The Online Community for Cactus and Succulent Growers
https://forum.bcss.org.uk/
If I remember my plant physiology lectures correctly, some red pigments lie on top of green chlorophyll to act as sunscreen whereas some plants have different photosynthetic pathways using red pigments as the trees above have filtered out almost all of the green light so they photosynthesise using the red light.ralphrmartin wrote: ↑Sun Jun 14, 2020 4:11 pm Here's something I find intriguing. When cactus seedlings get too much sun, they go red. Yet plants on the forest floor often have red underleaves. In one case red seems like a reaction to excess light, and in the other case to a lack of light. Why red in each case?
The reason advanced by David Attenborough for the red undersides is that it is a mechanism to reflect light that has passed through the leaf thickness and would otherwise be lost, so the plant gets a second bite at it. Presumably red colouration in seedlings is, as you say, protection against damage.ralphrmartin wrote: ↑Sun Jun 14, 2020 4:11 pm Here's something I find intriguing. When cactus seedlings get too much sun, they go red. Yet plants on the forest floor often have red underleaves. In one case red seems like a reaction to excess light, and in the other case to a lack of light. Why red in each case?
I don't by the looks of a bit of research! The phytochrome detects the far red light and then encourages greater concentrations of chlorophyll b.edds wrote: ↑Sun Jun 14, 2020 5:01 pmIf I remember my plant physiology lectures correctly, some red pigments lie on top of green chlorophyll to act as sunscreen whereas some plants have different photosynthetic pathways using red pigments as the trees above have filtered out almost all of the green light so they photosynthesise using the red light.ralphrmartin wrote: ↑Sun Jun 14, 2020 4:11 pm Here's something I find intriguing. When cactus seedlings get too much sun, they go red. Yet plants on the forest floor often have red underleaves. In one case red seems like a reaction to excess light, and in the other case to a lack of light. Why red in each case?
Since many leaves are slightly transparent when held upto the light maybe the light has shone through the leaves and burnt the other side.ralphrmartin wrote: ↑Sun Jun 14, 2020 4:11 pm Here's something I find intriguing. When cactus seedlings get too much sun, they go red. Yet plants on the forest floor often have red underleaves. In one case red seems like a reaction to excess light, and in the other case to a lack of light. Why red in each case?
Yes ... the structure of the plant has different pigments at different levels. Surprisingly, the infrared reflectance of cactus and succulents is very high compared to native UK plants.edds wrote: ↑Sun Jun 14, 2020 5:01 pmIf I remember my plant physiology lectures correctly, some red pigments lie on top of green chlorophyll to act as sunscreen whereas some plants have different photosynthetic pathways using red pigments as the trees above have filtered out almost all of the green light so they photosynthesise using the red light.ralphrmartin wrote: ↑Sun Jun 14, 2020 4:11 pm Here's something I find intriguing. When cactus seedlings get too much sun, they go red. Yet plants on the forest floor often have red underleaves. In one case red seems like a reaction to excess light, and in the other case to a lack of light. Why red in each case?
Not sure what wavelengths you mean, but go far enough into infrared and you are talking of heat rays. I'm not surprised that cacti want to reflect heat rays, while British plants want to soak up the sun most of the year, if indeed those are the wavelengths you mean.