THE IMPACT OF SUBLETHAL FREEZING DURING MATURATION ON PIGMENT CONTENT IN SEEDS OF BRASSICA-NAPUS

Degreening in canola seeds (Brassica napus cv. Westar) is disrupted by sublethal freezing. Both the minimum temperature reached and the moisture content at the time of freezing determine the impact on the seed. In general, the pigment content in the mature seed increases as the final minimum temperature decreases. The relationship between pigment content and the seed moisture content at the time of freezing is not as clear, as there is a peak in pigments associated with freezing in the 50% moisture range. Closer examination of the pigments shows a high proportion of chlorophylls and pheophytins, with relatively low amounts of dephytylated pigments. In comparison, freezing at the higher seed moisture contents produces mature seeds with higher concentrations of dephytylated pigments. These results, in addition to the changes noted in the chlorophyll-protein complexes, suggest that freezing at lower moisture contents induces pigment synthesis. Thus, there is evidence that sublethal freezing not only inhibits degreening, it actually exacerbates the problem by inducing renewed synthesis. © 1990, Gustav Fischer Verlag, Stuttgart. All rights reserved.