GRAVITROPIC REACTION IN THE GROWTH OF TEA ROOTS

In Japan, tea (Camellia sinensis (L.) Kuntze) seedlings are propagated by cutting. A root system of clonal plants by cutting consists of adv entitious roots and lateral roots. Most of the roots grow horizontally , which results in a shallow distribution of the root system. Such a s hallow root system could be one of the factors contributing to the det erioration of nutrient uptake and resistance to water stress. Gravitro pism of the roots is considered to be a decisive factor that controls the depth of a root system. The authors have investigated changes in t he growth direction of roots to gravitative stimulus, using several ki nds of roots (seminal roots, lateral roots and adventitious roots). Fu rthermore, amyloplasts in the root-cap cells, which are considered to be an equipment sensing gravistimulus, were observed. Seminal roots pr ominently showed orthogravitropism and contained many amyloplast parti cles in their root cap cells. Most lateral and adventitious roots show ed plagiogravitropism, growing in an angle to gravistimulus, and lacke d observable amyloplast particles in their root cap cells. The results suggest that the shallowing of root systems of clonal tea plants coul d be attributed to a gravitropic reaction of the adventitious and late ral roots composing the root system. There could also be a close relat ionship between the growth direction of roots and the presence of amyl oplasts in root-cap cells.