The Physiology of Adventitious Roots

Abstract

Adventitious roots are plant roots that form from any nonroot tissue and are produced both during normal development (crown roots on cereals and nodal roots on strawberry [Fragaria spp.]) and in response to stress conditions, such as flooding, nutrient deprivation, and wounding. They are important economically (for cuttings and food production), ecologically (environmental stress response), and for human existence (food production). To improve sustainable food production under environmentally extreme conditions, it is important to understand the adventitious root development of crops both in normal and stressed conditions. Therefore, understanding the regulation and physiology of adventitious root formation is critical for breeding programs. Recent work shows that different adventitious root types are regulated differently, and here, we propose clear definitions of these classes. We use three case studies to summarize the physiology of adventitious root development in response to flooding (case study 1), nutrient deficiency (case study 2), and wounding (case study 3).

Some physiological responses of wheat and bean to soil salinity at low matric suctions

“…This results in a decrease in essential nutrients for synthesis and maintaining chlorophyll and, subsequently, causes chlorophyll decay (Drew and Sisworo, 1977). Comparison of Figs 2 and 3 shows that the wheat CCI is less affected than that the bean CCI by low aeration (2 kPa suction), because wheat can adapt itself slightly to the soil anoxia by developing aerenchyma tissues and creation of adventitious roots (Steffens and Rasmussen, 2016).…”

Plant responses to flooding stress

“…To this end, plants can induce and/or constitutively develop aerenchyma, longitudinal connected gas spaces, which provide a rapid means of aerial gas exchange over long distances within the plant [5]. This is usually combined with a change in root architecture to minimize the distance (and therefore diffusive resistance) between the aerial surface and the flooded root tips [6], for instance via adventitious roots, which can create a collection of air conducting snorkels originating from the hypocotyl or stem into the anaerobic substrate. Often aerenchyma are combined with a barrier that prevents oxygen leakage into the surrounding anaerobic soil, which drastically improves flooding tolerance [7].…”

Regulation of Root Traits for Internal Aeration and Tolerance to Soil Waterlogging-Flooding Stress

“…New adventitious roots, containing aerenchyma, are formed from the stem in order to restore root functioning (i.e. water and nutrient uptake as well as anchorage; Visser and Voesenek, 2004;Sauter, 2013;Steffens and Rasmussen, 2016). When standing water occurs during deeper floods, adventitious roots also can emerge from the submerged portion of the stem.…”

“…Moreover, the generation of ROS is involved in the signaling of epidermal cell death (Steffens et al, 2012). Steffens and Rasmussen (2016) recently presented a conceptual model on signaling and the formation of adventitious roots in response to flooding stress.…”