Growth and morphological responses to different UV wavebands in cucumber (Cucumis sativum) and other dicotyledonous seedlings

Abstract

We examined the influence of short-term exposure of different UV wavebands on the fine-scale kinetics of hypocotyl growth of dim red light-grown cucumbers (Cucumis sativus L.) and other selected dicotyledonous seedlings to evaluate: (1) whether responses induced by UV-B radiation (280-320 nm) are qualitatively different from those induced by UV-A (320-400 nm) radiation, and (2) whether different wavebands within the UV-B elicit different responses. Responses to brief (30 min) irradiations with 3 different UV wavebands all included transient inhibition of elongation during irradiation followed by wavelength specific responses. Irradiations with proportionally greater short wavelength UV-B (37% of UV-B between 280 and 300 nm) induced inhibition of hypocotyl elongation within 20 min of onset of irradiation, while UV-B including only wavelengths longer than 290 nm (and only 8% of UV-B between 290 and 300 nm) induced inhibition of hypocotyl elongation with a lag of 1-2 h. The response to short wavelength UV-B was persistent for at least 24 h, while the response to long wavelength UV-B lasted only 2-3 h. The UV-A treatment induced reductions in elongation rates of approximately 6-9 h following exposure followed by a continued decline in rates for the following 15-18 h. Short wavelength UV-B also induced positive phototropic curvature in both cucumber and Arabidopsis seedlings, and this response was present in nph-1 mutant Arabidopsis seedlings defective in normal blue light phototropism. Reciprocity was not found for the response to short wavelength UV-B. The short wavelength and long wavelength UV-B responses differed in dose-response relationships and both short wavelength responses (phototropic curvature and elongation inhibition) increased sharply at wavelengths below 300 nm. These results indicate that different photosensory processes are involved in mediating growth and morphological responses to short wavelength UV-B (280-300 nm), long wavelength UV-B (essentially 300-320 nm) and UV-A. The existence of two separate types of hypocotyl inhibition responses to UV-B, with one that depends on the intensity of the light source, provides alternate interpretations to findings in other studies of UV-B induced photomorphogenesis and may explain inconsistencies between action spectra for inhibition of stem growth.

Comparison of Chlorophyll Fluorescence Parameters of Cucumis Sativus and Mentha Piperita Leaves Exposed to Short-Term UV-B Irradiation

“…Consequently, the decreases in Y and ETR 24 h after the end of the UV-B treatment in both species can be understood as manifesting physiological regulation of electron transport by increasing excitation energy quenching in photosystem II antennae. Shinkle et al (2004) examined the influence of short-term exposure to different UV wavebands on the fine-scale kinetics of hypocotyl growth of cucumbers (Cucumis sativus L.) grown in dim red light. The response to short-wavelength UV-B persisted for at least 24 h, while the response to long-wavelength UV-B lasted only 3 h. They concluded that different photosensory processes are involved in mediating the growth and morphological responses to short-wavelength UV-B (280-300 nm) and long wavelength UV-B (essentially 300-320 nm) (Shinkle et al, 2004).…”

“…Vulnerability to UV-B radiation varies greatly between plant species (Caldwell et al, 1998;Żuk-Gołaszewska et al, 2003;Kozłowska et al, 2007). Cereals generally are more tolerant as they are monocots with vertical leaves, whereas dicotyledonous plants, including oil rapeseed and cucumber, are more susceptible (Skórska, 2000a(Skórska, ,b, 2008Shinkle et al, 2004;Jansen et al, 2008). There are few published reports on the sensitivity of herbal plants such as peppermint to ultraviolet radiation (Maffei et al, 1999;Maffei and Scannerini, 2000).…”

Green Light Induces Shade Avoidance Symptoms

“…The addition of green light to a red and blue background decreases seedling dry mass (Went, 1957). Green light also increases stem growth rate in the developing seedling (Folta, 2004), whereas all other wavebands (including far red) promote growth inhibition (Parks et al, 2001;Shinkle et al, 2004). The addition of green wavebands has been shown to reverse blue light-induced effects on hypocotyl elongation and anthocyanin accumulation in seedlings (Bouly et al, 2007) as well as to affect flowering (Banerjee et al, 2007).…”

Modulation of enzyme activities and expression of genes related to primary and secondary metabolism in response to UV-B stress in cucumber (Cucumis sativusL.)

“…There is considerable intra-and interspecific variability in the sensitivity of crop plants to UV-B radiation, and the sensitivity of plants to UV-B radiation varies widely among species and cultivars (Teramura 1983, Bornman & Teramura 1993, Correia et al 1998, Mazza et al 2000. In addition, both the magnitude and extent of these UV-B responses are influenced by a number of other factors, including the physiological and developmental status of the plant, as well as the amount and spectral composition of associated background radiation, in particular ultraviolet-A (UV-A) and visible radiation (Shinkle et al 2004). Furthermore, solar UV-B radiation exclusion studies have indicated that ambient levels of solar UV-B radiation reduce biomass accumulation and grain yield in cucumber (Krizet et al 1997), lettuce (Krizet et al 1998), barley (Mazza et al 1999), soybean (Mazza et al 2000), maize (Gao et al 2004) and rice (Hidema & Kumagai 2006).…”