SummaryTaNAM transcription factors play an important role in controlling senescence, which in turn, influences the delivery of nitrogen, iron and other elements to the grain of wheat (Triticum aestivum) plants, thus contributing to grain nutritional value. While lack or diminished expression of TaNAMs determines a stay-green phenotype, the precise effect of these factors on chloroplast structure has not been studied. In this work we focused on the events undergone by chloroplasts in two wheat lines having either control or diminished TaNAM expression due to RNA interference (RNAi). It was found that in RNAi plants maintenance of chlorophyll levels and maximal photochemical efficiency of photosystem II were associated with lack of chloroplast dismantling. Flow cytometer studies and electron microscope analysis showed that RNAi plants conserved organelle ultrastructure and complexity. It was also found that senescence in control plants was accompanied by a low leaf enzymatic antioxidant activity. Lack of chloroplast dismantling in RNAi plants was associated with maintenance of protein and iron concentration in the flag leaf, the opposite being observed in control plants. These data provide a structural basis for the observation that down regulation of TaNAMs confers a functional stay-green phenotype and indicate that the low export of iron and nitrogen from the flag leaf of these plants is concomitant, within the developmental window studied, with lack of chloroplast degradation and high enzymatic antioxidant activity.
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Highlights•TaNAM-RNAi stay-green phenotype is coupled with maintenance of chloroplast structure.•That stay-green phenotype is associated with a high enzymatic antioxidant activity.•Chloroplast dismantling correlates with decay of iron and protein content in leaves.
The first rice phenological stages are commonly subjected to low temperatures (LT) in temperate crop areas. Here, plants of rice genotypes were analyzed according to their LT tolerance at seedling stage, using a realistic experimental temperatures range, and measuring quantitative and operator-independent parameters, fast-obtainable by non-invasive techniques. The ratios between values of these parameters determined in plants under LT condition with respect to the control condition were statistically analyzed. We have found a discriminant formula based on two parameters that allowed to differentiate between genotypes previously described as tolerant and sensitive to LT, with a very low general classification error. The application of the discriminant formula to score plants under LT, using all genotypes from the Rice Diversity Panel 1 which comprehensively represents the genetic variability of the O. sativa species, resulted in LT tolerance levels of its subspecies and subpopulations consistent with previous reports. In turn, a strong association between the LT tolerance score at the seedling stage and the panicle weight in plants under field LT during the vegetative stage, suggested that this scoring could be used as an indirect selection factor of genotypes with good yield traits and suited to LT prone environments.
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