In some green leaves the veins are darker than the main leaf area, in some others the veins are brighter than the main leaf area. In some cases this is obviously caused by additional pigments? But in many cases veins as well as main leaf area seemed to be pigmented by chorophyll. Concentration of the geen pigment may play a role, but also other factors like thickness, epidermal cell structure. Does anybody know answers or literature?
Klaus
Dear Klaus, that is an intriguing question. As far as I can go with my first studies on plant nutrition different vein colours normally indicate unbalanced nutrition, maybe, it is just a guess, some plants by simulating lack of nutrients can discourage insect from feeding on them. That should be reasonably easy of testing and someone might have a reference of a study already asking this question that I´m not aware of. Anyway good question that I´ll be following to see up to where we go! Thank you...
Dear Andre,
this is certainly correct. I have read about iron deficiency causing clorosis. But this is an response of an individual plant to deficient nutrients. My question aims at species that possess dark geen veins in their green leaves as compared to species that possess pale green veins in their green leaves.
Klaus
Dear Klaus:
Plant physiologists currently recognize three photosynthetic pathways; C3, C4 and CAM. These pathways may ultimately determine the physical size of photosynthetic cells and their physical distance from the vein. For example, in the C4 pathway the green, photosynthetic cells form a tight wreath (Kranz) around the vein. In CAM plants you might not see the veins at all as the photosynthetic cells are very big with swollen vacuoles filled with Malic Acid so the leaf may appear rather light green or blue to the eyes. Once again, I recommend Gurevitch, Scheiner and Fox (2006) "The Ecology of Plants" (second edition). Once again, I also refer you to literature on shade-tolerant plants in which there is a light and dark pattern on the leaf blade (often around the veins) or a green and yellow or a green and red or even a green and white pattern close to the veins. We may be looking at photosynthetic tissues where the chloroplasts are not green because those are the cells that MUST catch the green wave length where penetration of light is fragmented or diminished during active seasons of dense canopy growth over terrestrial herbs, shrubs or creeping lianes.
Now Klaus, you should be asking yourself why the petals of some flowers employ green veins as nectar guides or as "striated-star" patterns leading the insect to the center of the flower as is Echeandia macrocarpa.
Nice paper about the C4 photosynthesis evolution and developmental consequences for vein anatomy:
http://www.nature.com/nature/journal/v415/n6870/full/415451a.html
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