Abstract
Stress-adaptive cell plasticity in target tissues and cells for plant biomass growth is important for yield stability. In vitro systems with reproducible cell plasticity can help to identify relevant metabolic and molecular events during early cell reprogramming. In carrot, regulation of the central root meristem is a critical target for yield-determining secondary growth. Calorespirometry, a tool previously identified as promising for predictive growth phenotyping has been applied to measure the respiration rate in carrot meristem. In a carrot primary culture system (PCS), this tool allowed identifying an early peak related with structural biomass formation during lag phase of growth, around the 4th day of culture. In the present study, we report a dynamic and correlated expression of carrot AOX genes (DcAOX1 and DcAOX2a) during PCS lag phase and during exponential growth. Both genes showed an increase in transcript levels until 36 h after explant inoculation, and a subsequent down-regulation, before the initiation of exponential growth. In PCS growing at two different temperatures (21°C and 28°C), DcAOX1 was also found to be more expressed in the highest temperature. DcAOX genes’ were further explored in a plant pot experiment in response to chilling, which confirmed the early AOX transcript increase prior to the induction of a specific anti-freezing gene. Our findings point to DcAOX1 and DcAOX2a as being reasonable candidates for functional marker development related to early cell reprogramming. While the genomic sequence of DcAOX2a was previously described, we characterize here the complete genomic sequence of DcAOX1.
Highlights
Plant breeding makes use of in vitro systems for plant propagation, but these systems are ideal to isolate scientific questions related to stress responsiveness for later up-scaling of the knowledge to plant level
In PCS1 and PCS4 grown at 21◦C the peak on Rstruct_biomass is reached at day 7, since the speed of increase is slower
Previous studies in Primary Culture System (PCS) demonstrated that callus growth was significantly increased at 28◦C compared to 21◦C (Arnholdt-Schmitt, 1999), and our results showed that D. carota AOX1 (DcAOX1) responded to a higher growing temperature in the exponential phase of the PCS
Summary
Plant breeding makes use of in vitro systems for plant propagation, but these systems are ideal to isolate scientific questions related to stress responsiveness for later up-scaling of the knowledge to plant level. Phenotypic variability shown in in vitro culture systems is due to high genotype dependence, going from species level to the level of cultivar/variety and individual genotypes It can vary between organs/tissues and developmental stages (Cardoso et al, 2010 and references therein). This variability in response, known as in vitro recalcitrance, could be described as varying capacity for plant cells to adapt to new environmental conditions, i.e., the capacity to develop and express new cell programs. This general capacity is important at plant level when environmental conditions are changing. Efficient marker systems and reliable screening tools that can assist in identifying and selecting superior robust genotypes with differential adaptive plasticity are still important bottlenecks (Arnholdt-Schmitt et al, 2014, 2015a)
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