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October, 2006
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Responses to Salt Stress

JoVE 11120

Salt stress—which can be triggered by high salt concentrations in a plant’s environment—can significantly affect plant growth and crop production by influencing photosynthesis and the absorption of water and nutrients.

Plant cell cytoplasm has a high solute concentration, which causes water to flow from the soil into the plant due to osmosis. However, excess salt in the surrounding soil increases the soil solute concentration, reducing the plant’s ability to take up water. High levels of sodium are toxic to plants, so increasing their sodium content to compensate is not a viable option. However, many plants can respond to moderate salt stress by increasing internal levels of solutes that are well-tolerated at high concentrations—like proline and glycine. The resulting increased solute concentration within the cell cytoplasm allows the roots to increase water uptake from the soil without taking in toxic levels of sodium. Sodium is not essential for most plants, and excess sodium affects the absorption of essential nutrients. For example, the uptake of potassium—which regulates photosynthesis, protein synthesis, and other essential plant functions—is impeded by sodium in highly saline conditions. Calcium can ameliorate some effects of salt stress by facilitating potassium uptake through the regulation of ion

 Core: Biology


JoVE 11094

Plant morphogenesis—the development of a plant’s form and structure—involves several overlapping developmental processes, including growth and cell differentiation. Precursor cells differentiate into specific cell types, which are organized into the tissues and organ systems that make up the functional plant.

Plant growth and cell differentiation are under complex hormonal control. Plant hormones regulate gene expression, often in response to environmental stimuli. For example, many plants form flowers. Unlike stems and roots, flowers do not grow throughout a plant’s life. Flowering involves a change in the identity of meristems—regions of the plant containing actively-dividing cells that form new tissues. In addition to internal signals, environmental cues—such as temperature and day length—trigger the expression of meristem identity genes. Meristem identity genes enable the conversion of the shoot apical meristem into the inflorescence meristem, allowing the meristem to produce floral rather than vegetative structures. The inflorescence meristem produces the floral meristem. Cells in the floral meristem differentiate into one of the flower organs—sepals, petals, stamens, or carpels—according to their radial position, which dictates the expression of organ identity genes. The ABC hypo

 Core: Biology


JoVE 11059

Attitude is our evaluation of a person, an idea, or an object. We have attitudes for many things ranging from products that we might pick up in the supermarket to people around the world to political policies. Typically, attitudes are favorable or unfavorable: positive or negative (Eagly & Chaiken, 1993). And, they have three components: an affective component…

 Core: Psychology

Self-Discrepancy Theory

JoVE 11041

One influential perspective on what motivates people's behavior is detailed in Tory Higgin's self-discrepancy theory (Higgins, 1987). He proposed that people hold disagreeing internal representations of themselves that lead to different emotional states.  

According to the self-discrepancy theory, people hold beliefs about what…

 Core: Psychology

RNA Stability

JoVE 11009

Intact DNA strands can be found in fossils, while scientists sometimes struggle to keep RNA intact under laboratory conditions. The structural variations between RNA and DNA underlie the differences in their stability and longevity. Because DNA is double-stranded, it is inherently more stable. The single-stranded structure of RNA is less stable but also more flexible and can form weak internal bonds. Additionally, most RNAs in the cell are relatively short, while DNA can be up to 250 million nucleotides long. RNA has a hydroxyl group on the second carbon of the ribose sugar, increasing the likelihood of breakage of the sugar-phosphate backbone. The cell can exploit the instability of RNA, regulating both its longevity and availability. More stable mRNAs will be available for translation for a longer period of time than less stable mRNAs transcripts. RNA binding proteins (RBPs) in cells play a key role in the regulation of RNA stability. RBPs can bind to a specific sequence (AUUUA) in the 3’ untranslated region (UTR) of mRNAs. Interestingly, the number of AUUUA repeats appears to recruit RBPs in a specific way: fewer repeats recruit stabilizing RBPs. Several, overlapping repeats result in the binding of destabilizing RBPs. All cells have enzymes called RNases that break down RNAs. Typically, the 5’cap and polyA tail protect eukaryotic mRNA from degradation

 Core: Biology

What is Cell Signaling?

JoVE 10985

Despite the protective membrane that separates a cell from the environment, cells need the ability to detect and respond to environmental changes. Additionally, cells often need to communicate with one another. Unicellular and multicellular organisms use a variety of cell signaling mechanisms to communicate to respond to the environment.

Cells respond to many types of information, often through receptor proteins positioned on the membrane. For example, skin cells respond to and transmit touch information, while photoreceptors in the retina can detect light. Most cells, however, have evolved to respond to chemical signals, including hormones, neurotransmitters, and many other types of signaling molecules. Cells can even coordinate different responses elicited by the same signaling molecule. Typically, cell signaling involves three steps: (1) reception of the signal, (2) signal transduction, and (3) a response. In most signal reception, a membrane-impermeable molecule, or ligand, causes a change in a membrane receptor; however, some signaling molecules, such as hormones, can traverse the membrane to reach their internal receptors. The membrane receptor can then send this signal to intracellular messengers, which transduces the message into a cellular response. This intracellular response may include a change transcription, translation, protein activation,

 Core: Biology

Parental Care

JoVE 10921

Many animals exhibit parental care behavior, including feeding, grooming, and protecting young offspring. Parental care is universal in mammals and birds, which often have young that are born relatively helpless. Several species of insects and fish, as well as some amphibians, also care for their young.

Parental care can occur even before hatching in birds, when parents sit on their eggs to incubate them. After hatching, the parents provide food for their offspring, and may continue to brood their young to keep them warm. Both male and female birds provide parental care, depending on the species. In marsupial mammals, such as kangaroos, the embryos are often born at a very early stage and then crawl into their mother’s pouch. Here, the mother nurses and protects her offspring—sometimes for many months—until it can function more independently. Placental mammals are born more developed than marsupials, but they still require a lot of care. Mammalian parental care is mostly provided by the mother, triggered by the hormones of pregnancy and birth and the necessity of lactation for providing nutrients. Nursing is an essential kind of mammalian parental care since the mother’s milk is the primary source of food for the young. Mammals also often lick their newborns and carry them around—grooming, protecting, and bonding wi

 Core: Biology

The Spinal Cord

JoVE 10872

The spinal cord is the body’s major nerve tract of the central nervous system, communicating afferent sensory information from the periphery to the brain and efferent motor information from the brain to the body. The human spinal cord extends from the hole at the base of the skull, or foramen magnum, to the level of the first or second lumbar vertebra.

The spinal cord is cylindrical and contains both white and grey matter. In the center is the central canal, which is the remnant of the lumen of the primitive neural tube and is part of the internal system of cerebrospinal fluid cavities. In cross-section, the grey matter surrounding the central canal appears butterfly-shaped. The wings of the butterfly are divided into dorsal and ventral horns. The dorsal horn contains sensory nuclei that relay sensory information, and the ventral horn contains motor neurons that give rise to the axons that innervate skeletal muscle. White matter surrounds the gray matter and contains large numbers of myelinated fibers. The white matter is arranged into longitudinal bundles called dorsal, lateral, and ventral columns. Three membranes surround the spinal cord: the pia adheres closely to the surface of the spinal cord, followed by the arachnoid, and the dura mater—the tough outermost sheath. The spinal cord is divided into four different r

 Core: Biology

Muscle Contraction

JoVE 10869


In skeletal muscles, acetylcholine is released by nerve terminals at the motor end plate—the point of synaptic communication between motor neurons and muscle fibers. Binding of acetylcholine to its receptors on the sarcolemma allows entry of sodium ions into the cell and triggers an action potential in the muscle cell. Thus, electrical signals from the brain are transmitted to the muscle. Subsequently, the enzyme acetylcholinesterase breaks down acetylcholine to prevent excessive muscle stimulation.   Individuals with the disorder myasthenia gravis, develop antibodies against the acetylcholine receptor. This prevents transmission of electrical signals between the motor neuron and muscle fiber and impairs skeletal muscle contraction. Myasthenia gravis is treated using drugs that inhibit acetylcholinesterase (allowing more opportunities for the neurotransmitter to stimulate the remaining receptors) or suppress the immune system (preventing the formation of antibodies). Unlike skeletal muscles, smooth muscles present in the walls of internal organs are innervated by the autonomic nervous system and undergo involuntary contractions. Contraction is mediated by the interaction between two filament proteins—actin and myosin. The interaction of actin and myosin is closely linked to intracellular calcium concentrat

 Core: Biology

What is the Skeletal System?

JoVE 10863

The adult human skeleton comprises 206 bones that are connected through cartilage, tendons, and ligaments. The skeleton provides a rigid framework for the human body, protects internal organs, and enables movement and locomotion. The human skeletal system consists of the axial and appendicular skeletons. Bone tissue is continuously built up and chewed away by specialized bone cells which are essential to overall health. Dysregulated bone cells and incorrect levels of chemical compounds in the blood lead to bone diseases. The axial skeleton consists of 80 bones and is divided into three regions: the skull, the vertebral column, and the rib cage. The upper portion of the skull—the cranium—consists of eight bones that enclose the brain, while the lower part consists of 14 bones. The vertebral column consists of 33 vertebrae: seven cervical, 12 thoracic, five lumbar, five fused sacral vertebrae, and four fused coccygeal vertebrae. The rib cage adds stability to the vertebral column and also protects the lungs and heart. It consists of 12 pairs of ribs, which attach to the thoracic vertebra via the costovertebral joint. The anterior portion of the rib cage attaches to the sternum—the flat bone at the center of the front of the chest—via the costal cartilages. The first seven ribs on each side are known as true ribs, as their cartilages

 Core: Biology
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