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Development of characteristics of the C4 syndrome was studied in cotyledons and leaves of NADP‐ME type C4 Salsola richteri, a desert shrub. This species has seeds in which the cotyledons contain chloroplasts, storage proteins, and lipid bodies but no starch. Following imbibition (day 0), tissue types are already apparent in the cotyledons, and the chloroplasts have extensive grana stacking, but Kranz type anatomy and C4 photosynthesis have not developed. At day 0, there is high Rubisco and low phosphoenolpyruvate carboxylase (PEPC) content, distributed throughout all tissue. After 15 d of development in the dark, the cotyledons were in a C3‐like default condition with three distinct layers of chlorenchyma (hypodermis, mesophyll, and bundle sheath [BS]); all contained Rubisco in their chloroplasts. Light was required for development of the C4 syndrome, including differentiation of chloroplasts in mesophyll and BS cells, development of thick BS cell walls, selective compartmentation of Rubisco in BS cells a...

Three pathways of net carbon assimilation and reduction have been detected in certain higher plant. The three recognized pathways are: the reductive pentose phosphate, the C4-dicarboxylic, and crassulacean acid metabolism. Leaves of a given plant may exhibit at least one of these pathways. A plant exhibiting a particular one of these carbon pathways also will possess a distinctive leaf morphology. Plants with crassulacean acid metabolism will have fleshy leaves. In a light or electron microscope, the vascular bundle sheath cells of neither crassulacean nor pentose types of leaves will exhibit extensive development of organelles such as chloroplasts, mitochondria, ro peroxisomes. Plants using the C4-dicarboxylic pathway will exhibit, in light and electron microscopy, a dense concentration of these organelles in leaf bundle sheath cells. Thus leaf cell morphology, plus organelle distribution and biochemistry, are intimately related in a very specific manner such that photosynthesis in a given plant proceeds...