bluuebunny/crossref_metadata_2025 huggingface dataset:
Arbuscular mycorrhizae and nitrogen assimilation in maize after drought and recovery
Authors: Subramanian Kizhaeral S. , Charest Christiane
Published: March 2003

In a greenhouse experiment, the effect of arbuscular mycorrhizal (AM) fungus (Glomus intraradices Schenck & Smith) colonization on N assimilation in maize (Zea mays L.) was examined after well‐watered, drought and recovery periods. Seeds of selection cycles C0 (drought‐sensitive) and C8 (drought‐resistant) of the tropical maize cultivar Tuxpeño sequía were used for this study. Maize plants were exposed or not to drought stress for 3 weeks (45‐65 days after sowing, DAS) followed by 3 weeks of recovery (66‐86 DAS) at the preflowering stage. Root and shoot samples harvested at the end of the drought or well‐watered and recovery periods were determined for key enzymes involved in N assimilation (NR, nitrate reductase; NiR, nitrite reductase; GS, glutamine synthetase; GOGAT, glutamate synthase), protein and amino acid concentrations, and total N contents. Drought stress significantly (P ≤ 0.01 or P ≤ 0.001) decreased all the enzyme activities except NiR in the roots and shoots of both cultivars. After 3 weeks of drought, the AM roots of both cultivars had higher activities of NR (C0, 45%; C8, 26%), GS (C0, 76%; C8, 33%) and GOGAT (C0, 41%; C8, 53%) than non‐AM roots and were comparable to well‐watered plants. These enzyme activities were also enhanced in drought‐stressed AM shoots of C0 and C8. Total amino acid concentrations in AM plants of C0 were 4.6 and 1.6 times higher in roots and shoots, respectively, compared to non‐AM plants. The predominant amino acids detected were Ala, Arg, Asn, Asp, Gln and Glu which constituted approximately 56 and 75% of the total pool in roots and shoots, respectively. Soluble proteins and total N contents were also higher in AM plants than non‐AM plants under drought conditions. The enhancement of N‐assimilating enzymes and nitrogenous compounds in maize may indicate a transfer of NO3− through the extraradical mycelium or increased N assimilation due to the AM symbiosis. Our overall results suggest that AM association plays an important role in enhancing N assimilation or N nutritional status which enables the host plant to withstand drought conditions and recover after stress is relieved.
Responses of Scots pine seedlings to low root zone temperature in spring
Authors: Ryyppö A. , Iivonen S. , Rikala R. , Sutinen M.‐L. , Vapaavuori E.
Published: March 2003

The effects of root zone temperature (RZT) on growth, gas exchange, H+‐ATPase (EC 3.6.1.3; PM‐ATPase) activity and fatty acid composition of plasma membrane (PM) phospholipids in the roots of one‐year‐old seedlings of Scots pine (Pinus sylvestris L.) were studied for 10 days during flushing in spring. Nursery‐grown seedlings were transferred to cold storage (−5°C) in mid‐October, thawn in a cold room at 5°C in May, and transferred to hydroponic cultures at an air and root zone temperature of 5°C for a 3‐day adjustment period. The experiment started when the RZT was changed to either 5, 12 or 20°C and the air temperature was increased to 20/15°C (day/night). RZTs of 5 and 12°C were suboptimal for root growth, and also shoot growth was suppressed at 5°C. The degree and rate of phospholipid fatty acid saturation in the PM of roots was highest at RZT of 20°C and intermediate at 12°C, while no change in the degree of saturation occurred at 5°C. PM‐ATPase activities, measured at 5 and 12°C (real activities) were severely temperature‐limited, but the increasing potential activities (measured at 38°C) at these RZTs indicated delayed deacclimation of the root system. At RZT 20°C, the decline of C18:2/C16:0 ratio in combination with decreasing potential and real PM‐ATPase activities indicated, instead, fast deacclimation of the root system. Net photosynthesis of the seedlings was limited by non‐stomatal factors at the beginning of the experiment, but recovered from winter inhibition and later became limited by low stomatal conductance at RZTs of 5 and 12°C. Instead, at 20°C the net photosynthesis increased with increasing stomatal conductance during the experiment. We conclude that low RZT suppresses growth of roots and such changes in the PM as are needed for efficient uptake of water and nutrients. This, in turn, limits net photosynthesis and, thus, the availability of photosynthates for root growth in spring. On the other hand, a rise in RZT can rapidly induce the structural and functional changes in PM of the roots that are needed for the efficient gas exchange and growth of the Scots pine seedlings.
Gas exchange and metabolite fluctuations in green and yellow bands of variegated leaves of the monocotyledonous CAM species Agave americana
Authors: Raveh Eran , Wang Ning , Nobel Park S.
Published: March 2003

The variegated leaves of the Crassulacean acid metabolism (CAM) species Agave americana have a large central longitudinal green band with narrow yellow bands on either side. The yellow bands had 97% less pigment content, 84% lower ribulose‐1,5‐bisphosphate carboxylase/oxygenase activity, but only 20% lower phosphoenolpyruvate carboxylase activity than the green band. The green bands exhibited gas exchange typical of CAM plants, with most CO2 uptake occurring at night, leading to a daily net CO2 uptake of 127 mmol m−2 day−1. The yellow bands had some nighttime net CO2 uptake but a larger loss during the daytime, indicating that they were sink tissues. Nocturnal citrate and malate accumulations for the yellow bands were 65 and 75%, respectively, of those of the green bands; sucrose supported 64‐83% of their nocturnal acid accumulation. This is the first evidence that agaves, which are malic‐enzyme‐type CAM plants, use sucrose as the carbon source for nocturnal acid accumulation. About 44% of the carbon demand of the yellow bands can be supplied by sucrose diffusing via the symplast from the adjacent green band, about 25% from fructose and glucose diffusion, and some via the apoplast.
Relationship of chlorophyll, seed moisture and ABA levels in the maturing Brassica napus seed and effect of a mild freezing stress
Authors: Green Beverley R. , Singh Santokh , Babic Ivan , Bladen Chris , Johnson‐Flanagan Anne M.
Published: March 2003

Chlorophyll (Chl) retention by mature seed of canola as the result of an early frost or other environmental factors (the “green seed problem”) causes serious economic losses. The relationship of seed degreening to rate of moisture loss by seed and silique and the role of ABA in this process were investigated as a function of developmental age. During the normal predesiccation stage (28–45 days after pollination), seed of Brassica napus (cv. Westar) loses Chl rapidly but seed moisture slowly. After a mild freezing stress, there is a rapid loss of moisture from silique walls, followed by accelerated loss of seed moisture. Chl degradation ceases at 35–45% seed moisture. ABA levels in silique walls of frozen plants (determined by enzyme‐linked immunosorbant assay) increased after freezing, apparently in response to moisture loss. In contrast, ABA levels in the seed increased dramatically 1 day after freezing, then decreased to control levels. The influence of the rate of seed moisture loss on Chl degradation was investigated by fast and slow drying of isolated seed under controlled humidity conditions. Seed dried rapidly at 22% RH retained most of its Chl, whereas seed dried slowly at 86% RH lost Chl as fast or faster than seed on control (unfrozen) plants. In all treatments, Chl loss stopped at about 40% seed moisture.
Response of antioxidant enzymes to transfer from elevated carbon dioxide to air and ozone fumigation, in the leaves and roots of wild‐type and a catalase‐deficient mutant of barley
Authors: Azevedo R. A. , Alas R. M. , Smith R. J. , Lea P. J.
Published: March 2003

A catalase‐deficient mutant (RPr 79/4) and the wild‐type (cv. Maris Mink) barley (Hordeum vulgare L.) counterpart, were grown for 3 weeks in high CO2 (0.7%) and then transferred to air and ozone (120 nl 1−1) in the light and shade for a period of 4 days. Leaves and roots were analysed for catalase (CAT, EC 1.11.1.6), superoxide dismutase (SOD, EC 1.15.1.1) and glutathione reductase (GR, EC 1.6.4.2) activities. CAT activity in the leaves of the RPr 79/4 catalase‐deficient mutant was around 5‐10% of that determined in Maris Mink, but in the roots, both genotypes contained approximately the same levels of activity. CAT activity in Maris Mink increased in the leaves after transferring plants from 0.7% CO2 to air or ozone, reaching a maximum of 5‐fold, after 4 days in shade and ozone. For the catalase‐deficient mutant, only small increases in CAT activity were observed in light/air and light/ozone treatments. In the roots, CAT activity decreased consistently in both genotypes, after plants were transferred from 0.7% CO2. The total soluble SOD activity in the leaves and roots of both genotypes increased after plants were transferred from 0.7% CO2. The analysis of SOD isolated from leaves following non‐denaturing PAGE, revealed the presence of up to eight SOD isoenzymes classified as Mn‐SOD or Cu/Zn‐SODs; Fe‐SOD was not detected. Significant changes in Mn‐ and Cu/Zn‐SOD isoenzymes were observed; however, they could not account for the increase in total SOD activity.

In leaves, GR activity also increased in Maris Mink and RPr 79/4, following transfer from 0.7% CO2; however, no constant pattern could be established, while in roots, GR activity was reduced after 4 days of the treatments.

The data suggest that elevated CO2 decreases oxidative stress in barley leaves and that soluble CAT and SOD activities increased rapidly after plants were transferred from elevated CO2, irrespective of the treatment (light, shade, air or ozone).
Free radical scavenging as affected by accelerated ageing and subsequent priming in sunflower seeds
Authors: Bailly Christophe , Benamar Abdelilah , Corbineau Françoise , Côme Daniel
Published: March 2003

Lipid peroxidation resulting from loss of free radical scavenging is thought to be involved in deterioration of sunflower (Helianthus annuus L.) seeds during accelerated ageing. In other respects, presoaking of seeds in a solution of low water potential (osmopriming) has been demonstrated to reinvigorate aged seeds. The aim of the present work was to study the effect of osmopriming on the germination of aged sunflower seeds and to investigate whether this effect was associated with the restoration of antioxidant defence systems. Seeds were aged for 5 days at 45°C and 100% relative humidity and then primed for various durations up to 7 days at 15°C in a solution of polyethylene glycol 6000 at −2 MPa. Lipid peroxidation was estimated by measuring malondialdehyde (MDA) and conjugated diene contents, and the activities of superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR) were measured throughout the treatments. Accelerated ageing resulted in a marked decrease in the germination rate, and was associated with an increase in the levels of MDA and conjugated dienes, thus indicating lipid peroxidation. Ageing was also characterized by a decrease in the activities of CAT and GR. The activities of SOD and DHAR were much less altered. No APX activity was detected whatever the seed treatment. Priming of aged seeds progressively restored the initial germinative ability and resulted in a marked decrease in the levels of MDA and conjugated dienes, indicating a fall in lipid peroxidation processes. These effects of priming were also well correlated to the recovery of SOD, CAT and GR activities. Priming treatment for 7 days led to full restoration of the cell detoxifying mechanisms which were strongly altered during ageing. Glutathione content showed the same changes as GR activity. There existed a clear‐cut relationship between seed germinative energy, expressed as the germination rate, and the efficiency of free radical scavenging systems, in particular CAT and GR activities and glutathione content. The results suggest that the antioxidant defence systems might play a key role in seed vigour.
Cold hardiness of rhododendron cultivars grown in different photoperiods and temperatures
Authors: Väinölä Anu , Junttila Olavi , Rita Hannu
Published: March 2003

Two rhododendron cultivars, ‘Pohjola's Daughter’ and ‘Helsinki University’, were grown at +15 and +24°C, each combined with a photoperiod of 14 h (short day, SD) or 20 h (long day, LD). After a 112‐day growing season, they were subjected to a hardening regime of fortnightly decreasing temperature (+9, +5, +1 and −2°C) and a 12‐h photoperiod, except that part of the plants grown in LD had LD also at +9 and +5°C. At −2°C, all plants were in darkness. Controlled freezing tests of the leaves were performed before each change in temperature. The injury was evaluated visually and by electrolyte leakage (EL) tests. The observations on the visual assessment were analysed with logit models, and the EL data with non‐linear sigmoid functions. The visually scored 50% damage (VD50) correlated better with the EL tests than 10 or 90% damage. Photoperiod and temperature during the growing season affected the cold hardiness of both cultivars, but they differed in their responses. ‘Pohjola's Daughter’ benefited from SD as well as from high temperature, while ‘Helsinki University’ attained better hardiness at a cool growing season temperature and was less sensitive to photoperiod.
Elevated CO2 enhances plant growth in droughted N2‐fixing alfalfa without improving water status
Authors: De Luis I. , Irigoyen J. J. , Sánchez‐Díaz M.
Published: March 2003

The long‐term interaction between elevated CO2 and soil water deficit was analysed in N2‐fixing alfalfa plants in order to assess the possible drought tolerance effect of CO2. Elevated CO2 could delay the onset of drought stress by decreasing transpiration rates, but this effect was avoided by subjecting plants to the same soil water content. Nodulated alfalfa plants subjected to ambient (400 μmol mol−1) or elevated (700 μmol mol−1) CO2 were either well watered or partially watered by restricting water to obtain 30% of the water content at field capacity (ampproximately 0.55 g water cm−3). The negative effects of soil water deficit on plant growth were counterbalanced by elevated CO2. In droughted plants, elevated CO2 stimulated carbon fixation and, as a result, biomass production was even greater than in well‐watered plants grown in ambient CO2. Below‐ground production was preferentially stimulated by elevated CO2 in droughted plants, increasing nodule biomass production and the availability of photosynthates to the nodules. As a result, total nitrogen content in droughted plants was higher than in well‐watered plants grown in ambient CO2. The beneficial effect of elevated CO2 was not correlated with a better plant water status. It is concluded that elevated CO2 enhances growth of droughted plants by stimulating carbon fixation, preferentially increasing the availability of photosynthates to below‐ground production (roots and nodules) without improving water status. This means that elevated CO2 enhances the ability to produce more biomass in N2‐fixing alfalfa under given soil water stress, improving drought tolerance.
Effect of hypoxia on the antioxidative enzymes in aerobically grown rice (Oryza sativa) seedlings
Authors: Ushimaru Takashi , Kanematsu Sumio , Shibasaka Mineo , Tsuji Hideo
Published: March 2003

The development of the antioxidative system is repressed in rice (Oryza sativa L. cv. Yamabiko) seedlings germinated under water, but the system is synthesized within 24 h after exposure of the seedlings to air. In order to see whether this regulation of the antioxidative system is reversible, the changes were investigated after submergence of aerobically grown seedlings under water. Low survivability, no morphological change and a slight increase in activity of alcohol dehydrogenase (ADH; EC 1.1.1.1) were observed 24 h after the submergence. Activities of some antioxidative enzymes were decreased, but they were still higher than those in seedlings germinated under water. Superoxide dismutase (SOD; EC 1.15.1.1) in mitochondria, in addition to cytosolic forms of SOD, showed no significant changes, whereas plastidic SOD decreased drastically, which reflected the changes in the development of the corresponding organelles. Thus, the regulation of the antioxidative system was, in part, reversible. In contrast, catalase (EC 1.11.1.6) activity alone was increased by the shift from air to submergence.
Response of antioxidative enzymes to nickel and cadmium stress in hyperaccumulator plants of the genus Alyssum
Authors: Schickler Hedva , Caspi Hadar
Published: March 2003

The term ‘phytoremediation’ is used to describe the clean‐up of heavy metals from contaminated soils by plants. In this study, we examined Alyssum argenteum and Alyssum maritimum for their ability to accumulate Cd2+. We also exemined Ni2+ accumulation by A. maritimum with comparison with the known Ni‐hyperaccumulator A.argenteum, in a hydroponic system. Both species were tolerant to low levels of Cd2+, and accumulated high quantities under the experimental conditions. Only very low levels of Ni2+ were found in the shoot of A. maritimum, defining it as a non‐hyperaccumulator. The role of the antioxidative enzyme system was investigated in relation to Ni2+ and Cd2+ stress. In both species, superoxide dismutase (SOD) activity was elevated at high Cd2+ concentrations, while ascorbate peroxidase (APX) activity remained unchanged and glutathione reductase (GR) activity was reduced. In the presence of Ni2+, A. maritimum exhibited a typical antioxidative defense mechanism, as evidenced by the elevated activities of all three enzymes tested. A. argenteum exhibited a different enzyme response pattern, with a significant reduction in SOD activity, and elevated APX and GR activities only at the highest Ni2+ concentration.
Differential response of domestic and wild Lycopersicon species to chilling under low light: growth, carbohydrate content, photosynthesis and the xanthophyll cycle
Authors: Venema Jan Henk , Posthumus Freek , De Vries Michèl , Van Hasselt Philip R.
Published: March 2003

The response of five Lycopersicon species to 14 days moderate chilling at 10°C under low light (75 μmol m−2 s−1) and subsequent recovery was examined by measurements on relative shoot growth rate, leaf dry matter and carbohydrate content, CO2‐exchange and pigment composition. In addition, the susceptibility to dark chilling and temperature dependence of chloroplast electron transport were analyzed by Chl a fluorescence measurements. During 7 days of recovery at 25/20°C subsequent to chilling, the domestic tomato Lycopersiconesculentum (L.) Mill. cv. Abunda exhibited a small capacity for shoot regrowth (39%) compared to the low‐altitude wild species L. pimpinellifolium (Jusl.) Mill. PI187002 (82%) and three wild species originating from high altitude: L. peruvianum Mill. LA 385 (92%), L. hirsutum Humb. & Bonpl. LA 1777 (67%) and L. chilense Dunn. LA 1970 (71%). The inter‐specific differences in chilling sensitivity at the chloroplast level, analyzed by the decline of the maximum rate of induced Chl fluorescence rise (FR) after 40 h at 0°C and the temperature at which qP reached the value 0.5, correlated in general well with the measured differences at whole plant level, measured by the post‐chilling regrowth capacity. Chilling resulted in a larger increase in leaf dry matter content in L. esculentum (45%) and L. pimpinellifolium (37%) compared to the high‐altitude species (13–16%), which could be attributed to a stronger accumulation of both soluble sugars and starch in mature leaves of the domestic and low‐altitude species. Photosynthetic and dark respiration rates during chilling could not account for this difference. The recovery of photosynthesis was better in the high‐altitude species. Chl content per unit leaf area decreased more throughout the experiment in the domestic and low‐altitude species (63–73%) than in their relatives from high altitude (8–29%). In response to chilling, the domestic and low‐altitude species showed an increase in the total xanthophyll cycle pool on Chl basis, whereas the de‐epoxidation state of the xanthophyll cycle increased in the high‐altitude wild species. Both responses resulted in increased zeaxanthin levels in chilled leaves of all Lycopersicon species.
Effects of ascorbate feeding on chlorophyll fluorescence and xanthophyll cycle components in the lichen Parmelia quercina (Willd.) Vainio exposed to atmospheric pollutants
Authors: Calatayud Angeles , Deltoro Vicente I. , Abadía Anunciación , Abadía Javier , Barreno Eva
Published: March 2003

The effects of environmental stresses on photosynthetic responses, ascorbate levels and pigment composition were investigated in samples of Parmelia quercina (Willd.) Vainio from control and polluted regions of the northern Castellón area (Valencia, Spain). In response to sustained pollutant stress in the field, lichen thalli had closed PSII traps and exhibited lower rates of electron transport and non‐radiative energy dissipation. The xanthophyll concentration was not affected by exposure to atmospheric pollutants. The ascorbate concentration was lower in samples exposed to ambient air pollutants compared to control thalli. Ascorbate feeding of thalli from polluted sites stimulated electron flow, photochemical quenching and non‐radiative energy dissipation. Additionally, ascorbate feeding enhances the de‐epoxidation state of the xanthophyll pool in polluted thalli. The partial recovery for non‐radiative energy dissipation was presumably due to the interaction between the increased thylakoid pH gradient and de‐epoxidized xanthophylls. Furthermore, ascorbate feeding decreased photon excess in thalli from polluted sites owing to the stimulation of linear electron flow and non‐radiative energy dissipation. The present study suggests that atmospheric pollutants, besides their intrinsic toxicity, put on an additional burden by hampering the operation of photoprotective mechanisms.
A survey of photosynthetic carbon metabolism in 4 ecotypes of Phragmites australis in northwest China: Leaf anatomy, ultrastructure, and activities of ribulose 1,5‐bisphosphate carboxylase, phosphoenolpyruvate carboxylase and glycollate oxidase
Authors: Zheng W. J. , Zheng X. P. , Zhang C. L.
Published: March 2003

Four ecotypes of Phragmites australis from different habitats in northwest China were examined to compare their photosynthetic characteristics. In a swamp ecotype, the Δ13C value of leaf materials was −34.0‰, and bundle sheath cells contained a small amount of organelles and round‐shaped chloroplasts, as being similar to typical C3 plants. In a dune ecotype, the Δ13C value was −20.9‰ and bundle sheath cells contained oval‐shaped chloroplasts with poorly‐developed grana. In light and heavy salt meadow ecotypes, Δ13C values were −30.6‰ and −35.6‰, respectively. The shape of bundle sheath chloroplasts in the light salt meadow ecotype was intermediate between those of the swamp and dune ecotypes. Abundance of bundle sheath organelles in the heavy salt meadow ecotype was intermediate. The swamp ecotype had photosynthetic enzyme activities typical of C3 type plants, whereas the dune ecotype had an increased activity of phosphoenolpyruvate carboxylase (PEPC), a key C4 enzyme, and a decreased ribulose 1,5‐bisphosphate carboxylase (Rubisco) activity. The light salt meadow and heavy salt meadow ecotypes had substantial activities of PEPC, which indicates potential for C4 photosynthesis. These data suggest that this species evolved the C3‐like ecotype in swamp environments and the C4‐like C3‐C4 intermediate in dune desert environments, and C3‐like C3‐C4 intermediates in salt environments.
The plant‐growth‐promoting rhizobacteria Bacillus pumilus and Bacillus licheniformis produce high amounts of physiologically active gibberellins
Authors: Gutiérrez‐Mañero Francisco Javier , Ramos‐Solano Beatriz , Probanza Agustı´n , Mehouachi Jalel , R. Tadeo Francisco , Talon Manuel
Published: March 2003

The plant‐growth‐promoting rhizobacteria (PGPR), Bacilluspumilus and Bacillus licheniformis, isolated from the rhizosphere of alder (Alnus glutinosa [L.] Gaertn.) have a strong growth‐promoting activity. Bioassay data showed that the dwarf phenotype induced in alder seedlings by paclobutrazol (an inhibitor of gibberellin [GA] biosynthesis) was effectively reversed by applications of extracts from media incubated with both bacteria and also by exogenous GA3. Full‐scan gas chromatography‐mass spectrometry analyses on extracts of these media showed the presence of GA1, GA3, GA4and GA20, in addition to the isomers 3‐epi‐GA1 and iso‐GA3. Isotope dilution analysis indicated that epi‐GA1 was an artefact. Likewise, iso‐GA3 is also probably an artifact spontaneously formed during extraction and/or analysis. In both culture media, GA1 was present in higher concentrations (130–150 ng ml−1) than GA3 (50–60 ng ml−1), GA4 (8–12 ng ml−1) and GA20 (2–3 ng ml−1). The data indicated that culture of both bacteria accumulate bioactive C19‐gibberellins in relative high amounts and that these GAs appear to be physiologically active in the host plant. The evidence suggests that the promotion of stem elongation induced by the PGPR could be mediated by bacterial GAs.
Annonaceous acetogenins: Naturally occurring inhibitors of ATP synthesis and photosystem II in spinach chloroplasts
Authors: Chàvez Daniel , Mata Rachel , Iglesias‐Prieto Roberto , Lotina‐Hennsen Blas
Published: March 2003

The effects of squamocin (1), bullatacin (2) and motrilin (3), 3 bis‐tetrahydrofuran Annonaceous acetogenins, isolated from Annona purpurea (Annonaceae), were investigated on several photosynthetic activities in spinach thylakoids. The results indicated that compounds 1–3 significantly inhibited both ATP synthesis and uncoupled electron transport. In addition, they enhanced light‐activated Mg2+‐ATPase, and basal electron flow. Therefore, acetogenins 1–3 behave as uncouplers and Hill reaction inhibitors. Natural products 1–3 did not affect photosystem I (PSI) activity but they inhibited photosystem II (PSII) electron flow. The study of the partial PSII reactions from H2O to DCPIPox, H2O to SiMo and diphenylcarbazide to DCPIP established that the site of inhibition was at the oxygen‐evolving complex (OEC). Chlorophyll a fluorescence measurements confirmed the behavior of the Annonaceous acetogenins as water‐splitting enzyme inhibitors.
Bimodal patterns of floral gene expression over the two seasons that kiwifruit flowers develop
Authors: Walton Eric F. , Podivinsky Ellen , Wu Rong‐Mei
Published: March 2003

Polymerase chain reaction fragments with homology to the Arabidopsis floral meristem identity genes LEAFY and APETALA1 have been isolated from kiwifruit (Actinidia deliciosa [A. Chev.] C. F. Liang and A. R. Ferguson) and have been named ALF and AAP1, respectively. Northern hybridisation analyses have shown that ALF and AAP1 have bimodal patterns of annual expression in developing first‐order axillary buds and their subsequent shoots. This pattern of expression is consistent with the 2‐year cycle of axillary bud, flower and fruit development observed in kiwifruit. The first period of expression was early in first‐order bud development (late spring of the first growing season), when second‐order meristems are initiated, and the second, approximately 10 months later, when those meristems differentiate flowers (late spring of the second growing season). In situ hybridisation analyses on axillary buds collected during late spring of the first growing season have shown ALF expression throughout the developing first‐order buds and AAP1 expression was localised in developing second‐order axillary meristems. During the spring of the second growing season, transcript accumulation for both ALF and AAP1 is localised in differentiating flowers. Our results show that important developmental events are occurring very early in kiwifruit first‐order axillary bud development (spring of the first growing season) and it is likely that this includes floral commitment (evocation).
Increasing ploidy level in cell suspension cultures of Doritaenopsis by exogenous application of 2,4‐dichlorophenoxyacetic acid
Authors: Mishiba Kei‐ichiro , Okamoto Tomonori , Mii Masahiro
Published: March 2003

To clarify the causal factors for ploidy variation in plant cell culture, we attempted to alter ploidy distribution in cell cultures of a tetraploid cultivar of Doritaenopsis by changing the plant growth regulators (PGRs) in the culture medium. The original suspension cultured cells, which had been maintained in medium containing 0.1 mg l−1 1‐naphthaleneacetic acid and 1 mg l−1 benzyladenine, were transferred onto various gellan gum solidified media with a single application of PGRs, and the ploidy distributions of the cells were examined using flow cytometry analysis during 3 weeks of culture. Among the PGRs tested, 2,4‐dichlorophenoxyacetic acid (2,4‐D) and 4‐amino‐3,5,6‐trichloropicolinic acid caused a drastic reduction in the 4C‐cell proportion in cell cultures with an increased cell proportion of 8C or higher C‐values. In the case of 2,4‐D application, a reduction of cell viability was observed. A decreasing proportion was also observed in the 8C‐cell population accumulated by 2,4‐D treatment, following transfer back to the medium containing the standard PGR composition. These results suggest that the exogenous application of 2,4‐D arrested the cell cycle at G2 phase in the Doritaenopsis cells, and the removal of 2,4‐D might induce further endoreduplication or recover the mitotic cycle of the G2‐arrested cells.
Identification of genetic diversity and mutations in higher plant acquired thermotolerance
Authors: Burke John J.
Published: March 2003

Plants experience high air and soil temperatures during periods of drought and when fields receive limited irrigation. Elevated plant temperatures that occur under these conditions negatively impact plant health and productivity. Plants, like all organisms, respond to an elevation in temperature by the synthesis of heat shock proteins (HSP). The appearance of plant HSP is strongly correlated to the development of a condition termed ‘acquired thermotolerance’. Acquired thermotolerance is induced by pre‐exposure to elevated but non‐lethal temperatures and leads to enhanced protection of plant cells from subsequent heat induced injury. Although the correlation between the development of acquired thermotolerance and the appearance of HSP is strong, a cause‐and‐effect relationship between the two has been difficult to demonstrate. To understand the relationship between HSP and acquired thermotolerance, mutations would be required that result in a coordinate change in the expressions of HSP. This paper describes research efforts leading to the development of a screening procedure for the isolation and characterization of acquired thermotolerance mutants. This method for identifying mutants is based on the inhibition of chlorophyll accumulation in etiolated tissue following challenges at lethal temperatures and the prevention of this inhibition by pre‐incubation at a non‐lethal elevated temperature; i.e. acquired thermotolerance. Arabidopsis thaliana mutants deficient in varying levels of acquired thermotolerance have been identified from both the RLD and Columbia ecotypes and these mutants are currently undergoing a detailed characterization at both the protein and molecular levels.
Water sorption–desorption in conifer cuticles: The role of lignin
Authors: Reina José J. , Domínguez Eva , Heredia Antonio
Published: March 2003

Current information on the type and amount of biopolymers present in the epidermis of conifer species is still insufficient. This work presents the detailed morphology and chemical composition of Araucaria bidwillii cuticle after selective treatments to remove the different types of biopolymers. After removal of the waxes, cutin and polar hydrolyzable components, a lignin‐like fraction, which makes up 25% of the initial cuticle weight, was identified by GC‐MS and infrared spectroscopy. The isolated lignin is of G type, mainly formed by guaiacyl units. This composition indicates that the conifer cuticle investigated here has similar composition to other conifer‐isolated cuticles. Water sorption and desorption by the isolated cuticle and the different cuticle fractions, including lignin, were studied. The analysis of the isotherms, following distinct physicochemical models, gave useful information on the structural and physiological role of the different biopolymers present in the cuticle. Lignin fraction showed both a high water sorption and capability of retaining it in comparision to other cuticle components. Hysteresis effect on water sorption–desorption cycle and water cluster formations has also been studied, and their physiological role discussed.
Response of the cultivated tomato and its wild salt‐tolerant relative Lycopersiconpennellii to salt‐dependent oxidative stress: The root antioxidative system
Authors: Shalata Abed , Mittova Valentina , Volokita Micha , Guy Micha , Tal Moshe
Published: March 2003

The response of the antioxidant system to salt stress was studied in the roots of the cultivated tomato Lycopersicon esculentum Mill. cv. M82 (Lem) and its wild salt‐tolerant relative L. pennellii (Corr.) D'Arcy accession Atico (Lpa). Roots of control and salt (100 mM NaCl)‐stressed plants were sampled at various times after commencement of salinization. A gradual increase in the membrane lipid peroxidation in salt‐stressed root of Lem was accompanied with decreased activities of the antioxidant enzymes: superoxide dismutase (SOD; EC 1.15.1.1), catalase (CAT; EC 1.11.1.6), ascorbate peroxidase (APX; EC 1.11.1.11) and decreased contents of the antioxidants ascorbate and glutathione and their redox states. In contrast, increased activities of the SOD, CAT, APX, monodehydroascorbate reductase (MDHAR; EC 1.6.5.4), and increased contents of the reduced forms of ascorbate and glutathione and their redox states were found in salt‐stressed roots of Lpa, in which the level of membrane lipid peroxidation remained unchanged. It seems that the better protection of Lpa roots from salt‐induced oxidative damage results, at least partially, from the increased activity of their antioxidative system.
Effect of the tetrapeptide RGDS on somatic embryogenesis in Daucus carota
Authors: Blackman Sheila A. , Miedema Marc , Yeung Edward C. , Staves Mark P.
Published: March 2003

The present work examines the requirement for RGD‐binding sites, such as those in the plasma membrane protein integrin during somatic embryogenesis in carrot (Daucus carota L. cv. Scarlet nantes). It is possible to assay for this requirement by competitively inhibiting binding of the site to the natural RGD‐containing ligand by adding an excess of synthetic RGDS. We found that treatment of carrot callus cultures with RGDS (2.7 mM) inhibited the development of a normal shoot pole in carrot somatic embryos. The structures that formed contained separate zones of highly cytoplasmic and vacuolate cells and no evidence of embryonic organization, although occasionally a root‐like structure was observed. If the aspartic acid residue in the peptide was replaced by a chemically similar amino acid (glutamic acid), the resultant somatic embryos were indistinguishable from those developing in untreated cultures. These effects are similar to those reported in animal systems where the protein receptor involved has been identified as integrin. Our results are thus consistent with the conclusion that a binding site for a motif similar to the integrin‐binding site in a variety of animal extracellular matrix proteins exists in plants and appears to be important in somatic embryo development in carrot.
Consequence of restricted mitochondrial oxidative metabolism on photosynthetic carbon assimilation in mesophyll protoplasts: Decrease in light activation of four chloroplastic enzymes
Authors: Padmasree K. , Raghavendra A. S.
Published: March 2003

The patterns of light activation of 4 chloroplastic enzymes were examined in mesophyll protoplasts of pea (Pisum sativum) in the absence or presence of oligomycin (inhibitor of oxidative phosphorylation) or antimycin A (inhibitor of cytochrome pathway) or salicylhydroxamic acid (SHAM, inhibitor of alternative pathway). The results were compared with those of DCMU (inhibitor of photosynthetic electron transport). The light activation of NADP glyceraldehyde‐3‐phosphate dehydrogenase (NADP‐GAPDH), fructose‐1,6‐bisphosphatase (FBPase), phosphoribulokinase (PRK) (enzymes of the Calvin cycle) and NADP malate dehydrogenase (NADP‐MDH) (reflects chloroplast redox state) was more pronounced at limiting CO2 (0.1 mM NaHCO3) than that at optimal CO2 (1.0 mM NaHCO3). SHAM decreased markedly (up to 33%) the light activation of all 4 enzymes, while antimycin A or oligomycin exerted only a limited effect (<10% decrease). Antimycin A or oligomycin or SHAM had no significant effect on light activation of these 4 enzymes in isolated chloroplasts. However, DCMU caused a remarkable decrease in light activation of enzymes in both protoplasts (up to 78%) and chloroplasts (up to 69%). These results suggest that the restriction of alternative pathway of mitochondrial metabolism results in a marked decrease in the light activation of key chloroplastic enzymes in mesophyll protoplasts but not in isolated chloroplasts. Such a decrease in the light activation of enzymes could be also a secondary feedback effect because of the restriction on carbon assimilation.
How phenology influences physiology in deciduous forest spring ephemerals
Authors: Lapointe Line
Published: March 2003

Spring ephemerals of deciduous forest are adapted to take advantage of the high‐light period available in early spring. They appear shortly after snow melt and complete their aboveground growth, including fruit production, within 2 months. After they produce new buds, they senesce and enter dormancy. Dormancy is not very deep in spring ephemerals and during summer differentiation occurs in the bud of the apparently resting organ. Low soil temperatures release dormancy, and the shoots and roots then grow slowly over autumn and winter. The goal of this paper is to show how this characteristic phenology influences many aspects of spring ephemerals’ physiology, and the influences these different physiological parameters have on each other. Spring ephemerals have high photosynthetic rates that allow them to rapidly accumulate carbohydrates and complete their aboveground growth in a few weeks. To sustain high photosynthetic rates in early spring, the plants must be able to absorb water efficiently at low soil temperatures and to allocate large amounts of nutrients to the shoot to compensate for lower enzymatic activity at low temperatures. Nutrients are mainly absorbed in spring, although the root system is established in autumn. This means that a large amount of both carbohydrates and nutrients is translocated from the perennial organ to the developing shoot starting in autumn through early spring. Spring ephemerals have low nutrient absorption rates, but high resorption efficiency during leaf senescence. Nevertheless, their high nutrient needs restrict them to rich forest soils. The annual growth rate of spring ephemerals is very slow and this is more likely related to the inherent slow growth rate of the perennial organ than to their short leaf life. As soon as carbohydrate reserves are replenished in spring, sink limitation apparently builds up and induces leaf senescence. A better understanding of the factors controlling the growth rate of spring ephemerals is needed before we can predict these plants’ response to climatic changes.
Monophenolase activity of latent Terfezia claveryi tyrosinase: Characterization and histochemical localization
Authors: Pérez‐Gilabert Manuela , Morte Asunción , Honrubia Mario , García‐Carmona Francisco
Published: March 2003

The monophenolase activity of Terfezia claveryi tyrosinase (EC 1.14.18.1) is described for the first time. This enzyme is fully latent and can only be detected if SDS is present in the reaction medium. Monophenolase activity was localized within the ascocarp using histochemical techniques. A detailed kinetic study of the parameters affecting this activity has been carried out. Both the characteristic lag period and the steady‐state rate are affected by pH and the enzyme and substrate concentrations. The presence of catalytic concentrations of o‐diphenols affected the lag period but not the steady‐state rate. By increasing the concentration of o‐diphenols, it was possible to evaluate the enzyme activation constant, Kact, which showed a value of 7.2 μM. The experimental results are compatible with the mechanism previously described for tyrosinases from other sources.
Isolation and characterization of an extended thioredoxin h from poplar
Authors: Gelhaye Eric , Rouhier Nicolas , Laurent Pascal , Sautière Pierre‐Eric , Martin Francis , Jacquot Jean‐Pierre
Published: March 2003

A cDNA coding for a thioredoxin h has been isolated from a xylem/phloem poplar cDNA library by RACE‐PCR. The nucleotide sequence called popTrx‐h2 is homologous to other thioredoxins h isolated from plants but differs from the other thioredoxins h by presenting a 30 amino acid long N‐terminus extension. A variant of this cDNA lacking the N‐terminal extension was also generated by PCR. Both cDNAs have been introduced into an expression plasmid (pET‐3d) and the recombinant proteins have been expressed to a high level and purified from Escherichia coli cells. Protein sequencing showed that a part of the N‐terminal extension was cleaved in the E. coli cells, with the first 19 amino acids missing, suggesting the presence of a putative cleavage site in the N‐terminal extension of popTrx‐h2. Both recombinant proteins display unusual catalytic properties compared to other thioredoxins h characterized so far, i.e. a weak reduction by Arabidopsis thaliana NADPH‐dependent thioredoxin reductase, and a weak activation of the chloroplastic NADP‐malate dehydrogenase, a non‐physiological target enzyme. Northern blot experiments indicate that the transcripts of popTrx‐h2 are present in leaves and roots, albeit at a lower level compared to the earlier characterized popTrx‐h1.
Increased anthocyanin accumulation in aster flowers at elevated temperatures due to magnesium treatment
Authors: Shaked‐Sachray Liat , Weiss David , Reuveni Moshe , Nissim‐Levi Ada , Oren‐Shamir Michal
Published: March 2003

Temperature is one of the main external factors affecting anthocyanin accumulation in plant tissues: low temperatures cause an increase and elevated temperatures cause a decrease in anthocyanin concentration. Several metals have been shown to increase the half‐life time of anthocyanins, by forming complexes with them. We studied the combined effect of elevated temperatures and increased metal concentrations on the accumulation of anthocyanins in aster ‘Sungal’ flowers. It has been found that magnesium treatment of aster plants or detached flower buds, partially prevents colour fading at elevated temperatures. Anthocyanin concentration of aster ‘Sungal’ flowers grown at 29°C/21°C day/night, respectively, was about half that of flowers grown at 17°C/9°C. The activity of phenylalanine ammonia‐lyase (PAL) and chalcone isomerase (CHI) decreased as the temperature increased. Treatment of both whole plants and detached flower buds grown at elevated temperatures in the presence of magnesium salts, increased flower anthocyanin concentration by up to 80%. Measurement of magnesium following these treatments revealed an increased level of the metal in the petals, suggesting a direct effect. Magnesium treatment does not seem to cause increased synthesis of anthocyanin through a stress‐related reaction, since the activities of both PAL and CHI did not increase due to this treatment. The results of this study show that increasing magnesium levels in aster petals prevents the deleterious effect of elevated temperatures on anthocyanin accumulation, thus enhancing flower colour.
A new biochemical marker for aluminium tolerance in plants
Authors: Maltais Kim , Houde Mario
Published: March 2003

Al was shown to elicit the induction of several pathogenesis‐related genes, suggesting that a common signalling pathway may be involved in the early response to Al and pathogens. However, we found no evidence of oxidative burst involving either H2O2 or O2– during the first hours of Al exposure distinguishing the early response to Al from a common response to pathogen infection. We identified a strong superoxide dismutase insensitive nitro blue tetrazolium (NBT) reduction activity in the root tips of control plants. This activity was rapidly inhibited by Al exposure in the meristematic/distal transition zones of roots in all species examined. In wheat (Triticum aestivum), the inhibition of NBT reduction occurred in less than 1 min in vivo suggesting that Al either directly blocks an enzyme responsible for NBT reduction, or affects a signal pathway involved in the regulation of this activity. The sensitivity of NBT reduction to KCN and NaN3 suggests that an enzymatic, rather than a chemical reaction is involved. In tolerant plants, the inhibition of NBT reduction caused by Al was reversed within 24 h of exposure. The level of recovery was a function of the degree of Al tolerance. We show that NBT reduction is a simple biochemical marker allowing the rapid identification of tolerant individuals within a segregating population.
Root zone calcium modulates the response of potato plants to heat stress
Authors: Kleinhenz Matthew D. , Palta Jiwan P.
Published: March 2003

Potato plant growth and development are known to be severely impacted by heat stress. Here plants grown in a chemically inert medium of 1 : 1 quartzite : perlite (v : v) were subjected to either 35/25°C (stress) or 20/15°C (control) day/night air temperatures and four concentrations of root zone calcium (5, 25, 125 and 600 µM Ca) for 3 weeks. We report for the first time that potato plant growth under heat stress can persist at specific levels of Ca2+ in the root zone and that the Ca2+ level required for growth under heat stress exceeds that required for growth under normal temperatures. We also provide strong, initial evidence that the ability of high Ca2+ levels to mitigate heat stress effects results from shifts in meristematic activity. Total foliar mass and leaf area were essentially unaffected by Ca2+ level under control temperatures. Under heat stress, leaf area was reduced to about 5% of the control at 5 and 25 µM Ca but to only 70% of the control at 125 and 600 µM Ca. Likewise, total foliar mass was reduced under heat stress to about 30% of the control at 5 and 25 µM Ca but total foliar mass was greater under heat stress than control conditions at 125 and 600 µM Ca. This increase at higher Ca2+ concentrations was due primarily to axillary shoot growth. Anatomical studies of leaves grown under heat stress show that cell expansion was impaired by heat stress and this impairment was overcome by increasing root zone calcium levels. These results provide insight into the mechanism by which root zone Ca2+ may modulate plant response to heat stress.