Plastid development in a virescens barley mutant and chloroplast microtubules

Abstract

Development of plastids in a virescens mutant of ‘Gateway' barley was studied during greening of dark-grown seedlings and in seedlings grown in continuous light. Etioplasts of the mutant did not have a crystalline prolamellar body: however, prolamellar bodies were present in chloroplasts of the 4-day-old mutant when grown in continuous light. Upon illumination, the vesicles within etioplasts and young plastids of the mutant joined together to form grana lamellae and these were formed before the stroma lamellae. Formation of the lamellar system in the mutant was slow and the granal stacks were oriented irregularly rather than being all in the same direction within the plastid.The microtubules seen in the stroma of chloroplasts resembled cytoplasmic microtubules, but they were smaller in diameter and they were unlike them in their fixation properties and cold sensitivity. In the normal, microtubules were present in etioplasts and during formation of the lamellar system. However, in the mutant, they were observed only after formation of the lamellar system. From these findings, it was thought that the microtubules might perform a function in orienting the lamellar system of chloroplasts during their development.