Responses Of Purslane And Bermudagrass To Drought, Heat And Their Combined Stress

Abiotic stresses including drought and heat severely inhibit plant growth and development. However, little information is available to plants response to combined drought and heat. Moreover, response of plant to rehydration remains unclear. Purslane (Portulaca oleracea L.) and bermudagrass [Cynodon dactylon (L.) Pers] belong to C4 plant and show high tolerance to drought and heat when compared with C3 plants. In this study, physiological and molecular mechanisms of both C4 plants in response to combined drought and heat stress were characterized.1. Effects of drought and rehydration on physiological changes in purslane. Soil water content (SWC), leaf water content (LWC), malondialdehyde (MDA), proline, electrolyte leakage (EL), chlorophyll content, O2·-, SOD and POD activities were determined at designated time periods (5 d,10 d,15 d,22 d after drought and 3 h,1 d,3 d after rehydration). Progressive drought treatment for longer than 10 d significantly increased MDA, proline, EL, O2·-, and activities of SOD and POD, while rehydration for 1-3 d caused decline of these parameters. Conversely, drought stress decreased LWC and chlorophyll content, while rehydration increased LWC quickly and chlorophyll content gradually. These results indicated that the purslane has a great capability to cope with drought stress and activate many physiological mechanisms, which allow more efficient recovery during rehydration. These results provided the first physiological evidences for harvesting time of purslane.2. Effects of drought, heat and combined stress on physiological and metabolic changes in purslane. Both individual and combined stress treatments increased malondialdehyde (MDA), electrolyte leakage (EL), O2·- and activities of superoxide dismutase (SOD), peroxidase (POD), while declined chlorophyll content. No significant differences were found between control and treatments in leaf water content (LWC) and catalase (CAT) activity. Additionally,37 metabolic compounds were detected in purslane. Through pathway analysis,17 metabolites were directly involved in the glycolysis metabolic pathway. The results showed that combined drought and heat caused more serious damage in purslane than individual stress. To survive, purslane has a high capability to cope with environmental stress conditions through activation of physiological and metabolic pathways.3. Changes in physiological, transcriptional and proteomic in bermudagrass under droutht, head and their combined stress conditions. The results suggested that combined stress caused more serious damage in bermudagrass than individual stress as in purslane. The number of differentially expressed genes and proteins under heat were similar to that affected by combined stress, while drought treatment affected the least number of genes. Eight genes which were significantly affected by combined drought and heat stress based on the RNA seq data and iTRAQ data were selected and cloned for functional analysis. These genes were transferred to model plant Arabidopsis successfully. Drought and heat stress tolerance will be tested using these transgenic lines and putative target genes will be identified.In conclusion, combined drought and heat stress caused more severe damage to both persulane and bermudagrass. Identification of genes specifically affected by combined drought and heat stress will provide genetic resource to characterize mechanisms of plant response to combined stress.