Changes in leaf morphology, antioxidant activity and photosynthesis capacity in two different drought-tolerant cultivars of chrysanthemum during and after water stress

Two chrysanthemum cultivars, drought tolerant 'Nannong Xuefeng' and drought sensitive 'Nannong Jingyan' were subjected to 7-day drought stress by withholding irrigation, followed by re-watering for 3 days. We analyzed the biomass, morphological characteristics, physiological changes, and transcription profiles of genes involved in reactive oxygen species (ROS) scavenging. The biomass of 'Nannong Xuefeng' increased 67.5% by 7-day drought, while little increase was observed in drought sensitive 'Nannong Jingyan'. It showed that 'Nannong Xuefeng' had denser trichomes, lower stomata density and greater quantities of wax on leaf surfaces, i.e., 2.3- and 3-fold of wax in 'Nannong Jingyan', respectively. Leaves of 'Nannong-Jingyan' had a higher concentration of superoxide anion radicals, malondialdehyde, and proline, however, these indicators in 'Nannong Xuefeng' were stable throughout the duration of drought stress and rehydration. Other important factors leading to drought tolerance in chrysanthemums are associated with reduced ROS damage; these factors include higher activities of antioxidant enzymes, such as SOD (EC 1.15.1.1), POD (EC 1.11.1.7), and CAT (EC 1.11.1.6), and induced expression of genes encoding these enzymes and APX (EC1.11.1.11). Although stomatal conductance, net photosynthetic rate, transpiration rate, chlorophyll concentration, and chlorophyll fluorescence of the two cultivars both decreased with the reduced soil water content, the decreases occurred earlier and were more apparent in 'Nannong Jingyan' that in 'Nannong Jingyan'. In addition, 'Nannong Xuefeng' had a higher photosynthetic capacity during the stress. Our findings provide new insights into the mechanisms of drought tolerance in chrysanthemum plants. (C) 2013 Elsevier B.V. All rights reserved.