Pollen grains that would easily germinate on stigma are formed to germinate invitro, only when 10-220ppm of boric acid is added. This suggests that

Question

$\begin{array}{1 1} \text{a. Boron accelerates protein synthesis in polen grains} \\ \text{b.Boron has an abrasive effect on exine.} \\ \text{ c. Boric acid serves as a solvent for sporopollenin.} \\ \text{d. Pollen wall is boron deficient and high levels of boron occur in style and stigma.} \end{array} $