Rice (Oryza sativa L.) is an important food crop relied upon by billions of people worldwide. However, with increasing pressure from climate change and rapid population growth, cultivation is very water-intensive. Therefore, it is critical to produce rice that is high-yielding and genetically more water-use efficient. Here, using the stabilized fast-neutron mutagenized population of Jao Hom Nin (JHN) - a popular purple rice cultivar - we microscopically examined hundreds of flag leaves to identify four stomatal model mutants with either high density (HD) or low density (LD) stomata, and small-sized (SS) or large-sized (LS) stomata. With similar genetic background and uniformity, the stomatal model mutants were used to understand the role of stomatal variants on physiological responses to abiotic stress. Our results show that SS and HD respond better to increasing CO2 concentration and HD has higher stomatal conductance (gs) compared to the other stomatal model mutants, although the effects on gas exchange or overall plant performance were small under greenhouse conditions. In addition, the results of our drought experiments suggest that LD and SS can better adapt to restricted water conditions, and LD showed higher water use efficiency (WUE) and biomass/plant than other stomatal model mutants under long-term restricted water treatment. Finally, our study suggests that reducing stomata density and size may play a promising role for further work on developing a climate-ready rice variety to adapt to drought and heat stress. We propose that low stomata density and small size have high potential as genetic donors for improving WUE in climate-ready rice.

Biochemical and physiological traits of two soybean [Glycine max (L.) Merr.] genotypes differing in sensitivity to ozone (O3 ) were investigated to determine the possible basis for the differential response. Fiskeby III (O3 -tolerant) and Mandarin (Ottawa) (O3 -sensitive) were grown in a greenhouse with charcoal-filtered air for 4 weeks, then treated with O3 for 7 h·day(-1) in greenhouse chambers. Mandarin (Ottawa) showed significantly more leaf injury and hydrogen peroxide (H2 O2 ) and superoxide (O2 (-) ) production compared with Fiskeby III. Peroxidase activity in Mandarin (Ottawa) was 31% higher with O3 but was not significantly different in Fiskeby III. Ozone did not affect superoxide dismutase or glutathione reductase activities, or leaf concentrations of glutathione or ascorbic acid. Thus, variation in O3 response between Fiskeby III and Mandarin (Ottawa) was not explained by differences in antioxidant enzymes and metabolites tested. Ethylene emission from leaves declined in Fiskeby III following O3 exposure but not in Mandarin (Ottawa). Ozone exposure reduced quantum yield (ΦPSII ), electron transport rate (ETR) and photochemical quenching (qp ) in Mandarin (Ottawa) more than in Fiskeby III, indicating that efficiency of energy conversion of PSII and photosynthetic electron transport was altered differently in the two genotypes. Short-term exposure to O3 had minimal effects on net carbon exchange rates of both soybean cultivars. A trend toward higher stomatal conductance in Mandarin (Ottawa) suggested stomatal exclusion might contribute to differential O3 sensitivity of the two genotypes. Increased sensitivity of Mandarin (Ottawa) to O3 was associated with higher H2 O2 and O2 (-) production compared with Fiskeby III, possibly associated with genotype differences in stomatal function or regulation of ethylene during the initial phases of O3 response.

Drought is a major constraint in rainfed rice production and root architectural traits are important breeding targets for improving productivity under drought stress. A set of chromosome segment substitution lines (KDML105-CSSLs) and KDML105 were grown in the wet season at two sites (Rice Gene Discovery (RGD) and Ubon Ratchatani Rice Research Center (URRC)) in Thailand under wellwatered (WW) and drought stress (DS) treatments. RGD is characterized by having a heavy clay soil type while URRC's soil has a high percentage of sand and characterized by infertility. Root architecture traits varied within the population at both sites and exhibited plasticity in response to drought as affected by location by water regime interaction. Lateral root density increased by 77% with drought at RGD but decreased by 18% at URRC. The proportion of nodal roots that elongated more vertically increased under drought stress by 21%, at RGD. Root number per tiller was negatively associated with tiller number and biomass at RGD under drought, while lateral root density was negatively associated with biomass under drought at URRC. Eight QTL were identified for the number of nodal roots per tiller, lateral root density, and nodal root growth angle. Several candidate genes were identified by annotating the genes within the QTL regions. Our study presented genetic insights into root architectural traits with potential use in rice breeding programs for drought tolerance.

Gas-phase hydrogen peroxide (H 2 O 2 ) is very harmful to plants when combined with ozone (O 3 ). Information on ambient H 2 O 2 concentrations, especially for long durations, is limited not only in Thailand and South East Asia but also in Japan. The objective of the present research was to accumulate data of H 2 O 2 concentrations over long durations in Tokyo and Thailand. Hydrogen peroxide concentrations were monitored at

Lowland and upland rice are the two most important rice ecotypes and are grown under different ecosystems of contrasting soil water conditions. The study aimed to characterize root morphological, anatomical, and architectural traits and shoot physiological traits related to agronomic traits in Myanmar lowland and upland rice under drought conditions. Drought experiments were conducted in the field and in the greenhouse. The reduction in root traits under drought was observed in both lowland and upland rice except for the stele and xylem area. Stele area and xylem area were increased under drought in lowland rice while stele area in upland rice was decreased and was not changed in the xylem area. A positive relationship between agronomic traits and root traits of lowland rice was observed including the total number of nodal roots, root number per tiller, and a negative relationship in lateral root density more than anatomical traits. While upland rice illustrated the relationship between root anatomical traits and agronomic traits. In addition, a negative contribution to biomass by photosynthesis rate, stomatal conductance, and transpiration rate was observed in lowland and upland rice. These findings can help improve drought tolerance in rice by selecting the optimal root trait for each rice ecosystem.