The predicted increase in the frequency and magnitude of extreme heat spikes under future climate can reduce rice yields significantly. Rice sensitivity to high temperatures during the reproductive stage is well documented while the same during the vegetative stage is more speculative. Hence, to identify and characterize novel heat-tolerant donors for both the vegetative and reproductive stages, 71 rice accessions, including approximately 75% New Rice for Africa (NERICAs), were phenotyped across field experiments during summer seasons in Delhi, India, and in a controlled environment study at International Rice Research Institute, Philippines. NERICA-L-44 (NL-44) recorded high seedling survival (52%) and superior growth and greater reproductive success exposed to 42.2 ∘ C (SD ± 2.3) under field conditions. NL-44 and the heat-tolerant check N22 consistently displayed lower membrane damage and higher antioxidant enzymes activity across leaves and spikelets. NL-44 recorded 50-60% spikelet fertility, while N22 recorded 67-79% under controlled environment temperature of 38 ∘ C (SD±1.17), although both had about 87% fertility under extremely hot field conditions. N22 and NL-44, exposed to heat stress (38 ∘ C), had similar pollen germination percent and number of pollen tubes reaching the ovary. NL-44 maintained low hydrogen peroxide production and non-photochemical quenching (NPQ) with high photosynthesis while N22 avoided photosystem II damage through high NPQ under high-temperature stress. NL-44 with its reproductive stage resilience to extreme heat stress, better antioxidant scavenging ability in both vegetative tissue and spikelets and superior yield and grain quality is identified as a novel donor for increasing heat tolerance at both the vegetative and reproductive stages in rice.

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Wheat (Triticum aestivum L.) cv PBW 343 was grown in Hoagland solution devoid of nitrogen (-N) under two CO 2 levels viz. ambient (380 lL L -1 , AC) and elevated (600 ± 50 lL L -1 , EC) for 20 days in growth chambers. The rate of uptake, assimilation and accumulation of nitrate was compared. At lows nitrate concentration up to 0.5 mM, rate of nitrate uptake was higher in EC grown seedlings as compared to AC. Under non-limiting supply of external nitrate, the rate of uptake declined in EC grown seedlings. Nitrate reductase (NR) activity increased in EC grown seedlings at low external concentrations of nitrate. However, AC grown plants showed higher NR activity, but at very high concentrations of nitrate. EC grown plants showed low level of accumulation of nitrate in shoots under limited nitrate availability, indicating lower influx towards storage pool and more availability of nitrate in metabolic pool. Increasing nitrogen (N) fertilization therefore may not compensate for slower NO À 3 assimilation rates under EC, as uptake and assimilation both decline under nitrate sufficient conditions. Effective management practices and changes in the pattern of fertigation may be required in response to rising atmospheric CO 2 levels for wheat production.