SUPRA-PHYSIOLOGICAL LEVELS OF GIBBERELLINS / DELLAS MODIFY ROOT CELL SIZE / NUMBER AND ROOT ARCHITECTURE IN ROOT TIPS OF ARABIDOPSIS THALIANA SEEDLINGS. CONNECTIONS TO THE ROOT HAIR PATTERNING AND ABUNDANCE

A previous study showed that excessive GAs/DELLAs altered the arrangement, shape and frequency of hairs in root tips of A. thaliana seedlings by acting from the root sub-epidermal tissues. The present study showed that excessive GAs/DELLAs also modified root tip cell size/number in A. thaliana seedlings. While excessive DELLAs shortened and widened the root epidermal, cortical, endodermal and pericycle cells, excessive GAs, excepting the epidermal cells, generally narrowed them. However, no root cell size changes occurred when gai-1 was over-expressed at the root epidermis. Also, excessive DELLAs induced extra cells at the root epidermis, cortex, endodermis and pericycle and lateral root outgrowth, whereas excessive GAs induced extra cells at the root cortex and pericycle. Thus, excessive GAs/DELLAs might modify root tip cell size/number by acting from the sub-epidermal tissues of the root. This, in turn, might impact on the root hair patterning & abundance and the root architecture.