Photosynthesis, Carbohydrate Metabolism, and Yield of Phytochrome‐B‐Overexpressing Potatoes under Different Light Regimes

Abstract

Transgenic potatoes (Solanum tuberosum L.) overexpressing Arabidopsis thaliana (L.) Heynh. phytochrome B (phyB) have been reported to exhibit a substantially modified plant architecture, increased photosynthetic performance, reduced photoinhibition, delayed leaf senescence, and increased tuber yield. A greenhouse and a growth chamber experiment were conducted at Braunschweig, Germany, to elucidate the crop physiological basis for the yield differences between moderately phyB‐overexpressing transgenic (Dara‐5) and wild‐type potato plants. In the greenhouse experiment, Dara‐5 leaves showed a 23% greater leaf carbon exchange rate (CER) at light saturation, 32% greater leaf conductance, and 21% longer green leaf area duration (GLAD) than the wild‐type plants. The transgenic plants partitioned a considerably greater portion of their biomass to stems and roots, but tuber and total biomass yield did not significantly differ among genotypes. The leaves and stems of the transgenic plants had lower starch and soluble sugar concentrations but consistently higher N concentration than those of the nontransgenic plants. Light response curves showed increasing CER superiority of Dara‐5 leaves with increasing photosynthetic photon flux (PPF), suggesting higher productivity of the transgenic plants in high‐radiation environments. Therefore, the two genotypes were compared in growth chambers at low, medium, and high light levels of 300, 600, and 900 μmol m−2 s−1 PPF. Leaf CER of the transgenic plants reached 123, 115, and 120% of the wild‐type plants at low, medium, and high PPF, but only at low PPF did the transgenic plants produce significantly greater (+8%) tuber yield than the nontransgenic plants. It is supposed that enhanced C loss from respiration is responsible for the lack of consistent transgenic yield superiority.