When wheat and sugarcane leaves are fed with radioactive ${ }^{14} \mathrm{CO}_{2}$, in which molecu

Question

When wheat and sugarcane leaves are fed with radioactive ${ }^{14} \mathrm{CO}_{2}$, in which molecule would the radioactivity appear first in these plants?

Professor PC Thomas Classes · Answer

(a) : Wheat is a $C_{3}$ plant and sugarcane is a $C_{4}$ plant. In a $C_{3}$ plant, first product of photosynthesis is 3 -phosphoglycerate whereas in a $\mathrm{C}_{4}$ plant, first product of photosynthesis is a 4-C organic acid i.e., oxaloacetic acid which is reduced to malic acid (malate) or transaminated to form aspartate. In sugarcane, after exposure to ${ }^{14} \mathrm{CO}_{2}$ for approximately one second, more than $94 \%$ of fixed radioactivity is found to be present in malate, aspartate and oxaloacetate.