Occurrence of chlorophyll precursors in leaves of cabbage heads--the case of natural etiolation.

In the interior of cabbage (Brassica oleracea) heads (kale, white cabbage, Brussels sprouts), natural leaf etiolation takes place due to a limited light access and chlorophyll biosynthesis is inhibited in a consequence. Instead, apart from carotenoids, whose biosynthesis is not light-dependent, chlorophyll precursors accumulate, mainly protochlorophyllide and to a smaller extent also chlorophyllides a and b. Protochlorophyllide was also detected in green, light-exposed leaves of heads of all the investigated cabbage varieties. Protochlorophyll was not found in the investigated leaves. The analysis of xanthophylls composition showed that the central leaves of kale and white cabbage heads contain relatively high amounts of trans-neoxanthin and lutein epoxide which are found only in trace amounts in green leaves. This is the first systematic study on natural occurrence of chlorophyll biosynthesis precursors in different cabbage varieties.