Actomyosin and exocytosis inhibitors alter root hair morphology in Poa annua

Pharmacological agents, disturbing actin cytoskeleton and exocytosis, exert dramatic effects on root hair morphology in Poa annua L. roots. Inhibitors used in the present study induced two major types of root hair morphology disorders. The first type consisted of various types of hair tip branching induced either by general inhibitor of myosin ATPases, 2,3-butanedione mono xime, or by exocytosis inhibitors monensin and caffeine. Similar bifurcatio n of hair tip was induced in some root hairs with microtubule depolymerizat ion drug oryzalin. The second type of morphological anomaly was represented by swellings and bulging of growing root hair tips and was induced by part ial disintegration of actin filaments (AFs) via cytochalasin D. On the othe r hand, complete depolymerization of AFs with latrunculin B immediately sto pped the root hair growth although root hair initiation continued. Intrigui ngly, inhibitor-induced hair phenotypes closely resembled diverse root hair mutants of Arabidopsis thaliana, suggesting that pharmacological agents wh ich affect the actin-based cytoskeleton and exocytotic machinery can phenoc opy diverse root hair mutants. This pharmacological approach turns out to h e a promising additional avenue in our efforts to determine the identity of highly elusive factors controlling polarity of walled plant cells.