CELL-PROLIFERATION AND HAIR TIP GROWTH IN THE ARABIDOPSIS ROOT ARE UNDER MECHANISTICALLY DIFFERENT FORMS OF REDOX CONTROL

We provide evidence that the tripeptide thiol glutathione (GSH) partic ipates in the regulation of cell division in the apical meristem of Ar abidopsis roots. Exogenous application of micromolar concentrations of GSH raised the number of meristematic cells undergoing mitosis, while depletion of GSH had the opposite effect, A role for endogenous GSH i n the control of cell proliferation is also provided by mapping of GSH levels in the root meristem using the GSH-specific dye monochlorobima ne and confocal laser scanning microscopy. High levels of GSH were ass ociated with the epidermal and cortical initials and markedly lower le vels in the quiescent center. The mechanisms controlling cell division could also be triggered by other reducing agents: ascorbic acid and d ithiothreitol. Our data also reveal significant plasticity in the rela tionship between the trichoblast cell length and the hair it subtends in response to alterations in intracellular redox homeostasis. While m echanisms that control trichoblast elongation are influenced by nonspe cific redox couples, root hair tip growth has a more specific requirem ent for sulfhydryl groups, The responses we describe here may represen t the extremes of redox control of root plasticity and would allow the root to maintain exploration of the soil under adverse conditions wit h minimal cell divisions and root hair production or capitalize on a f avorable environment by production of numerous long hairs. Redox sensi ng of the environment and subsequent redox-dependent modulation of gro wth and development may be crucial components in the strategies plants have evolved for survival in a fluctuating environment.