Hsp21 is a chloroplast-localized small heat shock protein. How these small Hsps protect living cells is not fully understood. They seem to be involved in chaperone functions by protecting other proteins from irreversible denaturation. Small Hsps are also produced late in the seed maturation process. Hsp21 has also been shown to protect Photosystem II from temperature-dependent oxidative stress as well as having a role in fruit reddening and the conversion of chloroplasts to chromoplasts (1).