Root Tropisms: New Insights Leading the Growth Direction of the Hidden Half

Tropisms are essential responses of plants, orienting growth according to a wide range of stimuli. Recently, considerable attention has been paid to root tropisms, not only to improve cultivation systems, such as those developed for plant-based life support systems for future space programs, but also to increase the efficiency of root apparatus in water and nutrient uptake in crops on Earth. To date, the Cholodny–Went theory of differential auxin distribution remains the principal tropistic mechanism, but recent findings suggest that it is not generally applicable to all root tropisms, and new molecular pathways are under discussion. Therefore, an in-depth understanding of the mechanisms and functions underlying root tropisms is needed. Contributions to this special issue aimed to embrace reviews and research articles that deepen molecular, physiological, and anatomical processes orchestrating root tropisms from perception of the stimulus to bending. The new insights will help in elucidating plant–environment interactions, providing potential applications to improve plant growth on Earth and in space where microgravity diminishes or nullifies the gravitropism dominance.

Photodynamic inactivation of Botrytis cinerea by an anionic porphyrin: an alternative pest management of grapevine

Botrytis cinerea is a necrotic plant fungus that causes gray mold disease in over 200 crops, including grapevine. Due to its genetic plasticity, this fungus presents strong resistance to many fungicides. Thus, new strategies against B. cinerea are urgently needed. In this context, antimicrobial photodynamic treatment (APDT) was considered. APDT involves the use of a photosensitizer that generates reactive oxygen species upon illumination with white light. Tetra-4-sulfonatophenyl porphyrin tetra-ammonium (TPPS) was tested on B. cinerea using light. 1.5 µM TPPS completely inhibited mycelial growth. TPPS (12.5 µM) was tested on three grapevine clones from Chardonnay, Merlot and Sauvignon, grown in vitro for 2 months. Treated root apparatus of the three backgrounds increased thiol production as a molecular protection against photoactivated TPPS, leading to a normal phenotype as compared with control plantlets. Finally, 2-month-old grapevine leaves were infected with 4-day-old mycelium of B. cinerea pre-incubated or not with TPPS. The pre-treated mycelium was unable to infect the detached leaves of any of the three grapevine varieties after 72 h growth when subjected to a 16 h photoperiod, contrary to untreated mycelium. These results suggest a strong potential of photo-treatment against B. cinerea mycelium for future agricultural practices in vineyard or other cultures.

Photodynamic inactivation of Botrytis cinerea for a safe pest management of grapevine

Botrytis cinerea is a necrotic fungal plant pathogen responsible for the gray mold disease on more than 200 crops, including grapevine. Due to its genetic plasticity, this fungus presents a strong resistance to a large spectrum of fungicides. Thus, new fighting strategies against B. cinerea are urgently needed. In this context, antimicrobial photodynamic treatment (APDT) was considered. APDT involves the use of a photosensitizer that generates reactive oxygen species upon illumination. Tetra-4-sulfonatophenyl porphyrin tetra-ammonium (TPPS) was tested on B. cinerea; upon light exposure. 1.5 µM TPPS was shown to completely inhibit mycelial growth. A concentration of 12.5 µM TPPS was tested on three genetic background clones from Chardonnay, Merlot and Sauvignon, grown in vitro for 2 months. Treated root apparatus of the three backgrounds was able to increase thiol production as a molecular protection against photoactivated TPPS, leading to a normal phenotype as compared with control plantlets. Finally, two-month-old grapevine leaves were infected with four-day-old mycelium of B. cinerea pre-incubated or not with TPPS. The pre-treated mycelium was unable to infect the isolated leaves of any of the three grapevine varieties after 72 h growth when subjected to a 16 h photoperiod, contrary to untreated mycelium. These results on fungus, plantlets and Botrytis-grapevine leaves, in contact with a very low concentration of TPPS, suggest a strong potential of photo-treatment against Botrytis mycelium for future agricultural practices in vineyard or other cultures.