Differential Effects of Carbon Dioxide on the Growth Rates of Coleoptiles and the Enclosed Leaves of Hordeum vulgare L. seedlings

Carbon dioxide appears to modulate the growth rates of the barley(Hordeum vulgare L.) coleoptile and the enclosed leaves duringearly germination. Its effect is to stimulate the coleoptileto elongate at a rate equal to or greater than that of the enclosedleaves. Such stimulation was observed directly in barley coleoptilesfloated on CO₂-sarurated water or indirectly using a DCMU solution.This mechanism ensures that the tender leaves remain enclosedwithin the structurally strong coleoptile sheath until the shootpushes through the soil surface. It is suggested that CO₂ respiredby the enclosed leaves effects this modulation: the CO₂ couldpass into the coleoptile chamber and thence into the coleoptilevia stomata present on coleoptile inner walls.