Yoshihiro Shishido

Petiole length, chlorophyll and carbohydrate levels, and photosynthetic rates of June-bearing strawberry plants as influenced by red-light irradiation during storage under cool conditions

Abstract This study was conducted to assess the effects of red-light irradiation at low photosynthetically photon flux density (20 μmol m−2 s−1 PPFD) during storage at 15 °C for 15–16 days on the growth of new leaves, chlorophyll and carbohydrate levels, and photosynthetic rates of strawberry seedlings (Fragaria X ananassa Duch. var. ‘Nyoho’). Petiole length of new leaves that elongated under red-light irradiation for 8 h photoperiod at 15 °C was shorter than that of those elongated under metal halide lamps for 8 h photoperiod (400 μmol m−2 s−1 PPFD) at 27/15 °C or in continuous darkness at 15 °C. Red-light irradiation effectively inhibited the decrease in chlorophyll levels of the leaves that unfolded prior to storage (old leaves). However, the decrease in both reducing sugar and sucrose levels of the roots, crown and old leaves was not inhibited by red-light irradiation, and the values were the same as those for plants in continuous darkness during the entire experimental period. Leaves that were newly grown in continuous darkness had smaller areas, lower chlorophyll levels and lower photosynthetic rates compared to those grown under red-light irradiation when measured at the end of storage. The values for plants in continuous darkness increased rapidly, while those values for plants in red-light irradiation increased gradually under subsequent high temperature and long-day conditions, resulting in no apparent difference between treatments on days 2 to 5.

Effect of temporary changes in light intensity on carbon transport, partitioning and respiratory loss in young tomato seedlings raised under different light intensities

Tomato plants were grown under light intensities of 36 or 90 W m(-2) [photosynthetically active radiation (PAR)], and then the light intensity was changed to 36, 90 or 180 W m(-2) for 8 h to investigate the effect of temporary changes in light intensity on the carbon budget of photoassimilates from the third leaf using a (14)CO(2) steady-state feeding method. In the plants that were raised under 90 W m(-2), the photosynthetic rate increased when the light intensity was increased to 180 W m(-2), whereas no increase occurred in the plants that were raised under 36 W m(-2). Although the total amount of carbon fixed during the 8-h light period showed a large difference between plants grown at the two initial light intensities, the proportion of carbon exported during the light period did not differ apparently, irrespective of the change in light intensity. However, the amount of carbon exported during the time course was higher in plants that were raised under 90 W m(-2) than those raised under 36 W m(-2), irrespective of the change in light intensity. The partitioning pattern of (14)C-photoassimilates was not changed by the change in light intensity, irrespective of whether the light intensity was increased or not. However, the amount of (14)C-photoassimilates accumulated in each part differed according to the two initial light intensities. The carbon transport from a source leaf was also investigated through a quantitative analysis of carbon balance.