Drought stress is the most pervasive threat to plant growth, which disrupts the photosynthesis and its associated metabolic activities, while silicate (Si) application may have the potential to alleviate the damaging effects of drought on plant growth. In present study, the role of Si in regulating the photosynthesis and its associated metabolic events in Kentucky bluegrass (cv. Arcadia) were investigated under drought stress. Drought stress and four levels (0, 200, 400, 800 mg L(-1)) of Si (Na2SiO3.9H2O) were imposed on 1-year-old plants removed from field and cultured under glasshouse conditions. After 20 days of drought stress, the plants were re-watered to reach soil field capacity for the examination of recovery on the second and the seventh day. The experiment was arranged in completely randomized design replicated four times. Drought stress severely decreased the photosynthesis, water use efficiency, stomatal conductance, cholorophyll contents, Rubisco activity, and Rubisco activation state in Kentucky bluegrass. Nevertheless, application of Si had a positive influence on all these attributes, particularly under stress conditions. As compared to control, Si application at 400 mg L(-1) recorded 78, 64, and 48 % increase in photosynthesis, Rubisco initial activity, and Rubisco total activity, respectively, at 20 days of drought. Higher photosynthesis and higher Rubisco activity in Si-applied treatments suggest that Si may have possible (direct or indirect) role in maintenance of more active Rubisco enzyme and Rubisco activase and more stable proteins for carbon assimilation under stress conditions, which needs to be elucidated in further studies.
Keywords: Drought stress; Leaf soluble protein; Photosynthesis; Rubisco activity; Silicate; Turfgrass.