Regulation of the photosynthetic electron transport and specific photoprotective mechanisms in Ricinus communis under drought and recovery

Abstract

Ricinus communis is one of the major commercial non-edible oilseed crops grown in semiarid and arid environments worldwide and is reported as a drought tolerant species. Surprisingly, little is known about the mechanisms achieving this tolerance, especially in relation to photoprotection. The aim of this study was to analyze the association of the regulation of the photosynthetic electron transport and photoprotective mechanisms with drought tolerance in R. communis. Drought induced decreases in the relative water content, water potential and growth in R. communis exposed to 9 days of drought. After 6 days of rehydration, these parameters were completely recovered, demonstrating a potential of drought tolerance in this species. In addition, drought inhibited photosynthesis by stomatal and metabolic limitations (V cmax , J max , and Rubisco activity), with partial recovery after rehydration. Leaves displayed transient photoinhibition after 6 days of drought, which was completely recovered after 6 days of dehydration. The effective quantum yields and the electron transport rates of PSII and PSI were modulated to face drought avoiding the excess energy produced by decreases in CO 2 assimilation. NPQ was increased during drought, and it was maintained higher than control after the recovery treatment. In addition, the estimated cyclic electron flow was induced under drought and decreased after recovery. Photorespiration was also increased under drought and maintained at higher levels after the recovery treatment. Furthermore, antioxidative enzymes activities (SOD, APX, and CAT) were increased under drought to avoid ROS harmful effects. Altogether, we clearly showed that the modulation of photoprotective mechanisms and antioxidant enzymes are crucial to this species under drought. The implication of these strikingly strategies to drought tolerance is discussed in relation to agricultural and natural systems.

Mycorrhizal fungi reduce the photosystem damage caused by drought stress on Paris polyphylla var. yunnanensis

“…Leaf water content is an important indicator of plant exposure to drought stress, and drought stress in wheat leaves leads to a decrease in leaf water content, resulting in stomatal closure and growth arrest [20]. However, AMF inoculation contributed to the increase in water content of drought plants [21], a result similar to our experiments.AMF can enhance the water use e ciency of plants, as well as alter the content of osmotic substances in plant cells, thus helping plants to resist drought stress [22].…”

Effects of drought at different periods of wheat development on the leaf photosynthetic apparatus and productivity

“…A decrease in CO 2 input into the leaf due to stomata closure under drought inhibits Calvin cycle functioning, which reduces the use of primary products of photosynthesis -ATP and NADP•Н 2 and leads to the superreduction of ETC components (Ehonen et al, 2019). This induces the electrons from ETC to reduce molecular oxygen to its reactive species (ROS), primarily superoxide radical anions (Mehler reaction) (Neto et al, 2017). Oxygen superoxide radical anions are the source of the formation of hydroxyl radicals and hydrogen peroxide.…”

“…Yield losses under drought are associated with a decline in functional activity of photosynthetic apparatus in consequence of stomata closure and a decrease in leaf conductivity for CO 2 (Pinheiro & Chaves, 2011). In bright sunlight under water stress, when the rate of CO 2 assimilation in leaves is inhibited, there is a risk of oxidative damage to photosynthetic membranes by reactive oxygen species (ROS), which are formed through the accumulation of excess electrons in the electron transport chain (ETC) of chloroplasts and molecular oxygen reduction (Sade et al, 2011;Neto et al, 2017). The most important systems for photosynthetic apparatus protection from oxidative stress caused by ROS are antioxidant enzymes in chloroplasts (Singh et al, 2012;Caverzan et al, 2016).…”

Effect of drought on photosynthetic apparatus, activity of antioxidant enzymes, and productivity of modern winter wheat varieties

“…This is especially important under drought, when stomata are closed to reduce water loss, but CO 2 assimilation is inhibited due to decreased stomatal conductivity. This lowers the use of reducing and energy equivalents in the Calvin cycle, and leads to superreduction of the ETC components, which in turn increases the risk of photodestruction of its structures (Neto et al, 2017). Therefore, photorespiration, reducing the ETC "tension" and supplying CO 2 in the leaf, supports the functional state of the photosynthetic apparatus under stress conditions and protects it from damage.…”