Impact of Water Stress on Leaf Anatomy and Ultrastructure in Cynodon dactylon (L.) Pers. under Natural Conditions

Seasonal changes in leaf anatomy and ultrastructure were studied in a sward of Cynodon dactylon (L.) Pers. grown under Mediterranean field conditions and under water stress. Relative water content (RWC), leaf water potential (ψ), and specific leaf weight were determined. Anatomical measurements included leaf thickness and number and area of bundle sheath and mesophyll cells. Quantitative measurements from electron micrographs were used to evaluate the subcellular structure of mesophyll and bundle sheath cells from well-watered and water-stressed plants. In well-watered swards leaf mesophyll cell number was highest at the beginning of June, but in stressed plants the maximum was reached in the middle of July. Water stress decreased both mesophyll and bundle sheath cell areas during the experimental period, although there were no significant differences in plant water relations in autumn. Ultrastructural changes in bundle sheath cells under stress included increase in starch deposition in chloroplasts, chan...