Impact of Combined Heat and Drought Stress on the Potential Growth Responses of the Desert Grass Artemisia sieberi alba: Relation to Biochemical and Molecular Adaptation

Artemisia sieberi alba is one of the important plants frequently encountered by the combined effect of drought and heat stress. In the present study, we investigated the individual and combined effect of drought and heat stress on growth, photosynthesis, oxidative damage, and gene expression in A. sieberi alba. Drought and heat stress triggered oxidative damage by increasing the accumulation of hydrogen peroxide, and therefore electrolyte leakage. The accumulation of secondary metabolites, such as phenol and flavonoids, and proline, mannitol, inositol, and sorbitol, was increased due to drought and heat stress exposure. Photosynthetic attributes including chlorophyll synthesis, stomatal conductance, transpiration rate, photosynthetic efficiency, and chlorophyll fluorescence parameters were drastically reduced due to drought and heat stress exposure. Relative water content declined significantly in stressed plants, which was evident by the reduced leaf water potential and the water use efficiency, therefore, affecting the overall growth performance. Relative expression of aquaporin (AQP), dehydrin (DHN1), late embryogenesis abundant (LEA), osmotin (OSM-34), and heat shock proteins (HSP70) were significantly higher in stressed plants. Drought triggered the expression of AQP, DHN1, LEA, and OSM-34 more than heat, which improved the HSP70 transcript levels. A. sieberi alba responded to drought and heat stress by initiating key physio-biochemical and molecular responses, which were distinct in plants exposed to a combination of drought and heat stress.