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Accurately measuring cavitation resistance to understand how plants cope with drought

Root resistance to cavitation Guest post by Danielle Marias, Oregon State University.

 

Plant water transport systems from roots to stems to leaves are under negative pressure due to tension on the water column. This is caused by water loss through stomata – small pores on leaves – and is driven by how dry the atmosphere is, as described by the cohesion-tension theory. This tension or negative pressure puts plants at risk for cavitation. Cavitation is the conversion of water from liquid to vapor and can result in a gas-filled (embolized) vessel or tracheid that no longer transports water. Therefore, cavitation resistance is crucial to coping with and surviving drought.

Methods to assess cavitation resistance have been highly debated. It has been suggested that the standard centrifuge method, the most common and efficient method for measuring cavitation resistance, may have methodological artifacts and is not appropriate for roots. To investigate this, Pratt et al. (2015) compared the standard centrifuge method to two other independent types of measurements of cavitation in roots. This compelling study suggested that the standard centrifuge method accurately measures cavitation resistance and is appropriate for measuring cavitation resistance in roots. Because roots are generally more vulnerable to cavitation and embolism than stems and leaves, studies accurately measuring root cavitation are vital to understanding plant responses to drought as the severity and frequency of drought may increase with changing climate. Drought resistance and related topics in tree hydraulic functioning will also be covered in the forthcoming Special Issue in Tree Physiology.

 

Pratt, R.B., MacKinnon, E.D., Venturas, M.D., Crous, C.J., & Jacobsen, A.L. (2015) Root resistance to cavitation is accurately measured using a centrifuge technique. Tree Physiology, 24 February 2015 doi: 10.1093/treephys/tpv003
Abstract
Plants transport water under negative pressure and this makes their xylem vulnerable to cavitation. Among plant organs, root xylem is often highly vulnerable to cavitation due to water stress. The use of centrifuge methods to study organs, such as roots, that have long vessels are hypothesized to produce erroneous estimates of cavitation resistance due to the presence of open vessels through measured samples. The assumption that roots have long vessels may be premature since data for root vessel length are sparse; moreover, recent studies have not supported the existence of a long-vessel artifact for stems when a standard centrifuge technique was used. We examined resistance to cavitation estimated using a standard centrifuge technique and compared these values with native embolism measurements for roots of seven woody species grown in a common garden. For one species we also measured vulnerability using single-vessel air injection. We found excellent agreement between root native embolism and the levels of embolism measured using a centrifuge technique, and with air-seeding estimates from single-vessel injection. Estimates of cavitation resistance measured from centrifuge curves were biologically meaningful and were correlated with field minimum water potentials, vessel diameter (VD), maximum xylem-specific conductivity (Ksmax) and vessel length. Roots did not have unusually long vessels compared with stems; moreover, root vessel length was not correlated to VD or to the vessel length of stems. These results suggest that root cavitation resistance can be accurately and efficiently measured using a standard centrifuge method and that roots are highly vulnerable to cavitation. The role of root cavitation resistance in determining drought tolerance of woody species deserves further study, particularly in the context of climate change

Mnemonics are an Effective Tool for Adult Beginners Learning Plant Identification

Mnemonics are an Effective Tool The decline in interest in plants in biological education is an established phenomenon. Compared to animals, plants are under-represented in biology textbooks and other media. Biology teachers often avoid using plant examples in class due to their own lack of knowledge or interest, perpetuating the cycle. With botanical topics often relegated to single modules or lecture sets and limited opportunities for fieldwork, learning of species identification has inevitably suffered.

Species identification is a fundamental requirement for learning and understanding biodiversity, but it also plays a role in fostering concern for its preservation. Plant identification draws people’s attention to the wide variation in plant form, texture, colour, etc., increasing their interest in plants and their appreciation of biodiversity. Given the rapid rate of decline of plant species and consequences for wider ecosystems, there may be a greater need than ever to find ways to promote identification skills not only in the classroom but among the general public.

Most beginners are introduced to plant diversity through identification keys, which develop differentiation skills but not species memorisation. A paper in the Journal of Biological Education proposes that mnemonics, memorable ‘name clues’ linking a species name with morphological characters, are a complementary learning tool for promoting species memorisation.

In the first of two experiments, 64 adults in a group-learning environment were taught species identification using mnemonics, an educational card game and a text-based dichotomous key. In the second experiment, 43 adults in a self-directed learning environment were taught species identification using mnemonics and a pictorial dichotomous key. In both experiments, mnemonics produced the highest retention rates of species identification based on vegetative characters. The educational value of these findings is discussed for vegetative plant identification and broader applications. Participants in this study also enjoyed mnemonics more than a keying-out activity, suggesting that they could help to stimulate interest in botany.

Bethan C. Stagg and Maria E. Donkina. Mnemonics are an Effective Tool for Adult Beginners Learning Plant Identification. Journal of Biological Education 27 Feb 2015 doi: 10.1080/00219266.2014.1000360

Phytomonas: Trypanosomatids Adapted to Plant Environments

Phytomonas Over 100 years after trypanosomatids were first discovered in plant tissues, Phytomonas parasites have now been isolated across the globe from members of 24 different plant families. Most identified species have not been associated with any plant pathology and to date only two species are definitively known to cause plant disease. These diseases (wilt of palm and coffee phloem necrosis) are problematic in areas of South America where they threaten the economies of developing countries. In contrast to their mammalian infective relatives, our knowledge of the biology of Phytomonas parasites and how they interact with their plant hosts is limited. This review draws together a century of research into plant trypanosomatids, from the first isolations and experimental infections to the recent publication of the first Phytomonas genomes. The availability of genomic data for these plant parasites opens a new avenue for comparative investigations into trypanosomatid biology and provides fresh insight into how this important group of parasites have adapted to survive in a spectrum of hosts from crocodiles to coconuts.

Phytomonas: Trypanosomatids Adapted to Plant Environments. (2015) PLoS Pathog 11(1): e1004484. doi: 10.1371/journal.ppat.1004484

Seeing the Forest and the Trees: Research on Plant Science Teaching and Learning

CBE Life Sci Educ The September issue of CBE—Life Sciences Education is a Special Focus edition on plant science education:

Plant Behavior. CBE Life Sci Educ September 2, 2014 13:363-368; doi:10.1187/cbe.14-06-0100
Plants are a huge and diverse group of organisms ranging from microscopic marine phytoplankton to enormous terrestrial trees. Stunning, and yet some of us take plants for granted. In this plant issue of LSE, WWW.Life Sciences Education focuses on a botanical topic that most people, even biologists, do not think about—plant behavior.

Book Review: Plant Biology for Young Children. CBE Life Sci Educ September 2, 2014 13:369-370; doi:10.1187/cbe.14-06-0093
My Life as a Plant is an activity book targeted toward helping young children see the importance, relevance, and beauty of plants in our daily lives. The book succeeds at introducing children to plant biology in a fun, inquiry-based, and appropriately challenging way.

Understanding Early Elementary Children’s Conceptual Knowledge of Plant Structure and Function through Drawings. CBE Life Sci Educ September 2, 2014 13:375-386; doi:10.1187/cbe.13-12-0230
We present the results of an early elementary study (K–1) that used children’s drawings to examine children’s understanding of plant structure and function.

Effects of a Research-Infused Botanical Curriculum on Undergraduates’ Content Knowledge, STEM Competencies, and Attitudes toward Plant Sciences. CBE Life Sci Educ September 2, 2014 13:387-396; doi:10.1187/cbe.13-12-0231
This research-infused botanical curriculum increased students’ knowledge and awareness of plant science topics, improved their scientific writing, and enhanced their statistical knowledge.

Connections between Student Explanations and Arguments from Evidence about Plant Growth. CBE Life Sci Educ September 2, 2014 13:397-409; doi:10.1187/cbe.14-02-0028
In an analysis of 22 middle and high school student interviews, we found that many students reinterpret the hypotheses and results of standard investigations of plant growth to match their own understandings. Students may benefit from instructional strategies that scaffold their explanations and inquiry about how plants grow.

Beyond Punnett Squares: Student Word Association and Explanations of Phenotypic Variation through an Integrative Quantitative Genetics Unit Investigating Anthocyanin Inheritance and Expression in Brassica rapa Fast Plants. CBE Life Sci Educ September 2, 2014 13:410-424; doi:10.1187/cbe.13-12-0232
This study explores shifts in student word association and explanations of phenotypic variation through an integrative quantitative genetics unit using Brassica rapa Fast Plants.

Optimizing Learning of Scientific Category Knowledge in the Classroom: The Case of Plant Identification. CBE Life Sci Educ September 2, 2014 13:425-436; doi:10.1187/cbe.13-11-0224
The software program Visual Learning—Plant Identification offers a solution to problems in category learning, such as plant identification. It uses well-established learning principles, including development of perceptual expertise in an active-learning format, spacing of practice, interleaving of examples, and testing effects to train conceptual learning.

Attention “Blinks” Differently for Plants and Animals. CBE Life Sci Educ September 2, 2014 13:437-443; doi:10.1187/cbe.14-05-0080
We use an established paradigm in visual cognition, the “attentional blink,” to demonstrate that our attention is captured more slowly by plants than by animals. This suggests fundamental differences in how the visual system processes plants, which may contribute to plant blindness considered broadly.