Phenylalanine Ammonia-Lyase and Source-Flow-Sink Related Attributes in Rice Genotypes Subjected to High Night Temperatures

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.

Physiological and molecular attributes contribute to high night temperature tolerance in cereals

“…An outstanding HNT-tolerant rice cultivar, already identified as heat tolerant before (Jagadish et al, 2010), is N22, without any grain yield reduction after HNT exposure from panicle initiation to physiological maturity, compared to yield reductions of 16% and 9% for a susceptible and a high yielding cultivar, respectively (Bahuguna et al, 2017). N22 was also identified in other studies as highly HNTtolerant (Moura et al, 2017;Shi et al, 2013;Wu et al, 2017;Zhang et al, 2013). Furthermore, the rice genotypes PSBRc52, Swarna and IR8 were described as HNT-tolerant in the field (Zhang et al, 2013), while IR72, Nipponbare, Taipei 309 and LC-93-4 were HNT-tolerant in the vegetative stage in controlled chamber experiments (Glaubitz et al, 2014).…”

“…The increase under HNT suggests that the synthesis of secondary metabolites is activated. An in‐depth analysis of the PAL activity in rice leaves revealed stable enzyme activity in the tolerant cultivar N22 for control and HNT conditions, while for a sensitive cultivar an up‐regulation was only reported under HNT (Moura et al, 2017).…”

“…Pre‐adaptation mechanisms inherent under control conditions could play a role for a better performance at HNT, for example, PAL activity in leaves was stable at higher levels under control and HNT conditions in N22, whereas increased activity was only reported under HNT in a sensitive cultivar (Moura et al, 2017). Furthermore, N22 kept N‐translocation constant under HNT in comparison to a reduced N‐supply in sensitive cultivars (Shi et al, 2013).…”

Molecular and biochemical responses of horticultural plants and crops to heat stress

“…The activity of phenylalanine ammonia lyase is affected by many factors, whether biotic or abiotic such as light, temperature, plant hormones, inhibitors for RNA and protein biosynthesis, drought and mineral nutrition. It is proclaimed that low and high temperatures cause to produce soluble phenolics and hence increasing phenylalanine ammonia lyase activity (Moura et al, 2017). This enzyme stimulates the transformation of L-Phenyalanine into trans-cinnamic acid (by deamination reaction), which is the main go-between in the synthesis of phenolics (Rivero et al, 2001).…”

Cold Tolerance in Rice Plants: Phenotyping Procedures for Physiological Breeding

“…In this way, add to challenges associated to feed more than nine billions people in the next decades (Jacquemin et al, 2013;Fan et al, 2014), an additional question is related to how to supply the food crescent demand for world growth population in face of increasingly uncertainties about climate stability; which could lead to change of rain regime, besides of increases in frequency of heat and cold waves as predicted to be increasingly common in next decades. In this sense, abiotic and biotic stresses are the major constraints for agricultural productivity on the global scale and projected climate changes could increase their negative effects in the future (Brito et al, 2010Diola et al, 2011;Diola et al, 2013;Weber et al, 2014;Brito et al, 2016;Guimarães et al, 2017;Lisei-de-Sa et al, 2017;Moura et al, 2017a;Moura et al, 2017b) and its increasingly frequency of occurrence will probably influence the plant species distributions, productivity, carbon balance and negatively impacting on physiological resilience capacity of plants in a specific environment. Thus, is imperative to consider that the major challenge is how to overcome this barriers increasing rice production using less land, water, chemicals, and labor; additionally, considering the need to conserve the environmental and natural resources of degradation.…”