CHANGES IN VISCOELASTICITY OF PLANT CELL WALLS DURING GROWTH

Interest in the composition of plant cell walls has been on-going for centuries because the cell wall contains so many useful components. Plant cell walls are composed of cellulose, hemicellulose, pectin, and proteins and these materials form the basis for a wide range of products including clothing, biopolymers, and biofuels that are of great importance to humanity. Currently, there is great interest to understand the formation and growth of cell walls at the most basic biological level to quantify the genetic factors that control the wall organization and properties. The growth pattern of the onion gives an opportunity to study this process efficiently. Each layer of an onion bulb shows a different stage of growth with the outer layers being older and the inner layers being younger. Research groups have studied the chemical structure variation within the different layers. They have shown that the orientation of cellulose microfibrils and the Young’s modulus of the cells change during the growth. The aim of this thesis is to provide new information regarding the onion cell wall with respect to growth. Change in viscoelastic properties at the nano- and micro-scales during onion growth are observed for the different layers. The experimental results show a good correlation between the role of pectin in cell growth and the gradual variation of viscoelasticity in the wall structure. Atomic force microscopy (AFM), nanoscale infrared microscopy (Nano-IR), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), and confocal laser scanning microscopy (CLSM) are all used to understand cell wall change. Advisor: Joseph Turne