ELSEVIER Biochimica et Biophysica Act~ 1185 (1994) 295-.~12 i BB, The effects of ultraviolet-B radiation on the CFoF -ATPase Junwei Zhang a.~, Xiang Hu a.~, Lisa Henkow a, Brian R. Jordan b.2, A~ke Strid "'* Institutionen ]fir Biokemi och Biokemisk Teknologi, Kungliga Tekniska HiJgskolan. S-IO0 44 Stockholm. Sweden b Department of Molecular Biology. Horticulture Research Internauonal, WorthingRoad. Littlehampton. BNI7 6LP. tlK (Received 27 October 1993) Abstract The effects on the amount and activity of membrane-bound CFoFj-ATPase and isolated CFm-ATPase after exlx~ure of pea plants to supplementary UV-B have been studied. On a chlorophyll basis, the ATPase activity of thylakoids decreased by 25%, whereas the amount of the CFt-ATPase protein in the membranes declined by 60% after 4 days of UV-B exposure. Thus, the activity of the remaining functional enzyme molecules almost doubled over the experimental period. An activation was also found when the ATPase activity of isolated CF~ was measured. In addition, the abundance of mRNA transcripts for some of the CFn-ATPase subunits and other photosynthetic components was studied. Even after one day of supplementary UV-B, no mRNA transcripts for the nuclear-encoded 3' subunit and chlorophyll a/b-binding protein of the light-harvesting antenna ~.mp!ex could be found. The amounts of mRNA for the plastid-encoded/3 and • CF~-ATP~se subunits and the c¢trh:ome b and subunit IV of the cytochrome b/f complex were also substantially lowered but were still p,e:,cnt aftc ~ ~ ~ ,/of UV-B treatment. Key words: ATPase, CFoFn-; Cytochromc b/f complex; Ultraviolet-B; Gene expression; (P saris'urn) 1. Introduction The study of ultraviolet-B radiation (UV-B) effects on plant function has been prompted by the antici- pated increased influx of UV-B to the earth due to depletion of tf, e stratospheric ozone layer. Although the impact of UV-B on physiological parameters and morphological features has been extensively studied [1], our knowledge about effects of UV-B at the bio. chemical and molecular level in plants is ver~ limited [2]. This is true also for photosynthesis and the compo- nents participating in this process. * Corresponding author. Fax:+46 8 7q07509: e-r0ail:aake(abio chem.kth.se. x Present address: Institutionen f6r Biokemi och Biof~sik,G6teborgs Universitet och Chalmers Teknisk~ H6gsk~da, S-41296, G6teborg. Sweden. 2 Present address: New Zealand Institute for Crop and Food Re- search limited, Levitt Research Centre, Private Bag 4005, Levin, New Zealand. Abbreviations: CFoF~-ATPase.ATP gynthase of the thylakoid mere- Inane: CF~-ATPa~, the catalytic part of the ATP synthase: Rubisco, ribulose-l,5-bisphosphate carboxylase/oxygenase; UV-B, ultraviolet radiation between 2,~,0 and 320 nm. 0005-2728/94/$07.00 ~ 1994 Elsevier Science B.V. All rillhts reserved SSDI 0005-2728(94)00005- P The effects of UV-B on chloroplast components are of major importance. Inhibition of photosynthesis re- s,ilts f.~m the reduced efficiency of some important protein complexes, e.g., Photosystem 11, the CFoF I- ATPase (ATP synlhase) and ribulose-l,5-bisphosphate carboxylase/oxygenase (Rubisco) [3]. In contrast, the activities of Photosystem i and the cytochrome b/f complex are much less affected, it has been shown [4] thai the decrease in the amounts of Rubisco protein (= 35%) after 3 days of UV-B exposure was much smaller than the decrease of the corresponding activity ( -~ 65%). This suggests that a large proportion of the Rubisco proteins were inactivated or that all were partially activated. This is supported by the in vivo activation of active Rubisco, which was increased by approx. 35%. In recent studies on pea. P/sum satirum, we have shown that accumulation of mRNA transcripts for some of the chloroplast preteins involved in photosynthes/s are severely affected by UV-B. This is true for both chloroplast and nuclear-encoded proteins [4,5]. The g,:nes studied were psb A (chloroplast-encoded), which encodes the DI reaction centre protein of Photosystem !i, the cab gene (nuclear-encoded) for the chlorophyll a/b protein of the light-harvesting antenna complex !!