Defective Control of Growth Rate and Cell Diameter in Tip-Growing Root Hairs of the RHD4 Mutant of Arabidopsis Thaliana

The study investigated the effects of a recessive mutation in the RHD4 gene on the tip growth of root hairs in Arabidopsis thaliana. It was found that rhd4 mutant root hairs were half the length of wild-type hairs, exhibited increased and variable diameters, and grew more slowly with fluctuating growth rates. Ultrastructural analysis showed cell wall thickenings in some mutant hairs. Experiments with wild-type hairs in hyperosmotic conditions, which aimed to replicate the rhd4 phenotype, resulted in increased hair diameter and bulging, suggesting that osmotic stress could affect tip growth by altering turgor pressure and cytosolic calcium levels. The findings indicated that the RHD4 gene was essential for maintaining a consistent rate of tip growth in root hairs.