130 S. Signorelli et al.
this species compared to L. corniculatus when water loss must be prevented. In a
comparative analysis of L. corniculatus and T. pratense subjected to water stress
and heat, it was observed that T. pratense did not survive 5 days of combined stress,
while lotus was still alive (Signorelli et al. 2013b). In concordance, higher dry-
matter yield was observed in L. corniculatus compared to T. pratense under field
conditions subjected to summer water stress (Peterson et al. 1992 ).
6.3.2 Oxidative Stress
Most stresses induce ROS and alter the antioxidant–enzymatic response (Mahalin-
gam and Fedoroff 2003 ). However, little is known about how two or more stresses
affect the ROS production and the antioxidant response. Alterations induced by
water and heat stress on antioxidant response and oxidative damage in the model
legume L. japonicus (Sainz et al. 2010 ), in the forage legumes L. corniculatus and
T. pretense has been reported (Signorelli et al. 2013b).
SOD is the main enzymatic system responsible for cell detoxification and is well
documented in several plant species to increase in response to water deficit and heat
stress (Alscher et al. 2002 ). In L. corniculatus, the activity of Mn-SOD and Fe-SOD
increased as a consequence of water stress and combined stress (Fig. 6.2), but it did
not change under heat stress (Fig. 6.2). In the related model specie L. japonicus,
Cu/Zn-SOD immunodetection and the isoenzyme-specific activity assays con-
firmed that high-temperature treatment provoked a reduction in the Cu/Zn-SOD
protein content and activity. This is consistent with a failure to convert O 2 ●− to H 2 O 2
in the combined heat–drought condition. Additionally, in spite of the decreased Cu/
ZnSOD in the high-temperature treatment, the accumulation of O 2 ●− remains low,
Fig 6.2 SOD activity under drought and combined heat and drought stress. a SOD isoforms pro-
file. C control; D drought; H heat at 42 °C; D + H drought + heat at 42 °C. 40 and 200 mg of protein
were loaded in L. corniculatus and T. pratense, respectively. The gel is the most representative of
three replicates of native gels. b Total in vitro SOD activity. C control; D drought; H heat at 42 °C;
D + H drought + heat at 42 °C. One unit of SOD was defined as the amount of enzyme that inhibits
the rate of cytochrome c reduction by 50 %. Bars indicate the relative standard deviation. (Figure
modified from Signorelli et al. 2013b)