The effect of cytokinins and other plant hormones on the growth of cotyledonary axilars of flax (Linum usitatissimum), sunflower (Helianthus annuus) and pea (Pisum sativum)

Abstract

Flax seedlings were decapitated above the cotyledons. After one cotyledon was removed the growth of the bud of the remaining cotyledon was stronger in 90% of the plants. However, the application of the cytokinin benzyladenine (BA) to the bud of the removed cotyledon caused a growth correlative reversal and, by contrast, in 65% of the plants the bud of the removed cotyledon grew out. On the other hand, in sunflower seedlings, which have epigeal cotyledons similar to flax, after the removal of one cotyledon the growth of the axillary of the removed cotyledon was more intensive in 59% of the plants. Not even an application of BA to the remaining cotyledon of sunflower resulted in more intensive growth of the axillary of this cotyledon. When both cotyledons were left on the seedling, BA applied to one of the cotyledons of decapitated flax plants resulted in a highly significant stimulation of growth of the axillary of this cotyledon; in sunflower; however, the effect of the BA was insignificant. After decapitation of the stem of pea seedlings where both cotyledons remained, both axillaries grew out, but after a certain period of time one of them (the dominant one) achieved a growth correlative dominance over the other (inhibited). The present study is focused on whether an application of plant hormones onto the inhibited shoot is able to cause a growth correlative reversal, i.e. to change the inhibited shoot into a dominant one. The application of 0.12% BA can cause such a reversal virtually in all plants if the original difference in the length between the inhibited and dominating axillaries is 12–24 mm. A 0.12–0.5% concentration of gibberellin causes a reversal in 13–75% of the plants, but only if the difference between the dominant and inhibited shoot is 1–12 mm. A 0.03–0.25% concentration of IAA causes a reversal in 34–57% of the plants, if the difference in the length of the axillaries is 1–4 mm.