Cr. Jensen et al., SEED GLUCOSINOLATE, OIL AND PROTEIN CONTENTS OF FIELD-GROWN RAPE (BRASSICA-NAPUS L) AFFECTED BY SOIL DRYING AND EVAPORATIVE DEMAND, Field crops research, 47(2-3), 1996, pp. 93-105
The effect of soil drying on seed yield, oil, protein, and glucosinola
te contents was studied in rape (Brassica napus. L) grown in sandy and
loamy soils in lysimeters in the field. By controlling irrigation, th
e plants were exposed to early drought (ED) during the vegetative and
the flowering stage or late drought (LD) during the pod filling stage.
Under low evaporative demands (2-4 mm day(-1)) in 1991, seed and oil
yields were not significantly influenced by soil drying. Under high ev
aporative demands (4-5 mm day(-1)) in 1992, the ED and LD treatments o
n sand decreased the seed yield by 8% and 17% of the fully irrigated (
FI) treatment, respectively; oil yield was significantly decreased (17
% in both ED and LD treatments) on sand, only; protein yield was not s
ignificantly reduced by drought. In the fully irrigated treatment, the
glucosinolate content was 9.7 mu mol/g dry matter (d.m.) in 1991 and
13.7 in 1992. Both ED and LD treatments increased glucosinolate conten
t to between 11.7 and 24 mu mol/g d.m. in the two years. The results r
eveal that glucosinolate synthesis was increased when leaf or pod midd
ay water potential was less than - 1.4 MPa for extended periods. Below
this potential, the tissue turgor pressure of leaves and pods was low
or zero. When turgor was low and the number of stress days (SD) excee
ded 6.4, the glucosinolate content increased linearly with the number
of stress days by 1.49 mu mol (glucosinolate) g(-1) (d.m.) SD-1. Water
stress occurring during vegetative growth also increased seed glucosi
nolate content. It is proposed that glucosinolates are produced as sec
ondary metabolites in droughted tissue at low turgor and that under th
ese conditions glucosinolate precursors are produced for later use. In
1992 under severe stress, the glucosinolate content also correlated w
ith seed size.