Carrier of the growing fatty acid chain in fatty acid biosynthesis that plays a major role in the biosynthesis of fatty acids in leaves. Required for the biosynthesis of chloroplast photosynthetic membrane lipids such as monogalactosyldiacylglycerol, digalactosyldiacylglycerol and phosphatidylglycerol. Is essential for the biosynthesis of the cuticular wax and cutin polymers in leaves, and for the establishment of systemic acquired resistance (SAR). A number of isoforms are produced. According to EST sequences. By light. Down-regulated by sucrose in the dark. 4'-phosphopantetheine is transferred from CoA to a specific serine of apo-ACP by acpS. This modification is essential for activity because fatty acids are bound in thioester linkage to the sulfhydryl of the prosthetic group (By similarity). Small and chlorotic plants with altered cuticule and reduced levels of fatty acids in leaves. Belongs to the acyl carrier protein (ACP) family.