The greater trichome number on abaxial surface compared with adaxial surface is likely to be important during the paraheliotropic leaflet movement characteristic to senna in which abaxial surfaces are exposed to sun, past midday under high temperatures.
Maintenance of high carbon gain and water use efficiency over a wide range of stress levels, drought-deciduousness with re-allocation of resources to apical leaves, plasticity of stomatal and trichome numbers on a given leaflet surface, densely deposited epicuticular wax, isobilateral leaf anatomy with large bundle sheath extensions, and paraheliotropic leaflet movement are important in this regard.
The leaf responses measured included rolling, paraheliotropic movements, increase in reflectance and induction of Crassulacean acid metabolism (CAM).
Frequent responses of plants to drought include leaf rolling, paraheliotropic movements and increase in leaf reflectance (Begg, 1980; Ehleringer, 1980).
Under drought, leaves have a paraheliotropic movement whereby their angle relative to the horizontal plane increases with drought; also, they appear more reflective and the lamina rolls about its margins onto the abaxial surface.
latifolius would contract inwardly in a paraheliotropic fashion, thus minimizing leaf temperature and water loss.
These reductions in photosynthetic activity were accentuated by the paraheliotropic leaf movements of L.
Paraheliotropic leaf movements in Sirartro as a protective mechanism against drought-induced damage to primary photosynthetic reactions: damage by excessive light and heat: Planta 161:505-518.