The effects of albinism on the water relations and stem hydraulics of S. sempervirens shoots

Background/Question/Methods

Redwood trees are famous for their size. It is interesting however that the genetic capacity that allows the redwoods to grow indeterminately may also be responsiblefor mutations that result in an unusual phenotype known as the albino redwood. Although some albino individuals may have a small amount of chlorophyll in their leaves, the vast majority of these clumpy shoots exhibit a complete lack of photosynthetic pigment, rendering the stems and leaves white in appearance and completely dependent on theparent plant for carbon, not unlike a parasite. Albino plants are extremely rare, but a single study on albino citrus shoots showed that pigment-less mutants presented higher rates of transpiration and nearly double the amount of stomata on the leaf surface, as compared to the green foliage. Because nutrients, CO2 and even some sugars may move through the plant water transport tissue (xylem), these higher transport rates are thought to supply the albino shoot's demand for carbon and thus facilitate growth in absence of photosynthesis. We predicted that similar transport patterns would be operative in albino redwoods with the implication that these mutants would exhibit greater transpiration rates, increased stomatal density and increased xylem water transport capacity relative to greenfoliage.

Results/Conclusions

Preliminary data using gas-exchange, hydraulic, and anatomical methods indicate that contrary to our predictions, albino redwood xylem exhibits slightlyreduced water transport rates on account of smaller growth rings and conduit cell size, and that compared to xylem in green shoots, the albino xylem may be more vulnerable to transport failure due to drought stress. However in situ, these shoots do exhibit at least 30% higher rates of transpiration, which suggests the absence of stomatal control over water loss. S. sempervirens is the only species of conifer known to exhibit albinism, so this unusual trait will not only inform our understanding of plant water relations, but also the natural history of redwoods.