MicroscopyEducation
Images of Leaf Stomata: Little Things that Matter
Douglas Clark Paedia LLC, 15 Conrad Street, San Francisco, CA 94131-2924
dclark@paedia.com
Abstract: Stomata (singular, “stoma”) are tiny pores through which plants breathe. Stomata are found on the upper and lower sides of leaves, on flower petals, on stems, and on roots. Scientists survey plant surfaces to determine the density and size of stomata and relate these findings to properties of the environment, such as temperature and the amounts of sunlight, humidity, oxygen, and carbon dioxide in the air when a leaf is formed. Stomata of various plants are suitable subjects for classroom laboratory activities since they may be examined by light microscopy.
Keywords: Plants, stomata, light microscopy, focus stacking, quan- titative measurements
Introduction Stomata play an important role in life on Earth. Tey regu-
late the flow of gases and water vapor through a plant’s epider- mis in response to environmental stimuli and thus affect the health of the plant. Scientists study all aspects of the location, density, function, vulnerabilities, and susceptibilities of sto- mata. Some study stomata to provide clues to Earth’s past and present environment in order to understand climate change. Others study them to understand how to maximize crop yields, reduce the opportunity for forest fires, maximize water use effi- ciency, and minimize the intrusion of pathogens into plants. Leaves of terrestrial plants generally have more stomata on
their undersides. Floating leaves of aquatic plants have stomata only on their upper surfaces, while some underwater plants have no stomata at all. In some flowering plants (monocots, such as grasses) stomata are generally oriented similarly to one-another. In other flowering plants (dicots, such as roses) stomata are randomly oriented. A leaf contains several types of plant cells that serve vari-
ous functions (Figure 1). One particular kind of cell is called a “guard cell.” Guard cells are specialized cells that form a pair of lips at the periphery of each stoma. Guard cells swell and shrink based on conditions within a plant. When guard cells swell, they open a stoma on the surface of a leaf, as shown in Figure 1a. Water vapor and gases can flow through an open stoma to and from the interior of a plant. When guard cells lose water and shrink, as shown in Figure 1b, they close the stoma and prevent the loss of water vapor and limit gas exchange. Processes that control the opening and closing of stomata are discussed in references [1–8]. Most plants around the world have stomata that can be
seen with a microscope. Locating leaf samples, preparing them, and observing them with light microscopy is a very effective and inexpensive way of introducing students to science and the study of global environmental and agricultural questions.
12 doi:10.1017/S155192951800130X
Figure 1: Schematic representations of a leaf. Cross-sectional views (left) and plan views (right) of a single stoma (a) open and (b) closed on the underside of a leaf.
www.microscopy-today.com • 2019 January
Reasons for Studying Stomata Climate change. Scientists are studying and comparing
stomatal densities (Figure 2) in recent leaves and fossil leaves in order to better understand the effects and implications of global warming [2,3]. Water use efficiency of plants. One group of scientists
proposes manipulating stomatal function using combina- tions of physiological and molecular genetic methods in order to improve water use efficiency in plants. Tis is especially important regarding drought. In one paper the authors put it this way [4]: “Improving plant WUE [water use efficiency] and a plant’s ability to cope with reduced water availability is high on the scientific agenda. Stomata ultimately control 95% of all gaseous fluxes between the leaf and the environment. It follows that stomata represent an attractive target for manipulations aimed at reducing water loss.” Plant classification. Plant types are classified by the sizes,
shapes, and arrangements of their stomata [5]. Uptake of nutrients and chemical treatments. Foliar fer-
tilization is sometimes used in addition to ground fertilization. In foliar fertilization, nutrients and chemical treatments are applied to the leaves of a plant where they are absorbed through the leaf surface and through the stomata. Understanding of the
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52
