**1. Introduction**

Plant tissue culture includes techniques to propagate plants via somatic cells by using small parts called as explant on artificial growth mediums under sterile conditions. Shoots and roots are regenerated from explants, and consequently, the whole fertile plants are reconstituted under certain cultural conditions. Plant tissue culture belongs to totipotency meaning that a whole plant can be reproduced from a single cell in growth medium. Obtaining high-frequen‐

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

cy shoot regeneration is one of the major objectives for tissue culture studies that is also a prerequisite for an efficient transformation system and a clonal production of plants with interesting flowers and fruits massively for ornamental aims.

Plant tissue culture techniques have certain advantages overtraditional propagation methods. Via tissue culture methods, thousands of mature plants having desirable traits such as good flowers, fruits and odor can be produced in a short time; endangered species which cannot propagate in native environment can be cloned easily by vegetative parts; genetically identical plants can be produced with large quantities; genetically modified plants can be regenerated from cultured cells; production of disease-, pest- and pathogen-free plants increase the plant production; andplantshavingseedgerminationandgrowingproblems canbe easilyproduced.

Plantgrowthregulatorsasmediacomponentsaffectthe shootregenerationcapacityof explants. Tissue culture studies have tried to determine correct combinations of auxins and cytokinins for high-frequency adventitious shoot regeneration for related genotype. However, determination of optimum levels of auxins and cytokinins in growth medium is not the only way of increasing shoot regeneration capacity. It is reported that regeneration capacity of explant could be increased by adjusting the concentration, temperature and application period of NaOCl solutions used for surface sterilization [1] and manipulating physical microenvironment by altering distances among explants cultured resulted in increased shoot regeneration capacity [2]. Recently, it is noted that water capacity of the tissue affects explant's regeneration capacity significantly [3–5].

Source of life is based on water on the earth. Living is limited in a large proportion of terrestrial ecosystems according to water availability. The water content in an actively growing plant can be as much as 95% of its live weight. Wateris needed in a plant for photosynthesis. Carbon dioxide and oxygen which is required for photosynthesis cannot be used by plant if they are not soluble in water. For this reason, water is the main factor for plant's existence and growth. Mineral ions such as potassium (K+ ), sugars (glucose and sucrose) and amino acids are dissolved in water.

The decrease in growth, yield and quality by water stress has been reported in field conditions [6,7]. Plant survival is guaranteed by germination and seedling establishment and they are very important phases of plant life. Germination ratio diminishes with decreasing external water potential and there is a critical value of water potential for each species below which germination will not occur [8].

This chapter is aimed to show the effects of water deficiency in tissue on shoot regeneration capacity of the explants cultured under *in vitro* conditions. Moreover, increasing shoot regeneration frequency of explant by enhancing water content of the tissue is another issue this chapter focused on. All the results given here were based on three research studies.
