Write in brief how plants synthesize amino acids?

Plant can synthesize amino acids using ${\mathrm{NH}}_4^{+}$  in two ways :
i) Reductive amination:- Ammonia reacts with $\mathrm{\alpha }$ -ketoglutaric acid and form glutamic acid. 
$\mathrm{\alpha }$ -ketoglutaric acid
$+{\mathrm{NH}}_4^{+}+\mathrm{NADPH} \underset{\mathrm{dehydrogenase}}{\overset{\mathrm{Glutamate}}{\to }} \text{ glutamate }+{\mathrm{H}}_2\mathrm{O}+\mathrm{NADP}$
ii) Transamination:- It involves the transfer of an amino group from an amino acid to the keto group of keto acid.