Chlorophyll formtion and chloroplast development in maize mutants.

 

Cytological investigations of the chloroplasts in the white, luteus, virescent and pale green mutants revealed that complete cor­relation does not exist throughout between the size of the plastid and the chlorophyll content of the leaf. The correlation is positive in the whites. There the plastids are very small and are present in the form of proplastids; positive in the virescents where the plas­tids increase in size from proplastids to normal full‑sized plastids as greening proceeds in the leaf; and exists also in the pale greens when the plastids are just slightly smaller than normal. In the case of the luteus mutants there does not seem to be any obvious relation­ship between plastid size and chlorophyll formation. Some of the mutants that contain only a trace of chlorophyll have very small plastids while others with just as little chlorophyll have plastids of almost normal size. The same holds true for the mutants with a comparatively high chlorophyll content. Many have large plastids but some contain only the very small plastids.

 

By means of the chromatographic adsorption technique it was found that all of the luteus mutants studied contained a small amount of both chlorophyll A and B in addition to carotene and xanthophyll. In the very pale luteus plants the amount of chlorophyll present is so small that it is completely masked by the yellow pigments in the leaf.

 

All of the pale green mutants studied were also found to contain both chlorophylls.

 

The absorption spectra of the green pigments in the luteus and pale green plants, obtained with a Beckman Spectrophotometer, confirmed that they actually were chlorophyll A and B. This rules out the chlorophylls as the cause of the lethality of many of the pale green mutants.

 

One luteus mutant was found in which the formation of chlorophyll B is delayed until at least four days after the formation of chlorophyll A. At low temperatures (62F) chlorophyll B formation can be delayed for about two weeks. This affords the possibility of ascertaining whether or not photosynthesis can proceed in the presence of chlorophyll A only.

 

Drew Schwartz