Influence of UV‐B Radiation on Early Seedling Growth and Translocation of ⁶⁵Zn from Cotyledons in Cotton

Abstract

The influence of UV‐B radiation from filtered or unfiltered fluorescent sunlamps on early seedling growth and translocation of 65Zn from cotyledons to the shoot was examined in two cultivars of cotton, Acala and Gregg. Ten‐day‐old seedlings which had been irradiated in the greenhouse for 6 h continuously each day for 14 days with 0.81 or 1.61 W × m‐2 UV‐B radiation under two unfiltered FS‐40 sunlamps, showed pronounced phytotoxic damage. This was characterized at first by bronzing and glazing of the cotyledons and later by upward curling of the leaves and abscission. Leaf expansion, dry matter accumulation, and mobilization of 65Zn from the cotyledons was severely impaired in the young developing shoot under unfiltered UV‐B radiation. A significant stress response also was observed in seedlings exposed to 0.61 W × m‐2 UV‐B radiation through a polystyrene filter and 0.73 W × m‐2 UV‐B radiation through a cellulose‐acetate filter. This stress response was characterized by the formation of a red pigment in the petioles of the cotyledons, reduced leaf expansion, and reduced transport of 65Zn. Control seedlings exposed to 0.03 W × m‐2 UV‐B radiation through a mylar filter were green, had maximum leaf size and dry‐matter accumulation, and had the greatest percentage of 65Zn translocated from the cotyledons.

Specificity and Photomorphogenic Nature of Ultraviolet-B-Induced Cotyledon Curling in Brassica napus L

“…Furthermore, the curling process appears to be specific for UV-B, and the magnitude of the response is dependent on UV-B fluence in a manner that shows reciprocity with respect to length of exposure and fluence rate. UV-B-induced changes in cotyledon morphology and growth have been observed in many plant species including cucumber, cowpea, and cotton cotyledons, although, for the most part, the photobiological properties of these processes were not investigated (Ambler et al, 1975;Kulandaivelu et al, 1989;Takeuchi et al, 1989). The cotyledon curling response to UV-B may be particularly interesting in light of a recent report that the site for photoreception of the UV-B signal that triggers inhibition of hypocotyl elongation in deetiolated cucumber seedlings is in the cotyldon and does not involve inhibition of photosynthesis (Ballaré et al, 1991).…”

Effects of Ultraviolet-B Irradiances on Soybean

“…Earlier workers used germicidal lamps, which are essentially spectral line-source emitters with a major peak at 253.7 nm (UV-C region), as a UV irradiance source. There is a marked difference between the reactivity of 254 nm radiation and the 290-320 nm wave band in biological systems so conclusions from these earlier investigations must be viewed with caution.Studies using polychromatic UV-B radiation sources have generally employed UV-B flux densities equivalent to 35-50% ozone depletions (1,23,26). Only a few studies have examined the effects of UV-B radiation in lower flux densities and even fewer with high levels of PAR incident during growth (3).…”

“…Studies using polychromatic UV-B radiation sources have generally employed UV-B flux densities equivalent to 35-50% ozone depletions (1,23,26). Only a few studies have examined the effects of UV-B radiation in lower flux densities and even fewer with high levels of PAR incident during growth (3).…”

Inhibition of Seagrass Photosynthesis by Ultraviolet-B Radiation

“…Recently, UV-B irradiation has been shown effective in inhibiting leaf expansion (22,29,30), seedling growth (1,21), dark respiration (29), and ion transport (1), as well as altering membrane permeability (9)(10)(11). Ultraviolet-B radiation has also been shown to be a potent inhibitor of photosynthesis (4,5,16,26,29,30,35) and a number of partial reactions of phytosynthesis, including Chl synthesis (2,14), the Hill reaction 'This work was performed with the support of National Aeronautics and Space Administration contract NAS9-15516, National Science Foundation grant SER77-06567, and by a grant from the Dean 4 To whom all correspondence should be addressed.…”