The effects of drought on growth, pigments and 14CO2 assimilation were studied in three sorghum cultivars. Water stress applied either at the vegetative or at the reproductive stage was found to reduce relative growth and net assimilation rates. Root growth was less affected by water stress and in certain cases it was increased; consequently, the root/shoot ratio was improved. The sensitivity to drought stress was greater at the reproductive than at the vegetative stage. Dorado was the most drought‐tolerant and Giza 15 the least drought‐tolerant cultivar, as determined by calculation of the drought susceptibility index for total green leaf area and shoot dry weight. Short‐term water stress in the vegetative phase (7 days) improved the chlorophyll content in leaves, and long‐term stress in the vegetative and reproductive phases reduced chlorophyll content. Carotenoid content, in general, was not changed by drought stress. 14CO2 photoassimilation indicated that soluble, insoluble and consequently total photosynthates were reduced at the end of the stress period at both stages. Drought plus defoliation appeared to increase both chlorophyll content and 14CO2 photoassimilation, to a certain extent, as compared with drought alone.

The adverse effects of either NaCl or mannitol on growth, nitrogen content, and antioxidant system in Vicia faba seedlings were investigated. The role of exogenous ascorbic acid in increasing resistance to these stressors was also evaluated. Thus, with an increase in concentration of either NaCl or mannitol in culture media, a progressively greater significant decrease in percentage germination, in growth parameters, and in nitrogen constituents of the germinating beans, was observed. On the other hand, amide-, nitrate-, and total soluble-N contents appeared to show a progressive significant increase. Exogenous addition of ascorbic acid (4 mM) to the stressful media induced a pronounced significantly increased percentage germination and the growth attributes, whereas nitrogen constituents were variably changed in relation to values maintained in beans treated with either NaCl or mannitol. Furthermore, exogenous addition of ascorbic acid to NaCl or mannitol media induced a significant increase in the contents of ascorbate and glutathione and enzymatic antioxidant activities, in particular, in beans treated with the three highest concentrations of NaCl or mannitol, throughout the period of the experiments (12 days). Thus, ascorbic acid ameliorates the adverse effects of the stressful media; the magnitude of amelioration being a function of the type and the concentration of the stressful agent as well as of the duration of treatment. The importance of the above-mentioned changes in growth and metabolism to stress tolerance in broad bean is discussed.

Growth criteria (shoot height, root length and dry weight) of 14-d-old Vigna sinensis and Zea mays were mostly suppressed by waterlogging or salinization using artificial seawater mixture during the subsequent 3 weeks; the water level in pots was, respectively, kept at 120% or 60% of water field capacity. The suppression in growth induced by salinization was greater than that obtained by waterlogging. The pattern of changes in growth appeared similar to chlorophyll a and b as well as activity of d-aminolevulinic acid dehydratase (ALA-D). On the other hand, waterlogging significantly increased indole-acetic acid (IAA) in shoots of both species but salinity had a decreasing effect. Both treatments decreased gibberellic acid (GA 3) levels in shoots of Vigna sinensis and Zea mays as well as zeatin in shoots of Zea mays. Meanwhile, abscisic acid (ABA) was greatly accumulated in shoots of the stressed plants. Foliar application of 50 ppm kinetin counteracted the resulting reduction in growth and in chlorophylls of both species but partially lowered the inhibition in ALA-D activity. Moreover, kinetin increased IAA, GA 3 and zeatin in the stressed plants to mostly reach control levels, but markedly reduced ABA. These findings indicate that relief of the damage and restoration of normal conditions was maintained either partially or completely by application of kinetin. This recovery may be a consequence of several roles played by such hormones, which can cause triggering of the internal cellular metabolism and also induce alterations in the ratios of growth regulators. plant growth regulators / salinity / Vigna sinensis / waterlogging / Zea mays Résumé-La kinétine permet d'éviter l'effet de la submersion et de la salinité sur la croissance et affecte la production de régulateurs de croissance chez Vigna Sinensis et Zea mays. La croissance (hauteur des parties aériennes, longueur des racines et poids sec) de plantules de Vigna sinensis et Zea mays âgées de 14 jours a été arrêtée principalement par la submersion ou la salinisation en utilisant un mélange artificiel d'eau de mer durant les 3 semaines suivantes ; le niveau d'eau dans les pots a été maintenu respectivement à 120 % et 60 % de la capacité au champ. L'effet négatif sur la croissance induit par la salinisation était plus important que celui obtenu par la submersion. La forme des modifications de la croissance est apparue similaire pour la chlorophylle A & B, aussi bien que pour l'activité de l'acide d-aminolevulinique déhydratase (ALA-D). D'un autre côté la submersion a augmenté de façon significative la teneur en acide indolacétique (IAA) des parties aériennes des 2 plantes, mais la salinité a eu un effet décroissant. Les 2 traitements ont diminué les niveaux d'acide gibbérellique (GA 3) dans les parties aériennes de Vigna sinensis ou Zea mays, ainsi que celui de zéatine dans celles de Zea mays. Pendant ce temps, l'acide abscisique (ABA) était accumulé en abondance dans les parties aériennes des plantes stressées. L'application foliaire de 50 ppm de kinétine s'es...

Decreases in protein and changes in the free amino acid profile were ascertained in Vicia faba L. treated with chlorimuron-ethyl, imazethapyr, or propachlor. Valine, leucine, isoleucine, and total N were decreased by chlorimuron-ethyl and imazethapyr, while total soluble N was increased by all treatments. These changes were accompanied by decreases of the activities of acetohydroxy acid synthase (AHAS; EC 4.1.3.18), nitrite reductase (NiR; EC 1.7.7.1), glutamine synthetase (GS; EC 6.3.1.2), and glutamate synthase (NADH-GOGAT; EC 1.4.1.14). During the experimental period, the inhibition of GS activity preceded that of NiR and followed that of AHAS in samples treated with chlorimuron-ethyl or imazethapyr, while a reverse sequence was apparent in samples treated with propachlor. Therefore, the reduction in protein formation and the disturbance in free amino acid profile appears to be due to inhibition of AHAS following treatment with chlorimuron-ethyl or imazethapyr and to inhibition of NiR following treatment with propachlor.

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