Laboratory Report

Infrared Light Shines for Mycorrhizal Fungi

Infrared spectroscopy is a reliable tool for detecting fungi in grain and for other agricultural uses, but scientists have now discovered that it might be a good way to analyze the mycorrhizal associations of plant roots. Mycorrhizal fungi live in mutually beneficial relationships with nearly all kinds of plants. The fungi help plants by mining the soil for nutrients and water that would be difficult for the plant to obtain on its own. In return, the plants provide the fungi with food produced through photosynthesis. The standard methods for assessing mycorrhizal colonization of roots rely on microscopic examination or analyzing fatty acids of the fungi. The infrared method shows distinct spectral signatures for the components in the cell walls of mycorrhizal fungi. Since this type of testing does not destroy the sample, other analyses can be done on the same sample.

Agricultural Research Magazine, November/December 2010, Vol. 58, No. 10

New Mobile App Makes Plant ID a Snap

Imagine being able to point your handheld device at a leaf, snap a picture, and have an immediate identification of the plant, along with all kinds of information about it. It would be the first electronic field guide. Faculty members in the Computer Departments of Columbia University and University of Maryland, having previously developed human face recognition techniques, approached the chief botanist at the Smithsonian Institution to begin a collaborative effort to build a system for plant species identification. So far, only trees from New York City and the District of Columbia are included in the database. The not-for-profit organization Finding Species was hired and supervised by the Smithsonian to acquire the detailed species images seen in the Leafsnap app and on the leafsnap.com website.

The free app is available now for the iPhone, with iPad and Android versions to come later.

Seedless Cherimoya – Not Yet, but Coming

Many people have never tasted a cherimoya (Annona cherimoya), and some who have tasted it complain about the hard black seeds inside. Selections with seedless fruits have been around for years, but none so far have been found that produce an acceptable quantity or quality of fruit. A recent discovery in the closely related sugar apple (A. squamosa) has revealed a single gene mutation that results in a seedless fruit in which the outermost layer of the ovule fails to form, so no seed is produced, although the flesh around the ovule still develops normally. This same gene mutation has been found in the highly studied laboratory plant Arabidopsis, where it also causes seedlessness. Conventional breeding will be done between sugar apples and cherimoyas in hopes of developing a cherimoya-like fruit that is seedless. A specific gene for seedlessness in fruit or other crops has not been previously identified. There may be an opportunity to develop other seedless crops using this approach.

PNAS, March 2011, 108 (13): 5461-5465

Good Vein Design Confers Drought Tolerance

We are familiar with the idea that small leaf size is an adaptation to dry climates. One of the long accepted explanations for this suggests that the thin boundary layer over small leaves allows them to cool efficiently in a dry warm climate. But this explanation does not answer questions about why there are also small leaf adaptations in dry cool climates. A team of researchers at UCLA has focused on the characteristics of vein architecture found consistently in small leaves. They discovered a higher density of major veins in small leaves, which offer alternate pathways across the leaf in the event that one of the major veins becomes embolized with a bubble due to drought. This trend was observed across a range of plant species as well as within species when individuals were compared in both moist and dry environments. Evidence showed that leaf size and major vein density were linked genetically. There are, of course, other leaf features that contribute to drought tolerance: water storage capabilities, thick cuticles to reduce evaporation, or the presence of certain compounds in cell walls that prevents collapse and allows later “resurrection.” Species with these adaptations may be able to achieve relatively large leaf sizes in spite of dry climates. This study, however, provides a new mechanism for understanding the ecological distribution of leaf sizes, and may provide information for drought tolerance predictions.

Plant Physiology, 2011, 156 (2): 832-843

What Makes Invasive Plants Successful

There is most likely more than one mechanism that makes invasive plants good at what they do. In a UC Davis/University of Wisconsin study, four mechanisms of competition were investigated in the case of invasive velvet grass (Holcus lanatus) against coastal California’s seaside daisy (Erigeron glaucus). The following mechanisms were evaluated in a combination of field and greenhouse experiments: direct competition; indirect competition mediated by mammalian herbivores; interference competition via allelopathy; and indirect competition mediated by changes in the soil community. Results of the study showed that direct competition was most significant, but there were also changes in the soil community that negatively impacted seaside daisy and other species—even after velvet grass was removed.

American Journal of Botany, July 2011, 98 (2): 1086-1094