Effects of drought stress on growth and physiological and biochemical characteristics of Pittosporum pentandrum

In order to explore the mechanism of drought-tolerance of Pittosporum pentandrum, the growth and physiological and biochemical characteristics of 1-year-old P. pentandrum seedlings were analysis under four levels of drought stress including optimal water content(CK), mild drought stress(LD), moderate drought stress(MD)and heavy drought stress(HD) which were controlled by weighing the soil and pots. With the increase of drought stress, the heights and biomass of the seedlings decreased but the root/shoot ratio increased; net photosynthesis rate (Pn), transpiration rate (Tr), stomatal conductance(Gs), stomatal limitation(Ls)and water use efficiency(WUE)decreased while intercellular CO2 concentration (Ci)increased; the contents of K+ and Mg2+ decreased while the content of Ca2+ firstly increased and then decreased; the contents of soluble sugar and soluble protein increased while the content of proline firstly increased and then decreased; the contents of malondialdehyde and membrane permeability increased but the activity of catalase (CAT), peroxidase (POD), superoxide dismutase (SOD) and ascorbate peroxidase enzyme (APX) firstly increased and then decreased. These results indicated that the membrane lipid peroxidation increased and the growth was inhibited under drought stress. However, P. pentandrum protected the membrane structure and maintained normally physiological activity through improving the activities of the antioxidant enzymes system and accumulating osmotic regulation such as soluble sugar, proline ,soluble protein and Ca2+ which improve its tolerance to the drought stress.