PARENT SESSION
Posters P3B Photosynthetic acclimation: Ecophysiology, diverse environments. Abstracts (479-522)

Effects of polyploidy on photosynthetic performance in leaves of Phlox drummondii. Poonam Vyas^{1, 3}, Sachiko Funayama-Noguchi¹, Satoshi Yano^{1, 4}, Yuko Hanba², Ichiro Terashima^*,1, ¹ Dept. Biol., Grad. Sch. Science, Toyonaka, Osaka, Japan³ Present address:, Delhi, India⁴ Present address:, Okazaki, Aichi, Japan² Res. Inst. Biol. Resources, Kurashiki, Okayama, Japan

ABSTRACT- Autotetraploids of Phlox drummondii were artificially synthesized to study the effect of polyploidy on the photosynthetic characteristics of their leaves. Colchicine was applied to the shoot apieces of diploid progenitor (D), and autotetraploid shoot parts thus produced were termed as tetraploids at zero generation (C0) and their F1 tetraploids at 1st generation as C1. Autotetraplods from the same progenitors have been also maintained for more than 11 generations (C11). These plants were grown under the controlled condition at 0.2 mmol photons m^-2 s^-1 at 25/18C. Autotetraploid leaves were thicker and larger with 18 and 110% higher chlorophyll content in C0 and C11, respectively. The light-saturated rate of net photosynthesis increased by 43% in C0 and more than doubled in C11 along with increase in stomatal conductance (2.75 times in C11). Cell Size, mesophyll volume and chloroplast number per cell were much greater in tetraploids than in the diploid. C0 had larger cells than C11. The cumulated surface areas of mesophyll cells (Smes) and chloroplasts (Sc) facing intercellular spaces were highest in C11 followed by C0 and D. On the other hand, cell wall was thicker in the tetraploids than in the diploid plants. Concurrent measurements of the assimilation rate and carbon isotope discrimination indicated comparable internal conductance between the tetraploids and D. The remarkable increase in Sc probably overcame the resistance offered by thicker cell walls and contributed to the increase in internal conductance. Taken together, the tetraploids, in particular C11, showed better photosynthetic performance, although the internal conductance did not increase. The present results indicate the increase in the photosynthetic rate per unit leaf area in autotetraploids. However, other autotetraploids at zero generation did not necessarily perform better than their diploid progenitor. Thus, C11 has probably accumulated sufficient beneficial characters and gradually adapted over the years.

KEY WORDS: cell size, evolution, polyploidy, internal conductance