BIOLOGIA PLANTARUM 48 (1): 105-108, 2004 BRIEF COMMUNCIATION Growth, water content, and proline accumulation in drought-stressed callus of date palm J.M. AL-KHAYRI* and A.M. AL-BAHRANY** Date Palm Research Center* and Department of Horticulture**, College of Agriculture and Food Sciences, P.O. Box 55043, Al-Hassa 31982, Saudi Arabia Abstract This study was conducted to examine the response of date palm (Phoenix dactylifera L., cvs. Barhee and Hillali) calli to water stress. Callus derived from shoot tip explants was inoculated in liquid Murashige and Skoog medium containing 10 mg dm -3 α-naphthaleneacetic acid, 1.5 mg dm -3 2-isopentenyladenine, and 0 to 30 % (m/v) polyethylene glycol (PEG 8000) to examine the effect of water stress. After 2 weeks, callus growth, water content, and proline accumulation were assessed. Increasing water stress caused a progressive reduction in growth as expressed in callus fresh mass, relative growth rate, and index of tolerance. Both genotypes tested followed this general trend, however, cv. Barhee was more tolerant to drought stress than cv. Hillali. Increasing PEG concentration was also associated with a progressive reduction in water content and increased content of endogenous free proline. Additional key words: index of tolerance, osmotic adjustment, relative growth rate, tissue culture, water stress. ⎯⎯⎯⎯ Water availability is one of the principal limitations of crop production, particularly in the arid and semiarid regions where date palm is predominantly grown. The use of in vitro cultures to study stress responses is based on the fact that in vitro cultured cells behave similarly to cells of intact plants subjected to water deficit and salinity stress conditions (Attree et al. 1991). Moreover, species differing in drought tolerance at the whole plant level also usually exhibit differences in drought tolerance in cell cultures (Santos-Diaz and Ochoa-Alejo 1994a). Undifferentiated cells and callus cultures eliminate complications associated with genetic and morphological variability inherent to different tissues in whole plants. Moreover, cell culture systems eliminate all responses associated with water stress except those operative at the cellular level (Hasegawa et al. 1984, Newton et al. 1989). These studies involved the simulation of the effect of water stress by augmenting the culture media with polyethylene glycol (PEG) which induces osmoregulation through the accumulation of solutes such as proline. Although, various in vitro studies focused on aspects of plant regeneration in date palm (Omar et al. 1992, El Hadrami and Baaziz 1995, Veramendi and Navarro 1996, Al-Khayri 2001, Al-Khayri and Al-Bahrany 2001), little is known about physiological parameters affecting date palm in vitro cultures. Recently, the behaviour of date palm callus subjected to salt stress was elucidated (Al-Khayri 2002). Reports about the response of date palm callus to water stress are lacking, hence, this research was conducted. Cell suspension cultures of two date palm cultivars were exposed to varying degrees of PEG-induced water stress to examine growth response, water content, and proline accumulation. Shoot tips were separated from 3- to 4-year-old offshoots of date palm (Phoenix dactylifera L., cvs. Barhee and Hillali), surface sterilized in 70 % ethanol for 1 min followed by 15 min in 1.6 % m/v sodium hypo- chlorite containing a few drops of Tween 20, and rinsed ⎯⎯⎯⎯ Received 23 April 2002, accepted 24 November 2002. Abbreviations: MS medium - Murashige and Skoog medium medium; PEG - polyethylene glycol; RGR - relative growth rate. Acknowledgement: The authors wish to express their appreciation to Mr. Mohammed A. Abu-Ali for laboratory technical assistance with tissue culture aspects. *Corresponding author; fax: (+966) 3 8245310, e-mail: jkhayri@kfu.edu.sa 105