Plant organ senescence above- and belowground in trees: how to best salvage resources for new growth?

Autophagy-an underestimated coordinator of construction and destruction during plant root ontogeny

MAIN CONCLUSION

Autophagy is a key but undervalued process in root ontogeny, ensuring both the proper development of root tissues as well as the senescence of the entire organ. Autophagy is a process which occurs during plant adaptation to changing environmental conditions as well as during plant ontogeny. Autophagy is also engaged in plant root development, however, the limitations of belowground studies make it challenging to understand the entirety of the developmental processes. We summarize and discuss the current data pertaining to autophagy in the roots of higher plants during their formation and degradation, from the beginning of root tissue differentiation and maturation; all the way to the aging of the entire organ. During root growth, autophagy participates in the processes of central vacuole formation in cortical tissue development, as well as vascular tissue differentiation and root senescence. At present, several key issues are still not entirely understood and remain to be addressed in future studies. The major challenge lies in the portrayal of the mechanisms of autophagy on subcellular events in belowground plant organs during the programmed control of cellular degradation pathways in roots. Given the wide range of technical areas of inquiry where root-related research can be applied, including cutting-edge cell biological methods to track, sort and screen cells from different root tissues and zones of growth, the identification of several lines of evidence pertaining to autophagy during root developmental processes is the most urgent challenge. Consequently, a substantial effort must be made to ensure whether the analyzed process is autophagy-dependent or not.

Seasonal variations of heavy metals in water, sediment, and organs of Vossia cuspidata (Roxb.) Griff. in River Nile ecosystem: implication for phytoremediation

The present study aimed at investigating (1) the seasonal concentrations of heavy metals in different organs of Vossia cuspidata (Roxb.) Griff. in its main natural habitats in the River Nile ecosystem in Cairo, Egypt, (2) the bioaccumulation and translocation of heavy metals in the organs of V. cuspidata and its potentials as a phytostabilizer, and (3) the seasonal changes in the dry matter (DM) biomass of the organs. Two river islands were selected for seasonal sampling of water, sediment, and plant organs in eighteen randomly distributed quadrates (0.5 × 0.5 m each) during the period from February 2018 to January 2019. The total annual mean DM biomass was ≈ 18.7 ton ha-1. The aboveground organs had significant seasonal variations in DM biomass (p < 0.05). The belowground DM biomass represents 23% of the aboveground DM biomass. Belowground organs had the highest DM biomass values in winter for the roots (23.85 g DM m-2, 4.75% from the total DM) and spring for the rhizomes (108.96 g DM m-2, 37.3% from the total DM). Regardless of the heavy metals concentrations in water and sediment, V. cuspidata can accumulate Fe, Mn, Ni, and Pb at high levels. There was a statistically significant interaction between the effects of seasons and organs on the concentrations of Mn, Ni, and Pb at p < 0.001. The root was the main accumulating organ for the analyzed elements in the present study. Vossia cuspidata can transfer low concentrations of the analyzed metals from belowground to aboveground organs. We recommend V. cuspidata as a potential phytostabilizer to Fe, Zn, Mn, Cu, Ni, and Pb from the mainstream of River Nile.