Wind-pollinated plants—including trees, grasses, and weeds—produce most of the pollen that affects seasonal allergy sufferers. Wind-pollinated plants produce great amounts of pollen grains that are very small in size. For example, one ragweed plant can produce 1 billion dustlike pollen grains. These small pollen grains are capable of travelling long distances by the wind, potentially affecting large numbers of people who suffer from pollen allergies. Allergy symptoms can range from nuisance manifestations, such as itchy eyes and runny nose for those with allergic rhinitis (also known as hay fever) to severe health hazards for those with allergic asthma. Unfortunately for those who suffer such allergies, researchers in North America and Japan have reported earlier start dates for pollen seasons as well as increased concentrations of airborne pollen. These increases have occurred since (in North America) and before (in Japan) 1990, and the researchers attribute these changes to global climate change. See also: Allergy; Asthma; Global climate change; Pollen

Researchers are learning more about how plants respond to "alarm signals" released by other plants that are under attack by herbivores. To warn conspecifics about predators, many animals issue alarms by vocalizing or emitting odors. In the case of plants, warnings come in the form of volatile organic compounds emitted when an herbivore causes damage to a plant by eating a portion of the plant. Prior research has established that nearby plants can detect these volatiles and subsequently activate herbivore defense systems. Those systems produce chemicals that protect the warned plants from potential predators. A new study based on experiments involving the model organism Arabidopsis thaliana, commonly known as thale cress, has now shed light on the poorly understood mechanisms underlying this defense activation. The study shows that the volatiles induce specific epigenetic changes in the plant, meaning changes in the levels of genes that are expressed, or "switched on," due to an external environmental influence. The findings could help agriculturalists devise ways to boost plant's natural herbivory resistance and thus reduce farmers’ use of pesticides. See also: Agricultural science (plant); Agriculture; Epigenetics; Pesticide; Plant-animal interactions; Plant communication; Volatilization

Photosynthesis is a key natural process utilized by plants and is necessary for proper plant growth. Specifically, photosynthesis uses light to manufacture chemical compounds, including organic compounds—primarily carbohydrates—that are derived from carbon dioxide and a hydrogen source (such as water), most often with simultaneous liberation of oxygen. However, photosynthesis is relatively inefficient, and only a small portion of the available light is actually used to produce carbohydrates. Thus, scientists and farmers have been interested in enhancing the efficiency of photosynthesis, and thereby plant growth, through a variety of genetic engineering techniques. If these methods prove successful and safe, they could boost agricultural production and yield of some of the world's most important plants, including numerous food crops. See also: Agricultural science (plant); Biotechnology; Carbohydrate; Farm crops; Food; Genetic engineering; Genetically engineered plants; Genetically modified crops; Genetically modified organism (GMO); Genetics; Photosynthesis; Plant; Plant growth; Plant physiology

An international team of scientists led by German plant geneticist Jörg Kudla discovered a new signaling pathway in thale cress (Arabidopsis thaliana) that protects sensitive stem cells in the plant from too much salt in the soil. High concentrations of salt, such as sodium (Na), in soil can impair plant growth and cause some plants to stop growing altogether. Soil salinization is a serious threat to food production worldwide, especially in drier regions. To that end, salt tolerance can be a vital adaptation for plants—especially crop plants—to have. The researchers’ discovery supports an advanced model of plant salt tolerance on the cellular and organ scale. See also: Plant growth; Sodium; Soil; Soil fertility

Tiny granules found within the pollen sacs of numerous species of flowers may play a key role in allergic reactions associated with pollen. Measuring less than 4 micrometers (μm) in diameter (most being less than 1 μm), these granules are called orbicules, or Ubisch bodies, and they are composed of sporopollenin (a durable biopolymer found in spores and pollen grains) and produced within tapetum cells (which provide a layer of nutritive cells for pollen grain development). The orbicules are sometimes positioned in close contact with pollen grains and can be dispersed into the atmosphere when pollen is released from the anthers of flowers (note that each anther contains four pollen sacs, or microsporangia, in which pollen are produced). Although researchers have been puzzled by these structures, orbicules may act as allergens (that is, substances foreign to the body that cause allergy) and could be the critical factor for why pollen causes allergic reactions. See also: Allergy; Flower; Palynology; Plant organs; Pollen; Population dispersal

An artificial leaf is a solar cell that uses water and an electrical current generated from sunlight to produce hydrogen (for fuel) and oxygen. It is currently in development at laboratories worldwide. If successful, the artificial leaf could serve as an abundant and carbon-free source of hydrogen for use in fuel cells, in which hydrogen reacts with oxygen to produce water and electricity. In combination, artificial leaf and fuel cell technologies would yield very clean energy. See also: Electrolysis; Energy; Energy conversion; Fuel cell; Hydrogen; Oxygen; Solar cell

To better understand the nutritional effects (health benefits), chemical composition, growing conditions, and shelf life of microgreens, a team of researchers reviewed the science behind them in the Journal of Agricultural and Food Chemistry (October 2018). Microgreens are one- to three-inch-tall herb and vegetable seedlings harvested above their roots about 10 to 14 days after germination just as their first pair of leaves appear, visually looking more like stems and seed leaves (cotyledons). These very young vegetable greens have been used by chefs for years as a garnish because of their colors and flavors. Beyond esthetics, microgreens are packed more densely with nutrients than mature vegetables, making them an interesting subject for food and nutritional scientists. Among commercially grown microgreens are arugula, broccoli, green daikon radish, purple mustard, and red cabbage. See also: Broccoli; Cabbage; Food; Mustard; Nutrition; Radish; Seed; Seed germination

Using non-destructive imaging of living tissue in Arabidopsis plants, a team of researchers led by Cara M. Winter at Duke University in North Carolina has captured unprecedented details about how root growth occurs in real-time at the fundamental level of stem cells. These special cells give rise to all tissue types by “differentiating” into the specific kinds of cells comprising organs and other anatomical structures. Researchers have sought to understand how cellular differentiation works in nature to better grasp cell division as a whole and its role in certain diseases, such as cancer, that are caused by cells dividing out of control. See also: Cell (biology); Histology; Plant growth; Stem cell

Stellar explosions known as supernovae may be behind several anomalous rises in radiocarbon captured in tree rings over the past 40,000 years, according to a recent study that adds mounting evidence to the hypothesis that supernovae can impact Earth's climatology and biota. Nearly all of the time, the light shining from the stars in our sky is benign and dim. But every several thousand years, on average, one of these stars ends its stellar life as a supernova, blazing brighter than our entire galaxy and emitting tremendous amounts of gamma rays and other radiation. Researchers have speculated that these stellar explosions, if close enough to Earth, could degrade Earth's protective ozone layer and alter the climate. These nearby supernovae could even significantly irradiate the planet's surface and kill certain kinds of organisms while spurring potentially harmful mutations in others. Supernovae have thus emerged as a potential triggering event for the rare mass extinctions in Earth's history, during which a large percentage of life forms has inexplicably disappeared from the fossil record. See also: Gamma ray; Mass extinctions; Radiation; Star; Stratospheric ozone; Supernova

Tannins (tannic acids) are naturally occurring complex chemicals found in plants. These proanthocyanidin polyphenols are particularly prevalent in a variety of vascular plants, including fruits (especially grapes), teas, legumes, and grasses. Their taste is quite sharp or caustic, providing the distinctive astringency that humans associate with red wines, teas, and unripe fruits. In addition, tannins are used in the dyeing of textiles and in the tanning of leather products. See also: Dyeing; Fruit; Leather and fur processing; Phenol; Taste; Tea; Wine