Leaf movements and photoinhibition in relation to water stress in field-grown beans

Abstract

Photoinhibition in plants depends on the extent of light energy being absorbed in excess of what can be used in photochemistry and is expected to increase as environmental constraints limit CO2 assimilation. Water stress induces the closure of stomata, limiting carbon availability at the carboxylation sites in the chloroplasts and, therefore, resulting in an excessive excitation of the photosynthetic apparatus, particularly photosystem II (PSII). Mechanisms have evolved in plants in order to protect against photoinhibition, such as non-photochemical energy dissipation, chlorophyll concentration changes, chloroplast movements, increases in the capacity for scavenging the active oxygen species, and leaf movement or paraheliotropism, avoiding direct exposure to sun. In beans (Phaseolus vulgaris L.), paraheliotropism seems to be an important feature of the plant to avoid photoinhibition. The extent of the leaf movement is increased as the water potential drops, reducing light interception and maintaining a high proportion of open PSII reaction centres. Photoinhibition in water-stressed beans, measured as the capacity to recover F(v)/F(m), is not higher than in well-watered plants and leaf temperature is maintained below the ambient, despite the closure of stomata. Bean leaves restrained from moving, increase leaf temperature and reduce qP, the content of D1 protein and the capacity to recover F(v)/F(m) after dark adaptation, the extent of such changes being higher in water-stressed plants. Data are presented suggesting that even though protective under water stress, paraheliotropism, by reducing light interception, affects the capacity to maintain high CO2 assimilation rates throughout the day in well-watered plants.

Photosynthetic analyses of two native Atlantic Forest species in regenerative understory of eucalyptus plantation

“…These data are corroborated by the significant decrease in the quantum yield of the PSII (F v /F m ) in the EXU during the dry period, which also indicates that the plants have responded to the effects of water stress (Baker, 1993). The relationship between the water deficit and the enhancement of photoinhibition was reported by several authors (Alves et al, 2002, Pastenes et al, 2005, Zhou et al, 2007.…”

Photochemical Efficiency during the Establishment and Consolidation Phases of in Vitro Pinus radiata Micrograft Made from Scions of Different Ontogenetic Age

“…Only during the first day of in vitro introduction, a decrease in Fv/Fm was observed in basal scions (P = 0.01; Figure 3). Such small Fv/Fm reduction could be attributable to the physiological stress imposed by the excision from ortet, and then the in vitro introduction [39] [40]. Despite this, we find a fast scions Fv/Fm recovery, due to the in vitro culture conditions, which also exert the surpass of Fv/Fm values measured in the ortet Figure 2.…”

Alteration of photosynthetic pigments and antioxidant systems in tomato under drought with Tebuconazole and Hexaconazole applications

“…The chl-a, chl-b and total chlorophyll content of the drought treated tomato plant was decreased when compared to control plant. Photooxidation may be the potential reason for reduced leaf pigments under water limited conditions (Ahmedi et al, 2009) and which in turn enables the plants to minimize the light absorption by chloroplasts (Pastenes et al, 2005). The triazole treated plant increased the photosynthetic pigments but it was lower than that of control.…”