Limiting factors for panicle photosynthesis at the anthesis and grain filling stages in rice (Oryza sativa L.)

Abstract

SUMMARY Panicle photosynthesis is crucial for grain yield in cereal crops; however, the limiting factors for panicle photosynthesis are poorly understood, greatly impeding improvement in this trait. In the present study, pot experiments were conducted to investigate the limiting factors for panicle photosynthesis at the anthesis stage in seven rice genotypes and to examine the temporal variations in photosynthesis during the grain filling stage in the Liangyou 287 genotype. At the anthesis stage, leaf and panicle photosynthesis was positively correlated with stomatal conductance and maximum carboxylation rate, which were in turn associated with hydraulic conductance and nitrogen content, respectively. Panicle hydraulic conductance was positively correlated with the area of bundle sheaths in the panicle neck. During grain filling, leaf and panicle photosynthesis remained constant at the early stage but dramatically decreased from 8 to 9 days after anthesis. The trends of variations in panicle photosynthesis were consistent with those in stomatal conductance but not with those in maximum carboxylation rate. At first, the maximum carboxylation rate and respiration rate in the panicle increased, through elevated panicle nitrogen content, but then drastically decreased, as a result of dehydration. The present study systematically investigated the limiting factors for panicle photosynthesis, which are vital for improving photosynthesis and crop yield.

Photosynthesis – beyond the leaf

“…the seeds), due to longer CO 2 diffusion pathways and reduced light penetration (Henry et al, 2020;Simkin et al, 2020). Higher rates of respiration in panicles compared with leaves (Chang et al, 2020) suggest a substantial New Phytologist (2023) www.newphytologist.com contribution of respiratory CO 2 to photosynthesis (Sanchez-Bragado et al, 2020;Zhang et al, 2022) in these tissues, with reports of between 55% and 75% of respired CO 2 refixed in wheat and barley (Bort et al, 1996).…”

“…This hypothesis is supported by a recent study by Zhang et al . (2022) who explored control of photosynthesis in rice panicles at different stages of crop development and reported that at anthesis, panicle photosynthesis was dependent on both g s and biochemical function, and there was a positive correlation between g s and A . However, at grain filling, g s declined and net photosynthesis was correlated with g s rather than the carboxylation capacity of Rubisco ( Vc max ), indicating that A was primarily determined by stomatal behaviour.…”

“…This suggests that there is a possible switch between atmospheric CO 2 being the main supply for photosynthesis earlier in the season supported by higher g s , which switches to respiratory supply later in development, concurrent with a decrease in g s . At the same time, biochemical changes support refixation of respired CO 2 (Zhang et al ., 2022). However, changes in panicle g s could also be due to shifts in the osmotic and water status of the panicle.…”

“…However, to date, the majority of these studies have focused on leaves, and few have considered the contribution from other tissues (Simkin et al ., 2020). Green tissues other than leaves, including stems (Simkin et al ., 2020), ears/panicles (Maydup et al ., 2014; Rivera‐Amado et al ., 2020; Zhang et al ., 2022), green floral organs (Bertolino et al ., 2022), pods (Wang et al ., 2016) and fruit (Simkin et al ., 2020), have been reported to photosynthesize and contribute to varying degrees and to overall plant carbon gain. Wheat and rice panicles, which a large proportion of studies have focused on, have been reported to have high photosynthetic capacities (Brazel & Ó'Maoiléidigh, 2019; Chang et al ., 2020; Sanchez‐Bragado et al ., 2020), with panicle and ear photosynthesis reported to contribute between 10% and 60% to yield (Hu et al ., 2019) and spike photosynthesis positively correlated with yield (Molero & Reynolds, 2020).…”

Green Manure Amendment in Paddies Improves Soil Carbon Sequestration but Cannot Substitute the Critical Role of N Fertilizer in Rice Production

“…The seasonal precipitation between trial years is expected to be responsible for the difference of grain yield [38]. It has been proved that the ability of photosynthesis to synthesize carbohydrates after anthesis is a crucial factor affecting rice yield [20,39]. In this context, high-frequency precipitation after anthesis in 2020 (Figure 1) could reduce rice yield by affecting photosynthesis.…”