To determine whether natural plant growth regulators (PGRs) can enhance drought tolerance and the competitive ability of transplanted seedlings, 1.5-year-old jack pine (Pinus banksana Lamb.) seedlings were treated with homobrassinolide, salicylic acid, and two polyamines, spermine and spermidine, triacontanol, abscisic acid (ABA), and the synthetic antioxidant, Ambiol. PGRs were fed into the xylem for 7 days and plants were droughted by withholding water for 12 days. ABA, Ambiol, spermidine, and spermine at a concentration of 10 µg L(-1) stimulated elongation growth under drought, whereas ABA, Ambiol, and spermidine maintained higher photosynthetic rates, higher water use efficiency, and lower Ci/Ca ratio under drought compared with control plants. The damaging effects of drought on membrane leakage was reversed by Ambiol, ABA, triacontanol, spermidine, and spermine. Because ABA, Ambiol, and both polyamines enhanced elongation growth and also reduced membrane damage in jack pine under drought, they show promise as treatments to harden seedlings against environmental stress. The protective action of these compounds on membrane integrity was associated with an inhibition of ethylene evolution, with a reduction in transpiration rate and an enhancement of photosynthesis, which together increased water use efficiency under drought. Although most of the tested compounds acted as antitranspirants, the inhibition in membrane leakage in ABA-, Ambiol-, and polyamine-treated plants appeared more closely related to the antiethylene action.
Stress metabolism IX: Effect of salt stress on trigonelline accumulation in tomato. Can J. Plant Sci. 81: 487-498. The presence of quaternary ammonium compounds (QAC) and their accumulation in tomato (Lycopersicon esculentum Mill.) cv. Duke in response to different modes for causing NaCl stress were studied. Pre-germinated tomato seeds were grown in sand culture and 25-d-old seedlings were subjected to abrupt, progressive or prolonged salt stress using NaCl at various osmotic potentials. Plant water status was measured using psychrometry and quaternary ammonium compounds were visualized using thin-layer chromatography and then confirmed and quantified using nuclear magnetic resonance spectrometry. Leaf water potential and osmotic potential declined depending on the osmotic potential of the rooting medium and the mode of stress imposition. A greater decline in osmotic potential compared with the total water potential led to turgor maintenance in plants under progressive or prolonged NaCl stress. The QAC, trigonelline and choline were identified in tomato. Trigonelline, but not choline, accumulated rapidly in response to abrupt, progressive or prolonged NaCl stress. The threshold external water potential (ψ ext. ) for trigonelline accumulation was -0.565 MPa. Trigonelline accumulation correlated with changes in ψ L (r = -0.92***), ψ S (r = -0.94***) and ψ P (r = 0.85***). Trigonelline contributed only -0.035 MPa to the osmotic adjustment, suggesting that its role may also lie in areas other than osmoregulation. ) consécutivement à l'utilisation de diverses méthodes visant à induire un stress avec NaCl. Des semences de tomate prégermées ont été cultivées dans du sable puis les plants de 25 jours ont été soumis à un stress abrupt, graduel ou prolongé au sel par addition d'une solution de NaCl au potentiel osmotique variable. Le bilan hydrique des plantes a été établi par psychrométrie, après quoi on a déterminé la présence de composés d'ammonium quaternaire par chromatographie sur couche mince, confirmé celle-ci puis quantifié les CAQ par spectrométrie à résonance magnétique nucléaire. Le potentiel hydrique et le potentiel osmotique des feuilles diminuent en fonction du potentiel osmotique du milieu d'enracinement et du mode d'application du stress. Une diminution du potentiel osmotique supérieure à celle du potentiel hydrique total maintient la turgescence chez les plantes soumises à un stress graduel ou prolongé. Les CAQ trigonelline et choline ont été identifiés chez la tomate. La trigonelline s'accumule rapidement avec un stress abrupt, graduel ou prolongé au NaCl, mais il n'en va pas autant de la choline. La valeur limite du potentiel hydrique externe (ψ ext. ) à partir de laquelle la trigonelline s'accumule est de -0,565 Mpa. L'accumulation de trigonelline est corrélée à une modification des paramètres ψ L (r = -0,92***), ψ s (r = -0,94***) et ψ P (r = 0,85***). La trigonelline n'explique que -0,035 Mpa de la correction osmotique, ce qui donne à penser qu'elle pourrait jouer un rôle ailleurs que dans l'osmorég...
Rajasekaran, L. R., Stiles, A. and Caldwell, C. D. 2002. Stand establishment in processing carrots -Effects of various temperature regimes on germination and the role of salicylates in promoting germination at low temperatures. Can J. Plant Sci. 82: 443-450. The effects of various temperature regimes on carrot seed germination and the possibility of hastening germination at a low temperature using salicylates were studied. Seeds were incubated at various temperatures viz., 25, 20, 15, 10, 5 and 2°C. Salicylates such as, 2,6-dihydoxybenzoic acid (DHBA), acetylsalicylic acid (ASA), salicylic acid (SA) were supplied at 0, 1, 10, 100 and 1000 mg L -1 continually to the seeds incubated at 25 and 5°C until germination. Data on germination percentage were collected, and vigor value was calculated. Incubating seeds at various low temperature regimes significantly and proportionately reduced germination percentage and vigor value. The highest cumulative germination and vigor value was observed at 25°C. Critical threshold temperature for germination (GT 50 ) was 5°C. Seed treatment using salicylates hastened germination at 5°C. 2,6-dihydoxybenzoic acid 1, ASA 100 and SA 1 mg L -1 all were effective in hastening germination at 5°C. Among all the salicylates, ASA 100 mg L -1 was the most effective in advancing germination at 5°C. Salicylates at the highest concentration of 1000 mg L -1 inhibited germination significantly both at 25 and 5°C.
Rajasekaran, Lada R., Aspinall, D. and Paleg, L. G. 2000. Physiological mechanism of tolerance of Lycopersicon spp. exposed to salt stress. Can J. Plant Sci. 80: 151-157. The physiological mechanism of salt tolerance in Lycopersicon spp. was investigated. Ten Lycopersicon spp. were exposed to a gradual NaCl-induced decline in root zone water potential of -0.10 MPa d -1 for 10 d and maintained at -1.065MPa (221.4 mM NaCl) for a period of 20 d. Growth, water relations and accumulation of ions and compatible solutes, such as proline and the quaternary ammonium compound, trigonelline (methylated nicotinic acid), were studied and correlated. Salt tolerance, measured as growth, in selected Lycopersicon species of varying ecological habitats indicated that L. cheesmanii, native to a saline-coastal habitat, was the most tolerant and L. pennellii, the most sensitive. The commercial cultivar, L. esculentum 'Duke', ranked 7th in the order of relative tolerance to salt. All species accumulated proline in all organs in response to salinity; but there was no general relationship between the ability of these species to accumulate proline and their relative salt tolerance. Relative trigonelline accumulation in meristematic tissues of NaCl-stressed plants correlated with the salt tolerance of these species, however, as did their ability to (1) maintain turgor in the expanding leaves, (2) exclude Na + from the expanded leaves and (3) exclude Cl -from the root tissues.
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