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Copyright of Botany is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We examined the effects of temperature, ultraviolet-B (UVB) radiation and watering regime on aerobic methane (CH4) emission from six crops–faba bean, sunflower, pea, canola, barley and wheat. Plants were grown in controlled-environment growth chambers under two temperature regimes (24/20 and 30/26°C), three levels of UVB radiation [0 (zero), 5 (ambient) and 10 (enhanced) kJ m−2 d−1] and two watering regimes (well watered and water stressed). A gas chromatograph with a flame ionization detector was used to measure CH4 emission rates [ng g−1 dry weight (DW) h−1] from detached fresh leaves of each species and attached leaves of pea plants. Plant growth [stem height, leaf area (LA) and aboveground dry matter (AG biomass)] and gas exchange [net CO2 assimilation (AN), transpiration (E) and water use efficiency (WUE)] were also determined. We found that higher temperature, water stress and UVB radiation at the zero and enhanced levels significantly enhanced CH4 emissions. Crop species varied in CH4 emission, which was highest for pea and lowest for barley. Higher temperature and water stress reduced all growth parameters, whereas ambient and enhanced UVB decreased stem height but increased LA and AG biomass. Higher temperature decreased AN and WUE but increased E, whereas water stress decreased AN but increased E and WUE. Zero and enhanced UVB reduced AN and E. Growth and gas exchange varied with species. Overall, CH4 emission was negatively correlated with stem height and AG biomass. We conclude that CH4 emissions may increase under climatic stress conditions and this extra source might contribute to the ‘greenhouse effect'. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate the effects of elevated carbon dioxide and sucrose concentrations on Arabidopsis thaliana L. Heynh root growth, morphology, and architecture. Two levels of CO2, 360 (ambient) and 900 (elevated) μmol·mol–1, and various sucrose concentrations were used. A. thaliana plants grown on a phytagar medium in small chambers with elevated CO2 had longer roots, more lateral root growth and a more dichotomous branching pattern than plants grown in ambient CO2. Roots in elevated CO2 had wider root diameters, and showed considerably more secondary growth such as larger diameter vascular cylinders and better-developed periderm. Addition of sucrose to the media closely resembled the effects of elevated CO2. Further, the increase in sucrose concentration had a more pronounced effect on root morphology under ambient, than elevated CO2. Thus, both elevated CO2 and increased sucrose concentrations promote root growth by increasing their number, length, and diameter, and by changing the branching pattern from herringbone to dichotomous. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Botany is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A reduced red to far-red (R/FR) light ratio and low photosynthetically active radiation (PAR) irradiance are both strong signals for inducing etiolation growth of plant stems. Under natural field conditions, plants can be exposed to either a reduced R/FR ratio or lower PAR, or to a combination of both. We used Helianthus annuus L., the sunflower, to study the effect of reduced R/FR ratio, low PAR or their combination on hypocotyl elongation. To accomplish this, we attempted to uncouple light quality from light irradiance as factors controlling hypocotyl elongation. We measured alterations in the levels of endogenous gibberellins (GAs), cytokinins (CKs) and the auxin indole-3-acetic acid (IAA), and the effect of exogenous hormones on hypocotyl growth. As expected, both reduced R/FR ratio and lower PAR can significantly promote sunflower hypocotyl elongation when given separately. However, providing the reduced R/FR ratio at a low PAR resulted in the greatest hypocotyl growth, and this was accompanied by significantly higher levels of endogenous IAA, GA1, GA8, GA20 and of a wide range of CKs. Providing a reduced R/FR ratio under normal PAR also significantly increased growth and again gave significantly higher levels of endogenous IAA, GAs and CKs. However, only under the de-etiolating influence of a normal R/FR ratio did lowering PAR significantly increase levels of GA1, GA8 and GA20. We thus conclude that light quality (e.g. the R/FR ratio) is the most important component of shade for controlling hypocotyl growth and elevated growth hormone content. [ABSTRACT FROM AUTHOR]

Elevated CO2 appears to be a significant factor in global warming, which will likely lead to drought conditions in many areas. Few studies have considered the interactive effects of higher CO2, temperature and drought on plant growth and physiology. We grew canola (Brassica napus cv. 45H72) plants under lower (22/18°C) and higher (28/24°C) temperature regimes in controlled-environment chambers at ambient (370 μmol mol−1) and elevated (740 μmol mol−1) CO2 levels. One half of the plants were watered to field capacity and the other half at wilting point. In three separate experiments, we determined growth, various physiological parameters and content of abscisic acid (ABA), indole-3-acetic acid and ethylene. Drought-stressed plants grown under higher temperature at ambient CO2 had decreased stem height and diameter, leaf number and area, dry matter, leaf area ratio, shoot/root weight ratio, net CO2 assimilation and chlorophyll fluorescence. However, these plants had increased specific leaf weight, leaf weight ratio and chlorophyll concentration. Elevated CO2 generally had the opposite effect, and partially reversed the inhibitory effects of higher temperature and drought on leaf dry weight accumulation. This study showed that higher temperature and drought inhibit many processes but elevated CO2 partially mitigate some adverse effects. As expected, drought stress increased ABA but higher temperature inhibited the ability of plants to produce ABA in response to drought. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Botany is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Plants growing in the shade receive both low light irradiance and light enriched in far red (FR) (i.e. light with a low red (R) to FR ratio). In an attempt to uncouple the R/FR ratio effects from light irradiance effects, we utilized Stellaria longipes because this species has two distinct natural population ecotypes, alpine (dwarf) and prairie (tall). The alpine population occupies the open, sun habitat. By contrast, the prairie population grows in the shade of other plants. Both ‘sun’ and ‘shade’ ecotypes responded with increased stem elongation responses under low irradiance, relative to growth under ‘normal’ irradiance, and this increased growth was proportionally similar. However, only the shade ecotype had increased shoot elongation in response to a low R/FR ratio. By contrast, the sun ecotype showed increased stem elongation in response to increasing R/FR ratio. Varying the R/FR ratios had no significant effect on ethylene evolution in either sun or shade ecotype. Under low irradiance, only the sun ecotype showed a significantly changed (decreased) ethylene evolution. We conclude that R/FR ratio and irradiance both regulate growth, and that irradiance can also influence ethylene evolution of the sun ecotype. By contrast, R/FR ratio and irradiance, while having profound influences on growth of the shade ecotype, do not appear to regulate these growth changes via effects on ethylene production. [ABSTRACT FROM AUTHOR]

In white spruce, an improvement of somatic embryo number and quality can be achieved through experimental manipulations of the endogenous levels of reduced (GSH) and oxidized (GSSG) glutathione. An optimal protocol for embryo production included an initial application of GSH in the maturation medium, followed by replacement with GSSG during the remaining maturation period. Under these conditions, the overall embryo population more than doubled, and the percentage of fully developed embryos increased from 22% to almost 70%. These embryos showed improved post-embryonic growth and conversion frequency. Structural studies revealed remarkable differences between embryo types, especially in storage product deposition pattern and organization of the shoot apical meristem (SAM). Compared with their control counterparts, glutathione-treated embryos accumulated a larger amount of starch during the early stages of development, and more protein and lipid bodies during the second half of development. Differences were also noted in the organization of SAMs. Shoot meristems of control embryos were poorly organized and were characterized by the presence of intercellular spaces, which caused separation of the subapical cells. Glutathione-treated embryos had well-organized meristems composed of tightly packed cells which lack large vacuoles. The improved organization of the shoot apical meristems in treated embryos was ascribed to a lower production of ethylene. Differences in meristem structure between control and treated embryos were also related to the localization pattern of HBK1, a shoot apical meristem ‘molecular marker’ gene with preferential expression to the meristematic cells of the shoot pole. Expression of this gene, which was localized to the apical cells in control embryos, was extended to the subapical cells of treated embryos. Overall, it appears that meristem integrity and embryo quality are under the direct control of the glutathione redox state. [ABSTRACT FROM PUBLISHER]

The effect of long-term low-concentration (0.04-0.065 μ1 1&sup-1;) exposure to sulphur dioxide (SO2) on assimilate partitioning in Phleum pratense colonized by vesicular-arbuscular (VA) mycorrhizal fungi from field soil was examined by supplying leaves with 14CO2. Seeding were grown and exposed to SO2 for six weeks and then pulsed with 14CO2 for 15 min. The distribution of the 14C was analysed after a 12 h chase. SO2 fumigation had little effect on plant dry matter production, however, it had significant effects on the assimilation of 14CO2. Plants colonized by VA mycorrhizal fungi, both fumigated and controls, had a greater percentage of the total incorporated 14C in the roots, a significantly lower percentage of the total as 14C-labeled soluble carbohydrates in the shoots, and a greater percentage of the total as 14C-labeled amino- and organic acids in the shots and roots than non-mycorrhizal plants, SO2 exposure reduced root length, root length colonized by VA mycorrhizal fungi, and the length of root infected with arbuscules. IT appeared that colonization by VA mycorrhizal fungi in field soil had an overriding effect on carbon assimilation, use, and translocation in the host, and these probably affect host sensitivity to SO2 exposure. [ABSTRACT FROM AUTHOR]

The production of ethylene and carbon dioxide by Pinus radiata D. Don cotyledons cultured on shoot‐forming medium in sealed Erlenmeyer flasks was studied. To establish the role of these gases on morphogenesis three experimental approaches were used: (1) capping the flasks with serum caps on various days, and removing the serum caps at different stages of morphogenesis, (2) absorbing the gases by setting up traps singly and in combination during the various stages of differentiation and (3) incubating the cultures under continuous flow of constant gas mixtures. The results indicate that both ethylene and carbon dioxide, which build up during the first 10 to 15 days of culture, promote morphogenesis. Excessive accumulation after the initiation of buds causes some degree of dedifferentiation. When both the gases were eliminated from the flasks, bud formation and growth were inhibited. In the absence of oxygen, ethylene and carbon dioxide fail to influence growth and morphogenesis.

The glycinebetaine content of plants can be determined by simple isocratic high performance liquid chromatography. The method is applicable to extracts from a wide range of species and, in most cases, is suitably rapid and specific to be preferable to other methods of analysis. The chromatographic system employed permits accurate and sensitive ultraviolet detection, free of most interferences. Because the principle plant carbohydrates elute well before glycinebetaine, preparative ion exchange procedures can be simplified. Twenty-seven species, mostly inland halophytes, were screened by these methods and 13 were found to be glycinebetaine accumulators. On a dry weight basis, the glycinebetaine content of Salicornia europaea L. actually declined with exposure to progressively higher levels of NaCl. When expressed as a proportion of plant organic matter, however, patterns were more typical (up to 7.7% at higher salt concentrations). [ABSTRACT FROM AUTHOR]

Abstract: Global climate change, including global warming, will likely reduce soil moisture in many parts of the world. Few studies have examined the combined effects of temperature and watering regime on plant growth and physiological parameters, on time-course basis in early developmental stages. We grew canola (Brassica napus L. cv. 45H72) plants under lower (22/18°C) and higher (28/24°C) temperature regimes in controlled-environment chambers. One half of the plants were watered to field capacity and the other half at wilting point. In three separate experiments, we determined growth, gas exchange and endogenous abscisic acid (ABA) content in 1-week-old seedlings grown for another 1, 5 or 10days under the above-mentioned conditions. Higher temperature decreased stem height, leaf area, leaf area ratio (LAR) and water-use efficiency (WUE), but increased specific leaf weight (SLW), leaf weight ratio (LWR) and transpiration (E). Water stress reduced stem height, leaf number, leaf area, dry matter of individual organs and whole plant, LAR, net CO2 assimilation, E and WUE, but increased SLW and LWR. Overall, plant growth, dry matter, shoot:root weight ratio and ABA content increased with exposure duration, especially by day 10. However, higher temperature inhibited water stress-induced increases in ABA content. Interaction between watering regime and exposure duration was significant for all parameters of growth and dry matter as well as for LWR, WUE and ABA. No significant interaction was found between temperature and watering regime, between temperature and exposure duration, or among temperature, watering regime and exposure duration for any of the measured parameters. This study revealed that water stress strongly, but higher temperature to a lesser extent, affected canola seedlings, leading to reduced growth and dry matter, and the negative effects increased with time. [Copyright &y& Elsevier]

Abstract: Enhanced ultraviolet-B (UVB) radiation and water deficit affect plant growth and development. We determined the effects of UVB and drought stress on growth parameters and chemical attributes of two ecotypes (alpine and prairie) of Stellaria longipes under controlled-environment conditions. Clonal ramets of these ecotypes were grown under three UVB levels (0, 5, and 10kJm−2 d−1) and exposed to two watering regimes (well watered and drought stressed) for 21 days. Compared to the alpine, the prairie ecotype was taller, had higher number of nodes, and greater leaf area and specific leaf weight (leaf dry weight: leaf area), which resulted in increased dry matter in this ecotype. Overall, ‘prairie’ was higher in total chlorophyll (Chl), but lower in Chla:b ratio, flavonoids, and ethylene, than ‘alpine’. In both ecotypes, UVB and drought stress reduced growth and dry matter, whereas UVB increased carotenoids and flavonoids. Drought stress decreased ethylene evolution. These characteristics were also determined in plants growing in the field. In the field-growing plants, ‘prairie’ had higher growth and dry matter, but lower Chla:b ratio and flavonoids, than ‘alpine’. The two ecotypes responded differentially to UVB and watering regime, as ‘prairie’ appeared to be more sensitive to UVB and drought stress than ‘alpine’. [Copyright &y& Elsevier]