Lettuce inhibition

Encecalin (I) causes a dwarfing of lettuce shoots at concentrations from lOppm and up. On the other hand, eupatoriochromene (II) causes very little dwarfing of the seedling but does inhibit germination of lettuce at lOOppm and above. The concentration of these two chro-raenes in yellow starthistle may indeed allow for some effect to be exerted on the surrounding plant community. 

The dlterpene lactone 17-acetoxyacanthoaustralide (25) has minor effects, showing promotion of clover (112%), cucumber (109%) and Palmer amaranth (111%) and inhibition of carrot germination (91%). The flavonoid artemetin (26) at 0.05 mM concentrations slightly affects onion (93%), oat (91%) and promotes seed germinations In carrot (116%) and Palmer amaranth (113%). In closing, it is noteworthy to point out that lettuce and cress are not significantly affected by all ten sesquiterpene lactones as well as the dlterpene (25) and artemetin (26). 

The most concentrated (1 16, w/w) extract inhibited only lettuce, tomato, and ryegrass. The osmolarity of the solution was 40.3 mOsm, insufficient to affect germination of most seeds (2). 

Dilution to 1 20 eliminated inhibition in onion, oat, ryegrass, red clover, and cheatgrass. Further dilution to 1 40 limited inhibition to lettuce, carrot, and Palmer amaranth. At this concentration lovegrass germination was promoted. The addition of 0.1%... 

Allende, A., Mcevoy, J.L., Luo, Y.G., Artes, F. and Wang, C.Y. (2006) Effectiveness of two-sided UV-C treatments in inhibiting natural microflora and extending the shelf-life of minimally processed Red Oak Leaf lettuce . Food Microbiology, 23, 241— 249. 

Diet may counteract or substitute for chemical cues that influence sexual maturation. Male California voles, Microtus californicus, for instance, are inhibited in their sexual development by odors from their mothers or unrelated females. This effect is eliminated if the regular diet is enriched with fresh lettuce. In young females, uterus growth is stimulated by the odor of males but, in the absence of males, fresh lettuce added to the diet can accomplish the same effect (Rissman and Johnston, 1986). This can be seen as another case of adaptive redundancy of cues for an important function. 

Figure 3. The effect of wavelength on the germination of lettuce seeds which were initially irradiated to establish 50% germination. Additional red light (600-700 nm) further promotes germination most efficiently, whereas far-red light (700-750 nm) inhibits germination. (Action spectrum after Flint and Alister [15].)...

Sakamoto, A., Takeba, G., Shibata, D. Tanaka, K. (1990). Phytochrome-mediated activation of the gene for cytosolic glutamine synthetase (GSi) during inhibition of photosensitive lettuce seeds. Plant Molecular Biology 15, 317-23. 

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