study, suspensions of mutagenized sugarcane (Saccharum sp.) cells, originating from a stalk parenchyma explain of the Hawaiian variety 50–7209, were used to investigate the feasibility of isolating variants resistant to l‐canavanine, glyphosate [N‐(phosphonomethyl)glycine], ophiobolin A and orthovanadate. Rigorous retesting of clones which grew on selection media led to the identification of three cell lines, two of which were resistant to glyphosate and one to orthovanadate. No variants were isolated which showed a persistent resistance either to l‐canavanine or ophiobolin A.The results demonstrate that resistant variants do occur, or can be induced, in sugarcane cell suspensions and that they can be rescued and cultivated.
Morphogenesis in dormant embryonic shoots of Picea abies: Influence of the crown and cold treatment
Authors: Jansson Eva , Bornman Chris H. 
Published: April 2006

Retention of the crown, a plate of homogeneously thickened collenchymatous cells at the base of the embryonic shoot of Picea abies (L.) Karst., has marked effects on the induction of adventitious buds from the needle primordia. These effects were observed on embryonic shoots of three clones which were cold‐treated at 4 ± 1°C for nil, two, four and six months; and then excised either with or without the crown, before subculturing either directly on a medium lacking plant growth regulators or after application of 125 μM benzyladenine (BA) as a 3‐h pulse. Embryonic shoots retaining the crown and treated with BA responded reproducibly better than those lacking it. This was true both for the number of shoots that produced adventitious buds and for the numbers of adventitious buds per shoot. Differentiation of as many as five adventitious buds in a single needle primordium was observed, with development occurring nearly twice as early (7 as compared with 12 weeks) in the presence as in the absence of the crown. The response decreased progressively with increasing exposure to cold treatment.A number of anatomical changes occurred during culture in vitro. After 3 to 4 weeks a band of sclerenchymatous cells commenced differentiation at the centre of the crown. In embryonic shoots without the crown, a tissue which was identified as a wound periderm formed at the excision surface. Vascular unions were observed between the tissues of the newly — formed shoots induced from the needle primordia and those of the original shoot explants.
Breakdown of photosynthetic pigments and lipids in spinach leaves with ozone fumigation: Role of active oxygens
Authors: Sakaki Takeshi , Kondo Noriaki , Sugahara Kiyoshi 
Published: April 2006

In spinach (Spinacia oleracea L. cv. New Asia) plants fumigated with ozone in light, destruction of chlorophylls and carotenoids and formation of malondialdehyde (MDA), an indicator of lipid peroxidation, were observed. Chlorophyll a and carotenoids in leaves started to be broken down 6–8 h after the commencement of 0.5 ppm ozone fumigation, whereas MDA formation in leaves increased linearly for the initial 8 h of fumigation followed by a more rapid increase. In leaf discs excised from 6‐h fumigated plants, destruction of chlorophyll a and carotenoids and MDA formation proceeded in the light but were almost completely suppressed under an anaerobic condition. Effects of exogenously applied scavengers of active oxygen species suggest that active oxygens, especially superoxide radical (O2‐), participated in both the destruction of chlorophyll a and carotenoids and the formation of MDA. Ozone fumigation reduced the levels of endogenous scavengers of O2‐, superoxide dismutase (SOD) and L‐ascorbate, in leaves to one‐half the initial levels each by 3.5 and 8 h fumigation, respectively. The results indicate that the photosynthetic pigments and lipids were broken down by active oxygens accumulated in leaves as a result of the ozone‐induced destruction of physiological defense against oxygen toxicity.Activity of polyphenol oxidase in chloroplast membranes of 4‐h fumigated leaves increased to 240% of the initial level, suggesting that the thylakoid membranes had been affected severely before the pigment destruction. The relations between the pigment destruction and the disintegration of thylakoids are discussed.
Inhibition by mevinolin of plant growth, sterol formation and pigment accumulation
Authors: Bach Thomas J. , Lichtenthaler Hartmut K. 
Published: April 2006

To obtain information on the importance of a functional mevalonate synthesis for plant growth and development, we investigated the effect of mevinolin, a highly specific inhibitor of 3‐hydroxy‐3‐methylglutaryl (HMG) coenzyme A reductase (the mevalonate‐producing enzyme) on growth, sterol accumulation and pigment formation of radish seedlings (Raphanus sativus L. cv. Saxa Treib) and in part also wheat seedlings (Triticum aestivum L. cv. Kolibri). Mevinolin applied during germination inhibits root elongation and development of lateral roots in etiolated and light‐grown radish seedlings. This effect cannot be overcome by exogenous GA3, but by addition of mevalonic acid, the product of the internally inhibited reaction. This emphazises the specifity of the mevinolin effect and indicates that the biosynthesis of mevalonic acid is a mandatory requirement for root growth. In light‐grown radish seedlings mevinolin also affects hypocotyl length‐growth and inhibits sterol accumulation, but has little effect on the chlorophyll and carotenoid accumulation in the chloroplasts of the cotyledons. This indicates the possible presence of an independent mevalonate synthesizing pathway within the plastids and suggests a low transport rate of mevinolin from the radish roots to the cotyledons. When mevinolin is directly applied to the leaves at higher concentrations, it also reduces the light‐induced chlorophyll and carotenoid accumulation as has been shown with etiolated primary leaves of wheat. This inhibition is age‐dependent and proceeds to a higher extent in older than in younger etiolated leaf tissue. From our results we conclude that plastids possess an independent HMG‐CoA reductase.In the cotyledons of radish, mevinolin seems to induce a senescence retardation and sun‐type growth response, as has been evaluated by measuring the fast and slow chlorophyll fluorescence induction kinetics (Kautsky effect). These responses may be due to inhibitor‐induced changes in the intracellular phytohormone balance.
Rb+ uptake by isolated pea mesophyll protoplasts in light and darkness
Authors: Rahat Michaela , Reinhold Leonora 
Published: April 2006

Rb+ uptake into protoplasts isolated from the mesophyll of Pisum sativum L. cv. Dan has been followed at intervals of a few minutes in the light and in the dark. The progress curve for uptake in the dark decreased in slope after about 7 min; in the light, by contrast, the slope increased. This effect was more pronounced at pH 7 than at pH 5.5. The pH profile for uptake in the dark rose with increasing pH: in the light the profile flattened, or even fell somewhat, between pH 5.5 and pH 6.5, then rose again. In the dark the proton uncoupler carbonyl cyanide m‐chlorphenylhydrazone (CCCP) had little or no effect, either at pH 5.5 or at pH 7.4; in the light CCCP was strongly inhibitory, particularly at pH 7.4. Increasing concentrations of CCCP produced progressively more and more severe inhibition in the light, but in the dark produced a slight rise in uptake. The ATPase inhibitors quercetin, rutin and diethyl‐stilbestrol, as well as arsenate, all depressed uptake in the light, particularly at higher pH Dark uptake was sensitive only at pH 5.5, not at pH 7.4. In marked contrast to the case of methyl‐3 glucose, where protoplasts which were switched from light to dark took up sugar at the accelerated light rate for the first 7 min in the dark, a switch to darkness produced a Rb+ uptake rate below that for protoplasts held continuously in the dark. It is inferred that the mechanism of Rb+ uptake does not involve proton cotransport.Information regarding the membrane potential was obtained by following the distribution of tetraphenyl phosphonium (TPP+) between protoplasts and medium. The potential was more negative in the light than in the dark. It was also more negative at pH 7 than at pH 5 both in the light and in the dark. Treatment with CCCP produced no appreciable depolarization within the first 20 min, indicating thet the CCCP inhibition of Rb+ uptake in the light cannot be ascribed to a reduction in potential. An ATP‐fueled K+ porter, or K+‐H+ antiporter, seems the most likely explanation. The maintenance of the rising pH profile in the dark, despite the presence of a CCCP concentration which drastically inhibits light uptake, suggests that the profile does not depend on the operation of the proton pump.
Critical evaluation of the in vivo nitrate reductase assay for detection of two nitrate pools in wheat leaves
Authors: Høg Kirsten , Hartvigsen Marianne B. , Rasmussen Ole S. 
Published: April 2006

The usefulness of the nitrate‐free in vivo nitrate reductase assay for the study of nitrate pools in wheat leaves was investigated. Leaf sections from 7‐day‐old wheat seedlings, exposed 24 h before harvest to 1.5, 3.0 or 5.0 mM KNO3 were used. After 2 to 4 h of incubation nitrite production ceased, reaching a plateau. The time required to reach the plateau and the level of the plateau increased with increasing endogenous nitrate content. At nitrite plateau the amount of nitrate left in the tissue was independent of the original nitrate content in the tissue. Addition of nitrate at plateau caused resumed nitrite production. It is concluded that nitrate was the limiting factor in nitrite production.Oxygen inhibited nitrate reduction and stimulated further assimilation of nitrite. A considerable initial leakage of nitrate from tissue to the assay medium, followed by a slower continuous leakage, was observed throughout the incubation. N2‐flushing or inclusion of Triton X‐100 in the assay medium increased nitrite production by making more nitrate available for reduction. These treatments also increased the leakage of nitrate. At plateau levels the amount of nitrate left in the tissue was dependent on the oxygen tension in the assay medium. Under low oxygen tension nearly all nitrate in the tissue was available for reduction. Nitrite production at plateau is not a useful index for a metabolic nitrate pool and nitrate left in the tissue is not a useful index for a nitrate storage pool because both parameters are highly dependent on the oxygen tension in the assay medium. Further, in view of the considerable leakage, the nitrate‐free in vivo nitrate reductase assay cannot be used to detect two separate nitrate pools in wheat leaves.