Localization and Pattern of Graviresponse across the Pulvinus of Barley Hordeum vulgare

Abstract

Pulvini of excised stem segments from barley (Hordeum vulgare cv 'Larker') were pretreated with 1 millimolar coumarin before gravistimulation to reduce longitudinal cell expansion and exaggerate radial cell enlargement. The cellular localization and pattern of graviresponse across individual pulvini were then evaluated by cuffing the organ in cross-section, photographing the cross-section, and then measuring pulvinus thickness and the radial width of cortical and epidermal cells in enlargements of the photomicrographs. With respect to orientation during gravistimulation, we designated the uppermost point of the crosssection 0°and the lowermost point 1800. A gravity-induced increase in pulvinus thickness was observable within 400 of the vertical in coumann-treated pulvini. In upper halves of coumarintreated gravistimulated pulvini, cells in the inner cortex and inner epidermis had increased radial widths, relative to untreated gravistimulated pulvini. In lower halves of coumarin-treated pulvini, cells in the central and outer cortex and in the outer epidermis showed the greatest increase in radial width. Cells comprising the vascular bundles also increased in radial width, with this pattem following that of the central cortex. These results indicate (a) that all cell types are capable of showing a graviresponse, (b) that the graviresponse occurs in both the top and the bottom of the responding organ, and (c) that the magnitude of the response increases approximately linearly from the uppermost point to the lowermost. These results are also consistent with models of gravitropism that link the pattern and magnitude of the graviresponse to graviperception via statolith sedimentation.

Several aspects on the plant growth and development in space environment. Effect of simulated microgravity on auxin polar transport in inflorescence axis of Arabidopsis thaliana.

“…The activity of auxin polar transport across gravistimulated roots of maize was enhanced by the addition of calcium (Lee and Evans 1985). Moreover, there was differential sensitivity to IAA and gibberellic acid during gravistimulation of the leaf-sheath pulvini of oat and barley (Brock et al, 1994). The contents of IAA as well as ABA in maize seedlings grown under microgravity condition, however, were no different from those grown in normal gravity (Schulze et al 1992).…”

Molecular basis underlying rice tiller angle: Current progress and future perspectives

“…ules (Sack, 1997). Sedimented amyloplasts have been observed in some shoot tissues, including the coleoptiles and pulvinus (an enlarged section at the base of a leaf stalk in some plants) of monocots and the hypocotyls and inflorescence stems of dicots (Brock et al, 1989;Dayanandan et al, 1977;Fujihira et al, 2000;Fukaki et al, 1998;Morita and Tasaka, 2004;Sack and Leopold, 1985). In Arabidopsis hypocotyls and inflorescence stems, a single layer of endodermal cells was shown to be responsible for sensing gravity (Fukaki et al, 1998).…”

Gravity sensing and responses in the coordination of the shoot gravitropic setpoint angle

“…Sedimentable amyloplasts are observed in several shoot tissues, including the bundle sheaths and cells of the inner cortex in hypocotyls, the inflorescence stems of dicots, and the coleoptiles and leaf sheath pulvinus of monocots (Brock et al ., 1989; Hart, 1990). In Arabidopsis , the gravity‐sensing tissue in shoots has been identified as the endodermis (Fukaki et al ., 1996, 1998; Fig.…”