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Abstract
We selected the submerged macrophyte Vallisneria natans (Lour.) Hara for investigating the effects of nutrient loadings (nitrogen (N)-phosphorus (P) in mg·L-1: (1) 0.5, 0.05; (2) 1.0, 0.1; (3) 5.0, 0.5; (4) 10.0, 1.0) on root physiological characteristics using sand culture during the growth season (June to October). Results showed that the best root growth was in macrophytes exposed to moderate nutrient conditions (N-P 2, in 1.0 and 0.10 mg· L-1), and high nutrient loadings induced declines in root growth. Analysis of root antioxidant enzyme (superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT)) activities, protein content and cell ultrastructure revealed that the root of V. natans was subject to the stress of senescence during the end of the growth season. Moreover, high nutrient loadings increased oxidative stress in aging roots of V. natans, and made the cell ultrastructure of roots vulnerable to damage during senescence. The results for the changes in CAT activity suggest that CAT can serve as an important component of antioxidant defense mechanism in aging roots of V. natans to protect against nutrient loading induced oxidative injury in the early period.
Nous avons choisi le macrophyte submergé Vallisneria natans (Lour.) Hara pour étudier les effets des charges d’éléments nutritifs (azote (N)-phosphore (P) en mg·L-1 : (1) de 0,5, 0,05; (2) 1,0 0,1; (3) 5.0, 0.5; (4) 10.0, 1.0) sur les caractéristiques physiologiques des racines en utilisant une culture sur sable pendant la saison de croissance (juin à octobre). Les résultats ont montré que la croissance des racines était la meilleure pour les macrophytes exposées à des conditions modérées de nutriments (NP (2), 1,0 et 0,10 mg·L-1), et que des charges élevées en éléments nutritifs induisaient une baisse de la croissance des racines. L’analyse de l’activité des enzymes antioxydantes des racines (superoxyde dismutase (SOD), peroxydase (POD) et catalase (CAT)), de la teneur en protéines et de l’ultrastructure cellulaire ont révélé que la racine de V. natans était soumise à la contrainte de la sénescence au cours de la fin de la saison de croissance. En outre, des charges élevées en nutriments augmentaient le stress oxydatif dans le vieillissement des racines de V. natans, et rendaient l’ultrastructure cellulaire des racines vulnérable aux dommages pendant la sénescence. Les résultats sur les changements dans l’activité CAT suggéraient que CAT peut servir comme une composante importante du mécanisme de défense antioxydante dans le vieillissement des racines de V. natans pour se protéger contre la charge en nutriments induisant des lésions oxydatives dans la période initiale.
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