Root type governs mucilage secretion and border cell release in maize

Abstract

Root mucilage and border cells are important yet poorly differentiated components of rhizodeposition, and are commonly treated as homogeneous across root types. In maize (Zea mays L.), however, roots of distinct developmental origin may contribute unevenly to these inputs. Here, we quantified and compared mucilage secretion and border cell release from primary and aerial roots of the maize cultivar DH02 under controlled conditions. The primary roots were from seeds germinated for three days and the aerial roots were from plants grown for 21 days. Aerial roots secreted mucilage at a rate nearly four times higher than primary roots. In parallel, aerial roots released approximately six times more border cells than primary roots. While border cell width and area did not differ noticeably between root types, border cells from aerial roots (193.8 μm) were significantly longer than those from primary roots (142.6 μm). Mucilage secretion rate was positively associated with border cell release rate (R² = 0.60). Our findings demonstrate that rhizodeposition is strongly dependent on root type and phenological stage. Importantly, our results reveal that samples commonly referred to as mucilage inherently contain substantial cellular biomass, questioning current assumptions in mucilage quantification and modeling. By disentangling the contributions of mucilage and border cells from distinct root types, our study provides a refined conceptual and quantitative framework for incorporating rhizodeposits into soil process models and for interpreting plant-soil interactions under changing environmental conditions.