Learning Objectives During the 1930s Japanese scientists isolated a growth-promoting substance from cultures of a fungus that parasitizes rice plants. They called it gibberellin. Gibberellins (GAs) are a group of about 125 closely related plant hormones synthesized in the root and stem apical…
Learning Objective Identify the locations of synthesis, transport, and actions of cytokinins. Cytokinins are plant hormones that promote cytokinesis (cell division) are derivatives of the purine adenine. (They are not to be confused with cytokines.) The effect of cytokinins was first reported…
Learning Objectives The term auxin is derived from the Greek word auxein, which means “to grow.” While many synthetic auxins are used as herbicides, indole-3-acetic acid (IAA) is the only naturally occurring auxin that shows physiological activity (Figure ). Auxin is synthesized in apical…
Learning Objectives A plant’s sensory response to external stimuli relies on chemical messengers (hormones). Plant hormones affect all aspects of plant life, from flowering to fruit setting and maturation (Figure , and from phototropism to leaf fall. Just as in animals,…
Essential elements are indispensable elements for plant growth. Plants can absorb mineral nutrients and water through their root system, and carbon dioxide from the atmosphere. Mineral nutrients are divided into macronutrients and micronutrients. The macronutrients plants require are nitrogen, potassium, calcium, magnesium, phosphorus, sulfur, and…
Learning Objectives Nutrient cycles, also known as biogeochemical cycles, describe the movement of chemical elements through different media, such as the atmosphere, soil, rocks, bodies of water, and organisms. Nutrient cycles keep essential elements available to plants and other organisms. The…
Learning Objectives Plants obtain mineral nutrients from the soil, which serves as a natural medium for land plants. Soil is the outer loose layer that covers the surface of Earth. Soil quality is a major determinant, along with climate, of plant distribution…
Learning Objectives Plants are unique organisms that can absorb nutrients and water through their root system, as well as carbon dioxide from the atmosphere. Soil quality and climate are the major determinants of plant distribution and growth. The combination of…
Cucurbitaceae is a family of plants first cultivated in Mesoamerica, although several species are native to North America (Figure ). The family includes many edible species, such as squash and pumpkin, as well as inedible gourds. In order to grow and…
Plants respond to light, gravity, water, physical contact, temperature, and other environmental factors. Tropisms are a response involve directional growth toward or away from a stimulus. Positive phototropism in stems is mediated by blue-light receptors called photoreceptors and an auxin gradient. Positive gravitropism in roots and negative gravitropism in shoots involves specialized amyloplasts called statoliths as…