Index Table of contents 891 Chloroplast Membrane Lipids from Coffea sp. under Low Positive Temperatures F.L. PARTELLI 1 , H.D. VIEIRA 2 , I.P. PAIS 3 , V.L. QUARTIN 3,4 , P.S. CAMPOS 3 , A. FORTUNATO 4 , P. EICHLER 4 , A.P. VIANA 2 , A. RIBEIRO 4 , J.C. RAMALHO 4 1 Universidade Federal de Goiás - UFG, Escola de Agronomia e Engenharia de Alimentos. Campus II Samambaia. Caixa Postal 131, 74001-970, Goiânia - GO, Brazil 2 Universidade Estadual do Norte Fluminense Darcy Ribeiro - UENF, Centro de Ciências e Tecnologias Agropecuárias. Av. Alberto Lamego 2000, Parque Califórnia, 28013-602, Campos dos Goytacazes - RJ, Brazil 3 L-Instituto Nacional de Investigação Agrária / INRB, Av. República, Quinta do Marquês 2784-505 Oeiras, Portugal 4 Centro de Ecofisiologia, Bioquímica e Biotecnologia Vegetal / Inst. Inv. Científica Tropical, Av. República, Quinta do Marquês, 2784-505 Oeiras, Portugal SUMMARY Plants have acclimation mechanisms conferring them tolerance to environmental limiting conditions and better recovering ability after the stress ceases. The objective of this work was to evaluate the influence of low positive temperatures (chilling) on the photosynthetic structures of Coffea sp. genotypes, through the analysis of the chloroplast membrane lipid composition and leaf shedding. For that, two genotypes of Coffea canephora (clone 02 and 153) and one of C. arabica (Catucaí IPR 102) were used. Plants were placed in growth chambers under environmental controlled conditions with temperature 25/20 °C (day/night), irradiance 700-900 μmol m -2 s -1 , external CO 2 concentration ca. 380 μL L -1 , relative humidity 70% and a 12 h photoperiod. Plants were successively submitted to a gradual temperature decrease from 25/20 °C down to 13/8 °C (0.5 °C day -1 ), 3 days at 13/4 °C and 14 days at temperature of 25/20 °C, allowing the plants to recover. Conilon clone 02 was the most affected genotype, showing stronger leaf shedding, followed by clone 153, while Catucaí was less affected. The latter genotype usually showed a higher degree of lipid unsaturation, as well a higher proportion of linolenic acid and a lower of palmitic acid in phosphatidyglycerol, suggesting greater membrane fluidity. Quantitative and qualitative differences in chloroplast fatty acids and lipid classes, together with leaf shedding evaluation, may contribute to the management and adequate genotype selection for low temperature occurrence areas, thus constituting valuable tools in Coffea sp. breeding programs. INTRODUCTION The genus Coffea comprehends at least 103 species, but only C. arabica and C. canephora have worldwide commercial relevance (Davis et al., 2006). When cultivated in latitudes higher than 15 °C, coffee shows a clear decrease in growing rates in winter season (Libardi et al., 1998; Silva et al., 2004). However, coffee plants have acclimation mechanisms, which includes quantitative and qualitative membrane lipid modifications and increased ability of energy excess dissipation, conferring higher tolerance to low temperatures and recovering capacity after the stress finishes (Campos et al., 2003; Ramalho et al., 2003). In fact, when submitted to low temperatures some Coffea sp. genotypes may undergo an unsaturated fatty acid (FA) increase, such as in linolenic acid (C18:3), specially at the