Silicification of Root Tissues

Abstract

Silicon (Si) is not considered an essential element, however, its tissue concentration can exceed that of many essential elements in several evolutionary distant plant species. Roots take up Si using Si transporters and then translocate it to aboveground organs. In some plant species, root tissues are also places where a high accumulation of Si can be found. Three basic modes of Si deposition in roots have been identified so far: (1) impregnation of endodermal cell walls (e.g., in cereals, such as Triticum (wheat)); (2) formation of Si-aggregates associated with endodermal cell walls (in the Andropogoneae family, which includes Sorghum and Saccharum (sugarcane)); (3) formation of Si aggregates in “stegmata” cells, which form a sheath around sclerenchyma fibers e.g., in some palm species (Phoenix (date palm)). In addition to these three major and most studied modes of Si deposition in roots, there are also less-known locations, such as deposits in xylem cells and intercellular deposits. In our research, the ontogenesis of individual root cells that accumulate Si is discussed. The documented and expected roles of Si deposition in the root is outlined mostly as a reaction of plants to abiotic and biotic stresses.

Silicon distribution in leaves and roots of rice and maize in response to cadmium and zinc toxicity and the associated histological variations

“…The endodermis plays a crucial role in reducing metal transport toward the central cylinder, and in the present study, Si deposition was increased in the endodermis during Cd and Zn stress in rice and maize, which potentially increases the physical defense exhibited by the endodermis. Si is a normal component of the endodermis of cereals, and the mode of Si deposition may be impregnation or Si‐aggregate formation (Lux et al, 2020). Similar to our results, when maize plants were grown on Cd‐ and Zn‐enriched soil, the deposition of silica bodies was prominently observed in the endodermis of roots (da Cunha & do Nascimento, 2009).…”

Silicon recycling through rice residue management does not prevent silicon depletion in paddy rice cultivation

“…Plant-available Si: In addition to the different Si pools measured through the sequential extraction, we also estimate the soil Si fraction readily available to plants. Multiple methods exist to measure this soluble Si pool (Liang et al 2015;Sauer et al 2006). One way is to take the sum of Si M and Si Ads from the sequential extraction (Si M?Ads ), as Si M and Si Ads are both readily soluble and available to plants (Haynes 2014;Sauer et al 2006).…”

“…Si enhances plant resistance in a large variety of circumstances, including for example nutrient depletion, drought stress, pathogens and pest attacks. There is evidence for multiple combined beneficial effects of Si rather than one single mechanism (Guntzer et al 2012a;Liang et al 2015;Rizwan et al 2015). The functioning of these effects is, however, far from being fully understood and is still subject to debate (Coskun et al 2018).…”

“…It is generally accepted that Si uptake is achieved both by passive uptake (Si absorption along with water) and, for Si accumulators, by an active transport process using specific transporters (see Ma and Yamaji 2015 for a review); some authors, however, challenge this approach and have suggested that Si uptake could be a strictly passive process (Exley 2015;Exley et al 2020). After its absorption by the plant, part of the Si precipitates in roots (Lux et al 2020) while the rest is transferred with the xylem to aerial parts of the plants via the transpiration stream (Mitani and Ma 2005) and precipitates mostly in parts of the plants where transpiration takes place, forming amorphous silica structures known as phytoliths (Perry 2003;Piperno 2006). These structures vary greatly in size and shape inside a plant (e.g., Hodson 2016;Meunier et al 2017;Puppe et al 2017).…”

Effects of Combined Application of Potassium Silicate and Salicylic Acid on the Defense Response of Hydroponically Grown Tomato Plants to Ralstonia solanacearum Infection

“…Increasing numbers of reports have adequately documented the beneficial effects of silicon in enhancing the disease resistance of plants to several pathogens, but the exact mechanisms underlying this phenomenon remain controversial [4,9,12,13]. Some studies suggest that the enhanced resistance to disease in Si-accumulating plants has been linked with mechanical barriers, due to accumulation and polymerization of Si in different organs and limited pathogen penetration and invasion [8,9,[12][13][14][15]. Studies also showed that Si may play a more active role in enhancing plant resistance to pathogen infection by activating the defence responses in the host, including the production of defence proteins, antimicrobial compounds [16][17][18].…”