Chloe Simchick is a rising junior at the Milwaukee School of Engineering, majoring in BioMolecular Engineering. Chloe is working in Dr. Ram Dixit’s lab, characterizing patterns of twisted growth mutations in Arabidopsis by studying their mechanical properties.
Directional growth is a key survival trait in plants—growth towards light or deep into soil enables plants to capture maximal sunlight and obtain necessary nutrients, respectively. In elongating plant cells, microtubule arrays are organized laterally around cells and direct the deposition of cellulose microfibrils in the cell wall. These microfibrils resist tensile force exerted by inner turgor pressure, and thus constrict lateral cell expansion to drive anisotropic growth in the vertical direction. Arabidopsis thaliana ‘twisted’ mutants with skewed microtubule arrays adopt a left or right-handed skewed growth direction. It is assumed that this twisted growth is driven by a skewed cellulose microfibril array, but this has yet to be determined. Due to its imaging tractability and well-characterized anatomy, this work focuses primarily on twisted growth of the root. Current data has shown that while the direction of root twist is consistent, the magnitude of twist is not uniform across the length of the root. However, how twist affects root growth kinetics is unclear. Here we show that growth rates vary significantly between mutants spr1-3, spr2-2, and tua4 and the wild-type Col-0, and these differences are further magnified with the presence of microtubule-interfering drugs, oryzalin and taxol. Preliminary imaging of cellulose arrays using TIRF microscopy indicates that microfibrils align with cortical microtubules, but this will have to be further investigated using field emission scanning electron microscopy. Our investigation of root growth kinetics is critical for determining how twisted growth impacts plant development. By implementing microtubule-interfering drugs we demonstrated the importance of microtubule stability in directing growth. This work will further our understanding of how helical growth is directed and better inform us of the origins of growth chirality.