Post‐flowering night respiration and altered sink activity account for high night temperature‐induced grain yield and quality loss in rice (Oryza sativaL.)

Abstract

High night temperature (HNT) is a major constraint to sustaining global rice production under future climate. Physiological and biochemical mechanisms were elucidated for HNT-induced grain yield and quality loss in rice. Contrasting rice cultivars (N22, tolerant; Gharib, susceptible; IR64, high yielding with superior grain quality) were tested under control (23°C) and HNT (29°C) using unique field-based tents from panicle initiation till physiological maturity. HNT affected 1000 grain weight, grain yield, grain chalk and amylose content in Gharib and IR64. HNT increased night respiration (Rn) accounted for higher carbon losses during post-flowering phase. Gharib and IR64 recorded 16 and 9% yield reduction with a 63 and 35% increase in average post-flowering Rn under HNT, respectively. HNT altered sugar accumulation in the rachis and spikelets across the cultivars with Gharib and IR64 recording higher sugar accumulation in the rachis. HNT reduced panicle starch content in Gharib (22%) and IR64 (11%) at physiological maturity, but not in the tolerant N22. At the enzymatic level, HNT reduced sink strength with lower cell wall invertase and sucrose synthase activity in Gharib and IR64, which affected starch accumulation in the developing grain, thereby reducing grain weight and quality. Interestingly, N22 recorded lower Rn-mediated carbon losses and minimum impact on sink strength under HNT. Mechanistic responses identified will facilitate crop models to precisely estimate HNT-induced damage under future warming scenarios.

Carbon balance and source‐sink metabolic changes in winter wheat exposed to high night‐time temperature

“…Contrary to photosynthesis, an increase in night respiration indicates significantly higher carbon loss to maintain metabolic functions upon HNT exposure (Figures and ). A similar phenomenon has been documented in rice exposed to HNT under field conditions (Bahuguna et al, ). Night respiration is known to increase exponentially with temperature (Penning de Vries, Witlage, & Kremer, ).…”

High night temperature induced changes in grain starch metabolism alters starch, protein, and lipid accumulation in winter wheat

“…The negative impact of HNT on grain width was 2‐fold higher compared with grain length (Figure ), with a similar response recorded in field grown rice (Bahuguna et al, ; Shi et al, ). Premature termination of starch synthesis and deposition has been documented with post‐flowering high day temperature (>30°C) stress (Bhuller & Jenner, ; Hurkman et al, ).…”

“…To further complicate the scenario, different enzymes involved in grain starch metabolism, including sucrose synthase and starch synthase (SS), are sensitive to temperature changes and play a role in altering the final starch and protein ratio in the wheat grain. Impact of HNT affecting the enzymatic processes involved in grain starch metabolism has been documented in field grown rice (Bahuguna, Solis, Shi, & Jagadish, ). Similarly, in wheat, heat stress‐induced reduction in starch accumulation has been attributed to reduction in SS and adenosine diphosphate (ADP)‐glucose pyrophosphorylase in the endosperm (Hawker & Jenner, ; Hurkman et al, ).…”

Molecular and physiological responses during thermal acclimation of leaf photosynthesis and respiration in rice

“…Past studies on rice conducted during the vegetative (Glaubitz et al, ; Kurimoto, Day, Lambers, & Noguchi, ) and reproductive (Bahuguna, Solis, Shi, & Jagadish, ; Mohammed, Cothren, & Tarpley, ) phases of development have reported limited and variable levels of acclimation of R dark . By contrast, A n of rice shows strong thermal acclimation, with rates of net CO 2 uptake measured at the prevailing growth T being homoeostatic or increasing as growth T is increased from 15°C to 37°C (Nagai & Makino, ; Yamori, Noguchi, Hikosaka, & Terashima, ).…”