Cactus seedlings in the sun

[iann]

Only early morning and evening when the sun sneaks under the staging, but it still colours up the seedlings.

Turbinicarpus laui

Turbinicarpus valdezianus

Ariocarpus fissuratus

Mammillaria grahamii

[ralphrmartin]

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?

[el48tel]

Not green means a lower level of chlorophyll in the plant in proportion to the other pigments which are red through yellow in colour.

[edds]

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?

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.

[daydreamer]

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.

[edds]

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?

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.

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.

[Chris L]

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.

[el48tel]

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?

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.

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.

[ralphrmartin]

Surprisingly, the infrared reflectance of cactus and succulents is very high compared to native UK plants.

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.

[Licespray]

Interesting topic.

Ralph are those Ariocarpus out of humidity now?