Abstract Studies on adaptive processes in aquatic plants remain limited, despite increasing concerns regarding global climate change. Aerenchyma, crucial for survival in oxygen-deficient environments, can be formed either constitutively or inducibly. Nymphoides humboldtiana develops roots in both floating and subterranean conditions, potentially displaying distinct anatomical features that make it an ideal model for investigating responses to varying waterlogging scenarios. Predominantly schizogenous aerenchyma characterizes Nymphoides roots, although lysigenous types with collapsed gas spaces are also present. Key questions addressed include structural differences between roots under contrasting conditions, the processes of aerenchyma development, cell viability, and cell-wall composition. Bright-field microscopy and epifluorescence were used to examine developing roots under both conditions. Immunocytochemistry to identify cell-wall polymers in aerenchyma cells, and apoplastic tracer tests using hydroxyphenyltetrazolium sulfonate (HPTS) fluorochrome and Evan’s blue staining to observe cellular viability and transport dynamics were performed. Floating roots lack aerenchyma and display cortical parenchyma containing chloroplasts, whereas subterranean roots exhibit schizo-lysigenous aerenchyma. The absence of methyl-esterified pectins, pectic galactans, and arabinogalactan proteins in aerenchyma cell walls suggests roles in cell collapse (lysigeny) and loss of adhesion (schizogeny). Aerenchyma formation in N. humboldtiana appears non-constitutive, being absent in floating roots, while solute transport functions persist under both conditions, as verified through HPTS uptake. Our findings provide novel cytological and developmental insights into aerenchyma formation in subterranean roots of N. humboldtiana, contrasting with the absence of aerenchyma in floating roots and challenging the common assumption of constitutive aerenchyma formation in aquatic plants.
Trevisan et al. (Thu,) studied this question.