Most common tissue source for protoplast isolation is:
Fully expanded young leaves represent most common and convenient source for protoplast isolation across many species due to favorable physiological and structural attributes maximizing yield and viability. Young leaves have thin primary walls composed of cellulose hemicellulose and pectin not yet extensively lignified or suberized, allowing efficient enzymatic digestion within 4-12 hours using cellulase plus macerozyme mixture. Mesophyll cells are large highly vacuolated with minimal intercellular air spaces ensuring enzyme access, contain chloroplasts providing visual marker for intact protop
Ref: Evans & Bravo 1986 mesophyll protoplast; Bhojwani & Dantu leaf protoplast protocol.