Timing of salicylic acid application affects the response of maize (Zea mays L.) hybrids to salinity stress

The effect of genotype and timing of salicylic acid (SA) application on response of maize to salinity stress has been investigated. Single and triple hybrids (SH and TH, respectively) of maize were grown hydroponically and sprayed with 1 mM SA one week either before or after application of 150 mM NaCl. The effect of salinity on maize performance was stronger than that of SA regime or maize hybrid. The effect of treatments was most evident on root biomass but least evident on number of leaves. The genotypic difference in shoot biomass was vague in non-amended plants but emerged, in favor of the SH, in SA-amended plants. The more vigorous SH exhibited less pigment content (particularly the post-amended plants) and less salt resistance, with preferential native allocation of plant biomass to root compared with the TH. Salicylic acid, particularly the post amendment under salinity stress, was stressful to maize foliage but beneficial to roots. Salinity reduced root growth to a greater extent than shoot growth, with the production of wider and shorter blades; but SA led to the opposite effect. The effect of salinity on leaf chlorophyll a concentration was non-significant in the SH, versus an increase (in the post-amended plants) or a decrease (in the non-amended and pre-amended plants) of the TH. Sub-stomatal CO2 concentration (Ci) was higher in the SH than the TH, particularly in the post-amended plants. Both salinity and SA induced stomatal closure, reduced rates of transpiration and photosynthesis but increased Ci, with variable magnitudes in the two hybrids. Salinity increased concentrations of soluble sugars, proline and Na+ in the leaves, decreased K+ and phenolics concentrations but marginally affected protein concentration with limited effect of SA, which varied according to time of application. The further stressing effect of SA post-amendment to salt-stressed maize can be related to reduced stomatal conductance and concentrations of phenolics, proline and K+ but increased Na+ concentration of the shoot, particularly of the TH

Genotypic variability in salt tolerance of Vicia faba during germination and early seedling growth

Salt tolerance of four Egyptian Vicia faba L. cultivars – Nubaria 1, Nubaria 2, Sakha 1 and Giza 3 – was investigated at germination in relation to seed size. The variability in seed size was wide as seed index of Giza 3 was about half that of Nubaria 1. The four investigated cultivars can withstand up to 150 mM NaCl; with marginal reductions in germination capacity but with marked reductions in speed of germination and embryo growth. The vague genotypic variability among the four cultivars in germination parameters emerged more clearly under salt stress. The response of early emergence of the embryo to salt stress seems to differ from that of the subsequent extension of embryonic axis; since based on magnitude and speed of germination Nubaria 1 was the most salt sensitive cultivar but exhibited relatively high salt tolerance on the basis of embryo growth. The salt-sensitive Nubaria 1 produced smaller embryo, with shorter and thicker radicles than the other three cultivars. Germination speed and embryo growth were maximum but lag period was minimum for the medium-sized seeds. Length and thickness of the emerging radicles were affected more by the genotype than by salinity stress and nutrient supply during germination. The beneficial effects of nutrients on seed germination and embryo growth were more evident in the salt-tolerant Nubaria 2 than in the salt-sensitive Nubaria 1. Keywords: Embryo growth, Germination speed, Salinity, Seed index, Vicia fab

Kinetin alleviates the influence of waterlogging and salinity on growth and affects the production of plant growth regulators in Vigna sinensis and Zea mays

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 $\delta$-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.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 $\delta$-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'est opposée à la réduction résultante de la croissance et de la teneur en chlorophylle des 2 plantes, mais a partiellement réduit l'inhibition de l'activité de ALA-D. De plus, la kinétine a augmenté IAA, GA$_3$ et la zeatine dans les plantes stressées jusqu'à atteindre pratiquement le niveau du témoin, mais a réduit de façon marquée ABA. Ces résultats indiquent que l'état des dommages et la restauration des conditions normales a été atteint soit partiellement, soit complètement en appliquant la kinétine. Ce rétablissement pourrait être une conséquence de plusieurs rôles joués par de telles hormones qui peuvent induire le déclenchement du métabolisme cellulaire interne et aussi induire des altérations dans les rapports des régulateurs de croissance