Fatty-acid synthesis in plastids from maturing safflower and linseed cotyledons.

Plastids isolated from maturing, nongreen safflower (Carthamus tinctorius L.) cotyledons yielded unesterified fatty acids as the predominant product of fatty-acid synthesis from [1-(14)C]acetate. Exogenous reduced pyridine nucleotides were not required for this synthesis, but [1-(14)C]acetate incorporation was absolutely dependent on addition of ATP. Linseed (Linum usitatissimum L.) cotyledons are green during development and plastids isolated from them resembled leaf chloroplasts with developed grana. In contrast to the safflower plastids, those from linseed were able to carry out fatty-acid synthesis at low irradiances without the addition of either pyridine nucleotides or ATP. Intact linseed cotyledons were capable of net photosynthesis at rates up to 95 μmol·mg(-1) chlorophyll·h(-1). However, the low-light environment inside the linseed capsule (approx. 15% of external) means that photosynthesis will not contribute appreciably to the carbon economy of the developing seed and its main role may be to supply cofactors for fatty-acid synthesis.