241 Study of Proline, Soluble Sugar, and Chlorophyll A and B Changes in Nine Asian and One European Pear Cultivar under Drought Stress T. Javadi Department of Horticulture Faculty of Agriculture Kurdistan University Iran H. Ebrahimzadeh Department of Biology Faculty of Science Tehran University Iran K. Arzani Department of Horticulture Faculty of Agriculture Tarbiat Modares University Iran Keywords: water stress, Pyrus serotina, Pyrus communis, carbohydrates, amino acids Abstracts The effects of water stress on proline, soluble sugar and chlorophyll a and b in nine Asian and one European pear genotypes were studied. Asian pear genotypes were introduced to Iran by Dept. of Horticulture, Tarbiat Modares University from Belgium in 1998. Asian pear genotypes were KS6, KS7, KS8, KS9, KS10, KS11, KS12, KS13, and KS14. Also a native European pear ‘Shah Miveh’ was used. All genotypes were planted in 20 L pots in which three irrigation treatments were applied, control, - 0.5 MPa and -1.0 MPa, and the irrigations were applied when soil water potential reach -0.03, -0.5 and -1.0 MPa, respectively. A factorial experiment based on random- ized complete block design was used. Proline accumulation increased in water stress treatments and was highest in KS14 compared with other genotypes. RWC decreased in drought stress treatments and was lower in ‘Shah Miveh’. Under drought stress conditions (-0.5 and -1.0 MPa), total soluble sugar (TSS) was accumulated in leaves. TSS accumulated at the beginning of stress period more than at the end of stress period. In general, TSS was highest in KS14 and lowest in KS9. In addition, chloro- phyll a, b and total chlorophyll was reduced under drought stress conditions. Chloro- phyll content in KS9 and KS6 genotypes was lowest among genotypes under drought conditions. INTRODUCTION Drought is one of the major factors influencing and usually restricting crop growth over the world. The supply of water for horticultural crop is limited because there is no water or available water is needed for other uses or available water is not of a suitable quality. Inadequate water supply, in respect to growth, affect on many physiological aspects of plants. Through osmotic adjustment, some species actively accumulate solutes during water stress through a decrease in ψ s so that ψ p remains above levels critical for cellular expansion (Hsiao, 1973; Hsiao et al., 1976; Turner, 1979). Osmotic adjustment provides an effective mechanism to maintain sufficient turgor for stomatal opening and photo- synthesis (Lakso et al., 1984). Inorganic cations, organic acids, amino acids and sugars bring about osmotic adjustment (Turner, 1979). Proline can function as osmoprotectant when accumulated in the cytoplasm of cells (Kurt et al., 1997). Proline accumulated in many plant species under a broad range of stress condition such as water shortage, salinity, extreme temperature and high light radiation (Aspinall and Paleg, 1981; Delauney and Verna, 1993; Hare et al., 1999; Mansour, 2000). The objectives of this study were to evaluate the changes of some drought-related traits such as proline and soluble sugar. Also, changes of chlorophyll as well as changes of Proc. XXVII IHC-S2 Asian Plants with Unique Hort. Potential Eds.-in-Chief: Donglin Zhang et al. Acta Hort. 769, ISHS 2008