Abaxial Anthocyanin Layer in Leaves of Tropical Rain Forest Plants: Enhancer of Light Capture in Deep Shade

The permanent pigmentation of the leaves of tropical rain forest herbs with anthocyanin has traditionally been viewed as a mechanism for enhancing transpiration by increased heat absorption. We report measurements to ?+0.1?0C on four Indo-mal- esian forest species polymorphic with respect to color. There were no detectable differences in temperature between cyanic and green leaves. In deeply shaded habitats, any temperature difference would arise from black-body infrared radiation which all leaves absorb and to which anthocyanins are transparent. Reflectance spectra of the lower leaf surfaces of these species re- vealed increased reflectance around 650-750 nm for cyanic leaves compared with green leaves of the same species. In all spe- cies anthocyanin was located in a single layer of cells immediately below the photosynthetic tissue. These observations provide empirical evidence that the cyanic layer can improve photosynthetic energy capture by back-scattering additional light through the photosynthetic tissue.

Why Leaves Turn Red in Autumn. The Role of Anthocyanins in Senescing Leaves of Red-Osier Dogwood

Why the leaves of many woody species accumulate anthocyanins prior to being shed has long puzzled biologists because it is unclear what effects anthocyanins may have on leaf function. Here, we provide evidence for red-osier dogwood (Cornus stolonifera) that anthocyanins form a pigment layer in the palisade mesophyll layer that decreases light capture by chloroplasts. Measurements of leaf absorbance demonstrated that red-senescing leaves absorbed more light of blue-green to orange wavelengths (495���644 nm) compared with yellow-senescing leaves. Using chlorophyll a fluorescence measurements, we observed that maximum photosystem II (PSII) photon yield of red-senescing leaves recovered from a high-light stress treatment, whereas yellow-senescing leaves failed to recover after 6 h of dark adaptation, which suggests photo-oxidative damage. Because no differences were observed in light response curves of effective PSII photon yield for red- and yellow-senescing leaves, differences between red- and yellow-senescing cannot be explained by differences in the capacities for photochemical and non-photochemical light energy dissipation. A role of anthocyanins as screening pigments was explored further by measuring the responses PSII photon yield to blue light, which is preferentially absorbed by anthocyanins, versus red light, which is poorly absorbed. We found that dark-adapted PSII photon yield of red-senescing leaves recovered rapidly following illumination with blue light. However, red light induced a similar, prolonged decrease in PSII photon yield in both red- and yellow-senescing leaves. We suggest that optical masking of chlorophyll by anthocyanins reduces risk of photo-oxidative damage to leaf cells as they senesce, which otherwise may lower the efficiency of nutrient retrieval from senescing autumn leaves.

Anthocyanins in Leaves: Distribution, Phylogeny and Development

Red pigments, products of different metabolic pathways, occur in terrestrial plants. The flavonoid pathway contributes the greatest diversity, culminating in the prevalence of anthocyanins in the angiosperms. Anthocyanins are produced in flowers and fruits, and also in vegetative organs, but have been poorly researched in the latter. Anthocyanins are commonly produced in: 1. rapidly expanding leaves of tropical plants; 2. senescing leaves of temperate plants; 3. undersurfaces of floating leaves of aquatic plants; 4. abaxial surfaces of leaves of understory plants; and 5. leaves subjected to various environmental stresses. The distribution of anthocyanins in leaves, both in presence and in tissue distribution, is influenced by both phylogeny and development. Few species produce anthocyanins in leaf tissues derived from both dermal and ground embryonic tissue. These influences will be important in resolving the ecological roles of anthocyanins in leaves.

Anthocyanins in Leaves and Other Vegetative Organs: An Introduction

Although anthocyanins are most recognized as pigments contributing to coloration in fruits and flowers, they are also present in leaves and other vegetative organs. Although their presence has long been recognized, particularly because of their contribution to autumn coloration, the phenomenon has been poorly studied and is not well understood. In this chapter we review the history of research on anthocyanins in leaves, emphasizing the flurry of research at the end of the 19 th century as well as the growing body of contemporary research on the topic. We emphasize the various hypotheses of anthocyanin function that were mainly developed more than a century ago, and emphasize recent research that takes advantage of our dramatically increased understanding of whole plant physiology.

Epidermal cells functioning as lenses in leaves of tropical rain-forest shade plants

A ray tracing model has been developed to investigate the possible focusing effects of the convexly curved epidermal cell walls which characterize a number of shade-adapted plants. The model indicates that such focusing occurs, resulting in higher photosynthetic photon flux densities at certain locations within the leaf. It is postulated that there will be a corresponding increase in the rate of photosynthesis. In addition, leaf reflectance measurements indicate that this is generally less for the shade plants compared with sun species and would be advantageous in increasing the efficiency of energy capture. Either effect is important for plants which must survive at extremely low light levels.

The significance of chloroplast movement in leaves of tropical plants

The purpose of this research project was to contribute to the understanding of chloroplast movement in plants. Chloroplast movement in leaves from twenty tropical plant species ranging from cycads to monocots and varying in shade tolerance was examined by measuring changes in transmittance following 30 min. of exposure to white light at 1000 ��mol m���2 s ���1 in the wavelength range of 400���700 nm (photosynthetically active radiation, PAR). Leaf anatomical characteristics were also measured. Eighteen species increased significantly in transmittance (�� T) at this level of illumination. ^ Chloroplast movement was significantly correlated with palisade cell width suggesting that cell dimensions are a significant constraint on chloroplast movement in the species examined. In addition, �� T values were strongly correlated with values of an index of shade tolerance. ^ To further examine the relationship between palisade width and chloroplast movement, additional studies were conducted with a tropical aroid vine, Scindapsus aureus Schott. Scindapsus plants were grown under three different light treatments: 63% (control), 9.0% and 2.7% of full sunlight. Under these growing conditions plants produced markedly different palisade cell widths. Palisade cell width was again found to be correlated with transmittance changes. In addition, the observed increases in transmittance following exposure to the above illumination condition were correlated with absorbance of PAR. Fluorescence studies demonstrated that chloroplast movement helps protect Scindapsus aureus from the effects of photoinhibition when it is exposed to light at a higher intensity relative to the intensity of its normal environment. Ratios of variable fluorescence (Fv) to maximal fluorescence (Fm ) were higher in plants exposed to high light when chloroplasts moved than in plants where chloroplasts did not. ^ To further explore the role of chloroplast movement, studies were conducted to determine if transmittance changes could be induced in ten xerophytes at (1000 ��mol m���2 s���1), as well as two stronger light intensities (1800 ��mol m���2 s���1 and 2200 ��mol m���2 s ���1). Transmittance changes in the ten xerophytes were dependent upon the illumination intensity; nine out of the ten xerophytes changed in transmittance at 1800 ��mol m���2 s���1. For the other two intensity levels, only three out of the ten xerophytes tested exhibited transmittance changes, and for two species, a negative �� T value was obtained at 1000 ��mol m���2 s���1 . No relationship was found between cell dimensions and chloroplast movement, although all species had large enough chlorenchyma cells to allow such movements. ^ The results of the study clearly show that in non-xerophytes, palisade cell anatomy is a strong constraint on chloroplast movement. This relationship may be the basis for the relationship between chloroplast movement and shade tolerance. Although absorbance changes are relatively small, chloroplast movement was clearly shown to reduce photoinhibition. ^

Jane Smiley's "A Thousand Acres": A Feminist Revision of "King Lear"

Jane Smiley retells the tale of ���King Lear��� through the perspective of one of the evil sisters, in her novel ���A Thousand Acres���. While the literary canon places William Shakespeare and his plays at the top of the list, I disagree that the canon should denote what is considered ���classic��� and what would be disregarded. Jane Smiley's novel is not canonized, but why? Her feminist revision of ���King Lear��� answers why Goneril and Regan were so evil. I argue that ���King Lear��� (both the text and the play) does not provide the evidence of dysfunction that Smiley's novel exhibits. ���A Thousand Acres��� opens up questions about gender formation, issues that are misrepresented and occluded in Shakespeare's ���King Lear���. By bringing the trauma of incest to the forefront of the novel, its reverse emotional structures allow the reader to obtain a new perspective to a complex four-century-old play.

Resprouting and new leaves in mangrove forests, one year after Hurricane Wilma impacted the site, Shark River Slough

This material is based upon work supported by the National Science Foundation through the Florida Coastal Everglades Long-Term Ecological Research program under Cooperative Agreements #DBI-0620409 and #DEB-9910514. This image is made available for non-commercial or educational use only.

Can't see the snake for the leaves: enhanced edges disrupt depth perception.

This is an abstract of an invited talk presented at the AVA Animal Vision Meeting / Camocon 2015 in Liverpool UK, on the 23rd of August 2015.