Interpretations of gradients in δ13C value in thick photosynthetic tissues of plants with Crassulacean acid metabolism

✍ Scribed by Sharon A. Robinson; C. Barry Osmond; Larry Giles

• Book ID: 104659249
• Publisher: Springer-Verlag
• Year: 1993
• Tongue: English
• Weight: 668 KB
• Volume: 190
• Category: Article
• ISSN: 0032-0935
• DOI: 10.1007/bf00196621

✦ Synopsis

In Ceropegia dichotoma, Crassula argentea, Esheveria colorata, Kalanchob" beharensis, Opuntia ficus-indica, Sansveria stuckyi and Opuntia inermis the carbon-isotope ratio (613C) of tissues close to the epidermis is 2 4.3%o more negative than those in the centre of the leaf or cladode. The greatest change in ~13C value occurs between the epidermal layer and the layer of mesophyll tissue immediately underneath. Analysis of major metabolic and structural components in successive layers of Crassula argentea grown under controlled environmental conditions conducive to Crassulacean acid metabolism confirmed that much of the variation in 613C values of bulk carbon is caused by differences in chemical composition. Thus the steep gradient in 6~3C value at the epidermis reflects, in part, the contribution of more-negative 6~3C values of lipids in these tissues. Moreover, during nocturnal CO 2 fixation the amount of malic acid synthesised decreases with depth and the 6~3C value of the methanol-soluble fraction is less negative with distance away from the upper epidermis. These results are consistent with diffusion limitation to CO 2 uptake in these thick leaf tissues, which also contributes to the observed gradients in (~13C value.