Abstract
Phenylalanine ammonia-lyase (PAL) which is considered to be one of the main lines of cell acclimation against stress in plants, non-structural carbohydrates (NSC) accumulation and chlorophyll fluorescence parameters were quantified in two rice genotypes as a function of two temperature regimes: 22/30 °C (control) and 28/30 °C night/day (high night temperatures - HNT), imposed from heading to milk stage. The rice cultivars chosen were Nagina22 (N22) and BRS Querência (BRS-Quer), which are genotypes tolerant and sensitive to high temperatures, respectively. BRS-Quer genotype highlighted more sensitive responses maintaining higher PAL and peroxidase levels on seventh and twenty-first days after stress imposing. On the other hand, this genotype showed levels of fructose, glucose and sucrose decreasingly across stress period whether compared to N22. Both genotypes showed similarity for most of the chlorophyll fluorescence parameters. However, the photosynthesis induction curve highlighted that HNT caused decreases in some photochemical quenching of fluorescence as well as increases of non-phochemical quenching, affecting more prominently BRS-Quer genotype. N22 maintained unaltered the spikelet sterility and 1000-grain weight across temperature regimes showing a consistent trend with its stem NSC accumulation during stress period. The higher availability of soluble sugars shown by N22 at the end of stress period could be unloaded in spikelet formation and grain fillings contributing in their lower sterility rate and greater 1000-grain weight stability across the environments. These results indicate that selecting genotypes with higher capacity to stem NSC translocation beyond accumulation at HNT could lead to more grain yield stability in future climate scenarios.
Highlights
Abiotic and biotic stresses represent the major constraints that result in agricultural losses on the global scale and projected climate changes could increase their negative effects in the future (Brito et al, 2010, 2011, 2016; Diola et al, 2011, 2013; Weber et al, 2014; Guimarães et al, 2017)
Analysis of genotypes versus temperature regimes of the Phenylalanine ammonia-lyase (PAL) and peroxidase enzymes detected significant statistical interaction (P < 0.001) on seventh and twenty-first days after stress imposing. Both genotypes submitted to temperature regimes not shown significant differences in their peroxidase levels at control condition, except when submitted to HNT on seventy and twenty-first days after heading phase when BRS-Quer showed an increase of 80% and 21% for this enzyme, respectively (Figure 2)
Beyond other physiological approaches, PAL enzyme which catalyzes the first step of the phenylpropanoid was monitored on seventh and on twenty-first days after stress imposing in two contrasting rice genotypes for heat stress
Summary
Abiotic and biotic stresses represent the major constraints that result in agricultural losses on the global scale and projected climate changes could increase their negative effects in the future (Brito et al, 2010, 2011, 2016; Diola et al, 2011, 2013; Weber et al, 2014; Guimarães et al, 2017). Beyond of the predict impact of these extreme event on global population, remain unclear its influence on plant species distributions, productivity, carbon balance and physiological impact versus plant resilience capacity. In this sense, efforts and new strategies are imperative in the breeding program aiming to obtain new plant ideotypes for new climate scenarios. There is a consensus that in the future the high temperatures will become a bottleneck for crop yield and its stability In this way, projected climate changes could increase its negative effects in the future (Tian et al, 2015; Fan et al, 2016). Projected impact of climate change on crop yield has been extensively published in the last decade, yet are unexpressive studies that highlight the role of increase in nighttime temperatures on rice physiological response and, changes in the rice yield performance
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