Improving the quality of tissue-cultured plants by fixing the problems related to an inadequate water balance, hyperhydricity

In vitro tissue culture is a technique for accelerating plant propagation and supplying high- quality starting material which has a positive impact on product commercialization. Several obstacles may occur during the culture process, one of which is hyperhydricity. Hyperhydric shoots are characterized by extensive accumulation of water in the apoplast, the continuum of cell walls and intercellular air spaces which is almost completely flooded. The occurrence of hyperhydricity is a major problem in the micropropagation industry, since it reduces the quality and multiplication rate of microplants. Although numerous studies have been put forward to explain hyperhydricity, the underlying mechanism and causative factors of hyperhydricity are still debated. Understanding the underlying mechanisms and factors involved in the control of plant growth in vitro can greatly improve the quality of micropropagated plants. The research presented in this thesis succeeded in elucidating aspects of the mechanism, causality factors and methods to prevent hyperhydricity in in vitro grown Arabidopsis thaliana and Limonium sinuatum. Our study found that hypolignification of cell walls was an important causative factor in the development of hyperhydricity. The specific interaction of the plantlets, medium components and microenvironments were found to affect lignin biosynthesis, to lead to irregular stomatal features, abnormal anatomy of mesophyll cells and large intercellular spaces, to affect the water retention capacity and the transpiration rate. Exogenously applied calcium in combination with a specific lignin biosynthesis precursor, p-coumaric acid, and a stomatal opener (ALA) as supplements to the medium proved capable of reducing the occurrence or delaying the onset of hyperhydricity by stimulating cell wall lignin biosynthesis and modifying the pectin content of the leaves