Leaf Anatomy of C3-C4 Species as Related to Evolution of C4 Photosynthesis

Abstract

This study was undertaken to examine the degree of Kranz anatomy development in the species intermediate to C3 and C4 types (C3-C4) in Panicum, Neurachne, Flaveria, and Moricandia. In each genus, C3 and/or C4 species were used for comparison. Leaf transections from each species were examined by light and transmission electron microscopy. The percentages of leaf photosynthetic cell profiles partitioned to bundle sheaths were higher in C4 than in C3 species, while C3-C4 species tended to be in between. However, percentages for C3-C4 species in Moricandia and some C3-C4 Flaveria species were not greater than C3. When expressed on a cell profile area basis, C3-C4 species partitioned more photosynthetic tissue to bundle sheaths than C3 species Moricandia, but not in Flaveria. Neurachne minore S. T. Blake (C3-C4) partitioned a very small portion of cell profile area to the inner bundle sheaths (5%) compared to Neurachne munroi. F. Muell (C4) (21%). The percentage of organelles partitioned to bundle sheaths was much greater in C3-C4 than in C3 species. The average C3 percentage for mitochondria plus peroxisomes were 19,8, 8, and 19.5% for Neurachne, Flaveria, and Moricandia, respectively, compared to 41, 29, and 46.5% for the C3-C4 species. The CO2 compensation concentration was negatively related to the partitioning of tissue to bundle sheaths. It is concluded that all of the C3-C4 species examined have developed some degree of Kranz anatomy and that this altered anatomy is involved in their reduced apparent photorespiration.