Catalyzes the NADPH-dependent reduction of glutamyl-tRNA(Glu) to glutamate 1-semialdehyde (GSA). Probably involved in wound-induced supply of heme to defensive hemoproteins outside plastids. (S)-4-amino-5-oxopentanoate + NADP(+) + tRNA(Glu) = H(+) + L-glutamyl-tRNA(Glu) + NADPH Porphyrin-containing compound metabolism; protoporphyrin-IX biosynthesis; 5-aminolevulinate from L-glutamyl-tRNA(Glu): step 1/2. Porphyrin-containing compound metabolism; chlorophyll biosynthesis. Expressed in roots and flowers. Detected in leaves, hypocotyls and cotyledons. Not regulated by light. Up-regulated localy by wounding and reactive oxygen species. Not regulated by methyl jasmonate. No visible phenotype, but decreased heme content in roots. During catalysis, the active site Cys acts as a nucleophile attacking the alpha-carbonyl group of tRNA-bound glutamate with the formation of a thioester intermediate between enzyme and glutamate, and the concomitant release of tRNA(Glu). The thioester intermediate is finally reduced by direct hydride transfer from NADPH, to form the product GSA (By similarity). Belongs to the glutamyl-tRNA reductase family.