Silicon-induced mitigatory effects in salt-stressed hemp leaves

Silicon, a quasi-essential element for plants, improves vigour and resilience under stress. Recently, studies on textile hemp (Cannabis sativa L.) showed its genetic predisposition to uptake silicic acid and accumulate it as silica in epidermal leaf cells and trichomes. Here, microscopy, silicon quantification and gene expression analysis of candidate genes involved in salt stress were performed in hemp to investigate whether the metalloid protects against salinity. The results obtained with microscopy reveal that silicon treatment ameliorated the symptoms of salinity in older fan leaves, where the xylem tissue showed vessels with a wider lumen. In younger ones, it was difficult to assess any mitigation of stress symptoms after silicon application. At the gene level, salinity with and without silicon induced the expression of a putative Si efflux transporter gene 2 (low silicon 2, Lsi2). The addition of the metalloid did not result in any statistically significant changes in the expression of genes involved in stress response, although a trend towards a decrease was observed. In conclusion, our results show that hemp stress symptoms can be alleviated in older leaves by silicon application, that the metalloid is accumulated in fan leaves and highlight one putative rice Lsi2 orthologue as responsive to salinity.