EFFECT OF OSMOTIC STRESS ON PROLINE ACCUMULATION, PHOTOSYNTHETIC ABILITIES AND GROWTH OF SUGARCANE PLANTLETS (SACCHARUM OFFICINARUM L.)

Disease-free sugarcane plantlets derived from meristem cutting were photoautotrophically grown on the MS medium and subsequently exposed to 0, 100, 200, 300 or 400 mM mannitol for 7 days. Osmotic pressure in the culture medium was increased with increase in mannitol concentration, causing low water use efficiency (WUE) (r(2) = 0.88) and chlorophyll degradation (r(2) = 0.92). Chlorophyll a (Chl(a)), chlorophyll b (Chl(b)) and total carotenoids (Cx+c), concentrations in the osmotic stressed leaves decreased, especially in 400 mM mannitol treatment, degrading 44, 81 and 72%, respectively when compared to control. In contrast, proline content in osmotic stressed plantlets was accumulated and peaked at 2,236.75 mu mol g(-1) FW in 300 mM mannitol treatment. The WUE and chlorophyll degradation were correlated with maximum quantum yield of PSII (F-v/F-m) (r(2) = 0.75) and photon yield of PSII (Phi(PSII)) (r(2) = 0.83), respectively. The F-v/F-m and Phi(PSII) in drought acclimatized plantlets decreased, when non-photochemical quenching (NPQ) reached. The reduction of Phi(PSII) was positively related to net-photosynthetic rate (NPR) (r(2) = 0.85) as well as the proline content and NPQ (r(2) = 0.81). The NPR, stomatal conductance (G(s)) and transpiration rate (E) in osmotic stressed plantlets were significantly dropped, leading to growth reduction (r(2) = 0.95). The basic knowledge of osmotic stressed responses may further be applied as effective indices for drought tolerance in sugarcane breeding program.