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We examined the growth and physiological characteristics of Chlorophytum comosum and Chlorophytum comosum var. variegatum by hydroponics at different Cd 2+ concentrations (0, 20, 80, 200 μmol·L -1 ). The results showed that 20 μmol·L -1 Cd 2+ did not affect those two varieties, with no changes of single leaf area, total leaf area, chlorophyll (Chl) a content, Chl (a+b) content, carotenoid content, Chla/Chlb value, intercellular carbon dioxide concentration ( C i ) and transpiration rate ( T r ) compared with the control (CK). Under the 80 μmol·L -1 Cd 2+ stress, the initial fluorescence ( F o ) and non-photochemical quenching coefficient (NPQ) were the highest for both varieties. As for Cd 2+ at 200 μmol·L -1 , the biomass, chlorophyll content, maximum net photosynthetic rate ( P n ), stomatal conductance ( g s ), maximum photochemical quantum yield ( F v /F m ), actual photochemical quantum yield Y (II) , the transfer factor (TF) of both varieties and all parts biomass decreased to the lowest, while peroxidase (POD), ascorbic acid peroxidase (APX) and catalase (CAT) activities of two varieties and MDA content of C. comosum var. variegatum increased in different degrees. With the increases of Cd 2+ stress, the Cd content in organs of two varieties showed an increasing trend, with higher Cd accumulation in roots. C . comosum had higher Cd content and bioconcentration factor (BCF) in all organs than C . comosum var. variegatum . It suggested that two varieties had the ability to resist Cd stress. The tolerance of C . comosum was stronger, and thus could be considered as a green plant to remediate Cd contaminated water or soil.

In this study, the effects of exogenous abscisic acid (ABA) on the growth and physiolo-gical characteristics of Machilus yunnanensis seedlings were examined under well water supply conditions (70%-75% field capacity, FC) and different drought stress conditions, i.e., light drought stress (50%-55% FC) and severe drought stress (30%-35% FC), respectively. The results showed that drought stress reduced leaf relative water content, plant height, and total biomass of seedlings significantly decreased, as well as net photosynthetic rate and maximal photochemistry efficiency (F v /F m ), but enhanced root/shoot and malondialdehyde contents (MDA). Exogenous ABA improved the adaptability of seedlings under drought stress, especially under severe drought stress, with leaf relative water content being improved 21.0%. Plant height and biomass allocation were improved by exogenous ABA under drought, while root/shoot was improved by 1.1 times compared with the well watered plants. The accumulation of MDA was decreased, the activities of CAT and SOD were significantly increased, and the proline content was increased 6.7 times by exogenous ABA under drought. Exogenous ABA application alleviated the negative effect of drought on photosynthetic organs, reduced the decrease of net photosynthetic rate and stomatal conductance under drought, and enhanced F v /F m value. The results suggested that exogenous ABA treatment could enhance the resistance of M. yunnanensis to drought stress.