Abstract
Leafy vegetables usually absorb and retain heavy metals more readily than most of the other crop plants, and thus contribute ≥70% of the total cadmium (Cd) intake of humans. Caffeine mediates plant growth and has proved to be beneficial against pathogens and insects. Therefore, it was hypothesized that foliar applications of caffeine could alter metabolism and reduce Cd toxicity in spinach (Spinacia oleracea L.). Seven-day old spinach seedlings were provided with Cd (0, 50, and 100 µM) stress. Caffeine (0, 5, or 10 mM) foliar spray was given twice at after 20 days of seeds germination with an interval of one week. In results, Cd stress reduced photosynthetic pigments biosynthesis, increased oxidative stress, imbalanced nutrient retention, and inhibited plant growth. On the other hand, the caffeine-treated spinach plants showed better growth owing to the enhanced biosynthesis of chlorophylls, better oxidative defense systems, and lower accumulation and transport of Cd within the plant tissues. Furthermore, caffeine application enhanced the accumulation of the proline and ascorbic acid, but reduced MDA and H2O2 contents and Cd in plant leaves, and ultimately improved mineral nutrition of spinach plants exposed to different Cd regimes. In conclusion, exogenous application of caffeine significantly diminishes Cd stress by modulating physiological, biochemical, and growth attributes of spinach (Spinacia oleracea L.)
Highlights
High accumulation of heavy metal/Cd in root zone may result in lower uptake of water and reduces plant fresh weight
Foliar application of caffeine exerted positive effects on the studied growth attributes of spinach grown under Cd stress (Figure 1)
Spinach seedlings grown under 50 μM cadmium nitrate (Cd) stress and without foliar application of caffeine showed a remarkable reduction (26.5%) in the shoot fresh weight, in comparison with control plants
Summary
Soil is a necessary growth medium and a great source of nutrients for all kinds of crop cultivation [1]. It is readily available to plants with a high root-shoot translocation rate [2]. The widespread sources of Cd include wastewater and sewage sludge produced by industries and mining discharge [3]. Cd enters into the food chain by the excessive use of untreated wastewater for irrigation, phosphate fertilizers, pesticides, effluents from metal. Sustainability 2022, 14, 2806 synthesis industries, heating systems, power stations, waste incinerators, and mining [4]. Cd has a higher sedimentation rate in soils along with a high translocation rate from soil to plant root-shoot system. The mechanism of Cd-induced toxicity is the competitive Cd absorption at the root surface owing to its structural similarity with nutrient cations such as zinc and phosphorous [6]
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