Introduction Directory UMM :Data Elmu:jurnal:E:Environmental and Experimental Botany:Vol43.Issue2.Apr2000:

Environmental and Experimental Botany 43 2000 121 – 130 Fine structure, carbohydrates and photosynthetic pigments of sugar maize leaves under UV-B radiation Michael Barsig , Ralf Malz Institut fu¨r O 8 kologie u. Biologie, TU Berlin, D- 10587 Berlin, Germany Received 27 July 1999; received in revised form 7 October 1999; accepted 7 October 1999 Abstract Leaves of Zea mays were subjected to different scenarios of ultraviolet-B radiation in a sun simulator to determine the cellular vitality at the microscopic level and the contents of carbohydrates and photosynthetic pigments. The results show that the leaf morphology and fine structure of sugar maize leaves are only slightly affected by UV cut-off wavelengths down to 288 nm. At a microscopic level, a number about one third of epidermal cells, predominantly below leaf tips, are affected by supplemental UV-B. They showed partially collapsed or deformed cell walls and membranes. Underneath damaged epidermal cells, a slight enlargement of intercellular space could be observed. However, other cell components including thylakoid membranes and the epicuticular wax layer on the adaxial leaf surface remained unaffected. The leaf dry weight was not influenced by enhanced UV-B. The amount and structure of starch grains in leaf chloroplasts did not differ between UV treatments. There was no clear impact of enhanced UV-B on sucrose content. Carbohydrate partitioning was more significantly influenced by leaf exposure than by UV treatment. Only glucose was decreased under high UV-B. Changes in photosynthetic pigments were limited to a slight destructive effect of UV-B on chlorophyll b. The results presented in this study may be interpreted that sugar maize leaves have adapted efficiently to cope with supplemental UV-B radiation. Changes in epidermal cell layer due to their shield function may indicate that this remarkable resistance against enhanced UV-B radiation is not unlimited. © 2000 Elsevier Science B.V. All rights reserved. Keywords : Carbohydrates; Epidermis; Maize leaf; Photosynthetic pigments; Ultrastructure; UV-B; Wax layer; Zea mays www.elsevier.comlocateenvexpbot

1. Introduction

Global changes in the chemical composition of the atmosphere with a resulting thinning of the protective ozone layer can have considerable im- pacts on plant life Caldwell and Flint, 1994. Considerable higher intensity of ultraviolet-B UV-B radiation 280 – 320 nm at the Earth’s surface, resulting from anthropogenic depletion of the stratospheric ozone, can have potentially dam- aging effects to a wide range of plant species Teramura, 1990. UV-B effects on plants can comprise alterations of the genome, the chemical quality and the photosynthetic capacity of the Corresponding author. Tel.: + 49-30-31473197; fax: + 49- 30-31473177. E-mail address : ralfhniilinux.zrz.tu-berlin.de M. Barsig S0098-847200 - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 9 8 - 8 4 7 2 9 9 0 0 0 4 9 - 0 plant tissue Tevini, 1993. In some studies, it was shown that the ultrastructure of photosynthetic plant organs may be changed by UV-B radiation Santos et al., 1993; Lu¨tz et al., 1997; Barsig et al., 1998. However, the information on ultrastruc- tural changes by increasing UV-B is limited. Even though Zea mays is one of the most important cereal crops, knowledge of its resistance to en- hanced UV radiation is limited. Previous investi- gations have shown growth reductions or leaf damage in different maize cultivars Santos et al., 1993; Mark and Tevini, 1996. The sun simulator at the GSF Research Center near Munich, Germany, provides realistic white light conditions which is a prerequisite for ecolog- ically relevant UV experiments Meindl and Lu¨tz, 1996. For this study a realistic scenario of UV-B enhancement under intensive light conditions was simulated. Unrealistic high UV-B doses as used in previous investigations were avoided. The aim of this study is to describe UV-B effects on cell fine structure and on carbohydrate and pigment pools simultaneously. We investigated the impact of different UV-B irradiances on epicuticular wax structure, on the epidermis and the underlying cell layers. The structural stability of leaf components under enhanced UV-B is a prerequisite for their functional vitality. Therefore, carbohydrate and pigment content may be a possible marker. The initial hypothesis of this study was that the sugar maize cultivar Z. mays cv. saccharata Koern ‘Tasty Sweet’ is a UV-sensitive plant species at the level of leaf vitality.

2. Material and methods