Effects of Ultraviolet-B Radiation on Cotton (Gossypium hirsutum L.) Morphology and Anatomy

Abstract

Cotton (Gossypium hirsutum L.) crop, cultivated between 40 degrees N and 40 degrees 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.

Growth and physiological responses of sunflower plants exposed to ultraviolet-B radiation

“…These results contrast with the findings by SEARLES et al (2001), where one of the most evident response to UV-B radiation observed was an increase in UV-B absorbing compounds. The increase in UV-B absorbing compounds in response to enhanced UV-B radiation reported by several authors has been interpreted as an (KAKANI et al, 2003a). Also, the protective effects of trichomes against UV-B radiation damage have been demonstrated by mechanically removing the trichomes of Verbascum speciosum (MANETAS, 2003).…”

Efeitos da radiação ultravioleta-B sobre a morfologia foliar de Arabidopsis thaliana (L.) Heynh. (Brassicaceae)

“…Resultados similares de menores valores médios de densidade estomática, na face adaxial, foram encontrados para as folhas de Oryza sativa que se desenvolveram sob a ação da radiação UV-B (Dai et al 1995). No entanto, resultados diferentes foram obtidos para algodão, onde folhas tratadas com alta dose de radiação UV-B (16 kJm -2 .d -1 ) apresentaram maiores densidades estomáticas, em ambas as faces, do que as folhas controle (Kakani et al 2003b). Segundo os autores, a radiação UV-B parece afetar as plantas de maneira similar ao déficit hídrico, reduzindo a área foliar e ao estresse térmico, aumentando a densidade estomática.…”

“…A folha diminui a área exposta, mas aumenta a espessura da lâmina, devido ao incremento dos tecidos fotossintéticos e dos espaços intercelulares, garantindo assim o volume da folha (Lewis 1972;Smith et al 1997). Maior espessura também foi reportada para outras espécies estudadas sob a influência da radiação UV-B (Cen & Bornman 1993;Kakani et al 2003a), apesar de resultados contrários serem reportados na literatura (Correia et al 1998;Kakani et al 2003b).…”

Role of He-Ne laser pre-treatment in protecting Zea mays against the deleterious effects of ultraviolet radiations

“…Increas ed root biom ass, PA L activit y, r oot dr y weight, s hoot: root rati o, leaf ar ea, c hlor ophyll a, chl orophyll b, and tot al chl orophyll. T his result w as s upport ed with Kakani et al (2003) in various growt h parameters , and other inves tigations, whic h r eport ed a decr eas e i n plant length and leaf area wit h UV radiation (Teramur a et al, 1991;Bar nes et al, 1993;Hao et al, 2000;Z uk-G olasz ewsk a et al , 2003;Li u et al, 2013). This c ontradicti on m ay be due to t he use of higher U V A+ B r adiation.…”