Growth and physiological characteristics of wasabi plantlets cultured by photoautotrophic micropropagation at different temperatures

Abstract

In this study, wasabi plantlets were grown by photoautotrophic micropropagation under nine different day/night temperature regimes ranging from 10 °C/10 to 26 °C/26 °C. On day 28 of the culture, the dry weight and the leaf area were found to be highest under a constant air temperature of 18 °C/18 °C. Partitioning of plant biomass into stems increased whilst partitioning into leaves decreased with the increase in temperature. Whereas, partitioning of plant biomass into roots increased when the temperature increased from 10 to 18 °C but decreased with further increase in temperature to 26 °C. The shoot/root ratio showed an opposite trend compared with partitioning into roots, whereas the chlorophyll content of leaves increased when the temperature increased from 10 to 26 °C. The net photosynthetic rate of whole plantlets showed the same trend as plantlet biomass and was the highest in 18 °C/14 °C, 18 °C/18 °C, and 22 °C/18 °C treatments. By contrast, the value of the net photosynthetic rate per unit leaf area decreased sharply at temperatures ranging from 10 to 18 °C. A linear relationship between the net photosynthetic rate and RGR was clearly evident because of the large differences in the leaf area values. The specific leaf area of wasabi plantlets decreased slightly at temperatures ranging from 10 to 18 °C but increased substantially within the range of 18–26 °C; however, the leaf dry matter content showed an opposite trend. Low- and high-temperature ranges had contrasting effects on the leaf mass area and leaf nitrogen concentration. There was the high descent in dissolved oxygen concentration of culture medium at all treatments from day 0 to 7. Greater growth of wasabi plantlets in 18 °C/14 °C, 18 °C/18 °C, and 22 °C/18 °C treatments. Biomass allocation to leaves is more important than the net photosynthetic rate per leaf area for supporting a high relative growth rate.