Indian Journal of Experimental Biology Vol. 45, March 2007, pp. 261-267 Osmotic adjustment increases water uptake, remobilization of assimilates and maintains photosynthesis in chickpea under drought P S Basu*, Masood Ali & S K Chaturvedi Indian Institute of Pulses Research (ICAR), Kanpur 208 024, India Received 25 July 2006; revised 10 October 2006 Eight chickpea advanced breeding lines (ABLs) and their parents were evaluated for osmotic adjustment (OA), leaf carbohydrates and gas exchange under dryland field . These (ABLs) were derived from crosses between CTS 60543 × Kaniva and Tyson × Kaniva. Mean leaf water potential (LWP) fell down from –1.00 MPa at pre-stress level to about –2.25 MPa during terminal stress. Relative water content (RWC) showed periodic changes with alternate decrease or increase at certain interval, which also influenced the values of OA (low or high) in number of genotypes e.g. Kaniva, CTS 60543, Tyson and M 75. Significant variation in OA ranging 0.45 to 0.88 MPa was observed at high level of stress at –2.5 MPa. However, none of the genotypes showed stability of OA over the period of stress. Leaf starch declined even at mild stress (LWP,-1.6 MPa) resulting in an increase in hexose sugars and activation state of sucrose-phosphate synthase (SPS) that led to accumulation of sucrose. Both photosynthesis (P max ) and transpiration decreased concurrently in two chickpea lines M 129 and Tyson with increasing water stress. However, rate of decline in the photosynthesis slowed down even drought was further intensified. The observed periodic changes in OA, RWC and photosynthesis appeared to be associated with drought- induced changes in SPS and carbohydrates which modify water uptake of the leaves. Keywords : Cicer arietinum, Water stress, Leaf water potential, Relative water content, Sucrose, Hexose, Sucrose- phosphate synthase, Photosynthesis, Transpiration, ABLs, Starch Chickpea (Cicer arietinum L.) , an important winter food legume , is cultivated predominantly over 75- 80% in water-limiting environment. The crop usually faces terminal drought during pod filling stage leading to significant reduction in the grain yield 1 . Among various traits, osmotic adjustment (OA) is considered as an important physiological trait for adaptation to drought 2 . The osmotic adjustment in chickpea has been reported to be ranged from 0 to 1.3 MPa 3 . Osmotic adjustment increases water absorption, maintains cell turgor, photosynthesis and leaf area duration, helps stomatal opening, delays senescence and death 4 , reduce flower abortion 5 , and improves root growth as water deficits develop 6 . The greater osmotic adjustment leads to higher growth rate and dry matter production in pigeonpea under drought 7 . Genotypes of wheat and sorghum with a high capacity for OA had up to 60% higher yields than those with a low capacity 8,9 . The degree of OA has also been shown to be correlated with yield under dryland conditions in chickpea 8 . However, other workers 10 opined that osmotic adjustment may not have any direct effect on crop yields. Contradictory results suggested that chickpea probably cannot derive distinct advantage from osmotic adjustment in comparison to other crops. Therefore investigation was carried out to look for physiological significance of osmotic adjustment in chickpea under drought. Materials and Methods Experimental material⎯2-way crosses were made using chickpea genotypes with high osmotic adjustment (CTS 60543) and low OA (Kaniva) while another set having medium OA (Tyson) crossed with low OA (Kaniva). The populations were advanced to F 6 stage and eight advance breeding chickpea lines at F 6 stage were evaluated under rainfed for osmotic adjustment and other physiological traits. These breeding lines were M 39, M 51, M 55, M 75, M 86, M 93, M 110, M 129. No pre-sowing irrigation was applied before planting the material on 31 st October, 2004-05 at experimental site of Indian Institute of Pulses Research, Kanpur, India (20°27′N, 80°14′E). Irrigation was completely withdrawn throughout the crop season. The crop was subjected to complete dry weather till late podding stage with steady decrease in the soil moisture at given depth. The observations on ___________ *Correspondent Author : basups@satyam.net.in