ARS | Publication request: Chapter 6: Physiology and Developmental Morphology

Submitted to: Warm Season Grasses
Publication Acceptance Date: October 20, 2003
Publication Date: August 20, 2004
Citation: Moore, K.J., Boote, K.J., Sanderson, M.A. 2004. Chapter 6: Physiology And Developmental Morphology. Warm Season GRASSES.37 P.

Interpretive Summary: Warm-season grasses, as defined in this chapter, are those species that initially fix atmospheric carbon dioxide into four carbon molecules. This is in contrast to other species where the initial photosynthetic reaction produces a three-carbon molecule. Because of their unique carbon metabolism, warm-season grasses are often referred to as C4 species. Warm-season (C4) species account for nearly one- half of the world's grass species and included among them are many important food and forage crops. The characteristics of physiological and morphological responses to defoliation have various implications for grazing and harvest management of warm-season grasses. Defoliation management concepts have shifted from solely emphasizing the role of organic reserves to recognition of the concept of morphological plasticity and the importance of maintaining active growing points on the plant that may capitalize on stored carbon and nitrogen and rapidly reestablish the plant canopy.

Technical Abstract: Many warm-season grasses are tropical and subtropical in origin. In these areas warm-season grasses account for more than two-thirds of grass species. In this chapter, we discuss the physiology and development of warm-season grasses. We focus on biochemical, physiological, and environmental aspects that are unique to warm-season grasses and that account for their adaptation to specific environments, and the morphology and development of warm-season grasses as well as their responses to defoliation. Warm-season grasses have the C4 photosynthetic pathway. Characteristics of the C4 plants include a radial cell arrangement known as Kranz anatomy, where mesophyll cells surround bundle sheath cells. There are unique complements of enzymes specific to each of these cell types. This unique physiology enables warm-season grasses to thrive under high temperatures and limited soil moisture. Developmental morphology of warm-season grasses includes the processes by which organs change in form and number and progress to a particular state. The processes occur during three broad phases: seedling, vegetative, and reproductive development. The seedling phase encompasses the time from germination until the plant is autotrophic. During the vegetative phase, the prophyll emerges and the apical meristem produces leaf primordia at regular intervals. Stem internodes differentiate but do not elongate. The final leaf number on a grass tiller is generally constant and the emergence and appearance of leaves is controlled primarily by temperature. Once an environmental signal is received, the apical meristem switches from producing leaf initials to reproductive primordia. The expression of reproductive structures requires the induction and initiation of the apical meristem. Induction puts the meristem in a state to respond to the initiation signal. Once induced, the meristem can then respond to changes in daylength, which results in the development of the inflorescence, along with seed formation.