Functional role of mucilage-root border cells complex in the interface between plant root and soil

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In rhizosphere soil, mucilage and root border cells form a functional entity, the mucilage-border cells complex (MB complex). Firstly, the longevity of the released border cells into real soil was analyzed. Many of the border cells present in the rhizosphere soil for relatively longer duration at least more than 10 days. The longevity would depend on the origin of border cells; i.e., root cap layers when the cells are sloughed off. The cells from the inner layer would stay longer in soil due to its younger stage of the cell maturity. The MB complex is utilized by rhizosphere bacteria, which in turn are under strong grazing pressure of the soil food web, in particular protozoa. Next, we investigated the role of MB complex on the protozoan positive effects for plant growth. Weight of fully hydrated MB complex of 27 rice cultivars was firstly quantified. Secondly, 16 cultivars with different levels of MB complex production were selected for root border cells (RBC) enumeration. The weight of MB complex varied among the cultivars and some of the higher MB complex producing cultivars also produced higher number of RBC. Generally speaking, presence of protozoa enhanced lateral root growth and carbon ＆ nitrogen uptake. Further, upland cultivars responded well to amoebal effects as compared with the lowland cultivars. Positive correlation between MB complex production and increased lateral root growth by amoeba revealed that MB complex have a functional role of facilitating a symbiotic relationship with amoeba, which is the first evidence of the new role of MB complex.