Figure 1.
Raphides purified from kiwifruit.
Raphides, needle-shaped calcium oxalate crystals, were collected from kiwifruit homogenate through heavy media separation using a dense CsCl solution. (A) The SEM image of purified raphides (x400). (B) Further magnification of the left part of the image (A) (x1,500). The white bars in photos indicate 100 μm (or 0.1 mm). Raphides purified from kiwifruit had sharp needle-like shapes with smooth surfaces, and did not have grooves and barb-like shapes observed in raphides of Araceae plants [12].
Table 1.
Synergistic defensive effects of raphides and cysteine protease.
Figure 2.
A bioassay on synergistic defensive effects between raphides and cysteine protease.
Eight neonate larvae of the Eri silkmoth (Samia ricini, Saturniidae) (1.5 mg) were fed a leaf piece (3×3 cm pieces, ca. 0.1 g) of its host plant, the castor oil plant (Ricinus communis, Euphorbiaceae), painted either with calcium oxalate crystal (needle-shaped raphides purified from kiwifruits or commercially available amorphous crystals), with cysteine protease (bromelain) or with both for 1 day. (A) A control leaf piece of castor oil plant (painted only with CaCl2 and glycerol). (B) A leaf piece painted with raphides (42 μg/cm2 or 3.75 mg/g fresh leaf). (C) A leaf piece painted with amorphous calcium oxalate crystals (42 μg/cm2). (D) A leaf piece painted with bromelain (0.22 mg/cm2 or 5.76 unit/mg fresh leaf), a cysteine protease from pineapple stems. (E) A leaf piece painted with both bromelain (0.22 mg/cm2) and raphides (42 μg/cm2). (F) A leaf piece painted with both bromelain and amorphous calcium oxalate crystals (42 μg/cm2). Note that very strong defensive effects that resulted in high mortality were observed only when bromelain and raphides were fed together.
Table 2.
Synergistic defensive effects of raphides and cysteine protease in the low dose range.
Table 3.
Synergistic defensive effects of raphides and kiwifruit extract from which raphides were removed by centrifugation.