Osmolyte accumulation, antioxidant enzyme activities and gene expression patterns in leaves of orchardgrass during drought stress and recovery

Orchardgrass (Dactylis glomerata L.) grows on marginal soils that could be frequently subjected to water-deficit conditions. Mechanisms of grass plants in response to drought stress and rewatering remain largely unknown. The study was designed to investigate the different physiological and molecular responses of two genotypes of orchardgrass (drought-tolerant 'Baoxing' and drought-sensitive '01998') to drought stress and rewatering. The 'Baoxing' and '01998' were exposed to drought stress for 24 and 21 days in a growth chamber, respectively, allowing the leaf relative water content of both genotypes to drop to the same level (20%). 'Baoxing' exhibited higher net photosynthetic rate, free proline content, total soluble sugar (TSS) content and ornithine aminotransferase activity as well as lower electrolyte leakage compared with '01998'. After rewatering, 'Baoxing' recovered more rapidly in all parameters than '01998' except for TSS. In addition, significantly higher activities of superoxide dismutase (SOD), catalase and guaiacol peroxidase (POD) as well as lower malondialdehyde levels were observed in the 'Baoxing' when compared with the ` 01998' under drought stress and rewatering. Maintenance of higher transcripts levels of SOD and POD in 'Baoxing' suggests that SOD and POD could be involved in scavenging oxidative stress-induced reactive oxygen and removing hydrogen peroxide in orchardgrass through changes in the level of gene expression. Combined with antioxidant enzyme activity and gene expression levels, our results indicate that POD could play critical roles in recovery from drought damages. The results indicated both osmolyte accumulation and antioxidant enzymes could contribute to a better drought tolerance of 'Baoxing' than '01998'.