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Gas Exchange and Leaf Ultrastructure of Tinnevelly Senna, Cassia angustifolia, under Drought and Nitrogen Stress

^a Dep. of Biology, Xavier Univ. of Louisiana, 1 Drexel Drive, New Orleans, LA 70125
^b Dep. of Biological Sciences, Lehman College and the Graduate School of the City Univ. of New York, 250 Bedford Park Boulevard West, Bronx, NY 10468

View larger version (11K): [in a new window]   Fig. 1. Time schedule of measurements, and drought and foliar nitrogen treatments. The shaded area represents five drought cycles. Each of the first four drought cycles was 1 wk long, and the fifth drought cycle was 9 d long during which measurements were taken. N = foliar nitrogen treatment, M = measurements. After taking the measurements, all plants were transferred outdoor and allowed to flower and set pods with adequate watering.

View larger version (21K): [in a new window]   Fig. 2. Midday leaf water potential of water-stressed and well-watered senna plants, with or without foliar nitrogen (N) treatment, during the fifth drought cycle. Error bars indicate 95% confidence intervals.

View larger version (47K): [in a new window]   Fig. 3. Gas exchange characteristics and water use efficiency of water-stressed and well-watered senna plants in response to foliar nitrogen (N) treatment. Data are grouped into first 4 d, and last 5 d of the fifth drought cycle since no drought effect on any gas exchange variable was detected until the fifth day of drought. Error bars indicate 95% confidence intervals.

View larger version (24K): [in a new window]   Fig. 4. Polynomial regression of net photosynthesis vs. stomatal conductance in water-stressed senna plants, (A) with and (B) without foliar nitrogen treatment.

View larger version (168K): [in a new window]   Fig. 5. Leaf ultrastructure of senna. A, scanning electron micrograph of a cross-section of a senna leaflet. AB, abaxial; AD, adaxial; arrowhead, minor vein; BE, bundle sheath extension; M, mid vein; P, palisade mesophyll; T, trichome. Scale bar = 150 µm. B, epicuticular crystalline wax. Scale bar = 3.3 µm. C, close-up of a trichome surface showing micropapillate sculpturing. Scale bar = 7.5 µm.