Cadmium (Cd) is a heavy metal that is widely contaminating the environment due to its uses in industries as corrosive reagents, paints, batteries, etc. Cd can easily be absorbed through plant roots and may have serious negative impacts on plant growth. To investigate the mechanisms utilized by plants to cope with Cd toxicity, an experiment was conducted on maize seedlings. We observed that the plant growth and photosynthetic mechanism were negatively influenced during 20 days of Cd stress. The expression levels of ornithine decarboxylase (ORDC) increased in the six seedlings under Cd exposure compared to the control. However, Cd toxicity led to an increase in putrescine (Put) content only on day 15 when compared to the control plants. In fact, with the exception of day 15, the increases in the ORDC transcript levels did not show a direct correlation with the observed increases in Put content. Spermidine and Spermine levels were reduced on day 6 by Cd application, which was parallel with suppressed Spermidine synthase gene. However, an increase in Spermidine and Spermine levels was observed on day 12 along with a significant elevation in Spermidine synthase expression. On day 6, Cd was observed to start accumulating in the root with an increase in the expression of microRNA 528; while on day 15, Cd started to be observed in the shoot part with an increase in microRNA 390 and microRNA 168. These results imply that different miRNAs may regulate polyamines (PAs) in maize under Cd toxicity, suggesting a plant-derived strategy to commit a PAs/miRNA-regulated mechanism/s in different developmental stages (time points) in response to Cd exposure.

Drought stress hinders plant growth by reducing water availability, leading to stunted plants growth, lower photosynthesis rates, and decreased yields. This research explored the impact of the combination of Spirulina and sulfate-reducing bacteria on the growth and resilience of lettuce plants under three drought levels (80%, 60%, and 40%). Overall, drought reduced germination percentages, but at 40% level, Spirulina significantly improved germination rates. At higher drought levels, Spirulina and sulfate-reducing bacteria positively influenced germination compared to the control, with SRB showing the most pronounced effect. Root growth increased significantly under 60% drought, though no root elongation under different stress levels was impacted. Leaf area decreased with increasing drought, but sulfate-reducing bacteria significantly enhanced it, especially at 80% drought. Control plants’ relative water content decreased with increasing drought severity. However, the combination of Spirulina and sulfate-reducing bacteria at 60% drought mitigated this effect. Notably, under 60% and 80% drought, hydrogen peroxide levels increased, though the Spirulina and sulfate-reducing bacteria combined consistently elevated hydrogen peroxide levels in both 60% and 80% conditions. Superoxide dismutase activity rose by 80% in non-treated plants, while Spirulina and sulfate-reducing bacteria individually enhanced superoxide dismutase activity across moderate and high drought. Catalase activity decreased at 80% drought in control plants; however, an increase was observed with sulfate-reducing bacteria in 80% stress level. The F_v/F_m ratio and Pi_ABS declined as drought intensified, but sulfate-reducing bacteria improved these parameters at both 60% and 80% stress levels. ABS/RC and ET₀/RC ratios responded positively to sulfate-reducing bacteria under severe drought. These findings suggest that while Spirulina and sulfate-reducing bacteria enhance drought tolerance in lettuce, sulfate-reducing bacteria are especially effective under higher drought stress conditions.