STL concentration and composition.
Yields of extracts, calculated as [(g extract/ g dried leaves)·100],
were 14.8 and 24.1% for Control (’Bianco gigante’ without stress), and
13.3 and 25.0 % for stressed ’Bianco gigante’ in January and April
harvest, respectively. The interaction “light stress × harvest time”
was highly significant for all STLs and the latter factor, in
particular, more contributed than stress condition to the analysis of
variance for the total concentration (F =637) and for all the STLs
(Table 1). Light stress significantly affected STL concentrations, with
an increase of 338, 102, 94 and 35% in the April harvest of
cynaratriol, deacylcynaropicrin, 11,13-dihydro-deacylcynaropicrin and
grosheimin, respectively, compared to control (Figs. 2 and 3). A higher
concentration in the control was registered only in aguerin B. April
harvest showed the highest concentration for both total and single STLs,
except for grosheimin, deacylcynaropicrin and
11,13-dihydro-deacylcynaropicrin controls. The effect of harvest time
was more marked if combined with the light stress. For instance, an
increase of 221, 190 and 703% was registered from January to April in
the total, cynaropicrin and cynaratriol concentrations, respectively
(Fig. 2). Overall, cynaropicrin was the predominant STL of cultivated
cardoon leaf extracts (70 and 73
mg L−1 in April
harvest of control and light stress, respectively), followed by
cynaratriol (14.9 mg L−1 in April harvest of light
stress). Among minor STLs, aguerin B was the most abundant even if with
higher values in the control (3.6 mg L−1 in April
harvest).