The influence of plant growth regulators on the growth of the embryonic axes of red- and far-red-treated lettuce seeds

The influence of several plant growth regulators on the growth of the embryonic axes from red- and far-red-(R- and FR-)treated lettuce (Lactuca sativa L., cv. Grand Rapids) seeds was examined; as shown previously, the water potential of the axes from R-treated seeds has been lowered by 3.5–5.6 bars compared to that in axes from FR-treated ones. Kinetin and abscisic acid (ABA), when included in the incubation medium, reduced the elongation of the axes whereas fusicoccin stimulated it; however, these effects were the same in axes of both R- and FR-treated seeds. In contrast, elongation of axes from FR-treated seeds was stimulated by gibberellic acid (GA₃, but elongation of axes from R-treated ones was not affected by this hormone. This latter result indicates that gibberellins may be involved in the phytochrome-mediated growth responses in lettuce axes.When the root caps of the embryos were removed prior to light treatment, R was still able to induce a water-potential decrease in the embryonic axes, indicating that at least a portion of the active Pfr resides in the axis and not the root cap.Abbreviations ABA abscisic acid - FR far red light - GA₃ gibberellic acid - PEG polyethylene glycol - Pfr far-red-absorbing form of phytochrome - R red light