VARIATION IN THE GLUCOSINOLATE CONTENT OF OILSEED RAPE (BRASSICA-NAPUS L) LEAVES .1. EFFECT OF LEAF AGE AND POSITION

The glucosinolate content of oilseed rape (Brassica napus) leaves was monitored over the growth period 30-70 days after planting, and a comparison made between a single-low cultivar (low in erucic acid), Bienvenu, and a double-low cultivar (low in erucic acid and glucosinolate), Cobra. In older, fully-expanded leaves the glucosinolate concentration was very low (< 0.3-mu-mol/ml tissue water) and did not alter during the course of the experiment. In developing sixth leaves glucosinolate content increased rapidly and reached a maximum concentration (4-5-mu-mol/ml tissue water) 40 days after planting (6 days after leaf emergence). The concentration then declined, to about 1-mu-mol/ml after 60 days although the total glucosinolate content in leaves continued to increase until 50 days; much of the reduction in concentration was simply a result of leaf expansion. No major differences were seen between the two varieties in total glucosinolate content or in the individual compounds present. Cv. Cobra developed more quickly than cv. Bienvenu so direct comparison between leaves of the two cultivars was complex. When comparing the glucosinolate content of oilseed rape leaves, between cultivars or between treatments, it is vital to ensure that carefully matched leaves of comparable developmental age are selected.