Bioprocess engineering The large scale plant cell and tissue cultures have been considered as an alternative source of biochemicals over the last 40 years. Routien and Nickel received the first patent for the cultivation of plant tissue in 1956  and suggested its potential for the production of secondary metabolites . Shortly after that time, the National Aeronautics and Space Administration (NASA) started to support research of plant cell cultures for regenerative life support systems. Since early 1960s, experiments with plants and plant tissue cultures were performed under various conditions of microgravity in space (one-way spaceships, biosatellites, space shuttles and parabolic flights, the orbital stations Salyut and Mir) and accompanied by ground studies using rotating clinostat vessels . Growth, development and metabolism of plant cells and tissues have been studied to improve our understanding of plant cell biology and tissue physiology, and derive criteria for bioprocess design . Approaches to plant tissue bioprocess engineering The term ‘Plant Tissue Culture’ in this paper refers to the in vitro cultivation of any plant segment, whether a single cell, a tissue or an organ . There are five main types of plant tissue cultures: (1) seedlings of plants (plant cultures), (2) isolated embryos (embryo cultures), (3) isolated plant organs (organ cultures), (4) explant cultures (tissue or callus cultures), and (5) isolated cells or small aggregates dispersed in liquid media (cell or suspension cultures). The concept of using plant cell cultures is confined to the production of valuable natural products such as pharmaceuticals, flavors and fragrances, and fine chemicals – over 20 000 different chemicals are produced from plants, with about 1600 new plant chemicals added each year. According to an OECD report [6,7], plant derived drugs and intermediates account for approximately 9–11 billion US$ annually in the US alone. Generally, theGenerally, the plant products of commercial interest are secondary metabolites, which in turn belong to three main categories: essential oils, glycosides and alkaloids. The essential oils consist of mixture of terpenoids, which are used as flavoring agents, perfumes and solvents. The glycosides include flavanoids, saponins, phenolics, tannins, cyanogenic glycosides and mustard oils, which are utilized as dyes, food colors and medicinals (e.g., steroid hormones, antibiotics, digitalis). The alkaloids are a diverse group of compounds with over 4000 structures known; almost all naturally occurring alkaloids are of plant origin. Alkaloids are physiologically active in humans (e.g., cocaine, nicotine, morphine, strychnine) and therefore of a great interest for pharmaceutical industry . Secondary metabolites are currently being obtained commercially by extraction from whole plants. Large scale plant tissue culture is an attractive alternative to the traditional methods of plantation, as it offers two advantages: (1) controlled supply of biochemicals independent of plant availability (climate, pests, politics), and (2) well defined production systems which result in higher yields and more consistent quality of the product .