How exactly does cuticular transpiration occur in plants?

[Aafia]

Cuticle is the waxy layer on epidermis which prevents loss of water from leaves but some of the transpiration also occurs through cuticle. If cuticle is wax then it should prevent the water loss completely.

 

[Fervent Freyja]

Cuticle is the waxy layer on epidermis which prevents loss of water from leaves but some of the transpiration also occurs through cuticle. If cuticle is wax then it should prevent the water loss completely.

Yes, it should prevent most water loss. Gas exchange is regulated by stomata located on the epidermis, they also open during transpiration.

 

[Aafia]

Yes, it should prevent most water loss. Gas exchange is regulated by stomata located on the epidermis, they also open during transpiration.

But cuticle is just a layer, it is not opening. I want to know how some of the water is lost through cuticle if it repel water.

 

[256bits]

Cuticle is the waxy layer on epidermis which prevents loss of water from leaves but some of the transpiration also occurs through cuticle. If cuticle is wax then it should prevent the water loss completely.

If some transpiration occurs then it is fairly obvious that the cuticle does NOT prevent some water loss.

The "waxy" membrane is very thin, and not at all completely wax, and there may be polar regions where water can more easily penetrate the barrier.

That may not be the whole story of explanation, though, of water diffusion through the cuticle.
Some effect from water loving and water repelling forces also plays into the effect.

Read more,
http://jxb.oxfordjournals.org/content/52/363/2023.full
Year 2001, so a bit dated.

 

[jim mcnamara]

FWIW @Fervent Freyja gave you the correct definition of transpiration - think stomates.
Let's use the term leaky. Yes, some plants are leaky, others are not leaky at all.

Reason: plants occupy different habitats. And are well adapted. In simple terms that means plant species are adapted to function optimally (compared to the species that exist but do not compete as well in the same environment). That means the plants do not waste energy building things that they do not need to live and reproduce.

So. In what environment would a leaky cuticle be most likely to be detrimental?
1. Sonoran Desert
2. a pond in London

Or put another way, why should a plant spend energy and resources slapping together a super dense and completely contiguous layer of wax when it lives in a pond? Water is everywhere in pond.

Examples:
Water cress
Cactus (like prickly pear)

You can guess which of each of these plants lives best in #1 or #2. Plants in aquatic environments may have very little, and not contiguous (patchy), waxy cuticle on their leaves. Prickly pear has few, if any, leaves; they are spines instead. The plant stem has a really thick waxy epidermis.

 

[Fervent Freyja]

But cuticle is just a layer, it is not opening. I want to know how some of the water is lost through cuticle if it repel water.

The pore/stomata is surrounded by the cuticle and goes deeper into the epidermis. Water loss through the actual cuticle will be minimal. Cuticle doesn't grow in one smooth layer, the structure resembles scales layered on top of each other. Since plants growth isn't perfect, those scales aren't always aligned to cover the epidermis, they can move when bent or squeezed (allowing water to seep out) and open wounds to the top epidermis layer may seep water. Animals and weather often bend, bruise, crush, and cut plants that end up re-healing later on- there will be slight water loss for those circumstances.

 

[jim mcnamara]

There is also guttation - the very end of vasulcar bundles (veins) in leaves may terminate directly to "air". Example: lawn grasses are wet in the morning after an evening watering or rain. This is not dew. At night sap (mostly water) in the the xylem oozes out, due to root pressure, along edges and end of leaves. When the stomates open after dawn, they take over moving water via evaporation. You can sometimes see guttational water drops in extremely humid conditions, when transpiration does not work well. Guttation takes over. Cloud forest bamboos and swamp plants commonly do this, for example.

Poor man's analogy:
Guttation is sort of like a Plan B for plants that need to move out excess water, when transpiration (Plan A) does not perform well.

https://en.wikipedia.org/wiki/Guttation for pictures and text.