Response to Cadmium Toxicity: Orchestration of Polyamines and microRNAs in Maize Plant

Abstract

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.

Phenotypic and Proteomic Insights into Differential Cadmium Accumulation in Maize Kernels

“…Cd enters the environment through various channels such as nickel-Cd batteries, mining, metal smelting, urban pollution, and excessive use of compound fertilizers [3]. While Cd is a non-essential element in crops, it is absorbed by plants alongside other mineral ions, accumulating in plants and causing toxic effects, including physiological and morphological changes [4].…”

“…The impact of Cd on plants includes inhibiting seed germination [5], seedling growth [6], and root development [7], disrupting the absorption of other minerals, and inducing plant malformation [8]. Cd also triggers oxidative stress reaction in plants, leading to cell stability destabilization, reduced leaf chlorophyll content, impaired photosynthesis, and ultimately reduced crop yield and quality [4,9]. Under Cd stress, intracellular oxidative stress is intensified, causing protein oxidation, oxidative degeneration of cell membrane phospholipids, and damage to the DNA and RNA, which can ultimately result in cell death [9,10].…”