Annals of Botany 91: 817-826, 2003
© 2003 Annals of Botany Company
Effects of Ultraviolet-B Radiation on Cotton (Gossypium hirsutum L.) Morphology and Anatomy
1 Department of Plant and Soil Sciences, Box 9555, Mississippi State University, Mississippi State, MS 39762, USA
* For correspondence. Fax 001 662 325 9461, e-mail vgk3{at}ra.msstate.edu
Received: 4 November 2002; Returned for revision: 6 January 2003; Accepted: 10 February 2003
Cotton (Gossypium hirsutum L.) crop, cultivated between 40°N and 40°S, is currently experiencing 2–11 kJ m–2 d–1 of UV-B radiation. This is predicted to increase in the near future. An experiment was conducted to study the effect of enhanced UV-B radiation on vegetative and reproductive morphology and leaf anatomy of cotton in sunlit, controlled environment chambers. From emergence to harvest, cotton plants were exposed to 0, 8 or 16 kJ m–2 d–1 of UV-B in a square wave approach for 8 h from 0800 to 1600 h. Changes in plant height, internode and branch length, mainstem node number, leaf area, length and area of petals and bracts, and anther number per flower were recorded. Epidermal cell and stomatal density, stomatal index, leaf thickness, and epidermal, palisade and mesophyll tissue thickness were also measured. Initial chlorotic symptoms on leaves turned into necrotic patches on continued exposure to enhanced UV-B. Exposure to high UV-B reduced both vegetative and reproductive parameters and resulted in a smaller canopy indicating sensitivity of cotton to UV-B radiation. Enhanced UV-B radiation increased epicuticular wax content on adaxial leaf surfaces, and stomatal index on both adaxial and abaxial leaf surfaces. Leaf thickness was reduced following exposure to UV-B owing to a decrease in thickness of both the palisade and mesophyll tissue, while the epidermal thickness remained unchanged. The vegetative parameters studied were affected only by high levels of UV-B (16 kJ m–2 d–1), whereas the reproductive parameters were reduced at both ambient (8 kJ m–2 d–1) and high UV-B levels. The study shows that cotton plants are sensitive to UV-B at both the whole plant and anatomical level.
Key words: Gossypium hirsutum, cotton, UV-B, ultraviolet, wax, stomatal index, palisade, mesophyll, epidermal cell, scanning electron microscopy.
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