Light‐driven leaf movements^*

Abstract

Abstract. Mature leaves of many plants re‐orientate their laminae photonastically in response to non‐directional light signals, and/or phototropically in response to directional light signals, by flexing of pulvini, most commonly subtending their bases. Physiological and structural specializations of the pulvinus enable it to flex, by rapidly undergoing differential and repeatedly reversible axial volume changes (expansion/contraction) in opposite sectors of its motor tissue. Light‐driven leaf movements are adaptations that contribute to the efficiency of the photosynthetic apparatus in the leaf. The phototropic response maximizes the harvesting of photosynthetically radiant energy. The photonastic response to dark‐to‐light transitions increases the interception of light by unfolding the lamina. Another photonastic response modulates the interception of radiant energy by the lamina, allowing it to evade damage by light in excess of its photosynthetic capacity when the leaf is under stress. The same unidentified blue‐absorbing pigment system appears to be involved in all these responses. Non‐directional light signals are perceived in the pulvinus. Perception of directional light signals may be localized in other parts of the leaf in different plants: for example, the pulvinus in most leguminous species, and the lamina in malvaceous and at least one leguminous species. The perception of non‐directional and directional light signals, their transduction to differential volume changes in the target cells, and their transmission between the two where the sites are separate, are discussed.

Nonphotochemical Chlorophyll Fluorescence Quenching: Mechanism and Effectiveness in Protecting Plants from Photodamage

“…There are adaptations to control light absorption capacity as well as adaptations that deal with the light energy that has already been captured (Chow et al, 1988;Koller, 1990;Ruban, 2009;Cazzaniga et al, 2013;Xu et al, 2015a). At the molecular level, there is both long-term (acclimation) and short-term (regulatory mechanisms) control of the input of light energy into reaction centers.…”

Petiole twisting in the crowns of Psychotria limonensis: implications for light interception and daily carbon gain

“…This example may be more extreme than the case for the much shorter petioles of P. limonensis but it is possible that some potential for extension remained at the time of reorientation. Except for diurnal leaf movements, which involve a reversible swelling or shrinking of a pulvinus (Koller 1990), other phototropic responses occur in growing organs. Blue light-mediated phototropic bending of stems is caused by an inhibition of growth on the shaded compared to the illuminated side, with little or no net effect on overall growth, leading to a bending towards the light source.…”

“…At the plant crown level the pattern of self-shading as determined by the spatial arrangement of the leaves is an additional determinant of light capture and photosynthesis. Diurnal solar tracking and solar avoidance movements have been reported for a large number of species in open habitats (Ehleringer and Forseth 1980;Forseth and Ehleringer 1983;Kao and Forseth 1992;Koller 1990). These studies have focused on individual leaves with little consideration of the impact of these reorientations on the performance of whole plant crowns.…”

Morphing in nature and beyond: a review of natural and synthetic shape-changing materials and mechanisms

“…The pulvinus, an organ found at the base of leaves and inside the stem, consists of internal cells that swell and contract [88]. This enables plants to track the sun with leaves or flowers, and modulate their temperatures and rates of photosynthesis.…”