**4. The effect of water deficiency originated stress in explant on shoot regeneration capacity**

In the study conducted by Derelli et al. [5], the effects of water deficiency on shoot regener‐ ation capacity of the explant were evaluated. Flax (*L. usitatissimum* L.) cv. 'Clarck' seeds, which were obtained from 'Northern Crop Science Laboratories', North Dakota, USA, got used in the study. Before germination, seeds were surface sterilized with 40% commercial bleach containing 5% sodium hypochlorite at 10°C for 12 min with continuous stirring and then were washed three to four times with sterile water at the same temperature [31]. Sterilized seeds were germinated on MS medium in Magenta vessels. All cultures were incubated at 24 ± 1°C with a 16-h light/8-h dark photoperiod. Hypocotyl explants were removed as in 5 mm in length from 10-day-old sterile seedlings. Some of the hypocotyls were directly transferred to regeneration medium, while some of them were kept in sterile cabin under air flow for 30 min to decrease the water content of the tissue. Hypocotyl explants were cultured on MS medium which contains 1 mg l −1 BAP and 0.02 mg l −1 NAA. Four weeks after culture initiation, the results obtained from two pretreatment applications were compared with respect to regeneration percentage, shoot number per explant, the highest shoot length per explant and total shoot number per Petri dish.


\* Statistically significant at 0.05 level.

**Figure 6.** Regenerated shoots of cv. 'Omega' from (a) first pretreatment application, (b) second pretreatment applica‐

**Figure 5.** Shoot regeneration from hypocotyl explants of flax cv. 'Omega' [4]. (a) The first pretreatment application: hy‐ pocotyls dried for 30 min in sterile cabin and then they were imbibed to liquid MS medium containing 1 mg l−1 BAP and 0.02 mg l−1 NAA for 15 min, and consequently, cultured on MS medium without growth regulators, (b) the second pretreatment application: hypocotyls got dried by waiting for 30 min in sterile cabin and then were imbibed to liquid MS medium containing 1 mg l−1 BAP and 0.02 mg l−1 NAA for 15 min, and finally, cultured on MS medium having 1 mg l−1 BAP and 0.02 mg l−1 NAA and (c) non-pretreatment application: hypocotyl explants got directly cultured on

tion and (c) non-pretreatment application 6 weeks after culture initiation (bar = 1.0 cm) (original).

MS medium containing 1 mg l−1 BAP and 0.02 mg l−1 NAA.

8 Water Stress in Plants

**Table 1.** The effect of water deficiency in explant on tissue culture response of flax (*Linum usitatissimum* L.) cv. 'Clarck'.

The highest results in the study were obtained from the treatment in which hypocotyl explants were directly transferred to regeneration medium without drying. On the other hand, keeping explants under air flow in sterile cabin for 30 min led to evaporation of more water from the explant and consequently, a decrease in the regeneration capacity (**Table 1**). For this reason, while working in the sterile cabin, explants are to be isolated and placed on growth medium as quickly as possible to protect the regeneration capacity thinking that air flow in the environment can have negative influence on the tissue.

There was no difference between non-dried and dried explants with respect to regeneration percentage. Explants from both treatments formed shoots. The highest results were recorded from non-dried explants, which had higher water content than dried ones, as 4.85, 3.32 cm and 48.50 in shoot number per explant, the highest shoot length and total shoot number per Petri dish, respectively. On the other hand, the lowest results were obtained from dried explants as 4.10, 2.46 cm and 41.00, respectively (**Table 1**).

Lowerresults from dried explants could be attributed to a decreased water potential of explant tissue and difficulty in distribution of all solutes and growth regulators among cells.
