engleski

Superoxide dismutase activity, vegetative growth and ion content of salt-stressed watermelon is influenced by rootstock

The watermelon (Citrullus lanatus (Thunb.) Matsum & Nakai) is a crop with a high water demand, frequently grown under conditions of elevated root-zone salinity. Salt stress in the root zone causes both growth and yield reduction. A feasible strategy to improve salt tolerance of salt-sensitive genotypes is grafting onto resistant rootstocks, which may limit the uptake and translocation of Na+ and Cl- to shoots and leaves. Apart from osmotic stress and ion toxicity, one of the major consequences of salinity is oxidative stress, mediated by increased levels of reactive oxygen species (ROS) in the cell. Superoxide dismutase (SOD) plays an important role in stress alleviation, since it is the main scavenger of the superoxide anion, catalyzing its conversion into H2O2 and O2. In the present study, seedlings of watermelon were grown either ungrafted or grafted on three rootstocks: Strong Tosa, S1 (both Cucurbita maxima x Cucurbita moschata), or Emphasis (Lagenaria siceraria). The plants were exposed to NaCl-induced salinity stress (up to an electrical conductivity of EC=6.0 dS/m). The vegetative growth of all plants was substantially reduced at 6.0 dS/m, however, less in Strong Tosa-grafted plants. The leaf water content and specific leaf area decreased with salinity in all grafted plants. The plants generally demonstrated a greater capacity to regulate Na+ than Cl- leaf accumulation, Emphasis and Strong Tosa being most efficient in Na+ exclusion. Salinity induced an increase of SOD activity in grafted plants up to two-fold depending on the rootstock, indicating a build-up of a protective mechanism to reduce oxidative stress. In conclusion, the results demonstrate that the rootstock could improve growth performance and contribute to the alleviation of salt stress in watermelon grown under salinity. The increased tolerance of Strong Tosa-grafted plants may be ascribed to the ability to induce anatomical changes, induction of antioxidative enzymes (SOD) in response to salt stress, and to the efficiency of Na+ exclusion from the shoot.

superoxide dismutase; salt stress

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