Effects of plant growth substances on the conchocelis phase of Alaskan Porphyra (Bangiales, Rhodophyta) species in conjunction with environmental variables1

Abstract

The effect of plant growth substances (PGSs) on conchocelis growth of Alaskan Porphyra (P. abbottiae V. Krishnam., P. pseudolanceolata V. Krishnam., P. pseudolinearis Ueda) was investigated. Growth was measured under different combinations of PGS concentrations (0, 0.1, 0.2, 0.4, 0.8, 1.6, and 3.2 ppm), PGS type (gibberellic acid, kinetin, and indole‐3‐acetic acid), temperature (7, 11, and 15°C), and photoperiod (16:8 light:dark [L:D] cycle and 8:16 L:D cycle). Plant growth substances effectively promoted the growth of Porphyra conchocelis. Depending on culture conditions, growth rates were increased relative to controls 6.9%–31.7% for P. abbottiae, 4.7%–25.7% for P. pseudolanceolata, and 8.9%–35.1% for P. pseudolinearis. Maximal growth of P. abbottiae occurred with 0.8 ppm kinetin, 15°C, and short‐day conditions (8:16 L:D). Porphyra pseudolanceolata exhibited maximal growth with 0.4 ppm indole‐3‐acetic acid, 7°C, and long days (16:8 L:D). Indole‐3‐acetic acid also effected maximal growth of P. pseudolinearis at 0.4 ppm, 15°C, and long‐day conditions (16:8 L:D). For P. abbottiae and P. pseudolinearis, intermediate PGS concentrations (0.4–1.6 ppm) had the greatest growth‐stimulating effects, whereas for P. pseudolanceolata, higher growth generally occurred at lower concentrations (0.1–0.8 ppm). Kinetin and indole‐3‐acetic acid had more influence on the conchocelis phase than gibberellic acid. The PGS concentrations greater than 1.6 ppm had a diminishing effect on growth, especially in P. pseudolanceolata. For P. abbottiae and P. pseudolinearis, higher temperatures resulted in higher growth rates, in contrast to P. pseudolanceolata, which grew faster at the lower temperatures.