A morphological and cytological study of Petunia hybrida exposed to UV‐B radiation

Abstract

The aim of this study was to investigate whether the cytoskeleton, and in particular the microtubular system, is affected by enhanced levels of ultraviolet‐B (280–320 nm, 9 kJ m−2 day−1 biologically effective UV‐B radiation) radiation in epidermal cells of Petunia x hybrida Vilm, isolated from leaves of plants grown under UV‐B radiation and visible light. In addition, morphological changes during development were monitored. In a previous study microtubules were depolymerized and delays in the different stages of the cell cycle were found when protoplasts of Petunia were irradiated with UV‐B radiation (Staxén et al. 1993. Protoplasma 173: 70–76). Thus it was of interest to ascertain whether the cytoskeleton would be similarly affected in an intact system. Assuming an effect of UV‐B radiation on the microtubular system, we wished to determine whether this could be correlated to concomitant changes in leaf morphology. Plants of Petunia hybrida were grown in greenhouse conditions in the presence or absence of UV‐B radiation. During the course of the experiment, samples were taken from young, expanding leaves and from older, fully expanded leaves and prepared for localization and analysis of microtubules from the adaxial epidermal cells. Morphology rather than the cytoskeleton was affected by UV radiation, despite the fact that the epidermal cytoskeleton would most likely be affected, since it is located in the cells which form the first intercepting layer for incident radiation. Morphological changes under UV‐B radiation, as compared to those under control conditions, were reflected in earlier flowering and an increase in leaf number. Cell division was thus stimulated as was also evidenced from the increased leaf area. Our results indicate that the number of stomata differentiated on a leaf area basis was not altered although the number of stomata per epidermal cell was reduced.

Non-photosynthetic mechanisms of growth reduction in pea (Pisum sativum L.) exposed to UV-B radiation

“…The hypothesis that UV‐B acts on cell division requires confirmation through more detailed microscopic analysis. However, it is notable that Dickson & Caldwell (1978) showed that UV‐B altered the rate of cell division in Rumex patientia , resulting in smaller leaves and slower early growth rates, while in Petunia hybrida , increased leaf area under elevated UV‐B was attributed to increased cell division (Staxén & Bornman 1994). As cell division ceases earlier in epidermal tissues than in the mesophyll, the number of epidermal cells is determined at an early stage of development of the leaf primordium (Korner & Pelaez Menendez‐Riedl 1989).…”

Different stresses, similar morphogenic responses: integrating a plethora of pathways

“…(2005) to suggest that a short exposure to aluminium causes a fast change in cell patterning instead of a general toxic effect. Similarly, effects of UV‐B radiation on cell division are complex, with some studies reporting reductions in numbers of epidermal cells (Hopkins, Bond & Tobin 2002), and others increase in parenchyma cells (Staxen & Bornman 1994). Again, these data suggest changes in patterning rather than a general toxic effect.…”

Multivariate analysis of intraspecific responses to UV‐B radiation in white clover (Trifolium repensL.)

“…In other studies, UV‐B resulted in decreases of plant productivity, biomass and leaf area (Li, Yue & Wang 1998; Yuan et al 2000), increases in leaf thickness and specific leaf mass (Rozema et al 1997; Rozema et al 1999a) as well as changes in biomass allocation (Li et al 1998). UV‐B‐induced differences in leaf surface morphology include changes in the number and size of epidermal and stomatal cells (Stewart & Hoddinott 1993; Staxen & Bornman 1994; Visser et al 1997). Inhibition of photochemical efficiency, indicated by decreases in F v / F m , has been observed under UV‐B supplementation (Sprtova, Nedbal & Marek 2000), although – in general – photosystem II is not regarded a direct target of UV‐B, particularly under realistic elevation of UV‐B in the field (Nogues & Baker 1995; Allen, Nogues & Baker 1998).…”