Modification of Petunia Seedling Carbohydrate Partitioning by Irradiance

Abstract

<jats:p><jats:italic>Petunia × hybrida</jats:italic> Villm. `Red Flash' plants received either 10 or 20 mol·day<jats:sup>-1</jats:sup> photosynthetic photon flux (PPF) in growth chambers at: 175 μmol·m<jats:sup>-2</jats:sup>·s<jats:sup>-1</jats:sup> for 16 hours, 350 μmol·m<jats:sup>-2</jats:sup>·s<jats:sup>-1</jats:sup> for 8 or 16 hours, or 350 μmol·m<jats:sup>-2</jats:sup> s<jats:sup>-1</jats:sup> for 8 hours plus 8 hours of incandescent photoperiod extension (5 μmol·m<jats:sup>-2</jats:sup>·s<jats:sup>-1</jats:sup> PPF). The irradiation components of peak, total, and duration were examined. Doubling total PPF increased total carbohydrate (CHO) production by 60%, seedling dry weight (DW) by 30%, rate of seedling growth by 25%, and acid invertase activity by 50% compared to the other treatments, once the seedlings had reached the two-leaf stage. Seedlings receiving 20 mol·day<jats:sup>-1</jats:sup> PPF partitioned 14% more CHO into ethanol soluble sugars rather than starch, which may explain the increase in relative growth rate observed with supplemental irradiance treatments. Extending the photoperiod for 8 hours with 5 μmol·m<jats:sup>-2</jats:sup>·s<jats:sup>-1</jats:sup> PPF reduced total CHO production by 50% compared to the same treatment without photoperiodic lighting. Treatment with 350 μmol·m<jats:sup>-2</jats:sup>·s<jats:sup>-1</jats:sup> for 8 hours resulted in the highest O<jats:sub>2</jats:sub> evolution (8.8 μmol O<jats:sub>2</jats:sub>/min per dm<jats:sup>2</jats:sup>). Increasing the photoperiod from 8 to 16 hours gave the lowest rate of O<jats:sub>2</jats:sub> evolution (4.5 μmol O<jats:sub>2</jats:sub>/min per dm<jats:sup>2</jats:sup>). Previous reports of the importance of photosynthetic period in controlling partitioning between starch and sugars may have simply observed a decreasing rate of starch accumulation due to increased total PPF.</jats:p>

Comparison of Supplemental Lighting Provided by High-pressure Sodium Lamps or Light-emitting Diodes for the Propagation and Finishing of Bedding Plants in a Commercial Greenhouse

“…Albright et al (2000) documented a similar linear relationship between SDM and total accumulated radiation, from seeding to final harvest (35 d), for butterhead leaf lettuce (Lactuca sativa 'Ostinata'). Likewise, Graper and Healy (1992) found that an increased DLI led to increased growth rate and partitioning of carbohydrates into sugars for petunia 'Red Flash' seedlings.…”